Diet composition and resource overlap of sympatric native and introduced salmonids across neighboring streams during a peak discharge event

Species assemblages composed of non-native and native fishes are found in freshwater systems throughout the world, and interactions such as interspecific competition that may negatively affect native species are expected when non-native species are present. In the Smith River watershed, Montana, rainbow trout were introduced by 1930. Native mountain whitefish and non-native rainbow trout have presumably occurred in sympatry since the introduction of rainbow trout; however, knowledge about how these two species compete with one another for food resources is sparse. We quantified diet compositions of rainbow trout and mountain whitefish in the mainstem Smith River and in a tributary to the Smith River-Sheep Creek-to determine the degree of overlap in the diets of mountain whitefish and rainbow trout in the Smith River and between the mainstem Smith River and a tributary stream. Rainbow trout and mountain whitefish had generalist feeding strategies, which probably contribute to the amicable coexistence of these species. Diet overlap between rainbow trout and mountain whitefish was high (Pianka's index value = 0.85) in the Smith River and moderate in Sheep Creek (Pianka's index value = 0.57). Despite overlap in diets, some resource partitioning may alleviate resource competition (e.g., rainbow trout consumed far more Oligochaeta than mountain whitefish but fewer Brachycentridae and Chironomidae). Diet composition of rainbow trout and mountain whitefish did not differ greatly between the Smith River and Sheep Creek. Prey categories most commonly used by mountain whitefish at the population and individual levels (i.e., Ephemeroptera and Trichoptera) are sensitive taxa and many species within these orders have experienced extinctions and population declines. Therefore, future changes in resource availability or competition could be of concern.

Multi-scale habitat assessment of pronghorn migration routes

We studied the habitat selection of pronghorn (Antilocapra americana) during seasonal migration; an important period in an animal's annual cycle associated with broad-scale movements. We further decompose our understanding of migration habitat itself as the product of both broad- and fine-scale behavioral decisions and take a multi-scale approach to assess pronghorn spring and fall migration across the transboundary Northern Sagebrush Steppe region. We used a hierarchical habitat selection framework to assess a suite of natural and anthropogenic features that have been shown to influence selection patterns of pronghorn at both broad (migratory neighborhood) and fine (migratory pathway) scales. We then combined single-scale predictions into a scale-integrated step selection function (ISSF) map to assess its effectiveness in predicting migration route habitat. During spring, pronghorn selected for native grasslands, areas of high forage productivity (NDVI), and avoided human activity (i.e., roads and oil and natural gas wells). During fall, pronghorn selected for native grasslands, larger streams and rivers, and avoided roads. We detected avoidance of paved roads, unpaved roads, and wells at broad spatial scales, but no response to these features at fine scales. In other words, migratory pronghorn responded more strongly to anthropogenic features when selecting a broad neighborhood through which to migrate than when selecting individual steps along their migratory pathway. Our results demonstrate that scales of migratory route selection are hierarchically nested within each other from broader (second-order) to finer scales (third-order). In addition, we found other variables during particular migratory periods (i.e., native grasslands in spring) were selected for across scales indicating their importance for pronghorn. The mapping of ungulate migration habitat is a topic of high conservation relevance. In some applications, corridors are mapped according to telemetry location data from a sample of animals, with the assumption that the sample adequately represents habitat for the entire population. Our use of multi-scale modelling to predict resource selection during migration shows promise and may offer another relevant alternative for use in future conservation planning and land management decisions where telemetry-based sampling is unavailable or incomplete.