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

• Published in: Ecology of freshwater fish 2016-07, Vol.25 (3), p.376-392
• Main Authors: Whitney, James E., Gido, Keith B., Pilger, Tyler J., Propst, David L., Turner, Thomas F.
• Format: Article
• Language: English
• Subjects: ash flows; Endangered & extinct species; Extinction; fish conservation; forest fires; Native species; non-native fishes; occupancy modelling
• ISSN: 0906-6691; 1600-0633
• DOI: 10.1111/eff.12217

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.