Year of Award

2023

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Organismal Biology, Ecology, and Evolution

Department or School/College

Division of Biological Sciences

Committee Chair

Winsor Lowe

Commitee Members

Lisa Eby, Robert Hall, Bret Tobalske, Andrew Wilcox

Keywords

Gyrinophilus porphyriticus, climate change, survival, movement, growth, life history

Publisher

University of Montana

Subject Categories

Other Ecology and Evolutionary Biology | Population Biology | Terrestrial and Aquatic Ecology

Abstract

Understanding how organisms respond to environmental variability is a central goal in ecology – a goal made even more pressing by the herculean challenge global climate change presents to all organisms. Climate change is increasing the frequency and intensity of floods and droughts, which will likely have disproportionate effects on freshwater organisms. Many stream-associated species have multi-stage life histories. However, we lack an empirical understanding of life history and movement responses of these organisms to hydrologic disturbances, and how these responses may influence demographic rates. In my dissertation, I used a combination of growth, developmental, movement, and demographic data to understand individual and population responses to hydrologic disturbances in Gyrinophilus porphyriticus, a stream salamander.

In Chapter 1, I show that individual growth rates and mean size at metamorphosis increased with watershed area, my index of hydrologic intermittence. Population growth rates also tended to increase with watershed area. These results suggest that salamanders in hydrologically intermittent environments experience a reduction in body size and, consequently, fitness, which will be exacerbated as droughts increase due to climate change. In Chapter 2, I show that adult and larval downstream movement probability increased with discharge. The probability of terrestrial refuge use by adults also increased with discharge. Overall, my results suggest that headwater salamanders will experience more downstream movement as flood frequency and magnitude increase. These increases in downstream movement may be associated with increases in mortality due to the physical effects of flooding, and due to exposure to fish predators in downstream reaches. In Chapter 3, I show that stream drying intensity reduced larval recruitment, but increased the probability of metamorphosis (i.e., adult recruitment). Larval and adult recruitment were unaffected by flooding intensity, but larval and adult survival declined with flooding intensity. Although annual population growth rates declined with flooding and drying intensity, mean population growth rates were 1.0 between 2012 and 2021. Together, these results demonstrate population resilience to episodic hydrologic disturbances that was a consequence of compensatory effects of hydrologic extremes on the recruitment of new larvae vs. adults (i.e., reproduction vs. metamorphosis). I hope my work will help to predict and mitigate the effects of hydrologic extremes on stream salamanders and other headwater specialist taxa.

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