Hartwell H. Welsh

STREAM AMPHIBIANS AS INDICATORS OF ECOSYSTEM STRESS:A CASE STUDY FROM CALIFORNIA’S REDWOODS

Road construction of the Redwood National Park highway bypass resulted in a large accidental infusion of fine sediments into pristine streams in Prairie Creek State Park, California, during an October 1989 storm event. This incident provided a natural experiment where we could measure, compare, and evaluate native stream amphibian densities as indicators of stream ecosystem stress. We employed a habitat-based, stratified sampling design to assess the impacts of these sediments on the densities of aquatic amphibians in five impacted streams by comparing them with densities in five adjacent, unimpacted (control) streams. Three species were sampled in numbers sufficient to be informative: tailed frogs (Ascaphus truei, larvae), Pacific giant salamanders (Dicamptodon tenebrosus, paedomorphs and larvae), and southern torrent salamanders (Rhyacotriton variegatus, adults and larvae). Densities of amphibians were significantly lower in the streams impacted by sediment. While sediment effects were species specific,...

Distribution of Juvenile Coho Salmon in Relation to Water Temperatures in Tributaries of the Mattole River, California

Abstract In an attempt to define the upper thermal tolerance of coho salmon Oncorhynchus kisutch, we examined the relationship between the presence of this species and the summer temperature regime in 21 tributaries of the Mattole River of northwestern California. We characterized the temperature regime of each tributary by determining the highest average of maximum daily temperatures over any 7-d period (maximum weekly maximum temperature, MWMT) and the highest average of mean daily temperatures over any 7-d period (maximum weekly average temperature MWAT), by the use of hourly measurements throughout the summer. Coho salmon presence was determined by divers in late summer. Both variables that were used to describe the temperature regime provided good-fitting models of the presence or absence of coho salmon in separate logistic regressions, and both correctly determined the presence or absence in 18 of 21 streams, given the previous probability of a 50% likelihood of coho salmon presence. Temperature reg...

Habitat correlates of the southern torrent salamander, rhyacotriton variegatus (Caudata: Rhyacotritonidae), in northwestern California

Asystematic stratified sampling design was used to quantify the habitat relationships of the southern torrent salamander, Rhyacotriton variegatus, in northwestern California. We sampled 53 first to third order streams, each surrounded by at least 5-7 ha of relatively homogeneous forest or harvested forest habitat. Measurements of 121 attributes of the forest and stream environment were recorded in conjunction with area-constrained aquatic sampling for salamanders. A subset of 68 variables, grouped into 11 ecological components including attributes at the landscape, macrohabitat, and microhabitat scales, was used in a hierarchical analysis of habitat associations. Results from discriminant and regression analyses indicated that this species occurs within a relatively narrow range of physical and microclimatic conditions and is associated with cold, clear headwater to low-order streams with loose, coarse substrates (low sedimentation), in humid forest habitats with large conifers, abundant moss, and HO% canopy closure. Thus, the southern torrent salamander demonstrates an ecological dependence on conditions of microcli- mate and habitat structure that are typically best created, stabilized, and maintained within late seral forests in northwestern California.

HABITAT USE BY WESTERN POND TURTLES IN THE TRINITY RIVER, CALIFORNIA

Habitat associations of western pond turtles (Clemmys marmorata) were examined in a dammed and undammed tributary of the Trinity River in northwestern California to clarify the relations between habitat use and damming. The dammed tributary had more sedimentation, decreased water temperatures, increased canopy cover, and higher water velocities, all of which are potentially relevant to western pond turtles. The overall heterogeneity of aquatic habitats also was lower, possibly because of the dam. At both dammed and undammed sites, western pond turtles appeared to select for deep water with low velocities and the presence of underwater refugia. On the dammed tributary, western pond turtles were associated with basking structures, which may be particularly important because of the low water temperatures. On the undammed tributary, western pond turtles tended to be in slower-flowing portions of the river with denser canopy cover and higher water temperatures. Given the alterations of channel morphology and flow regimes associated with damming, the implications are that habitat suitability for western pond turtles is decreased. While damming may increase the amount of deep water along shores and promote formation of undercut banks, it eliminates low-velocity areas preferred by western pond turtles and lowers water temperatures. Habitat enhancement efforts should focus on restoring natural structural and hydrological features.

The trophic role of a forest salamander: impacts on invertebrates, leaf litter retention, and the humification process

Woodland (Plethodontid) salamanders are the most abundant vertebrates in North American forests, functioning as predators on invertebrates and prey for higher trophic levels. We investigated the role of Ensatina (Ensatina eschscholtzii) in regulating invertebrate numbers and leaf litter retention in a northern California forest. Our objective was to examine how salamander predation on invertebrates affects leaf litter retention and the amount available for soil-building and carbon capture at the litter-soil interface. We used field enclosures to quantify the effects of Ensatina on invertebrates and litter retention over two wet seasons, using moisture as a covariate. In the first year Ensatina reduced Coleoptera (beetles) and Diptera (flies) larvae >2 mm, adult Coleoptera, Collembola (springtails), and Formicidae (ants), and increased Oribatid mites, larvae <2 mm (Diptera and Coleoptera), Diplopoda (millipedes), and Aranaea (spiders) <2 mm by reducing their competitors and predators. A single Ensatina in ...

Habitat Correlates of the Del Norte Salamander, Plethodon elongatus (Caudata: Plethodontidae), in Northwestern California

A stratified systematic sampling design was used to quantify the habitat relationships of the Del Norte salamander (Plethodon elongatus) in northwestern California. We sampled 57 sites, each within at least 5-7 ha of relatively homogeneous forest or post-forest habitat, where we measured 83 characteristics of the environment. Salamander sampling consisted of area-constrained sampling of 7 x 7 m plots with at least 25% rock cover at each site. A subset of 43 variables was used in a hierarchical analysis of habitat associations using discriminant analysis and regression. Variables included attributes at the landscape, macrohabitat, and microhabitat scales. Results indicate a significant association of the Del Norte salamander with older forests with closed, multi-storied canopy (composed of both conifers and hard- woods), with a cool, moist microclimate, and rocky substrates dominated by cobble-sized pieces. These habitat attributes appear optimal for survival and reproductive success throughout most of the range of this species. The Del Norte salamander may require ecological conditions found primarily in late seral stage forests.

GARTER SNAKE POPULATION DYNAMICS FROM A 16-YEAR STUDY: CONSIDERATIONS FOR ECOLOGICAL MONITORING

Snakes have recently been proposed as model organisms for addressing both evolutionary and ecological questions. Because of their middle position in many food webs they may be useful indicators of trophic complexity and dynamics. However, reliable data on snake populations are rare due to the challenges of sampling these patchily distributed, cryptic, and often nocturnal species and also due to their underrepresentation in the eco- logical literature. Studying a diurnally active stream-associated population of garter snakes has allowed us to avoid some of these problems so that we could focus on issues of sampling design and its influence on resulting demographic models and estimates. From 1986 to 2001, we gathered data on a population of the Pacific coast aquatic garter snake (Thamnophis atratus) in northwestern California by conducting 3-5 surveys of the population annually. We derived estimates for sex-specific survival rates and time-dependent capture probabilities using population analysis software and examined the relationship between our calculated capture probabilities and variability in sampling effort. We also developed population size and density estimates and compared these estimates to simple count data (often used for wildlife population monitoring). Over the 16-yr period of our study, we marked 1730 snakes and had annual recapture rates ranging from 13% to 32%. The best approximating de- mographic model for our data demonstrated higher survival rates for females than males and showed low and annually variable capture probabilities for both. Annual population size estimates (converted to linear densities), ranged from 58 to 131 snakes/km. Mean annual field counts typically accounted for only 5-10% of the total population size estimated using capture-recapture models. We found no evidence for a changing population size throughout the study. We found a positive relationship between sampling effort and capture probabilities. We evaluate survey design options that would help us approach recommended levels of capture probabilities and thus increase the precision of our estimates, allowing derivation of more complex demographic models. Our results should be useful in the development of monitoring programs for snakes and other secretive wildlife species and provide target demographic rate values for restoration of related at-risk snake species.

COMPARATIVE DEMOGRAPHY OF CLEMMYS MARMORATA POPULATIONS IN THE TRINITY RIVER OF CALIFORNIA IN THE CONTEXT OF DAM-INDUCED ALTERATIONS

Western pond turtle (Clemmys marmorata) populations were examined on two forks of the Trinity River in northern Califoria, one of which is subject to the impacts of damming and one of which is free-flowing. Mark-recapture was conducted over a three-year period for each population, and the Jolly- Seber model was used to estimate population size. Size/age structures were compared with reference to potential impacts of damming on this species. The density of populations (turtles/ha) on the dammed fork (mainstem Trinity) did not differ significantly from that on the undammed fork (south fork Trinity). How- ever, both populations were much sparser than western pond turtle populations elsewhere. Higher-order streams, in general, do not appear to support high densities of western pond turtles, possibly because of the sparse distribution of resources. The mainstem population had an age structure dominated by adults relative to a population with a known stable age distribution, suggesting that damming of the mainstem Trinity may have negatively impacted juvenile turtles. Populations of western pond turtles (Clemmys marmorata) have experienced declines through-

Population Ecology of two Relictual Salamanders from the Klamath Mountains of Northwestern California

We investigated the population ecology of the southern Olympic salamander (Rhyacotriton variegatus) and the Del Norte salamander (Plethodon elongatus) in the Klamath Mountains of northwestern California. A random stratified sampling design was used to investigate the distribution and relative abundance of subpopulations (metapopulation structure) of both species. We investigated specific demographic and other ecological aspects of one subpopulation of each species at sites with the highest relative numbers of each as revealed by the metapopulation analyses. Mark-recapture studies were conducted over 3 yr at these sites to gather ecological information on populations of these salamanders that appeared to exist in optimum conditions. We report data on population parameters, reproductive biology, movement, and growth. We offer this approach as a way to evaluate potential long-term viability of highly specialized or relictual species. We emphasize the importance of integrating site-specific ecological data with information on metapopulation structure at landscape and bioregional scales for conservation planning.

Woodland salamanders as metrics of forest ecosystem recovery: a case study from California's redwoods

Woodland (Plethodontid) salamanders occur in huge numbers in healthy forests in North America where the abundances of many species vary along successional gradients. Their high numbers and trophic role as predators on shredder and decomposer arthropods influence nutrient and carbon pathways at the leaf litter/soil interface. Their extreme niche conservatism and low vagility offer further advantages to the use of these salamanders as metrics of forest ecosystem condition. Mill Creek is a 103 km2 commercially logged redwood forest watershed acquired as parkland where original primary forest is being restored. This study evaluated woodland salamanders as metrics of seral recovery at Mill Creek. Surface counts and body condition were examined in four sets of stands, two early seral, one mature, and one of primary forest (never harvested old-growth). Later seral sites were closer to the coast where fog increased available moisture; younger sites were further inland at higher elevations where fog was reduced. We distinguished the effects of geography and succession using ANCOVA with a PCA-derived landscape covariate. Both geography and succession increased counts of California Slender Salamanders (Batrachoseps attenuatus); advancing succession alone indicated increased counts of Ensatina (Ensatina eschscholtzii). Means and variances in body condition of these two species were lower in older stands; for the Del Norte salamander (Plethodon elongatus) only the means were lower. Coastal proximity increased mean body condition in E. eschscholtzii, but with P. elongatus it was the opposite. We modeled surface counts and body condition along environmental gradients associated with succession. The counts and body condition in two of three species when taken together suggested that the increased structural complexity in late-seral forest stands supported larger populations that appeared to be competing for limited resources and, thus, likely have greater population fitness than those in younger forests. B. attenuatus and E. eschscholtzii proved to be viable metrics of advancing succession with their numbers and body condition providing readily quantifiable measures of ecosystem recovery at Mill Creek.