Date of Award

5-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Wildlife and Fisheries Biology

Committee Chair/Advisor

Dr. Brandon Peoples

Committee Member

Dr. Kyle Barrett

Committee Member

Dr. Catherine M. Bodinof Jachowski

Committee Member

Dr. Stephen Midway

Abstract

Many well-supported hypotheses seek to explain invasion dynamics, but evidence for common patterns among regions and taxa remains inconclusive and often contradictory. Invasion ecology is fundamentally linked to spatial scale, and discrepancies in results among invasion studies may be attributed, in part, to a failure to fully consider scale dependency. In this dissertation, I investigate the sources of inconsistencies across spatial scales and large geographic extents using riverine fish communities across the conterminous United States. To do so, I tested three main ideas. First, that cross-scale interactions contextualize estimated invasion mechanisms among regions. My results demonstrate that local empirical support for native species richness and disturbance driving nonnative species richness is determined by regional cross-scale interactions with native gamma diversity and suggest that results of empirical invasion ecology research are dependent on geographic region. Second, that focusing on nonnative richness instead of dominance is a source of scale-dependency in invasion mechanisms. Local-scale invasion research is frequently conducted at small spatial extents with fine resolution data quantifying nonnative dominance (e.g., relative abundance), while data limitations often require macroscale research to coarsen data and use nonnative species richness at low spatial resolution. Therefore, I posit that some disparities between local and macroscale invasion studies stem from a weak relationship between nonnative species richness and dominance. I found clearly different relationships between the drivers of nonnative richness and dominance, indicating that these two metrics provide different information for our understanding of local invasion patterns. Most of our macroscale understanding of invasion ecology is based on nonnative species richness, which suggests that much remains unknown about the validity and applicability of invasion hypotheses. Third, that iii scale-dependency in the delineation of native status determines observed patterns in community invadedness across the landscape. Native status itself is inherently hierarchical and scale-dependent, yet defining spatial scale in invasion ecology has mainly focused on the spatial resolution and extent of the analysis. I evaluate the perceived invadedness of local fish communities based on definitions of native status at three spatial resolutions: biogeographic realm, region (HUC2), and province (HUC8). Compared to when regionally and provincially nonnative species are considered, I found the prevalence of nonnative fishes to be grossly underestimated using the traditional, broad spatial definition of native status. Overall, this research illustrates the important role of cross-scale and inter-regional variation in drivers and estimates of community invadedness. It also highlights key sources of variation that give rise to contradictory empirical support for fundamental invasion hypotheses across spatial scales, regions, and taxa. Accounting for these differences and choosing nonnative metrics and native status definitions appropriate for specific taxa and systems will critically advance our understanding of species invasions.

Author ORCID Identifier

https://orcid.org/0000-0002-3821-0324

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