Date on Master's Thesis/Doctoral Dissertation

12-2025

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Biology

Degree Program

Biology, PhD

Committee Chair

Yanoviak, Steve

Committee Member

Emery, Sarah

Committee Member

Christian, Natalie

Committee Member

Mehring, Andrew

Committee Member

Fritz, Kelley

Author's Keywords

insect ecology; arthropod rain; Barro Colorado Island; tropical; Formicidae; arboreal

Abstract

Tropical forests are structured by complex vertical linkages and nutrient exchanges between canopy and understory habitats. These linkages include the downward flux of organisms, the movement of canopy fauna, and the recycling of nutrients through litter and organic matter deposition. This dissertation investigates arthropod rain and its role in connecting the canopy and forest floor processes in a lowland tropical forest in Panama. Chapter 2 quantifies “arthropod rain”, the fall of canopy arthropods into the understory. Using pan and pole traps, I measured the composition, abundance, and biomass of arthropods falling from the canopy and assessed environmental drivers of the flux. Overall, 27 kg km-2 per month of arthropod rain fell from the canopy, and Hymenoptera (particularly ants) and Lepidoptera larvae dominated by biomass. While high wind events marginally increased the number of falling arthropods, overall biomass was largely stable across conditions. Overlap between taxa collected in pan and pole traps suggests that many fallen arthropods attempt to reascend to the canopy, revealing a unique vertical exchange between forest strata. Chapter 3 examines how arboreal ants mitigate the risks of falling to the forest floor. Through controlled drop experiments on leaves under varying conditions, I found that leaf inclination and surface wetness significantly reduced landing success. Most species landed more successfully by chance across leaf conditions, except Cephalotes atratus, which is unique in its gliding habit among tested ant species. These results highlight behavioral and biomechanical constraints associated with arboreal life and suggest that rainy conditions intensify the risks of canopy movement for wingless arthropods. Chapter 4 explores how canopy-derived arthropod nutrient inputs into leaf litter influence decomposition and arthropod communities by using experimental subsidies of cricket-derived nutrients under press and pulse regimes. High nutrient subsidies accelerated decomposition, followed by low nutrient subsidies, though neither induced major community reorganization. Although nutrient enrichment elicited guild- and taxon-specific responses, overall changes were modest. These findings indicate that nutrient subsidies can enhance detrital processing while maintaining the stability of diverse tropical arthropod communities. Together, these studies illuminate the interconnectedness of tropical forest canopies and understories. From the physical descent of organisms to their behavioral adaptations and ecological consequences on the forest floor, arthropods both shape and are shaped by vertical linkages.

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