Date of Award

8-30-2022

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Environmental Sciences

First Advisor

Beth A. Kaplin

Second Advisor

Eugene D. Gallagher

Third Advisor

Jarrett E. Byrnes

Abstract

Seed dispersal interactions help maintain tropical plant species diversity and community stability. These interactions can be analyzed with a network approach, examining the structure (topology) of links between dispersers and plants. The structure of seed dispersal network interactions can influence resilience and robustness to environmental change. The behavioral and physical traits of animal dispersers and the plants they disperse may influence their roles within these networks and the maintenance of network structure. In turn, changes in tree fruiting phenology brought on by climate change may disrupt network interactions with consequences for community stability. Differences in seed dispersal network structure between the Afrotropics and South American Neotropics were evaluated using network-level and corresponding species traits of seed dispersers related to their roles within the networks. I also examined changes in community-scale patterns of fruiting phenology and investigated climate predictors of fruit production over 24 years in a montane tropical forest in Nyungwe National Park (NNP), Rwanda. Seed dispersal networks were less specialized in the Neotropics than the Afrotropics, while frugivores with a high degree of frugivory played key roles within Afrotropical networks. Synchrony of fruit production in NNP increased and complementarity decreased during the last few years in the study of phenological patterns of fruit production. Pioneer species were more variable in phenological patterns than non-pioneer light-demander and shade-tolerant species, and the trends in synchrony varied by elevation. The strongest climate predictors of fruit production in NNP were irradiance 15-20 months prior, minimum temperatures 28-31 months prior, and rainfall 9-13 months prior to the fruit production response. Shade tolerant species varied much less seasonally and interannually in fruit production than non-pioneer light demander and pioneer species. This dissertation provides a long-term evaluation of changes in fruiting phenology and a starting point for more in-depth studies of tropical fruiting community responses to environmental change. By taking into account these findings of climate predictors of fruit production, long-term changes in phenological patterns, and patterns of species interactions at the biogeographical scale, we can better predict the consequences of global environmental change for tropical forest communities.

Comments

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