Evan Hockridge Thesis Defense (Andrew Davies, Advisor)

Title: Seeing the Forest Between the Trees: The Ecology of Open-Canopy  Ecosystems in Central African Rainforest Mosaics

Abstract: Central Africa’s rainforest ecosystems are defined by patterns of biodiversity, structure, and functioning that are unique among rainforest regions. However, many ecosystem types are overlooked in broad-scale interpretations of Central African ecology. In particular, open-canopy ecosystems embedded within rainforest mosaics are understudied at landscape scales despite their potential to influence ecology across levels of ecological organization. In this dissertation, I investigate the influence of multiple open-canopy ecosystems and habitats on rainforest ecology across scales. In Chapter 1, I measure the influence of vegetation structure and topography on habitat selection by mountain gorillas during nesting and daytime activity. I show that, at the group- and population-level, mountain gorillas select for fine-scale open-canopy habitat as they range through their forested landscape. In Chapter 2, I conduct the first landscape-scale study of the spatial ecology, abiotic determinants, and biodiversity of the bai ecosystem—a large forest clearing type unique to the Congo Basin. I find that bais are a spatially aggregated riparian ecosystem that provide habitat for species that otherwise cannot persist in the broader rainforest, thereby promoting biodiversity. In Chapter 3, I quantify the temporal dynamics of the bai ecosystem while testing potential drivers of bai change. I demonstrate that bais are maintained by an interaction between megaherbivore disturbance and the spatial distribution of soil nutrients, which together generate emergent stability at landscape scales. Lastly in Chapter 4, I investigate how rainforests interact with neighboring savannas, specifically the roles of abiotic and biotic drivers in shaping rainforest-savanna dynamics. I find that fine-scale biotic facilitation causes the rapid expansion of rainforests into savannas across scales, counteracting disturbances associated with savanna persistence, such as fire. In aggregate, this dissertation demonstrates how open-canopy ecosystems of all scales can be highly influential in the landscape ecology of Central African rainforest mosaics, ranging from the behavior of individual species to the dynamics of entire biomes.

Committee: Andrew Davies (Advisor), Paul Moorcroft (Chair), Naomi Pierce, Benton Taylor