Changes of species diversity in a simulated fragmented neutral landscape

To predict how ecological communities respond to large-scale patterns of fragmentation, both local and global processes need to be combined into an integrated modelling approach. Using neotropical rain forests as an illustration, we constructed a large metacommunity (200km×200 km) where all the trees ≥10 cm dbh are modelled, assuming panmixis within local communities (each 10km×10 km in size), and limited dispersal across communities. Under the assumption of neutrality, we simulated an equilibrium configuration, that we subsequently submitted to several scenarios of environmental fragmentation. Fragmentation leads to a significant reduction of species diversity in edge communities. After the disturbance, the system returns to equilibrium rapidly if the disturbance is not too widespread, due to dispersal from neighboring areas. However, post-disturbance levels of local diversity remain much lower that pre-disturbance ones, at least within ecological times. These results illustrate the claim that neutral landscape models exhibit a partly predictable ecological-time dynamics, mostly driven by the ability of the metacommunity to buffer accidents in local communities. Such a multi-scale model should be considered as a null scenario in testing more complex effects related to habitat fragmentation, such as genetic bottlenecks, or loss of keystone species.