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Temperature profoundly affects ecology, a fact ever more evident as the ability to measure thermal environments increases and global changes alter these environments. The spatial structure of thermalscapes is especially relevant to the distribution and abundance of ectothermic organisms, but the ability to describe biothermal relationships at extents and grains relevant to conservation planning has been limited by small or sparse data sets. Here, we combine a large occurrence database of >23 000 aquatic species surveys with stream microclimate scenarios supported by an equally large temperature database for a 149 000-km mountain stream network to describe thermal relationships for 14 fish and amphibian species. Species occurrence probabilities peaked across a wide range of temperatures (7.0-18.8°C) but distinct warm- or cold-edge distribution boundaries were apparent for all species and represented environments where populations may be most sensitive to thermal changes. Warm-edge boundary temperatures for a native species of conservation concern were used with geospatial data sets and a habitat occupancy model to highlight subsets of the network where conservation measures could benefit local populations by maintaining cool temperatures. Linking that strategic approach to local estimates of habitat impairment remains a key challenge but is also an opportunity to build relationships and develop synergies between the research, management, and regulatory communities. As with any data mining or species distribution modeling exercise, care is required in analysis and interpretation of results, but the use of large biological data sets with accurate microclimate scenarios can provide valuable information about the thermal ecology of many ectotherms and a spatially explicit way of guiding conservation investments., (© 2017 by the Ecological Society of America.)

Many freshwater fish species are considered vulnerable to stream temperature warming associated with climate change because they are ectothermic, yet there are surprisingly few studies documenting changes in distributions. Streams and rivers in the U.S. Rocky Mountains have been warming for several decades. At the same time these systems have been experiencing an increase in the severity and frequency of wildfires, which often results in habitat changes including increased water temperatures. We resampled 74 sites across a Rocky Mountain watershed 17 to 20 years after initial samples to determine whether there were trends in bull trout occurrence associated with temperature, wildfire, or other habitat variables. We found that site abandonment probabilities (0.36) were significantly higher than colonization probabilities (0.13), which indicated a reduction in the number of occupied sites. Site abandonment probabilities were greater at low elevations with warm temperatures. Other covariates, such as the presence of wildfire, nonnative brook trout, proximity to areas with many adults, and various stream habitat descriptors, were not associated with changes in probability of occupancy. Higher abandonment probabilities at low elevation for bull trout provide initial evidence validating the predictions made by bioclimatic models that bull trout populations will retreat to higher, cooler thermal refuges as water temperatures increase. The geographic breadth of these declines across the region is unknown but the approach of revisiting historical sites using an occupancy framework provides a useful template for additional assessments.

Fishes of the genus Cottus have long been taxonomically challenging because of morphological similarities among species and their tendency to hybridize, and a number of undescribed species may remain in this genus. We used a combination of genetic and morphological methods to delineate and describe Cottus schitsuumsh, Cedar Sculpin, a new species, from the upper Columbia River basin, Idaho-Montana, USA. Although historically confused with the Shorthead Sculpin (C. confusus), the genetic distance between C. schitsuumsh and C. confusus (4.84-6.29%) suggests these species are distant relatives. Moreover, the two species can be differentiated on the basis of lateral-line pores on the caudal peduncle, head width, and interpelvic width. Cottus schitsuumsh is also distinct from all other Cottus in this region in having a single small, skin-covered, preopercular spine. Haplotypes of mtDNA cytochrome oxidase c subunit 1 of C. schitsuumsh differed from all other members of the genus at three positions, had interspecific genetic distances typical for congeneric fishes (1.61-2.74% to nearest neighbors), and were monophyletic in maximum-likelihood trees. Microsatellite analyses confirmed these taxonomic groupings for species potentially sympatric with C. schitsuumsh and that fish used in morphological comparisons were unlikely to be introgressed. Its irregular distribution, in the Spokane River basin in Idaho and portions of the Clark Fork River basin in Montana, may have resulted from human-assisted translocation.

Unrestricted livestock grazing can degrade aquatic ecosystems, and its effects on native vertebrate species are generally mediated by changes to physical habitat. Recently, high estimated rates of cattle trampling on artificial redds within federal grazing allotments in southwestern Montana, USA, has raised concern that direct mortality from trampling may contribute to imperilment of native westslope cutthroat trout (Oncorhynchus clarkii lewisi). To explore the implications of cattle trampling, we built two mathematical models. First we used a temperature-driven model of egg-to-fry mortality representative of the developmental stages during which embryos would be vulnerable to trampling. Cattle trampling was an additional source of mortality (beyond natural mortality), and we modeled egg-to-fry mortality across a range of trampling rates (25-125% per month) for scenarios assuming low (0.60), moderate (0.81), and high (0.95) natural mortality. We then used a matrix model to determine how trampling affected population growth (lambda), assuming initially stable (lambda = 1.008) or slow-growing populations (lambda = 1.025 and 1.05). Cattle trampling concentrated over a few days when the embryos were most sensitive caused greater egg-to-fry mortality than when the same amount of trampling occurred over one month. Trampling caused a large increase in egg-to-fry mortality when that natural mortality was low, but the overall population-level effect was far less than might have been anticipated from the rate of trampling itself. Nonetheless, small reductions in population growth rate could be biologically significant for populations with little or no demographic resilience, and trampling rates as low as 25% could lead to negative population growth. The rapid reduction in resilience with increased trampling rates (>50%) means that even growing populations are less likely to recover from periodic fluctuations. The overall risk posed by trampling will depend on whether cutthroat trout populations face concurrent threats that have already reduced their abundance and resilience. Biologists can potentially use the egg-to-fry model and thermograph data to identify dates when limiting cattle presence in or near stream habitats would likely reduce mortality from trampling. Evaluation of grazing policies on federal lands may be needed to ensure that species conservation and land use concerns are equitably balanced.