No abstract

1. Amphibians are recognized both for their sensitivity to environmental perturbations and for their usefulness as cost-effective biometrics of ecosystem integrity (=system health). 2. Twenty-three years of research in headwater streams in the Klamath-Siskiyou and North Coast Bioregions of the Pacific Northwest, U.S.A., showed distinct patterns in the distribution of amphibians to variations in water temperature, % fine sediments and the amount of large woody debris (LWD). 3. Here, we review seven studies that demonstrate connections between species presence and abundance and these three in-stream variables. These data were then used to calculate realized niches for three species, the southern torrent salamander, the larval coastal tailed frog and the larval coastal giant salamander, relative to two of these environmental stressors (water temperature and % fine sediments). Moreover, multivariate generalized additive models were used to predict the presence of these three amphibians when these three stressors act in concert. 4. Stream-dwelling amphibians are shown to be extremely sensitive to changes in water temperature, amounts of fine sediment and LWD, and specific thresholds and ranges for a spectrum of animal responses can be used to manage for headwater tributary ecosystem integrity. 5. Consequently, amphibians can provide a direct metric of stream ecosystem integrity acting as surrogates for the ability of a stream network to support other stream-associated biota, such as salmonids, and their related ecological services.

We examined invertebrate prey, fish diet, and energy assimilation in relation to habitat variation for steelhead Oncorhynchus mykiss (anadromous rainbow trout) and rainbow trout in nine low‐order tributaries of the South Fork Trinity River, northern California. These streams spanned a range of environmental conditions, which allowed us to use bioenergetics modeling to determine the relative effects of forest cover, stream temperature, season, and fish age on food consumption and growth efficiency. Evidence of seasonal shifts in reliance on aquatic versus terrestrial food sources was detected among forest cover categories and fish ages, although these categories were not robust indicators of O. mykiss condition and growth efficiency. Consumption estimates were generally less than 20% of maximum consumption, and fish lost weight in some streams during summer low‐flow conditions when stream temperatures exceeded 15°C. Current 100‐year climate change projections for California threaten to exacerbate negative growth patterns and may undermine the productivity of this steelhead population, which is currently not listed as endangered or threatened. To demonstrate the potential effect of global warming on fish growth, we ran three climate change scenarios in two representative streams. Simulated temperature increases ranging from 1.4°C to 5.5°C during the summer and from 1.5°C to 2.9°C during the winter amplified the weight loss; estimated average growth for age‐1 fish was 0.4‐4.5 times lower than normal (low to high estimated temperature increase) in the warm stream and 0.05‐0.8 times lower in the cool stream. We conclude that feeding rate and temperature during the summer currently limit the growth and productivity of steelhead and rainbow trout in low‐order streams in the South Fork Trinity River basin and predict that climate change will have detrimental effects on steelhead growth as well as on macroinvertebrate communities and stream ecosystems in general.

of the herpetofauna of a northern California watershed: linking species patterns to landscape processes. Á/ Ecography 28: 521 Á/536.Ecosystems are rapidly being altered and destabilized on a global scale, threatening native biota and compromising vital services provided to human society. We need to better understand the processes that can undermine ecosystem integrity (resistanceresilience) in order to devise strategies to ameliorate this trend. We used a herpetofaunal assemblage to first assess spatial patterns of biodiversity and then to discover the underlying landscape processes likely responsible for these patterns. Reptiles and amphibians are a phylogenetically diverse set of species with documented sensitivity to environmental perturbations. We examined ecogeographic patterns of these taxa in aquatic and riparian environments across the landscape mosaic of the Mattole River watershed of northern California, USA. We analyzed species distributions relative to three primary vegetation types (grassland, second-growth forest, late-seral forest) and two hydrologic regimes (perennial vs intermittent). We sought evidence for the processes behind these patterns by modeling animal distributions relative to multi-scale compositional, structural, and physical attributes of the vegetation or hydrologic type. Total herpetofaunal diversity was higher along perennial streams, with reptile diversity higher in mixed grassland. Amphibian and reptile richness, and reptile evenness, varied significantly among the three vegetations. Evidence indicated that distinct assemblages were associated with each end of a seral continuum. Four amphibians were more abundant in late-seral forest, while two amphibians and two reptiles were more abundant in second-growth forest, or mixed grassland, or both. Two amphibians were more abundant along intermittent streams. Models for predicting reptile richness, or abundances of the two amphibian assemblages, indicated water temperature was the best predictor variable. Based on these results and the physiological limits of several sensitive species, we determined the primary processes influencing faunal assemblage patterns on this landscape have been vegetation changes resulting from the harvesting of late-seral forests and the clearing of forest for pasture. Comparing past with present landscape mosaics indicated that these changes have transformed the dominant amphibian and reptile species assemblage from a mostly cold-water and cool forest-associated assemblage to one now dominated by warm-water and mixed grassland/woodland species.