Using population ecology to advance stream community assembly

2019 Summer.Includes bibliographical references.To view the abstract, please see the full text of the document

Conservation of Bridle Shiner (Notropis bifrenatus) in Connecticut: Issues in Detecting an Elusive Species

Bridle Shiner (Notropis bifrenatus) is apparently declining over most of its range and is currently listed as a species of concern in Connecticut. Using an occupancy modeling framework in program PRESENCE, my study compared seining and electrofishing backpack unit detection probabilities of Bridle Shiner. This research indicated the apparent decline of Bridle Shiner in the state was in part due to changes in sampling gear used for statewide surveys. Seining used 50 years ago was demonstrably more effective at capturing Bridle Shiner than the currently favored and more frequently used electrofishing gear. In light of this recent finding, I seined at known historic sites in Connecticut and found that some populations once thought to be extirpated are in fact extant. Nonetheless, Bridle Shiner has a sharply reduced range in Connecticut, in that the number of site occurrences has declined 60% over 50 years. Using geospatial tools I identified landscape-scale habitat measures that were potential correlates of extirpation. Using logistic regression, I investigated metrics associated with land cover change, such as impervious surfaces and those indicative of habitat fragmentation and patch isolation. I found that the current Bridle Shiner distribution in Connecticut can be explained by areas of high forest cover and low impervious cover. My results provide needed context on declines in this species and potential avenues for conservation actions

Temperature variation generates interspecific synchrony but spatial asynchrony in survival for freshwater fish communities

Abstract Identifying environmental drivers of demographic variation is key to predicting community‐level impacts in response to global change. Climate conditions can synchronize population trends and can occur both spatially for populations of the same species, and across multiple species within the same local community. The aim of this study was to investigate patterns of temporal variation in survival for freshwater fish communities in two geographically close but isolated sites and to understand the amount of variation accounted for by abiotic covariates including metrics of water temperature and stream flow. Using mark‐recapture data, we estimated bi‐monthly apparent survival in a Bayesian Cormack‐Jolly‐Seber framework. The model included random effects to quantify temporal variance to understand species synchrony with the rest of the fish community and between sites. Study species included bluehead chub (Nocomis leptocephalus), creek chub (Semotilus atromaculatus), and striped jumprock (Moxostoma rupiscartes) in the southeastern USA. Results showed that survival varied over time and periods of low survival were associated with higher mean water temperature. However, temporal patterns of survival differed among species and between sites, where survival was synchronous among species within a site but asynchronous between sites for the same species despite their spatial proximity. Study streams differed in summer thermal regimes, which resulted in contrasting summer survival patterns, suggesting sensitivity of these fishes to warming. We found that interspecific synchrony was greater than spatial synchrony, where regional drivers such as temperature may interact with local habitat leading to differences in survival patterns at fine spatial scales. Finally, these findings show that changes in the timing and magnitude of environmental conditions can be critical in limiting vital rates and that some populations may be more resilient to climate variation than others