Date of Award:

12-2023

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Watershed Sciences

Committee Chair(s)

Charles P. Hawkins (Committee Co-Chair), Edward Hammill (Committee Co-Chair)

Committee

Charles P. Hawkins

Committee

Edward Hammill

Committee

Karen Mock

Committee

Kezia Manlove

Committee

Peter Wilcock

Abstract

Amphibians and reptiles (i.e., herptiles) are among the most threatened groups of species on Earth. The major threats to these species include the direct, indirect, and synergistic effects of habitat loss and fragmentation, invasive species, disease, overexploitation, and pollution. To protect and restore species, natural resource managers need effective, data-driven conservation plans that are grounded in sound knowledge of species distributions and habitat requirements. Species distribution models (SDMs) are popular tools used to assess species-habitat relationships. However, SDMs are sensitive to the choice and quality of input data, both of which can affect model accuracy and precision and lead to erroneous conservation decisions. Although many studies have used SDMs to understand the distributions and habitats of herptiles, results are often scale dependent and cannot be generalized because of regional differences in both biotic and abiotic settings. The goal of my research was to develop and evaluate SDMs for three species of concern in south-coastal California – the Arroyo Toad, California Red-legged Frog, and Western Pond Turtle to support their conservation planning. First, I assessed if the choice of climate data sets affected the performance and interpretation of climate-based SDMs. Results indicated that SDM accuracies were affected by the choice of climate data used. Second, I developed an SDM for the amphibian pathogen, Batrochochytrium dendrobatidis (Bd) to examine the factors that likely influence its occurrence. This model identified Bd hotspots and refugia across the study area. The predictors associated with Bd occurrence included the Normalized Difference Vegetation Index (NDVI), precipitation in the wettest quarter of the year, watershed slope, annual mean temperature, and percent impervious surface. Third, I assessed how current habitat suitabilities of the three target species vary in response to climatic conditions and how they are expected to vary by midcentury (2040-2069). Results revealed that future climate change will likely reduce the availability of suitable habitats for the Arroyo Toad and Western Pond Turtle but increase available suitable habitats for the California Red-legged Frog. These findings will help inform conservation management options for the target species by identifying planning units that should be prioritized for protection.

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