One of the greatest threats to biodiversity and the sustainable functioning of ecosystems is the clearing of forests for agriculture. Because litter-dwelling ants are very good bioindicators of man-made disturbance, we used them to compare monospecific plantations of acacia trees, cocoa trees, rubber trees and pine trees with the surrounding Neotropical rainforest (in contrast to previous studies on forest fragments embedded in industrial monocultures). Although the global level of species turnover was weak, species richness decreased along a gradient from the forest (including a treefall gap) to the tree plantations among which the highest number of species was noted for the cocoa trees, which are known to be a good compromise between agriculture and conservation. Species composition was significantly different between natural habitats and the plantations that, in turn, were different from each other. Compared to the forest, alterations in the ant communities were (1) highest for the acacia and rubber trees, (2) intermediate for the cocoa trees, and, (3) surprisingly, far lower for the pine trees, likely due to very abundant litter. Functional traits only separated the rubber tree plantation from the other habitats due to the higher presence of exotic and leaf-cutting ants. This study shows that small monospecific stands are likely sustainable when embedded in the rainforest and that environmentally-friendly strategies can be planned accordingly.
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RBINS Staff Publications 2017
Local extinction of specialist species due to fragmentation is one of the major causes of biodiversity loss. Increased extinction rates in smaller fragments are expected to result from both smaller local population sizes, which increase the effect of environmental or demographic stochasticity, and increased edge effects. However, the relative effect sizes of these two factors are still poorly investigated. We attempt to disentangle these effects on ground beetle communities of temperate broadleaved woodland fragments situated in one of the most urbanized regions in Belgium. Assemblages were sampled along transects that extended from 30 m outside to 100 m inside both small and large historic forest fragments. Although species assemblages within the forest were highly distinct compared to those sampled outside the forest, species turnover along these transects was less pronounced within forest fragments indicating only weak edge effects. The magnitude of edge effects did not differ significantly between large and small fragments. However, larger differences in species composition were observed with respect to fragment size, wherein highly specialized species persisted only in the largest fragment. In sum, increased local extinction processes in smaller fragments, which led to a strong reduction of specialized and wingless forest species, appeared to be the most important factor that drives changes in species composition in this historic and fragmented woodland complex.
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