Date Awarded

2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Virginia Institute of Marine Science

Advisor

Christopher J Patrick

Committee Member

David S Johnson

Committee Member

Donna M Bilkovic

Committee Member

Mary C Fabrizio

Committee Member

J Derek Hogan

Abstract

This dissertation addresses the escalating threat of aridification to global freshwater ecosystems due to anthropogenic climate change, focusing on South-Central Texas, USA, using a space-for-time approach along a precipitation gradient from semi-arid to sub-humid. Over the 2017-2020 survey period, I integrated community, stable isotope, climate, and hydrologic data.In Chapter 2, my initial assessment of fish and invertebrate communities along the precipitation gradient unveiled compositional shifts and other nuanced responses. Positive correlations between fish diversity and rainfall, coupled with unexpected invertebrate diversity patterns, underscored the role of water quality in shaping fish assemblages. Drier conditions imposed abiotic filters, reducing diversity and favoring taxa with specialized adaptations, particularly in semi-arid systems with a dominance of euryhaline and live-bearing taxa. Chapter 3 examined differences in allochthonous and autochthonous dependencies as well as overall food-web structure across the precipitation gradient. In drier climates, a shift from insect predation to herbivory was apparent, supported by stable isotope data indicating increased autochthonous assimilation, wider resource use, and reduced trophic levels. Invertebrate metrics suggested limited bottom-up effects, while niche dimensions indicated top-down control at Sub-Humid and competition at Semi-Arid and Transition sites to be important drivers of food web structure. In summary, aridification intensifies autochthonous production, fish herbivory, and invertebrate dietary overlap in semi-arid streams. Chapter 4, exploring ecological connectivity in coastal rivers, focused on inconspicuous amphidromous species. Stable isotope analysis quantified substantial estuarine assimilation and highlighted dam impacts on connectivity. Significant downstream to upstream connectivity, driven by completely amphidromous taxa, emphasized vulnerability to interruptions by dams, urbanization, and climate change. Dominance of Fundulidae, Cyprinidontidae, and Palaemonidae families facilitated estuarine nutrient subsidies. Chapter 5 addressed ecological impacts of hydrological disturbances, challenging prevailing notions about flood effects. Results revealed nuanced relationships influenced by long-term precipitation patterns, with varied impacts of drought events based on precipitation regimes. These findings contribute to a refined understanding of climate, hydrology, and fish communities, offering insights into how different precipitation regimes shape responses to hydrological disturbances. Specifically, my data highlighted Poeciliid resilience and reduced centrarchid abundances during hydrological droughts in hot and arid summers. This dissertation unveils nuanced ecological dynamics within semi-arid ecosystems, where abiotic filters, influenced by water quality, shape fish communities. The prevalence of euryhaline and live-bearing taxa, along with amphidromous species, underscores the vital role of estuarine connectivity in maintaining resilient coastal rivers, especially in arid climates. My findings elucidate intricate ecological responses to floods, droughts, and seasonality, contingent upon long-term precipitation patterns. As regions teeter on the brink of transitioning from mesic to semi-arid climates, my results foreshadow analogous transformations in stream ecosystems. This scholarly pursuit represents a substantial stride in advancing ecological understanding, offering vital insights for adept stewardship amid the challenges presented by climate-induced alterations.

DOI

https://dx.doi.org/10.25773/v5-jz6t-xa27

Rights

© The Author

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