Date of Graduation

5-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Biology (PhD)

Degree Level

Graduate

Department

Biological Sciences

Advisor

J. D. Willson

Committee Member

Ashley Dowling

Second Committee Member

Michelle Evans-White

Third Committee Member

Steve Beaupre

Keywords

food web, predator-prey relationships, reptile population, population dynamics, conservation biology

Abstract

Reptile populations are declining world-wide and the mechanisms behind many of these declines remain enigmatic. Food web interactions (i.e., reduced prey availability or increased predation) have been implicated behind some reptile declines. However, relatively little is known about predation on lizard and snake eggs, despite egg survival being important for population dynamics of some species. Ants are important predators of squamate reptile eggs in tropical and temperate systems. In Costa Rica, long-term declines in terrestrial anole lizards were linked with reduced leaf litter depth, a factor that could influence egg vulnerability to ant predation. Fire ants (genus Solenopsis) are aggressive generalist predators that are known to depredate reptile eggs. Over the past few decades, red imported fire ants (RIFA; Solenopsis invicta) have been introduced from South America to the U.S., where they have caused substantial ecological damage in their invasive range. RIFA invasion has coincided with population declines of terrestrial snake species in the southeastern U.S., but direct links between RIFA and snake declines remain primarily anecdotal. I used a tropical system (lowland tropical rainforest, Costa Rica) and a temperate one (southeastern U.S.) to test whether ant predation on reptile eggs could be driving enigmatic declines in squamate reptiles. I used a combination of field experiments, observational studies, laboratory incubation, and review of published literature to determine whether squamate reptile eggs were vulnerable to ant predation under different conditions. At La Selva Biological Station, Costa Rica, I tested whether leaf litter depth, nest microhabitat, or forest type influenced lizard egg predation rates and predatory ant activity. In the southeastern U.S., I tested whether eggs of different snake species were vulnerable to predation by RIFA at different points in incubation, and whether ecology and life history variables relating to vulnerability to ant predation (i.e., oviparity, geographic range overlap with RIFA, terrestrial/underground nests, etc.) predicted declining status across snake species. I found no support for leaf litter depth, nest microhabitat or forest type influencing ant predation in Costa Rica, but the results indicated that lizard and snake eggs were vulnerable to ant predation. Additionally, I found evidence that RIFA invasion is a major driver of snake population declines in the southeastern U.S. Although the mechanisms tested in this study remain uncertain, this study provides a baseline for future studies of ant predation on reptile eggs and highlights the need for additional studies on squamate reproduction and food web interactions.

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