Diet switching in a generalist mammalian folivore: fundamental to maximising intake.

Generalist mammalian herbivores exploit a diverse diet. A generalised feeding strategy utilises a mixed diet to obtain a range of nutrients and to reduce the detoxication load of similar groups of plant secondary metabolites (PSMs). There is limited research investigating how mammalian herbivores achieve this dietary mixing in their daily foraging activities. We investigated the patterns of, and behaviours associated with, dietary mixing in a generalist mammalian folivore, the common brushtail possum (Trichosurus vulpecula). Possums were offered foliage of two eucalypt species (Eucalyptus globulus and E. regnans) as either (a) Full choice: both species offered for 8 h; (b) Restricted choice: both species offered for 2x2 h blocks; (c) G-R no choice: E. globulus offered for the first 4 h, E. regnans offered for next 4 h; and (d) R-G no choice: E. regnans offered for first 4 h, E. globulus offered for next 4 h. We hypothesised that possums would maximise intake on the Full choice diet, where time availability was greatest in combination with a choice of foliage. We also hypothesised that diet switching, defined as the frequency of changing between food types while feeding, would play a fundamental role in maximising intake. Possums achieved maximum intake on the Full choice diet and minimum intake on the No choice diets. Although intake was similar between the Restricted choice and No choice diets, possums achieved this intake in half the amount of time when able to switch regularly between foliage on the Restricted choice diet. We conclude that a generalist herbivore's ability to effectively switch diets when foraging is fundamental to maximising intake. Hence, the degree of plant heterogeneity in an environment, and the spatial scale at which it occurs, may affect an herbivore's foraging decisions and, ultimately, influence its foraging efficiency.