Salamanders are cryptic and, though largely unrecognized as such, extremely abundant vertebrates in a variety of primarily forest and grassland environments, where they regulate food webs and contribute to ecosystem resilience-resistance (= stability) in several ways: (a) As mid-level vertebrate predators, they provide direct and indirect biotic control of species diversity and ecosystem processes along grazer and detritus pathways; (b) via their migrations, they connect energy and matter between aquatic and terrestrial landscapes; (c) through association with underground burrow systems, they contribute to soil dynamics; and (d) they supply high-quality and slowly available stores of energy and nutrients for tertiary consumers throughout ecological succession. Salamanders also can provide an important service to humans through their use as cost-effective and readily quantifiable metrics of ecosystem health and integrity. The diverse ecological roles of salamanders in natural areas underscore the importance of their conservation. * The U.S. Government has the right to retain a nonexclusive, royalty-free license in and to any copyright covering this paper. 405 406 DAVIC WELSH Key ecological functions refer to the primary ways that species use, influence, regulate, and alter biotic and abiotic environments-a concept recommended for multispecies planning, biodiversity conservation, and management of wildlifehabitat relationships (Johnson & O'Neil 2001). In this paper, we review literature on key ecological functions of salamanders in terrestrial and aquatic environments of North America. We offer suggestions for future research by noting basic gaps in knowledge. Nomenclature follows Collins & Taggart (2002). This review is particularly timely because natural areas are becoming increasingly modified by destabilizing factors such as habitat alteration, toxic chemicals, loss of wetlands, and introduction of exotic species (Aber et al. 2000). Nearly three fourths of forested ecosystems in North America are considered endangered because of threats to their integrity (Noss 1999). The decline in amphibian species, many associated with forests, is now well documented (Alford & Richards 1999, Houlahan et al. 2000, Kiesecker et al. 2004). Although most attention has been given to anurans, salamander populations also are declining (Welsh 1990, Petranka et al. 1993, Wheeler et al. 2003), with unknown consequences to ecosystem processes. Of the 234 identified salamander taxa in the United States, 67 (29%) have a conservation status rank of "imperiled or critically imperiled" in at least part of their range (NatureServe 2003), yet only 13 species are protected or proposed for protection under the United States Endangered Species Act (Semlitsch 2003a). Habitat modifications are cited most often as the causes for salamander declines (Dodd & Smith 2003), with estimated losses of salamanders in some habitats in the millions (Petranka et al. 1993). In addition, zoogeographic evidence suggests that salamander faunas globally are being i...
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, reflecting differential use of stream microhabitats, the shared vulnerability of these species to infusions of fine sediments is probably the result of their common reliance on interstitial spaces in the streambed matrix for critical life requisites, such as cover and foraging. Many streamdwelling amphibians are highly philopatric and long-lived, and they exist in relatively stable populations. These attributes make them more tractable and reliable indicators of potential biotic diversity in stream ecosystems than anadromous fish or macroinvertebrates, and their relative abundance can be a useful indicator of stream condition.
Terrestrial salamanders of the family Plethodontidae have unique attributes that make them excellent indicators of biodiversity and ecosystem integrity in forested habitats. Their longevity, small territory size, site fidelity, sensitivity to natural and anthropogenic perturbations, tendency to occur in high densities, and low sampling costs mean that counts of plethodontid salamanders provide numerous advantages over counts of other North American forest organisms for indicating environmental change. Furthermore, they are tightly linked physiologically to microclimatic and successional processes that influence the distribution and abundance of numerous other hydrophilic but difficult‐to‐study forest‐dwelling plants and animals. Ecosystem processes such as moisture cycling, food‐web dynamics, and succession, with their related structural and microclimatic variability, all affect forest biodiversity and have been shown to affect salamander populations as well. We determined the variability associated with sampling for plethodontid salamanders by estimating the coefficient of variation (CV ) from available time‐series data. The median coefficient of variation indicated that variation in counts of individuals among studies was much lower in plethodontids (27%) than in lepidoptera (93%), passerine birds (57%), small mammals (69%), or other amphibians (37–46%), which means plethodontid salamanders provide an important statistical advantage over other species for monitoring long‐term forest health.
Abstract. 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 a 1.5m 2 enclosure increased litter retention by 13.3% 6 3.6% (mean 6 SE) compared to controls, facilitating the capture of 200 kg/ha of carbon. At a similar density range-wide this would equate to 72.3 metric tons/yr of carbon in one season potentially sequestered in forest soil rather than entering the atmosphere. In the second year invertebrate densities doubled in response to early rains such that while salamanders reduced the numbers of the same taxa, effect sizes were lower compared to year one, producing biological effects that failed to achieve statistical significance. However, three taxa did significantly increase in year two (Annelida [worms], Psocoptera [barklice], and Chelonethida [pseudoscorpions]). Litter retention in year two was greater on treatment plots by 5.6% 6 4.6%; however, high variability across plots precluded statistical significance. Ensatina suppressed some invertebrate taxa, released others, increased leaf litter retention, and facilitated greater carbon capture in both years; however, the strength of the effects were modulated by the bottom-up effects of the timing and amount of precipitation in year two.
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