Changing species interactions and processes in tropical forests in the Anthropocene
Dunham, Amy E.
Doctor of Philosophy
Human activities have caused widespread species declines and habitat degradation, particularly in tropical forests. These changes are not just consequences of global change, but they are also themselves drivers of change. This is because as vertebrate assemblages are altered, ecological and evolutionary processes can be influenced by changes in species interactions. The consequences of this can be profound, but they are not fully understood. Here, we address three critical but understudied aspects of ecological and evolutionary cascades triggered by current global change patterns. In Chapter 1, we show that defaunation in an Afrotropical system can indirectly increase understory vegetation. We also report a sharp decrease in termite abundances and a 25% lower contribution of invertebrates to decomposition in defaunated compared to faunally-intact forest. Overall, this chapter indicates defaunation may indirectly affect understory vegetation and invertebrate communities with consequences for foodweb dynamics and processes on the forest floor that ultimately influence nutrient cycling. In Chapter 2, we take a finer-scale approach to look at how defaunation in a neotropical forest affects seed dispersal and the resulting spatial genetic structure of a dominant, animal dispersed palm. Using a genetic approach we find evidence for the first time that even in a generalist tree species (i.e. one able to gain dispersal from a broad suite of frugivores), defaunation can affect seed-dispersal, as indicated by the higher spatial genetic structure we find associated with defaunation. Ultimately, this chapter has implications for how defaunation influences the maintenance and spatial distribution of genetic variation for tropical plant communities. In Chapter 3, we move from investigating how species interactions and ecological processes are affected by local extinctions to how they are influenced by local habitat disturbance, an equally ubiquitous threat. In studying frugivore visitation to host plants, we find that indicators of past forest disturbance are associated with lower fruit removal rates and altered community composition of frugivore mutualists feeding on fruits of a neotropical palm. This chapter demonstrates that localized differences in forest structure resulting from past disturbance can influence species interactions for decades, potentially influencing seed dispersal services, plant demography and forest regeneration patterns.