Open Collections

Description

Forest fragmentation can have a myriad of ecological effects, and identifying the most important causal drivers can be challenging. For example, when forest fragmentation creates forest patches of differing sizes, this gradient in forest size could affect local communities by altering any of resource quality, abiotic conditions or colonization rates. Using a quasi-reciprocal transplantation design, our study of forest size effects on water-filled treeholes separates the size of the site from which litter originated from the size of site that received the litter in treeholes. This allows us to independently assess mediation by litter quality (effect of origin site area on resources) and mediation by abiotic and colonization mechanisms (effect of recipient site area). We placed artificial analogs of treeholes across a gradient of forest sizes in a highly fragmented landscape in Costa Rica, allowing natural colonization of these treeholes for 10 months before manipulating leaf litter origin in each treehole. One month after the manipulation we measured decomposition and invertebrate communities. Data was collected between December 2017 and December 2018 in and around Santa Cecilia, Costa Rica in various sized forest patches. Treeholes were placed in the field in the late Fall 2017 and left to colonize naturally until early October 2018. Treehole environmental data was taken and a leaf litter bag was deployed to each treehole in early October and then left for two months. Treeholes were destructively sampled and macroinvertebrates were preserved after two months in December. We found that the size of both origin and recipient sites could be important, but their relative importance differed between components of the treehole ecosystem. Litter originating from smaller sites supported higher decomposition rates and more invertebrates overall, consistent with a strong role for litter quality in mediating forest size effects on detrital-based communities. By contrast, invertebrate composition was more affected by the size of sites receiving the treeholes, consistent with site-specific factors such as abiotic conditions or colonization. Underlying this change in composition were family-specific responses of invertebrate taxa to recipient and origin site size. These results demonstrate that fragmentation can affect various parts of an ecosystem through different mechanisms, making it important to assess the impact of fragmentation at multiple levels.