UBC Theses and Dissertations
Losses of rare forest invertebrates and divergent rates of litter decomposition under different land uses Cuke, Melissa Erin
Habitat destruction and fragmentation are dominant disturbances in tropical landscapes, but consequences of these changes for invertebrates and ecosystem functioning are poorly described and explained. In northwestern Costa Rica I used pitfall sampling and litter bag experiments to investigate consequences of two land-use changes (forest conversion to orange groves and forest fragmentation) for litter invertebrates and decomposition. I infer effects of forest conversion and fragmentation based on comparisons of intact forest with orange groves and forest fragments, respectively. Invertebrate diversity differed among habitat types. Invertebrate family richness and evenness in orange groves were 24% and 56% lower, respectively, relative to intact forest. Beta diversity (dissimilarity in invertebrate composition) among orange groves was high, likely due to variation in microclimate with grove age and/or management regime. Forest patch diversity was similar to that of intact forest, and composition was marginally more dissimilar between forest patches than between intact forest sites. Consistency in local richness between intact and fragmented forest was largely attributed to a suite of disturbance-adapted taxa detected exclusively in forest patches. Approximately 11% of the families that were naturally common in intact forest were rare or range-limited in forest fragments. These results emphasize the need for large forest reserves to prevent considerable losses of intact forest fauna. Losses of intact forest invertebrates in both orange groves and forest patches were explained by habitat modification (increases in litter temperature) and were more likely for families that are naturally rarer. Forest conversion and fragmentation had divergent effects on litter decomposition. During the wet season, decomposition was 9% faster in orange groves relative to forest. This pattern was explained by higher temperatures and lower litter cover in orange groves; I discuss both indirect and direct microenvironment mechanisms. In contrast, dry season decomposition rates were 7% slower in forest fragments than those in intact forest. Fragmentation effects on decomposition were explained by the action of shredder and/or saprophagous macroinvertebrates, which enhanced decomposition rates in intact forest but not in forest patches. The seasonal aspect of these results emphasizes the importance of accounting for intra-annual variation when assessing disturbance effects in natural systems.
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