Metapopulation analysis indicates native and non‐native fishes respond differently to effects of wildfire on desert streams

Abstract

Ash flows and flooding associated with wildfires represent important but understudied sources of disturbance for fish populations. Knowledge concerning these disturbances is especially limited for larger streams where warm water species dominate. Fire-related disturbances have been hypothesised to differentially affect native and non-native fishes, although this hypothesis has only been tested for salmonids. The objective of our research was to contrast effects of uncharacteristically large wildfires followed by flooding on metapopulations of native and non-native fishes in the Gila River of southwest New Mexico. Probabilities of occupancy, colonisation and local extinction of fishes were calculated across sites before and during disturbance and were also measured across a broader spatial scale during disturbance to identify potential refuge locations. Occupancy was higher for native fishes than non-natives, but multiple wildfire and flood events increased extinction probabilities of native species. Responses of non-native species to wildfires were mixed; extinction of non-native salmonids increased during disturbance, while extinction of several warm water species remained unchanged or decreased. Several undisturbed sites were poor refugia for natives as they were impacted by non-native piscivores, dewatering, and fragmentation. However, despite exposure to multiple disturbances, sites located in large tributary and valley reaches were consistently occupied by native species, suggesting these habitats provided refugia. We suggest that management actions (forest thinning; prescribed burning) that restore a more natural disturbance regime of small and less severe fires coupled with habitat remediation activities (non-native removal; decreased water withdrawal; improved connectivity) might diminish extinction risk for native fishes exposed to wildfire disturbance.

River network architecture, genetic effective size and distributional patterns predict differences in genetic structure across species in a dryland stream fish community

“…; Whitney et al . , ). In all but two species, the number of significant deviations from HWP was consistent with the experiment‐wise error rate of α = 0.05 (Waples ) and application of Bonferroni correction resulted in low frequency of significant comparisons (<0.04).…”

“…), and this species was also reported to have high metapopulation extinction probabilities relative to other Gila River species (Pilger ; Whitney et al . ). Alternatively, A. chrysogaster is a small‐bodied, numerically dominant and widespread species.…”

“…This species exhibits large demographic fluctuations owing to its short lifespan and ‘boom–bust’ life cycle, presumably an adaptation to highly variable desert streams, making it an excellent colonizer following disturbances (Minckley & Deacon ; Minckley & Barber ; Whitney et al . ). Disturbance history and time since colonization (i.e.…”

Predicted Native Fish Response, Potential Rewards and Risks from Flow Alteration in a New Mexico Arid Mountain Stream

“…Sampling by Whitney et al . () approximately 3–16 river kilometres (rkm) from our study reach did not detect any spikedace (occupancy probability = 0), but loach minnow were detected (occupancy probability = 0.17), and both were detected at multiple upstream sites (Appendix in Whitney et al ., ). Loach minnow and spikedace were both found more frequently (Whitney et al ., ) at sites further downstream (8–20 km downstream of Gila Farms site, below Highway 180 bridge; Figure ).…”

“…Loach minnow and spikedace were both found more frequently (Whitney et al ., ) at sites further downstream (8–20 km downstream of Gila Farms site, below Highway 180 bridge; Figure ). We do not know if loach minnow or spikedace populations are present in our study reaches as no fish sampling was conducted in these locations, but we do know that they occupy sites both upstream and downstream (Whitney et al ., , ). Therefore, we used presence/absence information and density estimates of native fish in Whitney () for the Gila River (mean spikedace density 2.36/m 2 , mean loach minnow density 0.86/m 2 ) and Whitewater Creek (0.37 loach minnow/m 2 ; McMillan and Timmons, 2012) to inform both R o (long‐term average population size) and N o (initial population size).…”