Document Type

Dissertation

Degree

Doctor of Philosophy

Major

Biology, Ecology

Date of Defense

11-21-2019

Graduate Advisor

Robert E. Ricklefs

Co-Advisor

Iván Jímenez

Committee

Robert Marquis

Nathan Muchhala

Nigel Pitman

Abstract

At small spatial scales, the composition of species assemblages depends on local conditions and the dispersal of propagules from surrounding regions. In turn, processes taking place at broad temporal and spatial scales, including changes in regional physiography and climate, shape the species pools in these source regions. This dissertation seeks to understand the effects of regional and historical processes on the spatial distribution of Neotropical tree species. In chapter 1, I investigate regional enrichment of local species assemblages testing two hypothesis: i) local species assemblages are enriched by unfiltered species pools, which are composed of all species that can disperse to a locality, regardless of the suitability of the local environment; and ii) local species assemblages are enriched by filtered species pools, which are composed of all species that can disperse to a locality from similar environments. I found that unfiltered species pools enrich local species assemblages. In chapter 2, I explore two legacies of the Great American Biotic Interchange: i) a major contrast in plant family composition between lowland and montane tree floras, and ii) lowland floras form a nested gradient of species diversity from the Darien to the Tehuantepec region, whereas montane floras form a nested gradient in the opposite direction. I found marked differences in the representation of families between lowland and montane floras. However, lowland and montane floras do not exhibit the proposed nested gradients of diversity. In chapter 3, I focus on the effects of the Last Glacial Maximum on the distribution of palms across Neotropical lowland humid-to-superhumid forest. I explore the hypothesis of postglacial migration lags, which states that due to the effects of past glaciations species do not occupy all climatically suitable areas. I found that palm species had little opportunity to experience postglacial migration lags but, nonetheless, seem to exhibit such lags. This thesis illustrates how consideration of processes operating at different spatial scales in particular historical contexts contributes to our understanding of current patterns and dynamics of species distributions, providing a foundation for efforts directed at the conservation of biodiversity.

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