Literature DB >> 34851987

Trophic niche overlap between coyotes and gray foxes in a temperate forest in Durango, Mexico.

César Ricardo Rodríguez-Luna1, Jorge Servín2, David Valenzuela-Galván3, Rurik List4.   

Abstract

Resource partitioning, and especially dietary partitioning, is a mechanism that has been studied for several canid species as a means to understand competitive relationships and the ability of these species to coexist. Coyotes (Canis latrans) and gray foxes (Urocyon cinereoargenteus) are two canid species that are widely distributed, in Mexico, and they are sympatric throughout most of their distribution range. However, trophic dynamic and overlap between them have not been thoroughly studied. In order to better understand their ecological relationship and potential competitive interactions, we studied the trophic niche overlap between both canids in a temperate forest of Durango, Mexico. The results are based on the analysis of 540 coyote and 307 gray fox feces collected in 2018. Both species consumed a similar range of food items, but the coyote consumed large species while the gray fox did not. For both species, the most frequently consumed food categories throughout the year and seasonally were fruit and wild mammals (mainly rodents and lagomorphs). Coyotes had higher trophic diversity in their annual diet (H' = 2.33) than gray foxes (H' = 1.80). When analyzing diets by season, trophic diversity of both species was higher in winter and spring and tended to decrease in summer and autumn. When comparing between species, this parameter differed significantly during all seasons except for summer. Trophic overlap throughout the year was high (R0 = 0.934), with seasonal variation between R0 = 0.821 (autumn) and R0 = 0.945 (spring). Both species based their diet on the most available food items throughout each season of the year, having high dietary overlap which likely can lead to intense exploitative competition processes. However, differences in trophic diversity caused by differential prey use can mitigate competitive interactions, allowing these different sized canid species to coexist in the study area.

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Year:  2021        PMID： 34851987      PMCID： PMC8635360          DOI： 10.1371/journal.pone.0260325

Source DB:  PubMed          Journal:  PLoS One        ISSN： 1932-6203            Impact factor:   3.240


Introduction

The trophic dimension of species’ ecological niches is important because it can determine the structure of ecological communities due to the importance of food resources for animals [1]. Therefore, understanding the ways in which species partition these resource contributes to the understanding of interactions among sympatric species [2, 3]. When species occur in sympatry, the competitive exclusion principle [4] proposes that the species segregate their ecological niches in at least one of their dimensions in order to reduce interspecific competition [5-7]. Differences in size and physiological needs can allow predator species to coexist in the same area [8]. One of the most important forms of resource partitioning in ecological communities is differentiation of the use of food resources [1, 6]. Some degree of trophic overlap is relatively common, and varies among species, sites, and season [9], but cases of very high trophic overlap between ecologically similar species are limited [10]. Comparing the food habits of sympatric species reveals the overlap degree in their trophic niche, which can be interpreted as a measure of the potential for interspecific competition between species [11, 12], and thus provides information of the mechanisms that reduce their competitive interactions in order to maintain sympatry [13]. Also, it is important to state that sympatry can be achieved not only by trophic niche segregation, but also through segregation on other dimensions of ecological niche such as time and space [5–7, 14]. The relevance of niche segregation on each of its main dimensions (e.g. trophic, time and space) for allowing the coexistence of ecologically similar species varies among species and habitats but exploring the overlap on any of those niche dimensions, can provide useful insights on this topic [6]. Although there is abundant evidence of these kind of complex interactions among carnivorous mammals, these interactions are poorly understood for many species as well as the sort of niche segregation they present on any of the ecological niche dimensions [15, 16]. Therefore, we decided to explore the potential role that feeding ecology and trophic interactions among sympatric species of mammalian carnivores can have on their coexistence through trophic niche segregation. To explore these questions we chose studying coyotes (Canis latrans) and gray foxes (Urocyon cinereoargenteus), two common and widespread canid species, that are abundant at our study site and, sympatric over a large part of their range in North America [17, 18]; however, the ecological relations between them have received little attention [11]. These two canids are generalist-opportunist species that consume similar food items [17, 18] and they potentially compete for similar resources. In the northern portion of their distribution range, the diet overlap of these canids can vary between medium [19, 20] to high values [11, 21, 22]. But in the southern portion of its distribution range, trophic dynamic and dietary overlap between coyotes and gray foxes have not been thoroughly studied. In a tropical dry forest in southern Mexico, it was reported that they showed intermediate trophic niche overlap and low potential for interspecific competition between them [23]; while in the north of the country, in a temperate forest, they showed intermediate–high dietary overlap proportion [24]. As trophic level mechanisms that allow the coexistence of these two canids remain unclear, a study of food resource partitioning in sympatric coyote and gray fox populations in temperate forests will help to understand their competitive relations and to elucidate if trophic niche segregation could be a mechanism partly explaining a stable coexistence between these two canids. Our objective was thus to analyze the trophic interactions and evaluate the potential for interspecific competition for food resources between coyotes and gray foxes in a temperate forest of the Sierra Madre Occidental, in a protected reserve, in the state of Durango, Mexico. We analyzed the indigestible contents of feces of both species to determine their diet composition, the relative importance of different food items, and its seasonal variation. Using those data, we evaluated: (1) the trophic diversity of these two species, (2) whether this variable differed between the species, and (3) the similarity of diets as a measure of trophic niche overlap, considering a high overlap degree as an indicator of high potential for exploitative competition [13, 25]. We expected significant differences in trophic diversity between both species, and therefore, low trophic niche overlap. The larger coyote (up to 16 kg in the study area [26]) should consume a wider range of food resources, increasing its trophic niche breadth, in comparison to the smaller gray fox (3–5 kg [27]), as has been reported for this species in other parts of its geographic distribution range.

Materials and methods

Study area

We carried out this work in the buffer zone of “La Michilía” Biosphere Reserve (MBR), in the municipality of Súchil, Durango, Mexico, located between the coordinates 23° 21’–23° 28’ N and 104° 09’–104° 21’ W. The MBR is found in the transition zone between the Neartic and Neotropical biogeographic zones [25-29]. The MBR is bordered by the Sierra de Urica to the west, which is gently sloped, and by the Sierra de Michis on the east, which has steep depressions and marked slopes [30]. The altitude of the study zone varies between 2,000–2,985 m [31]. In the northern part of the MBR the climate is semi-dry temperate (BS1k) and in the rest of the MBR the dominant climate is temperate sub-humid (Cw [32]). Mean monthly temperatures range from 2°C in February to 22°C in July and the average annual precipitation ranged from 600–900 mm [32]. Dominant vegetation within the MBR is coniferous (Pinus spp.) and oak (Quercus spp.) forest, though there are also zones of natural grassland (Bouteloua spp.), xerophytic scrub (Arctostaphylos pungens, Acacia schaffneri), and aquatic vegetation; in addition, the MBR has transition zones among these vegetation types, leading to the formation of mixed forests [33] (Fig 1).
Fig 1

Geographic location of the study area in the buffer zone of La Michilía Biosphere Reserve (MBR), Durango, Mexico, showing the vegetation types and the location of the sampling transects.

Fig 1 was created by CRRL (the first author) using freely available resources and software (see methods). Therefore, it is an original not copyrighted image.

Geographic location of the study area in the buffer zone of La Michilía Biosphere Reserve (MBR), Durango, Mexico, showing the vegetation types and the location of the sampling transects.

Fig 1 was created by CRRL (the first author) using freely available resources and software (see methods). Therefore, it is an original not copyrighted image. Fig 1 was prepared by the first author (CRRL), for illustrative purposes only, to show location of the study area and vegetation types, using shape files about topography and vegetation types and land cover produced by Mexican National Institute of Geography and Statistics and publicly available for free, for any user at the following link (https://www.inegi.org.mx/datos/?t=0150). Shape files were projected to produce Fig 1 using QGIS software (v. 3.14.) that is free online to download at the following link (https://www.qgis.org/es/site/forusers/download.html).

Sample collection and identification

During 2018, we selected 23 sampling transects of variable length (between 750–2500 m), to opportunistically collect the feces of both canids along paths, main and secondary roads, and streams in the study area (Fig 1). Based on food-availability cycles in the study area [34], we performed sampling on 17 transects in winter (December 22–March 20) and spring (March 21–June 20), 23 in summer (June 21–September 20) and on 18 in autumn (September 21–December 21). We chose our sampling transects in accordance to the proportion of the main vegetation types present in the study area (ca 124 km2; Fig 1), 14 transects on mixed forest (Pinus spp.–Quercus spp., that represents 62.30% of the study area); 7 transects on pine forest (Pinus spp., 28.8% of the study area); 1 transect on oak forest (Quercus spp. 4.9% of the study area); and 1 in grasslands (Bouteloua spp., 4% of the study area). Prior to the formal collection of fecal samples, all feces were removed from the transects, allowing us to date the samples to the nearest month during the study period. In the studied area, there are more sympatric carnivores; however, they all produce quite distinctive feces and none can be easily confused with coyote or gray fox feces. Despite this, we were very careful to identify feces to the species level by size, shape, and color of each sample, based on information from specialized literature [35-37], and we considered as complementary evidence the presence of tracks of the focal species in the vicinity of the collection site. Subsequently, to reduce potential assignment error, we used feces maximum diameter as a criterion to identify canid species in the study area, see [34]. Thus, we assigned to C. latrans all feces that had maximum diameter between 18.01 and 33.00 mm, and to U. cinereoargenteus the feces with maximum diameter between 9.00 and 16.99 mm [35], and we excluded from data analysis all feces with maximum diameter between 17.00 and 18.00 mm and also any disaggregated feces sample. After this, we discarded 7.43% (n = 68) of the total feces we collected. We considered that feces collected on a particular season, were representative of the feeding habits of the studied species in that period of the year. We placed the collected feces individually in paper bags, labeled them with the species name, date, season, and geographic location, to be air dried. In the laboratory, we transferred all feces to nylon stockings and washed them with water and commercial detergent to remove soluble material. We then manually disintegrated the feces and dried them in a 65°C oven for 48 h [34]. After drying, we recovered all the undigested parts of food items (hairs, scales, exoskeletons, bones, skin, teeth, feathers, and seeds); in the case of hairs, we mounted samples of them on microscope slides to visualize their medulla and scale patterns [38]. We then identified the undigested fragments to the lowest taxonomic level possible using reference samples from the study area from the collection of the Laboratorio de Ecología y Conservación de Fauna Silvestre of the Universidad Autónoma Metropolitana–Unidad Xochimilco, as well as with published information about characteristics of teeth, bones and guarding hairs (mostly qualitative features) of different mammal species from several specialized references [38-44]. Identification of mammal species through their guarding hairs has proven to be reliable, particularly if based on qualitative features [45]. We classified the undigested fragments (i.e., food items) from both canids into six trophic categories: 1) fruits, 2) invertebrates, 3) reptiles, 4) birds, 5) livestock (caprine, ovine, and bovine), and 6) wild mammals. In the case of herbs and/or grass (n = 4), we assumed that they were incidentally ingested while consuming small prey or to aid in the digestive process [11], so we excluded them from subsequent analyses.

Sample analysis

For each species, the overall and seasonal representation of each food item and food category was expressed as: 1) number of occurrences (n), n = number of feces containing prey item i; and 2) frequency of occurrence (FO), FO (%) = (n / N) * 100, where N is the total number of feces [21, 46]. The FO measures the percentage of feces that contains a given prey item, and although it does not necessarily approximate the volumetric importance of items in the diet, it indicates the relative importance role of items in the diet [24, 47], how common an item was in the diet [48], and can provide valuable insight into carnivore ecology [21, 49]. We used Clench’s asymptotic species accumulation model to estimate the completeness of the sampling. To do this, the data of food items found in feces were randomized 1000 times with the program EstimateS version 9.1.0 [50]. Additionally, we used Fisher’s exact test [51] to analyze whether the distribution of prey items among the trophic categories varied between species and between seasons. We also calculated Shannon’s diversity index (H’ [52]) to estimate the trophic diversity, and to identify possible significant differences in trophic diversity between species and among seasons using a Hutcheson’s t test [53], with the program Past 4.03 [54]. To estimate the trophic niche overlap we used Horn’s index (R [55]), corrected to avoid bias due to under sampling [56]. The index values range from 0 (no overlap) to 1 (complete overlap). For most of the statistical analysis we used R version 4.0.2 program [57]. Since our data is based on the collection and analysis of feces of the studied species, in Mexico there is no need to obtain a permit for this. We do not collect and handle individuals of the studied species, therefore, we did not have to adhere to a particular ethic guideline for handling and studying animals. To be able to do our research activities inside La Michilía Biosphere Reserve we inform the authorities about the objectives and needs of our research before starting our field work. We were acknowledged that they received our research protocol and that they did not have any issues in letting us do our research inside the protected area.

Results

We accumulated nearly 28 km of transect sampling effort for winter and spring, almost 30 for autumn and 37 km for winter. We were able to collect a total of 915 fecal samples, but only analyzed 847, 540 from coyotes and 307 from gray foxes. More than 90% of all feces samples were collected as expected, for both species, on mixed and pine forest where the majority of the sampling transects were located. However, we ran a Chi-square goodness of fit test and noticed that we collected significantly less feces samples than expected (considering the proportion of vegetation types on the study area) for both species on grasslands and more than expected on oak forest for coyote and in pine forest for gray fox (χ2 = 9.58, df = 3, p = 0.022, for coyote; χ2 = 63.64, df = 3, p < 0.001, for gray fox), suggesting that they use habitats differently. We identified 25 different food items for the coyote and 17 for the gray fox. We explored how well our sample represents the diet for both species through the Clench model, that predicted 27.16 food items for coyote (R = 0.998) and 18.76 food items for gray fox (R = 0.978). Thus, we reached 92.05% and 90.62% of the total food items expected, for coyote and gray fox, respectively.

Overall diet composition

Fisher’s exact test indicated that prey items distribution across trophic categories differed significantly (p < 0.001) between coyote and gray fox feces. In the case of coyotes, we identified 25 different food items from all six trophic categories. The category with the highest frequency of occurrence value was fruits (FO = 68.52), followed by wild mammals (FO = 47.59%) and invertebrates (FO = 6.48; Table 1). The fruits category was represented by cedar fruits (Juniperus deppeana), which was the predominant food item in coyote feces (FO = 39.07), followed by fruits of pointleaf manzanita (A. pungens; FO = 29.44). Among wild mammals category, rodents were the most frequent food item, represented by seven species; the most frequently consumed were mice of the genus Peromyscus (FO = 10.74) and Sigmodon (FO = 8.52). In the same category, the next most frequent food items were from the orders Lagomorpha, represented by Sylvilagus audubonii and Lepus californicus from Leporidae family (FO = 8.52); and Artiodactyla, represented by Odocoileus virginianus (FO = 3.15), Pecari tajacu (FO = 2.04) and the exotic species Sus scrofa (FO = 1.67). Among invertebrates, the most frequent food item was of the order Coleoptera (FO = 5.00), while, among birds, was Meleagris gallopavo (FO = 2.41). In the livestock category, we found remnants of cattle (Bos taurus), goats (Capra hircus), and sheep (Ovis aries), all with low FO values ≤ 1.11 (Table 1) and we consider that it might come from the consumption of dead animals more than representative of predation on domestic animals.
Table 1

Total number of samples (N) and trophic diversity (H’) of the coyote and gray fox, as well as overall number of occurrences (n) and frequency of occurrence (FO%) of food items by trophic category, in both canids diets, in the buffer zone of La Michilia Biosphere Reserve (MBR), Durango, Mexico.

CoyoteGray fox
N = 540N = 307
H’ = 2.33H’ = 1.80
Food item and trophic category n i FO% n i FO%
Wild mammals category 257 47.59 88 28.66
CARNIVORA
Mephitidae122.2210.33
Procyonidae
Nasua narica 10.1920.65
Procyon lotor 10.1900
ARTIODACTYLA
Cervidae
Odocoileus virginianus 173.1500
Tayassuidae
Pecari tajacu 112.0400
Suidae
Sus scrofa 91.6700
RODENTIA
Sciuridae
Sciurus nayaritensis 101.8530.98
Otospermophilus variegatus 71.3020.65
Geomyidae
Thomomys umbrinus 71.3030.98
Heteromyidae
Heteromys irroratus 50.9300
Cricetidae
Peromyscus sp.5810.743611.73
Reithrodontomys sp.10.1930.98
Sigmodon sp.468.52196.19
LAGOMORPHA
Leporidae468.52165.21
UNIDENTIFIED264.8130.98
Livestock category 12 2.22 0 0
ARTIODACTYLA
Bovidae
Bos taurus 61.1100
Capra hircus 40.7400
Ovis aries 20.3700
Birds category 24 4.44 12 3.91
GALLIFORMES
Phasianidae
Meleagris gallopavo 132.4110.33
Unidentified112.04113.58
Reptiles category 10 1.85 3 0.98
Invertebrates category 35 6.48 29 9.45
COLEOPTERA275.00247.82
ORTHOPTERA81.4851.63
Fruits category 370 68.52 259 84.36
ERICALES
Ericaceae
Arctostaphylos pungens 15929.449129.64
PINALES
Cupressaceae
Juniperus deppeana 21139.0716854.72
For gray foxes, we identified 17 different food items, belonging to 5 of the 6 trophic categories considered. The category with the highest frequency of occurrence value was fruits (FO = 84.36), followed by wild mammals (FO = 28.66) and invertebrates (FO = 9.45; Table 1). We did not find any traces of livestock in gray fox feces. Within fruits category, J. deppeanna was the most frequently consumed food item (FO = 54.72) followed by A. pungens (FO = 29.64). Within the wild mammals category, rodents were the most frequent food item, represented by six species, among which the most consumed were of the genus Peromyscus (FO = 11.73), followed by species of the order Lagomorpha (FO = 5.21). Among the most frequent invertebrate food item were Coleoptera (FO = 7.82), while among birds, the most frequent prey items corresponded to unidentified species (FO = 3.58; Table 1). Trophic diversity was significantly higher (t = 7.03, df = 814.22, p < 0.001) for coyotes (H’ = 2.33) than for gray foxes (H’ = 1.80). While Horn index was R = 0.934 (CI 95%; 0.898–0.969), which indicates high dietary overlap proportion, as well as very similar resource use spectra, between these two canid species.

Seasonal diet composition

Fisher’s exact test showed significant differences in food items distribution across the trophic categories in species feces between seasons for coyotes (p < 0.001) and for gray foxes (p < 0.001). In the case of coyotes, food items in the wild mammals category were the most frequent remains in feces during winter (FO = 60.32) and spring (FO = 63.08), the first half of the year; while during the second half of the year were food items in the fruits category: summer (FO = 84.10) and autumn (FO = 66.67). Frequency of occurrence of birds (FO: 3.59–5.13) and invertebrates (FO: 4.17–7.18) was relatively constant throughout the year, and reptiles were present only in winter (FO = 1.59) and spring (FO = 4.10). Livestock were consumed in all seasons except for autumn, with low values between FO = 1.54 in summer and FO = 3.08 in spring (Fig 2, Table 2).
Fig 2

Seasonal occurrence of food items (expressed as proportion), by trophic categories, in the coyote and gray fox diets in the buffer zone of the La Michilía Biosphere Reserve, Durango, Mexico.

Table 2

Seasonal number of samples (N) and trophic diversity (H’) of the coyote and gray fox, as well as seasonal number of occurrences (n) and frequency of occurrence (FO%) of food items by trophic category, in both canids diets, in the buffer zone of La Michilia Biosphere Reserve (MBR), Durango, Mexico.

CoyoteGray fox
WinterSpringSummerAutumnWinterSpringSummerAutumn
N = 126N = 195N = 195N = 24N = 87N = 92N = 78N = 50
H’ = 2.16H’ = 2.30H’ = 1.47H’ = 1.57H’ = 1.88H’ = 1.77H’ = 1.36H’ = 0.36
Food item and trophic category n i FO% n i FO% n i FO% n i FO% n i FO% n i FO% n i FO% n i FO%
Wild mammals category 76 60.32 123 63.08 50 25.64 9 37.50 39 44.83 34 36.96 10 12.82 5 10.00
Mephitidae64.7631.5431.5400.0011.1500.0000.0000.00
N. narica10.7900.0000.0000.0022.3000.0000.0000.00
P. lotor10.7900.0000.0000.0000.0000.0000.0000.00
O. virginianus43.17115.6421.0300.0000.0000.0000.0000.00
P. tajacu22.3863.0831.5400.0000.0000.0000.0000.00
S. scrofa43.1731.5421.0300.0000.0000.0000.0000.00
S. nayaritensis32.3842.0531.5400.0022.3011.0900.0000.00
O. variegatus10.7921.0321.0328.3311.1500.0011.2800.00
T. umbrinus00.0052.5621.0300.0022.3011.0900.0000.00
H. irroratus21.5900.0031.5400.0000.0000.0000.0000.00
Peromyscus sp.2217.462713.8573.5928.331618.391415.2245.1324.00
Reithrodontomys sp.00.0010.5100.0000.0000.0011.0922.5600.00
Sigmodon sp.107.942914.8763.0814.1778.0577.6133.8524.00
Leporidae1310.32199.74126.15312.5078.0599.7800.0000.00
Unidentified75.56136.6752.5614.1711.1511.0900.0012.00
Livestock category 3 2.38 6 3.08 3 1.54 0 0.00 0 0.00 0 0.00 0 0.00 0 0.00
B. taurus21.5931.5410.5100.0000.0000.0000.0000.00
C. hircus00.0021.0321.0300.0000.0000.0000.0000.00
O. aries10.7910.5100.0000.0000.0000.0000.0000.00
Birds category 6 4.76 10 5.13 7 3.59 1 4.17 5 5.75 4 4.35 3 3.85 0 0.00
M. gallopavo32.3873.5931.5400.0011.1500.0000.0000.00
Unidentified32.3831.5442.0514.1744.6044.3533.8500.00
Reptiles category 2 1.59 8 4.10 0 0.00 0 0.00 2 2.30 1 1.09 0 0.00 0 0.00
Invertebrates category 7 5.56 13 6.67 14 7.18 1 4.17 0 0.00 9 9.78 18 23.08 0 0.00
Scarabaeidae32.38126.15115.6414.1722.3088.701417.9500.00
Orthoptera43.1710.5131.5400.0000.0011.0945.1300.00
Fruits category 75 59.52 115 58.97 164 84.10 16 66.67 66 75.86 76 82.61 71 91.03 46 92.00
A. pungens6148.418744.62105.1314.173540.234548.911114.1000.00
J. deppeana1411.112814.3615478.971562.503135.633133.706076.924692.00
Gray foxes showed a different pattern of consumption than coyotes, since the most frequent trophic category in all seasons was fruits (FO ≥ 75.86), followed by wild mammals, which were most frequent in winter (FO = 44.83) and spring (FO = 36.96). During the summer and autumn, fruits category frequency increased, reaching a maximum value of FO = 92.00, and frequency of occurrence of wild mammals decreased (Fig 2, Table 2). The highest frequency of occurrence value of invertebrates was during the summer (FO = 23.08), and no invertebrates were found on its feces in autumn. On the other hand, birds FO values were relatively constant (3.85–5.75), except in autumn when no bird remains were found in the feces. Reptiles were present only in winter (FO = 2.03) and spring (FO = 1.09) seasons (Fig 2, Table 2). The coyote’s trophic diversity values were highest in winter and spring (H’ = 2.34 and H’ = 2.40, respectively), which did not differ significantly from each other (t = -0.55, df = 325.26, p = 0.58), and the minimum values were in summer (H’ = 1.61) and autumn (H’ = 1.57), which also did not differ significantly (t = 0.16, df = 39.62, p = 0.87). For this species, the remaining pairwise comparisons between seasons shows significant differences using Hutchenson’s t tests (Table 3). In the case of gray foxes, like coyotes, the highest trophic diversity values occurred during winter (H’ = 1.97) and spring (H’ = 1.83), which did not statistically differ from each other (t = 1.02, df = 232.93, p = 0.31), while the lowest value occurred during the autumn (H’ = 0.42). The rest of the comparisons between seasons showed significant differences (Table 3). When comparing the seasonal trophic diversity values between species, this parameter differed significantly during all seasons except for summer, when there was no evidence of statistically significant differences (t = 1.27, df = 267.16, p < 0.205; Table 3).
Table 3

Seasonal trophic diversity of coyotes and gray foxes, and significance values of Hutcheson’s t test between seasons, in the buffer zone of La Michilía Biosphere Reserve (MBR), Durango, Mexico.

CoyoteGray fox
WinterSpringSummerAutumnWinterSpringSummerAutumn
H’ = 2.16H’ = 2.30H’ = 1.47H’ = 1.57H’ = 1.88H’ = 1.77H’ = 1.36H’ = 0.36
Coyote Winter H’ = 2.16----
Spring H’ = 2.30NS----
Summer H’ = 1.47 *** *** ----
Autumn H’ = 1.57 ** *** NS----
Gray fox Winter H’ = 1.88 ** *** ** NS----
Spring H’ = 1.77 *** *** NSNSNS----
Summer H’ = 1.36 *** *** NSNS *** ** ----
Autumn H’ = 0.36 *** *** *** *** *** *** *** ----

Minimum number of samples between comparisons was 74, degrees of freedom varied between 37.71–407.10. Significance values are indicated as follows: P ≤ 0.001 “***”, P ≤ 0.01 “**”, P ≤ 0.05 “*”, and P > 0.05 “NS”.

Minimum number of samples between comparisons was 74, degrees of freedom varied between 37.71–407.10. Significance values are indicated as follows: P ≤ 0.001 “***”, P ≤ 0.01 “**”, P ≤ 0.05 “*”, and P > 0.05 “NS”. Trophic niche overlap between coyotes and gray foxes through seasons sampled was high (≥ 82.10%). The highest overlap proportion value occurred in winter with R = 0.905 (IC 95%; 0.823–0.986) and spring with R = 0.945 (IC 95%; 0.866–0.998), then decreasing in summer with R = 0.870 (IC 95%; 0.821–0.919) and showing the lowest overlap in autumn with R = 0.821 (IC 95%; 0.673–0.968).

Discussion

In the study area we found that fruits were the most frequently consumed food item year-round in coyote’s diet, as has been reported for this species in coniferous forests habitats in Oregon and Maine [58, 59] and in some desert, coastal, tropical deciduous forest, and urban environments [23, 60–64]. But, this results contrast with previous works in the MBR [24, 34], although former work represents a partial approximation of the diet throughout the year during the summer and spring, and with works in other parts of coyote’s distribution which report wild mammals as the most consumed trophic category year-round in temperate forest of Mexico [65-67], the United States of America [13, 68–74], and Canada [75-77]. However, despite the above, changes in the frequency of occurrence of the different trophic categories through the seasons coincide with data reported for this species for which the highest consumption of wild mammals occurred during the first half of the year, in winter and spring, and the main consumption of fruits occurred in the second part of the year, in summer and autumn [34, 64, 68, 74, 78–82]. Our results support that the coyote behaved as opportunistic feeder with general diet [68, 83]. This species is characterized by its adaptability to different habitat conditions, which is reflected in its diet, in such a way that coyotes took advantage of the seasonal availability of mammals and fruits. As was reported in the study area [34], we found that the highest consumption of wild mammals occurred in winter: mainly rodents, lagomorphs, and artiodactyls, which coincides with data reported for this species, since rodents of the genus Peromyscus and Sigmodon as well as lagomorphs (L. californicus and S. audubonii) were the elements that accounted for the highest proportion of consumption [11, 13, 24, 34, 65]. This species has also been reported to consume larger species, such as white-tailed deer (O. virginianus), which in the case of the present study had high FO values, below rodents and lagomorphs, but which may present higher importance values in other distribution areas [66, 68, 74, 76, 84–88]. These high values of mammal consumption during the first half of the year can be explained by the high demand for high-quality foods, since these periods coincide with the breeding season (1 January–15 March) and gestation (16 March–30 April [89]), such that foraging activity increases markedly in the study area to increase reproductive success [26, 90]. On the other hand, in summer and autumn, fruit frequency was higher; the most consumed fruits were from cedar (J. deppeana), a species which has high availability during this season, July-November [34], while the main consumption of A. pungens was during the winter and spring, which coincides with the low-water period in this area, just when the fruits of this shrub mature and fall to the ground; thus, coyotes consume the fruit and help disperse the seeds of this species which has an important role in this type of ecosystem, especially in restoring soils and retaining moisture at the beginning of secondary ecological succession [91]. Although our work shows that the rest of the food categories were complementary elements in the coyote diet, their importance and frequency of consumption vary depending on the habitat type where this canid resides, since in desert regions there is a higher consumption of invertebrates and reptiles [92, 93] and in anthropized environments, an important consumption of livestock (FO ≥ 25%), including cattle, poultry, and domestic cats has been reported [94-97]. It is cautionary to state that domestic animal remnants detected in coyote´s feces is likely represent carrion consumption more than predation events. In fact, in the study area there are few reports of livestock predation events from local people, and none reported in the study year of our work. Overall feeding habits of the gray fox that we describe in this work, in which the main trophic category was fruits followed by wild mammals, coincide with the feeding patterns reported in similar biomes in North America [20, 70, 98, 99], in central Mexico [100], in Guatemala [101], and in some areas of moist tropical forest in Mexico [23, 102] and Belize [103]. The gray foxes’ most consumed trophic category throughout the year was fruits. However, the frequency of consumption of this and the rest of the categories differed significantly among seasons. During winter there was higher consumption of wild mammals, as has been reported in the central and eastern USA, where leporids and rodents are the gray fox’s main prey [18, 104]. The lowest consumption of fruits occurred in the winter and increased gradually through the autumn, when it represented more than 90% of the diet. During autumn, foxes consumed almost exclusively cedar (J. depeanna) fruits. Invertebrates was also highly consumed by gray foxes, which have been reported to be mainly consumed in the summer [18, 19, 23, 105–107], the wettest season, as was the case in our study. The variation in the frequency of consumption in the trophic categories that make up the diets of these two canids shows their ability to adapt to different habitat conditions. In the case of the coyote, it has been reported that this species responds to changes in resource availability by modifying their preferences when an important food source becomes less abundant [20, 34, 108, 109]. This also appears to occur with gray foxes, since they have also demonstrated their adaptability to changes in the availability of food resources, whether due to stochastic events, temporal variation, or differences in the habitat types they occupy [18, 20, 23, 24, 102]. As expected, yearly trophic diversity of the coyote (H’ = 2.33) was higher than that of the gray fox (H’ = 1.80). Seasonally, this parameter differed between the two species in all seasons except for the summer, when the diversity of the dietary elements of the two species was more similar (82.15%). Coyotes had its highest trophic diversity in spring (H’ = 2.40), and this was higher than that of the gray foxes (H’ = 1.97). During this season, the coyote consumed three different species of livestock (B. taurus, O. aries and C. hircus) and three species of large wild mammals (O. virginianus, P. tajacu and the exotic S. scrofa), which the gray foxes did not consume at any time during the year. This is consistent with the prediction that sympatric carnivore species will partition prey species according to their body size [8], which may reflect the different energy requirements associated with size [13]. This has been previously reported in the coyote with respect to the gray fox [11, 24] and to other species of foxes in the Americas, such as the San Joaquín kit fox (Vulpes macrotis mutica [110, 111]), the swift fox (Vulpes velox [13]), and the red fox (Vulpes vulpes [112, 113]). We expected that both species should have low trophic niche overlap in the area, however, despite the differences we found in trophic diversity between these two species, trophic niche overlap between coyotes and gray foxes in the study area was high overall (93.4%) and seasonally (82.1–94.5%), since both species consumed many of the same food items that were available in the MBR; this suggests that there could be some level of exploitative competition. However, the relevance of each trophic category differed between species. The FO of wild mammals was 1.6 times higher in the coyote’s than in the gray fox diet. Invertebrates and fruit presented FO values, 1.45 and 1.23 times higher, respectively, in the gray fox than in the coyote diet. Also, livestock was consumed only by the coyote. Taken together, this suggests that even when the overlap value of the diet is high, each species consumes with different emphasis some of these shared resources, which may mitigate potential competition for food resources [8]. Our results coincided with the only previous study investigating the similarity of the diets of these two sympatric canids in the study area, that reported high trophic overlap, with a Pianka index value of O = 0.832 [24]. Given that the abundance of potential prey should be similar for both predator species, some of the differences detected in the use of prey could reflect differences in the feeding ecology of these two species [24], so competitive interactions over food resources are mediated by distinct foraging patterns that result in a differentiation of the consumption of some of the elements of the diets of these species. This resource partitioning pattern by ecologically similar species is a niche segregation strategy that can facilitates the coexistence between them [5, 6, 19, 70]. However, it should also be pointed out that this difference in consumption patterns could also be due to differential use of the habitat (e. g. spatial segregation), which has been shown to be important in reducing competitive interactions between coyotes and gray foxes [19, 70, 114]. We collected more or less fecal samples by vegetation type than expected by its proportion on the study area, however we consider that not much inference about food resources consumed by habitat type can be derived from the location site of the feces sample, since an animal can consume resources at one place, and defecate several hours later in a different habitat type. However, t differences among habitats in the success to collect feces samples, indeed can provide some evidence of differential use of vegetation types, something that is in accordance with our findings about spatial ecology and habitat use data obtained at the same site [114]. Additionally, different behavioral strategies can also be employed by species to facilitate coexistence with a dominant species [115]. In the case of interactions between the coyote and the gray fox, it has been shown that the strategies employed by subdominant species include spatial [19, 116] and temporal [116] predator avoidance. Both canid species showed opportunistic food habits, although the trophic diversity of the coyote was higher than that of the gray fox, mainly because coyote incorporated larger prey into its diet than gray fox did not. However, the two species consumed quite similar range of food items, that varied in proportion and frequency among seasons, so they showed high trophic niche overlap, and therefore some potential for exploitative competition in the study area. For a better understanding on how the different foraging strategies of each species can help minimize their overlap in the trophic niche and facilitate their coexistence, more detailed research is needed on the availability and spatio-temporal dispersion of food resources in the different habitat types in the area. Such information could also provide insights on how the implementation of different management actions of habitats and/or species can affect both canid species persistence in this Natural Protected Area.

Undigested remains 2018.

Undigested remains from 2018 coyote and gray fox feces. (XLSX) Click here for additional data file.

Resumen.

(DOCX) Click here for additional data file. 9 Aug 2021 PONE-D-21-19581 Trophic niche overlap between coyotes and gray foxes in a temperate forest in Durango, Mexico PLOS ONE Dear Dr. Valenzuela-Galván, Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process. The manuscript is well written and the data presented are valuable. However, several parts can be improved following the reviewers' suggestions (see also the attached file). Particular care must be given to the introduction and conclusion (discuss mechanisms allowing niche overlap and coexistence) and the methods (more details on the transects and fecal collection). Please submit your revised manuscript by Sep 23 2021 11:59PM. 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The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented. Reviewer #1: Partly Reviewer #2: No ********** 2. Has the statistical analysis been performed appropriately and rigorously? Reviewer #1: Yes Reviewer #2: Yes ********** 3. Have the authors made all data underlying the findings in their manuscript fully available? The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. 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(Please upload your review as an attachment if it exceeds 20,000 characters) Reviewer #1: This manuscript provides a simple, straightforward examination of dietary niche overlap between sympatric coyotes and gray foxes. As the authors point out, there is a lack of data examining the partitioning of these two ecologically similar and highly overlapping carnivores. I believe the authors’ research provides valuable information on the dietary niches of these two species. However, I also note a number of points that could be addressed to strengthen the manuscript. 1. The introduction could benefit from a bit more thoughtful expansion. The authors state that high trophic overlap for ecologically similar species is rare (line 45), but I might disagree. There are many sympatric generalist species, including carnivores (such as foxes, coyotes and bobcats), that can have high trophic overlap but coexist through mechanisms such as fine-scale spatial and/or temporal partitioning. In fact, the authors mention a study where coyotes and gray foxes can be found to have high dietary overlap (line 55). I believe it would strengthen the introduction to discuss the mechanisms which allow sympatric species with overlapping trophic niches to have stable coexistence. The authors mention that trophic niche segregation may allow stable coexistence (line 64), but what about circumstances (such as the findings in this manuscript) where trophic niche overlap is high but coexistence still appears to occur? 2. The transition from the broad introduction to the authors’ specific research seems a bit abrupt. Further discussion on how the reasoning and application of this research may be prudent. 3. In the Sample Collection and Identification section, a few points may benefit from clarification which could improve future design replication: a. How were transects allocated with respect to vegetation type? What was the length(s) of each transect? b. This is quite minor, but it feels inappropriate to say all feces were removed from the study area (line 99). Instead, “all feces were removed from the transects” might be more appropriate. c. Were there any other sympatric carnivores that could be mis-identified as grey fox or coyote (e.g. Mephitidae species or other Vulpes species)? Especially if so, were all other scats cleared from transects during each survey? 4. Although the authors mention sampling transects in each vegetation type, and that coyote food item consumption may vary by habitat type (line 276), vegetation type is not included in any analysis or discussion. The authors find high dietary overlap, but do not discuss any other mechanisms which may facilitate stable coexistence. Examining the spatial overlap (site based or vegetation type based) of both species occurrences and dietary items may further illuminate the mechanisms which allow for sympatry of these two species. While this is briefly mentioned as a potential mechanism (lines 325 – 326), the authors likely have the necessary data to examine a spatial component as well (location and vegetation association of scat samples) to improve their findings. 5. The authors do a good job of thoroughly reviewing the findings in the discussion, but could strengthen their conclusions with greater connections back to the introduction. The authors do not relate back to their prediction in the introduction (lines 73 – 77), and I believe this would be important especially because the authors found high and not low trophic niche overlap. Due to these findings, further discussion on if/how stable coexistence may be occurring could be beneficial. The final conclusion in the discussion feels a bit lacking and leaves the reader wondering how these findings are applicable and where researchers/managers might benefit and move forward. 6. The authors have generally written a nice manuscript, but it could be improved with some editing to correct grammar and improve sentence flow. A few examples are: a. Lines 33 – 35: the first “difference” would read better as “differences” ; “these different body sizes canid species” perhaps instead could be “these different sized canid species” b. Line 47 and 59: what is “them” referencing ? c. Line 55: “its distribution the overlap of its diets” – what is “its” referencing? d. Lines 61 – 65 and lines 73 - 77: these sentences are a bit hard to work through and could be improved with grammatical changes and/or being broken into two sentences. Reviewer #2: The subject is interesting. However, it lacks many details of the methodology in the collection of samples. It is important to have information on the period with which the transects traveled, if in all the collections they traveled the same transects. This is due to the fact that generalist and opportunistic species such as the coyote and the gray fox can vary their diet in reduced time and space. On the other hand, the morphological characterization of the excrements would be convenient to strengthen it with some chemical or molecular technique; because its morphology is similar and the probability of error is high. On the other hand, it is important to include complementary material with the characteristics of the hair of the identified species because several are similar. ********** 6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files. If you choose “no”, your identity will remain anonymous but your review may still be made public. Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy. 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Submitted filename: PONE-D-21-19581.pdf Click here for additional data file. 30 Aug 2021 DETAILED DESCRIPTION ON HOW DO WE ATTEND ALL COMMENTS AND SUGGESTIONS DONE BY THE ASSOCIATE EDITOR AND BY TWO REVIEWERS MANUSCRIPT PONE-S-21-24256 Trophic niche overlap between coyotes and gray foxes in a temperate forest in Durango, Mexico authored by César Ricardo Rodríguez-Luna, Jorge Servín, David Valenzuela-Galván (as corresponding author) and by Rurik List Requests of the Associate Editor and/or by the journal 1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf R= We have done the required changes, and double checked that we do follow correctly PLOS ONE’s style requirements in the newer corrected version we are now submitting. 2. Please include your full ethics statement in the ‘Methods’ section of your manuscript file. In your statement, please include the full name of the IRB or ethics committee who approved or waived your study, as well as whether or not you obtained informed written or verbal consent. If consent was waived for your study, please include this information in your statement as well. R= Since our data is based on the collection and analysis of feces of the studied species, in México there is no need to obtain a permit for this. We do not collect and handle individuals of the studied species, therefore, we did not have to adhere to a particular ethic guideline for handling and studying animals. In México, to be able to do research activities inside a Natural Protected Area, it is customary to inform the authorities of the NPA about the objectives and needs of the particular research; we did that before starting our research at La Michilia Biosphere Reserve. Since it is only needed to inform the authorities of the NPA, we only received verbal confirmation that they received our research protocol and that they do not had any issues in let in us to do our research, that provides useful information for the management of natural resources within the NPA. 3. In your Data Availability statement, you have not specified where the minimal data set underlying the results described in your manuscript can be found. PLOS defines a study's minimal data set as the underlying data used to reach the conclusions drawn in the manuscript and any additional data required to replicate the reported study findings in their entirety. All PLOS journals require that the minimal data set be made fully available. For more information about our data policy, please see http://journals.plos.org/plosone/s/data-availability. "Upon re-submitting your revised manuscript, please upload your study’s minimal underlying data set as either Supporting Information files or to a stable, public repository and include the relevant URLs, DOIs, or accession numbers within your revised cover letter. For a list of acceptable repositories, please see http://journals.plos.org/plosone/s/data-availability#loc-recommended-repositories. Any potentially identifying patient information must be fully anonymized. Important: If there are ethical or legal restrictions to sharing your data publicly, please explain these restrictions in detail. Please see our guidelines for more information on what we consider unacceptable restrictions to publicly sharing data: http://journals.plos.org/plosone/s/data-availability#loc-unacceptable-data-access-restrictions. Note that it is not acceptable for the authors to be the sole named individuals responsible for ensuring data access. We will update your Data Availability statement to reflect the information you provide in your cover letter R= We have now uploaded a raw data base as supporting information that contains all needed data for anyone to perform the same analysis we did and present in our manuscript and to replicate the reported study findings in their entirety. 4. We note that Figure (1) in your submission contain map images which may be copyrighted. All PLOS content is published under the Creative Commons Attribution License (CC BY 4.0), which means that the manuscript, images, and Supporting Information files will be freely available online, and any third party is permitted to access, download, copy, distribute, and use these materials in any way, even commercially, with proper attribution. For these reasons, we cannot publish previously copyrighted maps or satellite images created using proprietary data, such as Google software (Google Maps, Street View, and Earth). For more information, see our copyright guidelines: http://journals.plos.org/plosone/s/licenses-and-copyright. We require you to either (1) present written permission from the copyright holder to publish these figures specifically under the CC BY 4.0 license, or (2) remove the figures from your submission: 1. You may seek permission from the original copyright holder of Figure (1) to publish the content specifically under the CC BY 4.0 license. We recommend that you contact the original copyright holder with the Content Permission Form (http://journals.plos.org/plosone/s/file?id=7c09/content-permission-form.pdf) and the following text: “I request permission for the open-access journal PLOS ONE to publish XXX under the Creative Commons Attribution License (CCAL) CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). Please be aware that this license allows unrestricted use and distribution, even commercially, by third parties. Please reply and provide explicit written permission to publish XXX under a CC BY license and complete the attached form.” Please upload the completed Content Permission Form or other proof of granted permissions as an "Other" file with your submission. In the figure caption of the copyrighted figure, please include the following text: “Reprinted from [ref] under a CC BY license, with permission from [name of publisher], original copyright [original copyright year].” 2. If you are unable to obtain permission from the original copyright holder to publish these figures under the CC BY 4.0 license or if the copyright holder’s requirements are incompatible with the CC BY 4.0 license, please either i) remove the figure or ii) supply a replacement figure that complies with the CC BY 4.0 license. Please check copyright information on all replacement figures and update the figure caption with source information. If applicable, please specify in the figure caption text when a figure is similar but not identical to the original image and is therefore for illustrative purposes only. The following resources for replacing copyrighted map figures may be helpful: USGS National Map Viewer (public domain): http://viewer.nationalmap.gov/viewer/ The Gateway to Astronaut Photography of Earth (public domain): http://eol.jsc.nasa.gov/sseop/clickmap/ Maps at the CIA (public domain): https://www.cia.gov/library/publications/the-world-factbook/index.html and https://www.cia.gov/library/publications/cia-maps-publications/index.html NASA Earth Observatory (public domain): http://earthobservatory.nasa.gov/ Landsat: http://landsat.visibleearth.nasa.gov/ USGS EROS (Earth Resources Observatory and Science (EROS) Center) (public domain): http://eros.usgs.gov/# Natural Earth (public domain): http://www.naturalearthdata.com/ R= figure 1 was created by CRRL (the first author) using shape files about topography and vegetation types and land cover produced by INEGI (Mexican National Institute of Geography and Statistics) and publicly available for free, for any user at the following link (https://www.inegi.org.mx/datos/?t=0150). Shape files were projected to produce figure 1 using QGIS software (v. 3.14.) that is free online to download at the following link (https://www.qgis.org/es/site/forusers/download.html). We stated now in our corrected version within the Methods section the source for this information and we stated now at the figure 1 caption that it was done in that way by CRRL and therefore we do not need to seek permission from anyone. Reviewer's Comments to the Author Reviewer #1: This manuscript provides a simple, straightforward examination of dietary niche overlap between sympatric coyotes and gray foxes. As the authors point out, there is a lack of data examining the partitioning of these two ecologically similar and highly overlapping carnivores. I believe the authors’ research provides valuable information on the dietary niches of these two species. R= we thank and appreciate reviewer’s considerations to our manuscript. However, I also note a number of points that could be addressed to strengthen the manuscript. 1. The introduction could benefit from a bit more thoughtful expansion. The authors state that high trophic overlap for ecologically similar species is rare (line 45), but I might disagree. There are many sympatric generalist species, including carnivores (such as foxes, coyotes and bobcats), that can have high trophic overlap but coexist through mechanisms such as fine-scale spatial and/or temporal partitioning. In fact, the authors mention a study where coyotes and gray foxes can be found to have high dietary overlap (line 55). I believe it would strengthen the introduction to discuss the mechanisms which allow sympatric species with overlapping trophic niches to have stable coexistence. The authors mention that trophic niche segregation may allow stable coexistence (line 64), but what about circumstances (such as the findings in this manuscript) where trophic niche overlap is high but coexistence still appears to occur? R= we have now added more information and a more thoughtful expansion on the issues mentioned by reviewer 1 to our introduction. 2. The transition from the broad introduction to the authors’ specific research seems a bit abrupt. Further discussion on how the reasoning and application of this research may be prudent. R= We have added a bit more information about our reasoning of our research and why we consider that might provide insights on how the trophic niche segregation can explain partially the coexistence of sympatric ecologically similar species. Also, we modified the writing to solve the abrupt transition between the broad introduction and our specific research. 3. In the Sample Collection and Identification section, a few points may benefit from clarification which could improve future design replication: a. How were transects allocated with respect to vegetation type? What was the length(s) of each transect? R= We have provided now information about the number of transects, its length and location in relation to vegetation. b. This is quite minor, but it feels inappropriate to say all feces were removed from the study area (line 99). Instead, “all feces were removed from the transects” might be more appropriate. R= we accept and add this suggestion to our ms. c. Were there any other sympatric carnivores that could be mis-identified as grey fox or coyote (e.g., Mephitidae species or other Vulpes species)? Especially if so, were all other scats cleared from transects during each survey? R= In the studied area, there is only two wild canid species, but indeed, there are more sympatric carnivores, however, all produce quite distinctive feces and none can be easily confused with coyote or gray fox feces. In our original version of the manuscript, we stated that we identify all collected feces based on size, color, shape, length and maximum diameter and its comparison with the data for feces of different mammalian carnivore species published on field guides for different areas of the country. We discarded any collected feces that could be assigned to other species different of Coyote or Gray Fox. Asides, in the area, a previous study (Servin and Huxley, 1991) collected and measured different morphological data of a quite big sample of feces of Coyote and Gray Fox. We used the morphological data produced by them, to classify our collected feces as Coyote or Gray Fox feces, discarding all feces with maximum diameter falling in the overlapping area of the diameter distribution range of each species. We have added a bit more detail of this to our corrected version of the manuscript. 4. Although the authors mention sampling transects in each vegetation type, and that coyote food item consumption may vary by habitat type (line 276), vegetation type is not included in any analysis or discussion. R= we have now changed our figure one to show the vegetation types and the distribution sampling transects in the studied area. Asides, in the text of the manuscript we briefly mention how many sampling transects were located on each vegetation type and we explain in the manuscript that fecal samples of both species were collected on all vegetation types and sampling was in accordance to the proportion of each habitat type. We added a couple of lines to our discussion stating that although feces were collected in all habitat types, not much inference about food resources consumed by habitat type can be derived from the location site of the feces sample, since an animal can consume resources at one place, and defecate several hours before at a different habitat type. The authors find high dietary overlap, but do not discuss any other mechanisms which may facilitate stable coexistence. Examining the spatial overlap (site based or vegetation type based) of both species occurrences and dietary items may further illuminate the mechanisms which allow for sympatry of these two species. While this is briefly mentioned as a potential mechanism (lines 325 – 326), the authors likely have the necessary data to examine a spatial component as well (location and vegetation association of scat samples) to improve their findings. R= We appreciate this reviewer’s observation and we have now expanded our discussion to include information about any other mechanism that can facilitate stable coexistence. 5. The authors do a good job of thoroughly reviewing the findings in the discussion, but could strengthen their conclusions with greater connections back to the introduction. The authors do not relate back to their prediction in the introduction (lines 73 – 77), and I believe this would be important especially because the authors found high and not low trophic niche overlap. Due to these findings, further discussion on if/how stable coexistence may be occurring could be beneficial. The final conclusion in the discussion feels a bit lacking and leaves the reader wondering how these findings are applicable and where researchers/managers might benefit and move forward. R= We also thank and appreciate this reviewer’s observation, and we have considered and modified as suggested, our discussion. 6. The authors have generally written a nice manuscript, but it could be improved with some editing to correct grammar and improve sentence flow. A few examples are: a. Lines 33 – 35: the first “difference” would read better as “differences”; “these different body sizes canid species” perhaps instead could be “these different sized canid species” b. Line 47 and 59: what is “them” referencing? c. Line 55: “its distribution the overlap of its diets” – what is “its” referencing? d. Lines 61 – 65 and lines 73 - 77: these sentences are a bit hard to work through and could be improved with grammatical changes and/or being broken into two sentences. R= we have done all suggested changes and also we reviewed our manuscript to edit and correct any grammar inconsistencies and tried to improve more our sentence flow. Reviewer #2 The subject is interesting. However, it lacks many details of the methodology in the collection of samples. It is important to have information on the period with which the transects traveled, if in all the collections they traveled the same transects. This is due to the fact that generalist and opportunistic species such as the coyote and the gray fox can vary their diet in reduced time and space. R= Similar request was done by reviewer 1. We have added all this detail to our corrected version of the manuscript, including information of sampling effort, sampling periods and if the same transects were travelled always. On the other hand, the morphological characterization of the excrements would be convenient to strengthen it with some chemical or molecular technique; because its morphology is similar and the probability of error is high. R= We have now provided more detail on the procedure we followed to minimize the potential misidentification of feces, and the conservative procedure implemented to assign with most confidence a feces sample to coyote or gray fox. The molecular or chemical methods suggested by the reviewer are indeed different procedures to assign to species a collected feces, however we already review all collected feces and we not have the possibility or the resources to implement those methods. On the other hand, it is important to include complementary material with the characteristics of the hair of the identified species because several are similar. R= We have now provided more detail on the procedure we followed to identify food items found on feces samples. Regarding its suggestion to include complementary material (e.g. microscopic slides), all the microscopic slides of guarding hairs we prepared with hairs obtained from the feces samples, are part of an ongoing undergraduate thesis work and therefore cannot be publicly shared yet. Those slides were compared to published microscopic images of guarding hairs of different mammal species that are included in several books, whose references were already cited in our original manuscript and still are in our corrected version of the ms. We appreciate a lot the comments and observations done by reviewer 2, and we thank him to let us know who he is: Dr. Octavio Monroy-Vilchis, a researcher we followed and respect. Submitted filename: Response to Reviewers- PONE-S-21-24256.pdf Click here for additional data file. 8 Oct 2021 PONE-D-21-19581R1Trophic niche overlap between coyotes and gray foxes in a temperate forest in Durango, Mexico PLOS ONE Dear Dr. Valenzuela-Galván, Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process. The authors adequately addressed all the reviewers' comments. However, I agree with Rev 1 in that readability of the manuscript must be improved, and English grammar and structure thoroughly checked and revised. Once these issues are addressed, I will be happy to accept the manuscript. Some minor changes are suggested below (please revise the entire manuscript for other typos or errors). Please submit your revised manuscript by Nov 22 2021 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file. Please include the following items when submitting your revised manuscript: If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter. A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'. A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'. An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'. If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols. We look forward to receiving your revised manuscript. Kind regards, Nicoletta Righini, PhD Academic Editor PLOS ONE Journal Requirements: Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice. Additional Editor Comments (if provided): Some minor revisions: L. 16: Resource partitioning, and especially dietary partitioning, is ….. L. 18: Mexico – without accent L. 18: Better put ‘in Mexico’ after ‘widely distributed’ L. 20: HAVE not been L. 40- understanding the ways in which species partition these resources L. 46- IT is relatively common… L. 61- ..THEIR coexistence.. L. 68- THESE canids l. 70 – HAVE not been thoroughly studied L. 77- a mechanism partly explaining L. 127- We CHOSE L. 128-131: ‘spp.’ must not be italicized, only the name of the genus goes in italics, e.g. Pinus spp. L. 132- formal collection of FECAL samples L. 134- however THEY all produce.. L. 135- careful to IDENTIFY feces L. 138: IN the vicinity of the collection site (delete ‘DE’) L. 145: Please rephrase (season considered and considered…) L. 145: we assigned feces TO any.. L. 146- feces collected IN a particular season WERE representative… L: 147: IN that period of the year. L. 148-49: In THE laboratory….and washed THEM with water L. 160: trough THEIR guarding hairs L. 167: the overall and SEASONAL representation L. 170: the percentage of feces that CONTAINS…and although IT DOES not necessarily… L. 185: Mexico without accent L. 190 : and that they DID NOT HAVE any issues in LETTING us do… L. 194: FECAL samples L. 201: we EXPLORED L. 337: detected in coyote’s feces likely represent carrion… L. 340: COINCIDE with the feeding patternS L. 373-374- IN the area…..differences we found IN trophic diversity L. 378: However, the relevance of each…. L. 379: IN the coyote’s than IN the gray fox diet L. 379: Delete ‘and’ at the beginning of the sentence L. 395: FECAL samples L. 398-399: shouldn’t this be ‘ defecate several hours LATER..’? (not ‘before’) L. 399: IN a different habitat type L. 399- However, differences among habitats in the success… L. 401: in accordance WITH our findings L. 410 – FOR a better understanding L. 411: can help minimize L. 415: IN this Natural Protected Area [Note: HTML markup is below. Please do not edit.] Reviewers' comments: Reviewer's Responses to Questions Comments to the Author 1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation. Reviewer #1: (No Response) ********** 2. Is the manuscript technically sound, and do the data support the conclusions? The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented. Reviewer #1: Yes ********** 3. Has the statistical analysis been performed appropriately and rigorously? Reviewer #1: Yes ********** 4. Have the authors made all data underlying the findings in their manuscript fully available? The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified. Reviewer #1: Yes ********** 5. Is the manuscript presented in an intelligible fashion and written in standard English? PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here. Reviewer #1: Yes ********** 6. Review Comments to the Author Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters) Reviewer #1: The authors thoughtfully addressed the initial review comments. My only minor comment is that the manuscript requires a final proof-read to eliminate any typos and improve readability through correcting some grammar and sentence structure. A few examples from the Introduction, but not a thorough list, are below: • Line 46: what is the subject of “is relatively common” ? • Line 54 – 57: This sentence is a bit difficult to understand • Line 57: “this kind” should be changed to “these kind” to match the plural of “interactions” o Also on line 62: “this questions” should be changed to “these questions” • Line 62: “choose” should be “chose” • Line 63: there should not be a comma after “species” ********** 7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files. If you choose “no”, your identity will remain anonymous but your review may still be made public. Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy. Reviewer #1: No [NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.] While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step. 4 Nov 2021 DETAILED DESCRIPTION ON HOW DO WE ATTEND ALL COMMENTS AND SUGGESTIONS DONE BY THE ASSOCIATE EDITOR AND BY TWO REVIEWERS Journal Requirements: Please review your reference list to ensure that it is complete and correct. R= We have done so; all cited references are in the reference list, that is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice. R= we are not citing any retracted paper. We have not changed our previous reference list. We have done, only minor changes for some references (e.g. added page numbers for a reference that did not have that information). Additional Editor Comments (if provided): Some minor revisions: L. 16: Resource partitioning, and especially dietary partitioning, is ….. L. 18: Mexico – without accent L. 18: Better put ‘in Mexico’ after ‘widely distributed’ L. 20: HAVE not been L. 40- understanding the ways in which species partition these resources L. 46- IT is relatively common… L. 61- ..THEIR coexistence.. L. 68- THESE canids l. 70 – HAVE not been thoroughly studied L. 77- a mechanism partly explaining L. 127- We CHOSE L. 128-131: ‘spp.’ must not be italicized, only the name of the genus goes in italics, e.g. Pinus spp. L. 132- formal collection of FECAL samples L. 134- however THEY all produce.. L. 135- careful to IDENTIFY feces L. 138: IN the vicinity of the collection site (delete ‘DE’) L. 145: Please rephrase (season considered and considered…) L. 145: we assigned feces TO any.. L. 146- feces collected IN a particular season WERE representative… L: 147: IN that period of the year. L. 148-49: In THE laboratory….and washed THEM with water L. 160: trough THEIR guarding hairs L. 167: the overall and SEASONAL representation L. 170: the percentage of feces that CONTAINS…and although IT DOES not necessarily… L. 185: Mexico without accent L. 190 : and that they DID NOT HAVE any issues in LETTING us do… L. 194: FECAL samples L. 201: we EXPLORED L. 337: detected in coyote’s feces likely represent carrion… L. 340: COINCIDE with the feeding patternS L. 373-374- IN the area…..differences we found IN trophic diversity L. 378: However, the relevance of each…. L. 379: IN the coyote’s than IN the gray fox diet L. 379: Delete ‘and’ at the beginning of the sentence L. 395: FECAL samples L. 398-399: shouldn’t this be ‘ defecate several hours LATER..’? (not ‘before’) L. 399: IN a different habitat type L. 399- However, differences among habitats in the success… L. 401: in accordance WITH our findings L. 410 – FOR a better understanding L. 411: can help minimize L. 415: IN this Natural Protected Area R= ALL 42 requested changes were done in the new version of the manuscript Review Comments to the Author Reviewer #1: The authors thoughtfully addressed the initial review comments. My only minor comment is that the manuscript requires a final proof-read to eliminate any typos and improve readability through correcting some grammar and sentence structure. A few examples from the Introduction, but not a thorough list, are below: • Line 46: what is the subject of “is relatively common” ? • Line 54 – 57: This sentence is a bit difficult to understand • Line 57: “this kind” should be changed to “these kind” to match the plural of “interactions” o Also on line 62: “this questions” should be changed to “these questions” • Line 62: “choose” should be “chose” • Line 63: there should not be a comma after “species” R= ALL 6 requested changes were done in the new version of the manuscript. Asides, we have carefully reviewed the manuscript and corrected how we were using the square brackets for the references and some minor misspelling errors. Submitted filename: response-letter-plosone-nov2021.doc Click here for additional data file. 8 Nov 2021 Trophic niche overlap between coyotes and gray foxes in a temperate forest in Durango, Mexico PONE-D-21-19581R2 Dear Dr. Valenzuela-Galván, We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements. Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication. An invoice for payment will follow shortly after the formal acceptance. To ensure an efficient process, please log into Editorial Manager at http://www.editorialmanager.com/pone/, click the 'Update My Information' link at the top of the page, and double check that your user information is up-to-date. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org. If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org. Kind regards, Nicoletta Righini, PhD Academic Editor PLOS ONE 19 Nov 2021 PONE-D-21-19581R2 Trophic niche overlap between coyotes and gray foxes in a temperate forest in Durango, Mexico Dear Dr. Valenzuela-Galván: I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department. If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org. If we can help with anything else, please email us at plosone@plos.org. Thank you for submitting your work to PLOS ONE and supporting open access. Kind regards, PLOS ONE Editorial Office Staff on behalf of Dr. Nicoletta Righini Academic Editor PLOS ONE
  10 in total

1.  The competitive exclusion principle.

Authors:  G HARDIN
Journal:  Science       Date:  1960-04-29       Impact factor: 47.728

2.  Resource partitioning in ecological communities.

Authors:  T W Schoener
Journal:  Science       Date:  1974-07-05       Impact factor: 47.728

3.  Neotropical region: a shapefile of Morrone's (2014) biogeographical regionalisation.

Authors:  Peter Löwenberg-Neto
Journal:  Zootaxa       Date:  2014-05-26       Impact factor: 1.091

4.  Interference competition and niche theory.

Authors:  T J Case; M E Gilpin
Journal:  Proc Natl Acad Sci U S A       Date:  1974-08       Impact factor: 11.205

5.  A test for comparing diversities based on the Shannon formula.

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Journal:  J Theor Biol       Date:  1970-10       Impact factor: 2.691

Review 6.  Complex interactions among mammalian carnivores in Australia, and their implications for wildlife management.

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Journal:  Biol Rev Camb Philos Soc       Date:  2005-08

7.  Competition and intraguild predation among three sympatric carnivores.

Authors:  Jose M Fedriani; Todd K Fuller; Raymond M Sauvajot; Eric C York
Journal:  Oecologia       Date:  2014-03-03       Impact factor: 3.225

8.  Effects of urbanization on resource use and individual specialization in coyotes (Canis latrans) in southern California.

Authors:  Rachel N Larson; Justin L Brown; Tim Karels; Seth P D Riley
Journal:  PLoS One       Date:  2020-02-05       Impact factor: 3.240

9.  Differential Habitat Use or Intraguild Interactions: What Structures a Carnivore Community?

Authors:  Matthew E Gompper; Damon B Lesmeister; Justina C Ray; Jay R Malcolm; Roland Kays
Journal:  PLoS One       Date:  2016-01-05       Impact factor: 3.240
  10 in total

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