Response of fish assemblages to habitat fragmentation caused by downstream impoundments within the Upper Wabash River Basin, Indiana.

摘要

Understanding the effects of impoundments on fish assemblages in upstream tributaries has received little attention, but is necessary in order to conserve isolated populations of native fishes. This study was conducted to investigate the impacts of fragmentation on fish assemblages, movement patterns, survival, and metapopulation dynamics in tributaries upstream of impoundments by comparison with nearby unfragmented streams. Spatial patterns of species distributions indicated significant upstream effects of impoundment. Mean fluvial specialist richness was greater in unfragmented streams, whereas mean fluvial generalist richness was significantly greater in fragmented streams. Greater piscivore abundance and a shift in composition were also observed. A mark-recapture survey was conducted on seven species of stream fishes to determine if movement patterns differed between fragmented and unfragmented streams. Differences in median distance moved, skewness of the distribution, directional bias, and the relationship between body size and probability of movement were observed. Based on the same mark-recapture study, survival was estimated using program MARK. Overall survival rates were lower in fragmented streams for five of the eight species. Monthly survival rates for all species except green sunfish and longear sunfish were lower in fragmented streams. Extinction probabilities, calculated from a three-year survey of seven species of stream fish, were highest for rainbow darter (theta = 0.645) and lowest for green sunfish (theta = 0.266). In contrast, colonization probabilities were highest for green sunfish (ϕ = 0.458), but lowest for rainbow darter (ϕ = 0.109). Extinction probabilities scaled with stream area for all species and colonization scaled with area for four species. The species studied here conform to metapopulation models based on patch size. The metapopulation capacity of fragmented landscapes model was used to assess possible results of changes in habitat area and connectivity on metapopulation size and fraction of patches occupied. Model predictions of patch occupancy rates were reasonably accurate, but uniformly lower than the observed patch occupancy values. In most instances, metapopulation capacity was sensitive to habitat addition while patch occupancy estimates were more sensitive to habitat loss. The results indicate that impoundments significantly alter assemblage structure, movement patterns, and survival which may have important repercussions for the persistence of native fishes.