Biodiversity trends are as bad as expected
In a recent work published in Science, Dornelas et al. (2014) analyzed a large sample of local biodiversity time series, involving more than 35,000 terrestrial and aquatic species from biomes across Earth. Their analysis revealed a systematic change in local community composition and a net biodiversity loss at the global scale. However, the authors were surprised by the absence of negative trend of biodiversity at local scale. We think that Dornelas et al.’s work is very important to the field of biodiversity conservation, not because their last result is contrary to expectations (as stated by the authors), but because their combined results confirm that the scientific community has an accurate understanding of the effects of ongoing anthropogenic pressures on biodiversity processes and patterns. According to the ecological niche theory (Hutchinson 1957; Futuyma and Moreno 1988), massive habitat changes driven by human activities should favor the expansion of (regional and exotic) generalist species, and specialists of Human-altered habitats, while reducing the fitness and range of many species specialized to the ‘‘old’’ disappearing habitats (along with their specific hosts, symbionts and parasites). From the local to the global scale, these two opposed trends should result in a functional and taxonomic homogenization of communities (as defined in Olden et al. 2004). This theoretical expectation was confirmed by tracking temporal changes in average habitat specialization of species at the community level (Clavel et al. 2011). At the local and regional scales, theory and modeling indicate that habitat disturbance (Devictor and Robert 2009), permanent changes of habitats into habitats of lower carrying capacity (Teyssèdre and Robert 2014), and high dispersal rates between biogeographical provinces (Rosenzweig 2001; Teyssèdre and Robert 2014) are expected to increase species richness—until a certain level of habitat modification—as observed in the field (e.g., Sax