The impact of anthropogenic disturbances on the genetic diversity of terrestrial species: A global meta-analysis.

Human activities are primarily responsible for habitat loss and changes in natural environments around the world. It has been suggested that populations inhabiting human-modified landscapes experience reduced gene flow, inbreeding depression, and loss of alleles due to genetic drift. However, empirical evidence shows the contrasting effects of anthropogenic disturbances on the genetic diversity of species. We performed a meta-analysis of 61 studies that compared the genetic diversity of plant and/or animal populations in disturbed and more preserved areas (316 paired comparisons) to investigate the genetic responses to different disturbance types. There is a negative effect (effect size: -0.45; 95% confidence interval: -0.61, -0.29) of disturbances on genetic diversity, in which the most detrimental effects are caused by the loss of connectivity and forest cover. The methodological approach can explain part of the heterogeneity among the genetic responses detected by primary studies: (a) studies using the number of effective alleles did not detect genetic erosion, while all other indices revealed negative responses to disturbances; and (b) only studies performed with transferred or a combination of transferred and specific microsatellites detected negative responses. The effects on animal populations are more detrimental than in plant populations. Only plant species with a shrub life form, self-incompatible reproductive systems, and biotic pollination and seed dispersal showed negative responses to disturbances. Despite heterogeneity among studies, there is an overall negative effect of disturbances on genetic diversity, which indicates that remaining populations inhabiting human-modified landscapes have reduced evolutionary potential and are prone to local extinction.