Date of Award

Fall 12-1-2020

Degree Type


Degree Name

Doctor of Philosophy (PhD)


Biological, Environmental, and Earth Sciences

Committee Chair

Jacob F. Schaefer

Committee Chair School

Biological, Environmental, and Earth Sciences

Committee Member 2

Melvin L. Warren Jr.

Committee Member 3

Brian F. Kreiser

Committee Member 3 School

Biological, Environmental, and Earth Sciences

Committee Member 4

John Brian Alford

Committee Member 5

Carl P. Qualls

Committee Member 5 School

Biological, Environmental, and Earth Sciences


Typified by their branching pattern, headwaters are numerically abundant as the density of these habitats increases with increasing distance from the base of a dendritic river system. Connectivity among headwaters is complex, resulting in the spatial isolation of populations. Headwater specialists have evolved a suite of traits that permit these species to permanently reside within these habitats. The spatial configuration and connectivity of headwaters has repercussions for metapopulations and meta-assemblages. I investigated how multi-scale processes and connectivity influenced the patch occupancy, coexistence, movement ecology, population structure, and gene flow of headwater specialists. In chapter two, I used occupancy modeling to assess the patch occupancy and coexistence of three benthic stream fishes. Patch occupancy of each species was influenced by distinct habitat variables. Species co-occurrences were best explained as independent occurrences within a stream-reach according to species specific habitat associations. In chapter three, I used stream fish assemblages to examine how confluence size, as a metric of connectivity, and land cover influenced in-stream habitat, movement behavior, movement rate, and assemblage change at four headwater confluences. Results from hierarchical modeling and multivariate analyses suggested that, generally, habitat change, and movement behavior were related to land cover. There was also indirect evidence that movement rate and assemblage change were more influenced by land cover than confluence size. These findings suggest that land cover may alter the effect of confluence size on movement and assemblage change within headwaters. In chapter four, I used a comparative framework to examine how connectivity influences two benthic headwater fishes ecological response to landscape heterogeneity using presence-absence and genetic data. I further examined whether river system size altered connectivity and thus influenced the ecological response of both species. Occupancy modeling was used to elucidate species-landscape gradient relationships assuming populations occupied discreet habitat patches. Linear mixed effects models of genetic distance were used to identify whether these relationships changed as a consequence of discrepancies in connectivity between habitat patches. Our results suggested connectivity modified the impact of environmental and anthropogenic gradients on species ecological responses. Further, river system size affected connectivity, thus influencing species-landscape gradient relationships.


Joshua Hubbell