Retreat Sites Research Articles

Influence of flooding on delta15N, delta18O, 1delta15N and 2delta15N signatures of N2O released from estuarine soils--a laboratory experiment using tidal flooding chambers.

The influence of flooding on N2O fluxes, denitrification rates, dual isotope (delta18O and delta15N) and isotopomer (1delta15N and 2delta15N) ratios of emitted N2O from estuarine intertidal zones was examined in a laboratory study using tidal flooding incubation chambers. Five replicate soil cores were collected from two differently managed intertidal zones in the estuary of the River Torridge (North Devon, UK): (1) a natural salt marsh fringing the estuary, and 2 a managed retreat site, previous agricultural land to which flooding was restored in summer 2001. Gas samples from the incubated soil cores were collected from the tidal chamber headspaces over a range of flooding conditions, and analysed for the delta18O, delta15N, 1delta15N and 2delta15N values of the emitted N2O. Isotope signals did not differ between the two sites, and nitrate addition to the flooding water did not change the isotopic content of emitted N2O. Under non-flooded conditions, the isotopic composition of the emitted N2O displayed a moderate variability in delta18O and 2delta15N delta values that was expected for microbial activity associated with denitrification. However, under flooded conditions, half of the samples showed strong and simultaneous depletions in 1delta15N and delta18O values, but not in 2delta15N. Such an isotope signal has not been reported in the literature, and it could point towards an unidentified N2O production pathway. Its signature differed from denitrification, which was generally the N2O production pathway in the salt marsh and the managed retreat site.

FITNESS BENEFITS OF RETREAT-SITE SELECTION: SPIDERS, ROCKS, AND THERMAL CUES

Although animals are widely assumed to select habitats in ways that enhance organismal fitness, there are few empirical data to demonstrate this link. We studied flat rock spiders (Hemicloea major, Gnaphosidae) from eastern Australia, where these highly modified (dorsoventrally flattened) spiders live under loose surface rocks on sandstone outcrops. Field surveys showed that the rocks used as diurnal retreat sites by spiders were relatively thin with low canopy cover and a rocky substrate and therefore were likely to experience high temperatures and large thermal fluctuations. Laboratory trials suggest that this nonrandom rock use is a direct response to thermal cues; juvenile spiders selected warmer over cooler retreat sites. To investigate consequences of habitat selection on fitness-related traits, we maintained cohorts of juvenile spiders at cycling-temperature regimes corresponding to those measured in the field under rocks that were fully, partially, or never exposed to direct sunlight (diel thermal ranges of 16.2°–37.8°C, 15.5°–31.2°C, and 15.2°– 24.3°C). Survival rates were high for all groups over the eight-week study, but hotter conditions accelerated growth and development. Our data thus confirm that thermal cues are used in retreat-site selection and that selection of warmer retreat sites will confer fitness benefits to flat rock spiders.

CANOPY STRUCTURE, MICROCLIMATE, AND HABITAT SELECTION BY A NOCTURNAL SNAKE, HOPLOCEPHALUS BUNGAROIDES

Forest structure strongly influences ambient environmental conditions such as light and temperature, but most studies on habitat selection by mobile organisms have either ignored canopy structure or treated it as a dichotomous variable (e.g., shady or sunny). Furthermore, the predominance of active diurnal species as model organisms in such studies has left many unanswered questions about the importance of vegetation-related variables for nocturnal and sedentary species (e.g., what does shade mean to an organism that moves at night and sits in a cave all day?). We used hemispherical photography to quantify canopy structure and examine its role in determining the thermal microenviron- ments available to a rock-dwelling nocturnal snake (Hoplocephalus bungaroides) across two different spatial scales. The narrow plateaus inhabited by the snakes in southeastern Australia are highly heterogeneous with respect to vegetation: east-facing aspects are dense- ly covered whereas west-facing aspects are patchy mosaics. We found that temperatures of potential retreat sites increased with increasing canopy openness, but the definitive deter- minant of retreat-site temperature was incident radiation intensity, which depended upon the location of canopy gaps relative to the sun path. This factor restricted the snakes to west-facing cliff tops, and there only to an optimal subset of rocks that received adequate irradiance. Moreover, thermal regimes of retreat sites displayed higher maxima and were evening shifted relative to randomly sampled rocks in the same area. Our results suggest that thermally suitable retreat sites are a limiting resource, and that local increases in vegetation density might contribute to the decline of this endangered species.

Retreat Site Selection during Winter in the Green and Golden Bell Frog, Litoria aurea Lesson

Amphibians use a range of microhabitats as retreat sites to escape adverse climatic conditions. We conducted two outdoor experiments using a brick pile and shallow trays of water containing aquatic vegetation to assess retreat site selection during winter in the endangered frog Litoria aurea. A multivariate habitat model in the first experiment indicated that frogs preferred to rest close to the edges of the brick pile that received afternoon sunlight and in small gaps between bricks, whereas in the second experiment, frogs showed no preference for terrestrial or aquatic habitats. These results suggest that L. aurea is a generalist in winter habitat choice, although resting positions in terrestrial situations are likely related to site aspect, microhabitat, and temperature.

Hot rocks or no hot rocks: overnight retreat availability and selection by a diurnal lizard.

I used radio telemetry to determine the effects of substrate size and composition on overnight retreat site selection by western fence lizards (Sceloporus occidentalis). In watersheds of northern California (USA), these lizards occupy two habitat types differing in substrate characteristics: rocky cobble bars found in the dry, active channels of rivers and grassy upland meadows. Rocky substrates, found almost exclusively on cobble bars, provided warmer potential retreat sites than all available retreat sites on meadows during the first 5 h of inactivity. Only cobble and sand substrates provided retreats with temperatures within the preferred daily active range (32-36 degrees C) during the inactive period for these lizards (1900-0900 hours). Females on a cobble bar used rocks as retreats on >90% of nights during the breeding season whereas females on a meadow used wood (>70% of nights) and burrows (>25% of nights). In contrast to females, cobble bar males used rocks significantly less frequently (<70%) and slept in the open air significantly more frequently (25% vs. <1%). Cobble bar females further, showed a significant preference for cobbles 15 cm thick, whereas the rocks used by males did not differ significantly in thickness from those measured in randomly placed transects. Rocks 15 cm thick were the warmest retreats commonly available on this habitat type. Thus, thermal microenvironments available to and chosen by gravid female lizards differ considerably between river and non-river habitats.

Planning for the rising tides: the Humber Estuary Shoreline Management Plan

The Humber Estuary Shoreline Management Plan provides the framework for investment in defences to reduce the risk of flooding to people, property and the environment. A key issue is the rise in sea level, which is reducing the standard of protection provided and is increasing erosion. The plan is developed from detailed geomorphological and ecological studies, and extensive consultation with interested organisations and the community. It takes into account the urban and industrial development on the floodplain, high-grade agricultural land, the historic environment and the Humber's status as an outstanding site for wildlife, which is protected under the Habitats Directive. A key aim is wherever possible to work with natural processes. Another is to ensure that there is no net loss of protected inter-tidal habitat. The options investigated include changes to the existing alignment of the embankments. The overall strategy provides for a continuing line of defence around the estuary and tidal rivers but with the use of managed retreat in some places. The creation of new inter-tidal habitat by this means is to gain more stable and cost-effective defences, and to offset the loss of protected sites, including by coastal squeeze. Further studies are in progress to appraise potential managed retreat sites.

How age, sex, and reproductive condition affect retreat-site selection and emergence patterns in a temperate-zone lizard, Elgaria coerulea

Minimising predation risk is critical to fitness in all animals. For animals that utilise retreat sites as an anti-predator strategy, there are many factors that influence retreat site selection and determine when to emerge from a hiding place. In this paper we test for seasonal and daily variation in cover use in a temperate-zone lizard (Elgaria coerulea). We also test for age- and sex-related differences in capture-site temperature, cover use, and sprint speed. We conducted a mark-recapture study on Elgaria coerulea in south-eastern British Columbia, Canada. We recorded temperature, precipitation, lizard’s position, proximity to cover, and rock size. The results showed seasonal variation in both retreat-site selection and emergence patterns. Lizards selected thicker rocks during the summer compared to spring, perhaps to avoid lethal high temperatures. Adult males used larger, thicker rocks than adult females and juveniles. Emergence patterns also differed between the sexes. The probability of capturing an adult female in the open steadily increased over the summer, while male emergence declined over the season. The tendency to be in the open also increased with the amount of rain that fell the previous day. This study shows that while remaining under cover is important in Elgaria coerulea, specific circumstances (lethal temperatures, reproduction, precipitation) will modify their cover use.

Use of Native Forest and Eucalyptus Plantations by Eleutherodactylus Frogs

We examined population densities, movements, and habitat use of common coqui (Eleutherodactylus coqui), the most common and widespread species of frog in Puerto Rico, in native forest and eucalyptus plantations in 2 forest reserves of the Cordillera Central between July 1997 and June 1998. We established 4 grids of bamboo retreat sites on stands of native forest and eucalyptus plantations in each reserve. We established sampling points within trapping grids to quantify vegetation and determine habitat use. Sampling was conducted during the wet and dry seasons. We used mark-recapture for population estimation. Population estimates and maximum distances moved were determined using program CAPTURE. During the dry season, common coqui population densities were similar in 3 of the 4 study grids, but 1 eucalyptus site had significantly lower densities. We found no differences in adult frog density among study sites during the wet season. Horizontal movements differed between forests, albeit not significantly. Our results indicate that plant species richness did not affect common coqui density. Coqui density was influenced more by vegetation structure than by plant species composition. Five habitat variables (midstory epiphyte load, midstory stem count, ground-cover stem count, total epiphyte load, total basal area) were correlated with adult common coqui density. Eucalyptus plantations in montane regions of Puerto Rico provide suitable habitat for the common coqui. However, suitability may be linked to threshold basal area levels of 18-28 m 2 /ha.

Size-dependent predation by snakes: selective foraging or differential prey vulnerability?

I staged replicate encounters between unrestrained lizards and snakes in outdoor enclosures to examine size-dependent predation within the common garden skink (Lampropholis guichenoti). Yellow-faced whip snakes (Demansia psammophis) forage widely for active prey and most often consumed large skinks, whereas death adders (Acanthophis antarcticus) ambush active prey and most often consumed small skinks. Small-eyed snakes (Rhinoplocephalus nigrescens) forage widely for inactive prey and consumed both small and large skinks equally often. Differential predation may reflect active choice by the predator, differential prey vulnerability, or both. To test for active choice, I presented foraging snakes with an inert small lizard versus an inert large lizard. They did not actively select lizards of a particular body size. To test for differential prey vulnerability, I quantified variation between small and large lizards in behavior that is important for determining the outcome of predator--prey interactions. Snakes did not differentiate between integumentary chemicals from small and large lizards. Large lizards tend to flee from approaching predators, thereby eliciting attack by the visually oriented whip snakes. Small lizards were more mobile than large lizards and therefore more likely to pass by sedentary death adders. Additionally, small skinks were more effectively lured by this sit-and-wait species and less likely to avoid its first capture attempt. In contrast, overnight retreat site selection (not body size) determined a lizard's chances of being detected by small-eyed snakes. Patterns of size-dependent predation by elapid snakes may arise not because of active choice but as a function of species-specific predator tactics and prey behavior. Copyright 2002.

Retreat site selection and social organization in captive electric fish, Apteronotus leptorhynchus.

Gymnotiform fish use their electric organ discharge for electrolocation and communication. They are active nocturnally and seek retreat sites during the day. We examined retreat site selection in Apteronotus leptorhynchus by assessing their preference for retreat tubes that differed in opacity and dimension. Isolated fish preferred opaque to clear tubes, long and narrow diameter tubes to short, wide diameter tubes, and open-ended to closed tubes. We also assessed how groups of fish distributed themselves in tubes according to sex and electric organ discharge frequency under four conditions: (1) unlimited tube availability, (2) limited tube availability, (3) variation in tube opacity, and (4) variation in tube dimension. When tube availability was unlimited, fish generally preferred to occupy tubes alone. However, females, but not males, often cohabited tubes with consexuals. When tube availability was limited, females were more often than males found outside of tubes. When tubes varied by opacity and dimension, fish clustered most commonly in preferred tube types (opaque and long tubes). Males with the highest electric organ discharge frequencies usually occupied the most preferred tube type. Thus, fish have clear preferences in selecting retreat sites and groups of fish reveal their dominance relationships when presented with variation in retreat sites.

Radiotelemetric Study of Habitat Use by the Arboreal Snake Hoplocephalus stephensii (Elapidae) in Eastern Australia

Simply classifying a species as “arboreal” may tell us little about the ways that it uses above-ground habitats. For example, some species of arboreal snakes select exposed positions on branches, others lie among foliage, and yet others exploit crevices within the trunk. These different structural niches may involve fundamentally different patterns not only of habitat selection criteria but also of morphological, behavioral, and ecological traits. We implanted miniature radio-transmitters in 16 adult Stephens' banded snakes (Hoplocephalus stephensii) in a forest managed for timber production in northeastern New South Wales, and relocated these snakes regularly over a two-year period to clarify their patterns of habitat use. Unlike the vast majority of Australian elapid species, H. stephensii are primarily arboreal. Radio-tracked snakes were in trees on > 80% of observations, generally hidden within hollows. The snakes remained inactive in trees for three to five months during winter each year. Snakes in wet sclerophyll forest sometimes foraged in tall sedges, whereas snakes in rain forest spent little time on the ground. Attributes of 139 trees used by the snakes were compared with those of 1437 trees in randomly selected plots. Snakes selected old, large trees with many hollows or extensive vine cover. Except for being above ground, the retreat sites used by these arboreal elapids were structurally similar to those used by their terrestrial relatives. The tree attributes important to H. stephensii thus differ profoundly from those important to many other species of arboreal snakes.

Habitat‐specific behavioural thermoregulation by black rat snakes (Elaphe obsoleta obsoleta)

Thermoregulation is thought to be the most important factor influencing habitat selection by terrestrial ectotherms, at least in temperate climates. The cost‐benefit model of thermoregulation predicts that ectotherms should invest more in thermoregulation when the costs of doing so are low (when the thermal quality of the habitat is high). However, the extent to which ectotherms vary their thermoregulatory behaviour according to the thermal quality of habitats is currently unknown. We studied the relationship between habitat use and thermoregulation in 53 black rat snakes using temperature‐sensitive radio‐transmitters. Among the habitats available to black rat snakes, edges had the highest thermal quality, retreat sites and forest were intermediate, and open habitats had the lowest thermal quality. Black rat snakes experienced more favourable body temperatures while in barns (retreat sites) than in edges, and in edges than in forest. During the day, the effectiveness and the extent of thermoregulation by the snakes were equal in barns and forest, but much lower in edges. In fact, black rat snakes selected thermally favourable microhabitats less than their availability while in edges. Therefore, more favourable body temperatures were not necessarily achieved in thermally superior habitats by increased thermoregulation, but simply because favourable temperatures were encountered more often in those habitats. This result is contrary to the central prediction of the cost‐benefit model of thermoregulation and we suggest that this model should be modified to put more emphasis on other costs of thermoregulation, such as increased predation risk or lost foraging opportunities.

Experimental evidence of an age-specific shift in chemical detection of predators in a lizard.

The risk posed by predation is one of the most fundamental aspects of an animal's environment. Avoidance of predators implies an ability to obtain reliable information about the risk of predation, and for many species, chemosensory cues are likely to be an important source of such information. Chemosensory cues reliably reveal the presence of predators or their presence in the recent past. We used retreat site selection experiments to test whether the Australian scincid lizard Eulamprus heatwolei uses chemical cues for predator detection and avoidance. Both adult and juvenile lizards were given the choice of retreat sites treated with scents from invertebrate predators, as well as sympatric and allopatric snake predators. Some of the snake predators were known to eat E. heatwolei, while others did not pose a predation threat. All invertebrate predators posed a risk to juveniles, but not adults because of their size. We found that juvenile E. heatwolei avoided predator odors more strongly than adults. Juveniles avoided both invertebrate predators and snakes, and the strongest response was toward the funnel web spider, the only ambush predator used in this experiment. This result may demonstrate the importance of predator ecology in the evolution of predator detection mechanisms, with chemical cues being more useful in detecting sedentary predators than active predators. Adult lizards showed no avoidance behavior toward predator odors. This result suggests an age specific shift in predator avoidance behavior as lizards get older and become too large for many predators. However, adults showed no response to the odor from the red-bellied black snake, a known predator of adult E. heatwolei. This finding further demonstrates the importance of predator ecology when examining communication between predators and prey. Chemical cues, which are persistent long after predators have vacated the area, may not be useful in detecting the red-bellied black snake, a wide-ranging active forager.

Trading Heat and Food for Safety: Costs of Predator Avoidance in a Lizard

I examined the long-term consequences of a trade-off between predation risk and resource acquisition for the garden skink (Lampropholis guichenoti) by rearing hatchlings to maturity in outdoor enclosures covered with snake predator scent (mimicking high predator densities) or control scent (mimicking low predator densities). Open areas provided optimal foraging and basking sites but were covered with scent, whereas retreat sites provided suboptimal foraging and basking opportunities and were not scented. During the initial six months of the experiment, lizards reared in enclosures covered with scent from a natural predator became active later in the day, showed reduced mobility, and selected “safer” substrate microhabitats than did lizards raised in enclosures covered with control scent. These behavioral shifts reduced opportunities to forage and bask for lizards in the predator-scented enclosures. During the study, however, lizards from predator-scented enclosures became gradually less responsive to snake chemical cues, and after one year there were no differences in the activity patterns and substrate microhabitat use of lizards in both treatments. This pattern of behavior is paralleled by variation in growth rates of lizards. Throughout the study, lizards exposed to predator scent were lighter and shorter than were lizards exposed to control scent. However, this result reflects differential rates of growth by lizards only during the first six months of the experiment. Nevertheless, lizards that grew slowly early in life, as a consequence of predator avoidance, attained smaller body sizes at maturity and produced lighter clutch masses and offspring. Thus, predator avoidance tactics employed early in a lizard's life can impose long-term fitness costs.

TRADING HEAT AND FOOD FOR SAFETY: COSTS OF PREDATOR AVOIDANCE IN A LIZARD

I examined the long-term consequences of a trade-off between predation risk and resource acquisition for the garden skink (Lampropholis guichenoti) by rearing hatchlings to maturity in outdoor enclosures covered with snake predator scent (mimicking high predator densities) or control scent (mimicking low predator densities). Open areas provided optimal foraging and basking sites but were covered with scent, whereas retreat sites provided suboptimal foraging and basking opportunities and were not scented. During the initial six months of the experiment, lizards reared in enclosures covered with scent from a natural predator became active later in the day, showed reduced mobility, and selected “safer” substrate microhabitats than did lizards raised in enclosures covered with control scent. These behavioral shifts reduced opportunities to forage and bask for lizards in the predator-scented enclosures. During the study, however, lizards from predator-scented enclosures became gradually less responsive to snak...

The impact of habitat fragmentation on dispersal of Cunningham's skink (Egernia cunninghami): evidence from allelic and genotypic analyses of microsatellites.

The effects of habitat fragmentation on processes within and among populations are important for conservation management. Despite a broad spectrum of lifestyles and the conservation significance of many reptiles, very little work on fine-scale population genetics has been carried out on this group. This study examines the dispersal patterns of a rock crevice-dwelling lizard, Cunningham's skink (Egernia cunninghami), in a naturally vegetated reserve and an adjacent deforested site. Both genotypic and genic approaches were employed, using microsatellite loci. The spatial organization of individuals with respect to pairwise relatedness coefficients and allele frequencies, along with assignment tests, were used to infer dispersal characteristics for both sexes in a natural and a cleared area. The distribution of relatedness in both habitats was spatially structured, with E. cunninghami showing high pairwise relatedness within their rocky retreat sites. Analysis of relatedness over different spatial scales, spatial autocorrelation of alleles and assignment tests, all indicated that both sexes in the cleared area show less dispersal than their counterparts in the reserve. Furthermore, deforestation may inhibit female dispersal to a greater extent than that of males. The geographical structuring of allele frequencies for adults in the cleared area, but not the reserve, indicates that habitat fragmentation has the potential to alter at least the microevolution of E. cunninghami populations.

The ecology of an Australian reptile icon: how do blue-tongued lizards (Tiliqua scincoides) survive in suburbia?

Although most species of large reptiles in the Sydney region are now restricted to remnant bushland, the blue-tongued lizard (Tiliqua scincoides) remains abundant. How has this large, slow-moving reptile managed to persist in the suburbs? We implanted radio-transmitters into 17 adult blue-tongued lizards and tracked them for six months (October 1998 to March 1999). Radio-tracked animals utilised 5–17 suburban backyards, but each lizard spent most of its time in a few ‘core’ areas near 2–7 shelter sites. Males had larger home ranges than females (mean of 12700 v. 5100 m 2 ) and moved further between shelter sites. Gravid females (mean home range 1000 m 2 ) were more sedentary. Lizards used corridors of dense vegetation to move between retreat sites, and actively avoided crossing roads. In sunny weather, lizards typically basked close to their overnight shelter for 1–4 h each morning until they obtained body temperatures of approximately 32°C. They maintained high body temperatures while moving about in the afternoon. In combination, the following ecological factors may facilitate persistence of blue-tongued lizards at our suburban study sites. (i) The most important subgroup of the population in terms of conservation are gravid females, which are highly sedentary and, thus, less likely to encounter the dangers of suburbia. (ii) The more ‘expendable’ males move about much more, but mostly in times and places that involve minimal risk from humans and their domestic pets. (iii) Lizards show strong site fidelity, spending up to 70% of their time in ‘safe’ locations; importantly, they avoid roads. (iv) Blue-tongued lizards readily utilise ‘artificial’ shelter sites and the commensal prey species (e.g. snails) found in most gardens. (v) These lizards can grow rapidly, mature early, and produce large litters. Because blue-tongued lizards have a long life span (over 30 years in captivity), populations of adults may persist for many years in the absence of recruitment.

DO NOCTURNAL ECTOTHERMS THERMOREGULATE? A STUDY OF THE TEMPERATE GECKOCHRISTINUS MARMORATUS

Current paradigms relating to reptilian temperature regulation are derived almost entirely from data on diurnally active species, although many reptile species are nocturnal. We investigated the extent and behavioral mechanisms of temperature regulation in the nocturnal, rock-dwelling marbled gecko Christinus marmoratus during spring and summer. During the daytime, we recorded body temperatures of lizards sheltering beneath rocks, as well as operative temperatures (the equilibrium body temperatures that animals would attain in given microclimates) beneath randomly chosen rocks available to the lizards. These measurements were compared with reference to the lizard's set-point (or target) temperature range (Tset), which we determined in a laboratory thermal gradient. In both seasons, lizard body temperatures were closer to Tset than were randomly sampled operative temperatures, despite mean operative temperatures being 7°C below and 6°C above Tset in spring and summer, respectively. The mean body temperature of geckos was 7°C higher, and the accuracy and effectiveness of temperature regulation were also much higher, during summer than during spring. The more severe physiological consequences of thermoconformity during summer, as well as a more constraining thermal environment during spring, are advanced as reasons for this seasonal pattern. At least two behavioral mechanisms allow C. marmoratus to achieve a regulated body temperature. First, operative temperatures within retreat sites selected by geckos were closer to Tset than were operative temperatures beneath available rocks, suggesting retreat-site selection as a thermoregulatory mechanism. Second, lizard body temperatures were closer to Tset than were operative temperatures at random positions within selected retreat sites. This observation, together with correlative evidence relating lizard body temperature to the maximum and minimum operative temperatures beneath selected retreat sites, indicates that positional and/or postural adjustments were also employed as thermoregulatory mechanisms. This study suggests that nocturnal lizards are capable of regulating body temperature to an extent that is comparable to that of diurnal lizards. Our findings have implications for understanding the thermal physiology and ecology of nocturnal ectotherms.

Solid phase partitioning of metals in managed retreat soils: field changes over the first year of tidal inundation

Sequential extraction methods were used to determine the effect of saline inundation on partitioning behaviour of metals in soils at Orplands Managed Retreat site, Essex, UK. A suite of metals (Al, Ca, Cr, Cu, Fe, K, Li, Mn, Ni, Pb and Zn) were analysed in sequential extracts from samples of soil cores extracted immediately before breaching of sea walls in 1995 and 1 year after. Generally, partitioning of most metals was dominated by associations with the residual fraction and an absence of associations with the exchangeable fraction indicating a relatively uncontaminated environment. Changes in partitioning were predominantly limited to the top 8 cm of the soil profile where a decaying mat of vegetation from the pre-inundation surface resulted in high moisture contents and low redox potentials. In this zone, the predominance of metal associations with the residual fraction was replaced by associations with more labile fractions. In the surface layer deposited after breaching, Ca was dominantly associated with the carbonate fraction, which indicates biogenic import from adjacent estuarine sediments.

Determinants of Salamander Distributions along Moisture Gradients

Abstract I examined how the distributions of the plethodontid salamanders Desmognathus monticola, D. fuscus, Eurycea cirrigera, Plethodon cinereus, and P. glutinosus were related to interspecific differences in the characteristics of their retreats and differences in their dehydration and rehydration rates. There was little spatial overlap between the terrestrial species, Plethodon cinereus and P. glutinosus, and the largest two semiaquatic species, Desmognathus monticola and D. fuscus. Terrestrial species occupied retreats that were considerably drier than those of semiaquatic species, but they selected larger cover objects. Body size appeared to influence microhabitat use as well. Among both the terrestrial and the semiaquatic salamanders, large species used wider cover objects, deeper retreats, and occupied cooler retreat sites than smaller species. Among the semiaquatic salamanders, larger species were found closer to water than smaller species. Rehydration rates paralleled habitat use. Species found ...