Gyrinophilus Porphyriticus Research Articles

Chemically Mediated Predator Avoidance in the Barton Springs Salamander (Eurycea sosorum)

Predation is a dominant and influential factor in most ecological communities. However, little is known about how the federally endangered Barton Springs Salamander, Eurycea sosorum, responds to predators. Using captive-hatched (predator-nasalamanders, we examined the antipredator response of E. sosorum to chemical cues from (1) native Western Mosquitofish (Gambusia affinis), (2) introduced Redbreast Sunfish (Lepomis auritus), (3) native Largemouth Bass (Micropterus salmoides), and (4) a blank water control. Salamanders decreased activity (antipredator behavior) in response to all fish treatments but not to the blank water control. There was no difference between the response to the G. affinis and L. auritus, but salamanders responded less to these treatments than to M. salmoides. The antipredator response to G. affinis may be an ontogenetic hold over as G. affinis has been found to consume amphibian larvae and eggs. In an additional study to test whether antipredator behavior was a generalized response to all fish species, we found that E. sosorum did not respond to small, nonnative, nonpredatory Guppies (Poecilia reticulata). This suggests that the observed behavior in our first experiment represents antipredator behavior specific to the species tested. Overall, these results indicate that E. sosorum has innate recognition of predatory fish, and that the stronger antipredator response to M. salmoides over the other fish species may be an outcome of risk assessment. The antipredator response to G. affinis has management implications as G. affinis is sympatric with the largest population of E. sosorum, and may be consuming both eggs and larvae of these salamanders.

Decoupling of genetic and phenotypic divergence in a headwater landscape

In stream organisms, the landscape affecting intraspecific genetic and phenotypic divergence is comprised of two fundamental components: the stream network and terrestrial matrix. These components are known to differentially influence genetic structure in stream species, but to our knowledge, no study has compared their effects on genetic and phenotypic divergence. We examined how the stream network and terrestrial matrix affect genetic and phenotypic divergence in two stream salamanders, Gyrinophilus porphyriticus and Eurycea bislineata, in the Hubbard Brook Watershed, New Hampshire, USA. On the basis of previous findings and differences in adult terrestriality, we predicted that genetic divergence and phenotypic divergence in body morphology would be correlated in both species, but structured primarily by distance along the stream network in G.porphyriticus, and by overland distance in E.bislineata. Surprisingly, spatial patterns of genetic and phenotypic divergence were not strongly correlated. Genetic divergence, based on amplified DNA fragment length polymorphisms, increased with absolute geographic distance between sites. Phenotypic divergence was unrelated to absolute geographic distance, but related to relative stream vs. overland distances. In G.porphyriticus, phenotypic divergence was low when sites were close by stream distance alone and high when sites were close by overland distance alone. The opposite was true for E.bislineata. These results show that small differences in life history can produce large differences in patterns of intraspecific divergence, and the limitations of landscape genetic data for inferring phenotypic divergence. Our results also underscore the importance of explicitly comparing how terrestrial and aquatic conditions affect spatial patterns of divergence in species with biphasic life cycles.

Climate change is linked to long-term decline in a stream salamander

Amphibian declines have been documented worldwide and several have been linked to climate change, but the long-term data needed to detect declines are largely restricted to pond-breeding species. This limits our knowledge of population trends in other major groups of amphibians, including stream salamanders, which have their greatest diversity in North America. I hypothesized that increasing air temperature and precipitation in northeastern North America caused abundance of the stream salamander Gyrinophilus porphyriticus in a New Hampshire population to decline between 1999 and 2010. I found a significant decline in abundance of G. porphyriticus adults over this 12-year period, and no trend in larval abundance. Adult abundance was negatively related to annual precipitation, which is predicted to increase further in the Northeast due to climate change. Analysis of a 6-year capture–mark–recapture data set for the same population showed no temporal variation in larval and adult detectability, validating the abundance data, and no variation in larval and adult survival. However, survival during metamorphosis from the larval to adult stage declined dramatically. These results suggest that increasing precipitation is causing a decline in adult recruitment, which, if it persists, will lead to local extinction. A likely mechanism for the decline in adult recruitment is mortality of metamorphosing individuals during spring and fall floods, which have increased in volume and frequency with the increase in precipitation. More broadly, this study presents strong evidence that the amphibian decline crisis extends to North America’s stream salamanders, and shows the critical need to collect population data on these species.

Can natural selection maintain long-distance dispersal? Insight from a stream salamander system

Dispersal distributions are often characterized by many individuals that stay close to their origin and large variation in the distances moved by those that leave. This variation in dispersal distance can strongly influence demographic, ecological, and evolutionary processes. However, a lack of data on the fitness and phenotype of individual dispersers has impeded research on the role of natural selection in maintaining variation in dispersal distance. Six years of spatially explicit capture-mark-recapture data showed that survival increased with dispersal distance in the stream salamander Gyrinophilus porphyriticus. To understand the evolutionary implications of this fitness response, we tested whether variation in dispersal distance has a phenotypic basis. We used photographs of marked individuals to measure head, trunk, and leg morphology. We then tested whether dispersal distances over the six-year study period were predicted by these traits. Dispersal distance was significantly related to leg morphology: individuals with relatively long forelimbs and short hindlimbs dispersed the farthest. These results support the hypothesis that positive fitness consequences maintain phenotypes enabling long-distance dispersal. More broadly, they suggest that natural selection can promote variation in dispersal distance and associated phenotypes, offering an alternative to the view that dispersal distance is driven by stochastic or landscape-specific mechanisms.

Explaining long‐distance dispersal: effects of dispersal distance on survival and growth in a stream salamander

Long-distance dispersal (LDD) may contribute disproportionately to range expansions, the creation of new evolutionary lineages, and species persistence in human-dominated landscapes. However, because data on the individual consequences of dispersal distance are extremely limited, we have little insight on how LDD is maintained in natural populations. I used six years of spatially explicit capture-mark-recapture (CMR) data to test the prediction that individual performance increases with dispersal distance in the stream salamander Gyrinophilus porphyriticus. Dispersal distance was total distance moved along the 1-km study stream, ranging from 0 to 565 m. To quantify individual performance, I used CMR estimates of survival and individual growth rates based on change in body length. Survival and growth rates increased significantly with dispersal distance. These relationships were not confounded by pre-dispersal body condition or by ecological gradients along the stream. Individual benefits of LDD were likely caused by an increase in the upper limit of settlement site quality with dispersal distance. My results do not support the view that the fitness consequences of LDD are unpredictable and instead suggest that consistent evolutionary mechanisms may explain the prevalence of LDD in nature. They also highlight the value of direct CMR data for understanding the individual consequences of variation in dispersal distance and how that variation is maintained in natural populations.

Individual and seasonal variation in the diet of the endangered Barton Springs Salamander (Eurycea sosorum): An application of stable isotope analysis to the conservation of an endangered species

Individual and seasonal variation in the diet of the endangered Barton Springs Salamander (Eurycea sosorum): An application of stable isotope analysis to the conservation of an endangered species

Individual and seasonal variation in the diet of the endangered Barton Springs Salamander (Eurycea sosorum): An application of stable isotope analysis to the conservation of an endangered species

AbstractIt is well known that many species show strong temporal variation in diet. Long-term dietary trends may be important in assessing the effects of ecological change such as global warming, land use change, or introductions of invasive species. Short-term variation in food sources or prey selection may be crucial for understanding population dynamics in poorly understood species. The Barton Springs Salamander (Eurycea sosorum) is an endangered species endemic to four small spring outflows in downtown Austin, Texas. This species remains aquatic throughout life and inhabits benthic rocky substrate. While little is known about its foraging ecology, E. sosorum is assumed to be a generalist predator with the abundant amphipod Hyalella azteca as its primary food source. The salamander’s secretive behavior and obscure microhabitat make direct foraging observations impossible. Thus, stable isotope applications may be the only feasible means of estimating diet in these animals. Measurements of [delta]^13^C and [delta]^15^N for wild-caught Eurycea sosorum and a suite of potential invertebrate prey (amphipods, chironomids and planarians) were taken in November 2007, February 2008, May 2008 and August 2008. Quantitative invertebrate censuses track seasonal changes in invertebrate relative abundance. A multi-source mixing model is applied to field isotope data, and a distribution of likely prey item contributions to salamander diet is obtained for each season. Measurement of [delta]^13^C and [delta]^15^N from captive-bred E. sosorum raised on a constant diet indicate minimal fractionation of [delta]^13^C (<1‰) and approximately 2.3‰ enrichment in [delta]^15^N per trophic level. Mixing model results show that salamanders feed nearly equally on planarians (53-57% of diet) and amphipods (43-47% of diet) during the course of the study, and that chironomids do not contribute to the diet of E. sororum. The relative isotopic relationship between the three prey items and salamander tissue remains constant over the course of the study. Furthermore, individual variation in salamander diet is large in all seasons (range of 6-8‰ of [delta]^13^C values for individual salamanders), potentially reflecting the highly clumped prey item distributions or individual specialization on different food resources.Stable isotope techniques allow investigation of how diet composition responds to temporal changes in prey availability in field populations and the degree to which intrapopulation diet variation influences overall population diet estimates. This work provides conservation biologists at Barton Springs with essential information on the diet and ecology of E. sosorum, which is being used to improve species management plans that will be applicable to other spring systems.

What drives long‐distance dispersal? A test of theoretical predictions

Long-distance dispersal (LDD) may contribute disproportionately to species persistence in fragmented landscapes, non-native invasions, and range shifts in response to climate change. However, direct data on LDD are extremely limited, leaving us with little understanding of why it occurs. I used six years of mark-recapture data on the stream salamander Gyrinophilus porphyriticus to test theoretical predictions of how variation in habitat quality affects LDD. Frequency of LDD was quantified using the kurtosis of yearly movement distributions from recaptured animals in a 1-km headwater stream. Temporal and spatial variation in habitat quality were quantified with spatially explicit data on the body condition and dispersion of individuals throughout the study stream. Using information-theoretic model selection criteria, I found that LDD increased during periods of low average body condition and low spatial variation in body condition. Consistent with basic theory, my results indicate that temporal variation in habitat quality is critical to initiating dispersal, and that LDD increases when animals must move farther to encounter higher-quality habitat. This suggests that information on how habitat quality varies in time and space can be useful for predicting LDD. More broadly, this study highlights the value of direct data on animal movement for testing dispersal theory.

Detection of Batrachochytrium dendrobatidis in Endemic Salamander Species from Central Texas

A nested PCR protocol was used to analyze five endemic salamander species from Central Texas for the presence of the emerging pathogen, chytrid fungus (Batrachochytrium dendrobatidis). Chytrid fungus was detected from samples of each of the five species sampled: with low abundance, in the Texas salamander (Eurycea neotenes) (1 positive out of 16 individuals tested; 1/16), the Blanco River Springs salamander (E. pterophila) (1/20), the threatened San Marcos salamander (E. nana) (1/17), and the endangered Barton Springs salamander (E. sosorum) (1/7); much higher abundance was obtained for the Jollyville Plateau salamander (E. tonkawae) (6/14), which has recently been petitioned for addition to the USA endangered species list. With one exception, sequences of PCR products were identical to the 5.8S rRNA gene, and nearly so for the flanking internal transcribed spacer (ITS) regions of B. dendrobatidis which confirmed the detection of chytrid fungus, and thus demonstrated the presence of this pathogen in populations of endangered species in Central Texas. These confirmations were obtained from nonconsumptive tail clippings which confirms the applicability of historically collected samples from other studies in the examination of the fungus across time.

Demography and movement of the northern spring salamander in four New Hampshire headwater streams

An understanding of local population biology is critical in addressing basic and applied questions in ecology. Population dynamics are a function of local demographic rates and movement, and these two processes are linked by both ecological and evolutionary factors. Consequently, investigations of basic population ecology provide insight into emergent biological properties such as patterns of community structure and local adaptation. Likewise, efforts to manage and conserve species, including monitoring programs, are greatly improved by a comprehensive understanding of population biology (BIEK et al. 2002). Empirical study on the relative contributions of local demographic rates and dispersal to population dynamics is especially critical to amphibian conservation, where this information is necessary for assessing both the validity and causes of population declines (WAKE 1990). In an intensive 3-yr study on the northern spring salamander (Gyrinophilus porphyriticus), LOWE (2003) showed that upstream-biased movement contributed to the equality of population growth rates in upstream and downstream sections of a 1000-m stretch of stream in northern New Hampshire, USA. He also showed that population growth rates were relatively stable over time, and that survival probabilities were similar for adults and larvae. However, the generality of these patterns is unknown. We used mark-recapture methods to assess natural variation in the population biology of the spring salamander in multiple headwater streams.

Forest succession and prey availability influence the strength and scale of terrestrial‐aquatic linkages in a headwater salamander system

Summary1. Trophic linkages between terrestrial and aquatic ecosystems are common and sensitive to disruption. However, there is little information on what causes variation in the strength and spatial scale of these linkages.2. In the highly aquatic adults of the headwater salamander Gyrinophilus porphyriticus (family Plethodontidae), use of terrestrial prey decreases along a gradient from early‐ to late‐successional riparian forests. To understand the cause of this relationship, we tested the predictions that (i) terrestrial prey abundance is lower in late‐successional forests, and (ii) G. porphyriticus adults cannot move as far from the stream to forage in late‐successional forests, thus limiting access to terrestrial prey.3. We established 100‐m long study reaches on six headwater streams in the Hubbard Brook Experimental Forest, New Hampshire. Three reaches were in early‐successional forests and three were in late‐successional forests. We conducted pitfall trapping for invertebrate prey in June and July of 2005, with three traps at 0, 2, 5 and 10 m from the stream at each reach. In June, July and August of 2004 and 2005, nighttime salamander surveys were conducted at each reach along ten, 10‐m long by 2.5‐m wide transects perpendicular to the stream.4. Abundance of terrestrial prey was consistently lower in late‐successional forests, suggesting that consumption of terrestrial prey by G. porphyriticus is affected by prey abundance. Contrary to our prediction, G. porphyriticus adults moved farther from the stream in late‐successional forests, suggesting that habitat conditions in late‐successional forests do not limit movement away from the stream, and that lower abundances of terrestrial prey in these forests may cause salamanders to move farther from streams.5. Our results provide novel insight on the extent of terrestrial habitat use by G. porphyriticus. More broadly, these results indicate that major habitat gradients, such as forest succession, can affect the strength and scale of terrestrial‐aquatic linkages. Application of this insight to the design of vegetation buffers along headwater streams would have widespread benefits to freshwater ecosystems.

Linking movement behaviour to dispersal and divergence in plethodontid salamanders

To better understand the evolutionary and ecological effects of dispersal, there is growing emphasis on the need to integrate direct data on movement behaviour into landscape-scale analyses. However, little is known about the general link between movement behaviour and large-scale patterns of dispersal and gene flow. Likewise, although recent studies suggest that nonrandom, directionally biased movement and dispersal can promote evolutionary divergence, the generality of this mechanism is unknown. We test the hypothesis that directionally biased movement and dispersal by plethodontid salamanders interact with the topography of headwater areas to affect genetic and phenotypic divergence. Movements by Gyrinophilus porphyriticus and Eurycea bislineata show contrasting directional biases: upstream bias in G. porphyriticus and downstream bias in E. bislineata. Consistent with predictions of how these biases interact with slope to affect dispersal and gene flow, genetic distance increased with slope in G. porphyriticus and decreased with slope in E. bislineata over a standardized distance of 1 km along six headwater streams. In both species, phenotypic divergence in relative trunk length was positively related to genetic divergence. These results indicate that landscape-scale patterns of dispersal and gene flow are closely related to movement behaviour in G. porphyriticus and E. bislineata, and underscore the value of information on movement behaviour for predicting and interpreting patterns of dispersal and gene flow in complex landscapes. This study also provides new evidence that directionally biased movement and dispersal can be important sources of intra- and interspecific variation in population divergence, and highlights the value of explicit, a priori predictions in landscape genetic studies.

IMPACT OF CANNIBALISM ON PREDATOR–PREY DYNAMICS: SIZE-STRUCTURED INTERACTIONS AND APPARENT MUTUALISM

Direct and indirect interactions between two prey species can strongly alter the dynamics of predator-prey systems. Most predators are cannibalistic, and as a consequence, even systems with only one predator and one prey include two prey types: conspecifics and heterospecifics. The effects of the complex direct and indirect interactions that emerge in such cannibalistic systems are still poorly understood. This study examined how the indirect interaction between conspecific and heterospecific prey affects cannibalism and predation rates and how the direct interactions between both species indirectly alter the effect of the cannibalistic predator. I tested for these effects using larvae of the stream salamanders Eurycea cirrigera (prey) and Pseudotriton ruber (cannibalistic predator) by manipulating the relative densities of the conspecific and heterospecific prey in the presence and absence of the predator in experimental streams. The rates of cannibalism and heterospecific predation were proportional to the respective densities and negatively correlated, indicating a positive indirect interaction between conspecific and heterospecific prey, similar to "apparent mutualism." Direct interactions between prey species did not alter the effect of the predator. Although both types of prey showed a similar 30% reduction in night activity and switch in microhabitat use in response to the presence of the predator, cannibalism rates were three times higher than heterospecific predation rates irrespective of the relative densities of the two types of prey. Cumulative predation risks differed even more due to the 48% lower growth rate of conspecific prey. Detailed laboratory experiments suggest that the 3:1 difference in cannibalism and predation rate was due to the higher efficiency of heterospecific prey in escaping immediate attacks. However, no difference was observed when the predator was a closely related salamander species, Gyrinophilus porphyriticus, indicating that this difference is species specific. This demonstrates that cannibalism can result in the coupling of predator and prey mortality rates that strongly determines the dynamics of predator-prey systems.

Larval salamanders and channel geomorphology are indicators of hydrologic permanence in forested headwater streams

Regulatory agencies need rapid indicators of hydrologic permanence for jurisdictional determinations of headwater streams. The study objective was to assess the utility of larval salamanders and habitat variables for determining stream permanence across a large geographic area. We sampled four core forests (61 sites in IN, KY, and OH) in spring (April–May) and summer (August–September) over a 2-year period. Sites in each forest were selected to cover a gradient of permanence, from perennial to ephemeral. Salamanders were collected by both benthic core sampling and timed visual search on each site visit. Classification and regression tree (CART) models were used to identify indicators of seasonal permanence at core sites that were then tested using data collected from 6 satellite forests (52 sites) located nationwide. Southern two-lined salamanders, Eurycea cirrigera , were numerically dominant and were the only species included in CART models. Salamander diversity declined with distance from the Appalachians and strong longitudinal changes in assemblage composition were evident within streams. Abundance of E. cirrigera was positively correlated with watershed area, whereas dusky salamanders, Desmognathus spp., and spring salamanders, Gyrinophilus porphyriticus , comprised a greater proportion of salamander communities at intermittent sites within their range. Spring and summer CART models incorporated E. cirrigera abundance and measures of channel geomorphology to accurately classify approximately 80% of core sites as either ephemeral, intermittent or perennial. When applied to validation data from national satellite forests, correct classification rates were >85% for intermittent and ephemeral sites, but were only ∼20% for perennial sites. These findings suggest that larval plethodontid salamanders and habitat variables can be valuable predictors of headwater stream hydroperiod, but indicators are largely limited to the regional scale.

Speciation with gene flow could be common

The likelihood of speciation in the face of homogenizing gene flow (i.e. without complete geographical isolation) is one of the most debated topics in evolutionary biology. Demonstrating this phenonemon is hampered by the difficulty of isolating the effects of time since population divergence vs. gene flow on levels of molecular genetic differentiation. For example, weak genetic differentiation between taxa could be due to recent divergence, gene flow, or a combination of these factors. Nonetheless, a number of convincing examples of speciation with gene flow have recently emerged, owing in part to the development of new analytical methods designed to estimate gene flow specifically. A recent example of speciation with gene flow in salamanders (Niemiller et al. 2008) further advances our understanding of this phenonemon, by showing that gene flow between cave and spring salamanders was ongoing during speciation, rather than having occurred after a long period of allopatric divergence. Future work on the ecological and genetic factors reducing gene flow will likely increase our understanding of the conditions that faciliate divergence in the face of gene flow.

Recent divergence with gene flow in Tennessee cave salamanders (Plethodontidae:Gyrinophilus) inferred from gene genealogies

Cave organisms occupy a special place in evolutionary biology because convergent morphologies of many species demonstrate repeatability in evolution even as they obscure phylogenetic relationships. The origin of specialized cave-dwelling species also raises the issue of the relative importance of isolation vs. natural selection in speciation. Two alternative hypotheses describe the origin of subterranean species. The 'climate-relict' model proposes allopatric speciation after populations of cold-adapted species become stranded in caves due to climate change. The 'adaptive-shift' model proposes parapatric speciation driven by divergent selection between subterranean and surface habitats. Our study of the Tennessee cave salamander complex shows that the three nominal forms (Gyrinophilus palleucus palleucus, G. p. necturoides, and G. gulolineatus) arose recently and are genealogically nested within the epigean (surface-dwelling) species, G. porphyriticus. Short branch lengths and discordant gene trees were consistent with a complex history involving gene flow between diverging forms. Results of coalescent-based analysis of the distribution of haplotypes among groups reject the allopatric speciation model and support continuous or recurrent genetic exchange during divergence. These results strongly favour the hypothesis that Tennessee cave salamanders originated from spring salamanders via divergence with gene flow.

Amphibian use of man-made pools on clear-cuts in the Allegheny Mountains of West Virginia, USA

Timber harvesting can alter habitats of forest-dwelling species and these alterations can be highly detrimental to species such as amphibians that are intimately associated with habitat temperature and moisture regimes. Consequently, information on conservation practices that can reduce impacts on these species can be useful to prevent local extinctions. Twenty-two of 40 pools constructed by the Fernow Experimental Station, USDA Northern Research Station, Parsons, West Virginia in 1993 on primitive haul roads in two clearcut areas on McGowan Mountain, Tucker County, WV were monitored for 3 years to determine their potential use by anurans. Monthly samples (April through September) of water chemistry and amphibian captures were taken to evaluate amphibian use of these pools. Anurans that used the pools to breed were Bufo americanus americanus, Rana sylvatica, Psuedacris brachyphona, and Hyla chrysoscelis. Desmognathus ochrophaeus and Gyrinophilus porphyriticus porphyriticus were also found in ponds but no evidence of breeding was discovered. By 1994, 14 of the 22 pools that held water were used by anurans for reproduction. Species richness of anurans that bred in pools was primarily dependent on pond depth. Man-made small but deep ponds placed carefully such that their hydroperiods are long enough for larvae to complete development (i.e., near seepages) provides breeding habitat for some frogs species, as well as refugia for non-breeding frogs and salamanders in clear-cut areas. Pools constructed at strategic locations on primitive roads have the potential to reduce adverse impacts of timber harvesting on some amphibian populations.

ACUTE TOXICITY OF ACIDITY IN LARVAE AND ADULTS OF FOUR STREAM SALAMANDER SPECIES (PLETHODONTIDAE)

High levels of acid deposition have severely affected streamwater chemistry in the southern Appalachians. Plethodontid stream salamanders living in and around headwater streams rely on cutaneous respiration and are highly susceptible to changes in water quality. We examined the sensitivity to low pH conditions in four stream salamanders by monitoring the response to six pH treatments ranging from pH 2.75 to 6.5. To quantify acid tolerance, we determined median lethal concentrations (LC50) in 96-h laboratory bioassays. This is the first study to quantify the level of sensitivity of stream salamanders to acidic conditions, indicating that stream salamanders are acid tolerant compared with many other lotic organisms. We found that acid tolerance is a species-specific trait with intraspecific variation shaped by life stage and body size. Mortality occurred at pH levels less than 4.2. The acid sensitivity of Desmognathus quadramaculatus larvae (LC50 = pH 3.95) was highest compared to sensitivity of Eurycea cirrigera larvae (LC50 = 3.6), Gyrinophilus porphyriticus larvae (LC50 = 3.5), and Pseudotriton ruber larvae (LC50 = 3.5). Larval survival was lower than adult survival in low pH treatments for E. cirrigera (adult LC50 = 3.1) and D. quadramaculatus (adult LC50 = 3.5). Salamanders responded to sublethal exposure to acidity with lethargic movements and decreased swimming speed. These results suggest that episodic acid events that cause streamwater pH to drop near 4.2 may cause mortality or induce sublethal effects, such as slower swimming speed. Because salamander larvae are more sensitive to acidic conditions than adults, we recommend that population monitoring programs extend methodology to include reliable estimates of larval population sizes.

Self‐organisation in streams: the relationship between movement behaviour and body condition in a headwater salamander

Summary1. When movement behaviour is correlated with traits affecting fitness, it may affect population performance directly, independent of extrinsic habitat conditions.2. In a previous 3‐year, capture–recapture study, upstream movement by the salamander Gyrinophilus porphyriticus compensated for low reproduction in the upper 500 m of Merrill Brook, a first‐order stream in northern New Hampshire (U.S.A.). This immigrant subsidy resulted from excess reproduction in the downstream section (i.e. the lower 500 m of stream length) and from consistently upstream‐biased movement by salamanders. Reproduction in the two stream sections was positively correlated with mean body condition. Using 6 years of capture–recapture data, this study examines whether the movement behaviour of G. porphyriticus is related to body condition and thereby directly influences mean body condition and reproduction in the two sections of Merrill Brook.3. Upstream‐biased movement and greater mean body condition in the downstream section were consistent across 6 years of data collection. In Merrill Brook and four other streams, however, individuals with high body condition were more likely to move upstream and low‐condition individuals were more likely to move downstream. Movement direction was unrelated to the size, sex and initial location of individuals. Body condition was positively related to growth rate, further supporting its link to reproductive potential, and positively autocorrelated through time in individuals that moved.4. Results of this 6‐year study suggest that the movement behaviour of G. porphyriticus partially compensated for environmental factors differentiating mean body condition and reproduction along Merrill Brook and illustrate the potential for this form of self‐organisation to occur in linear habitats such as streams and rivers.

Use of amphibians to define riparian zones of headwater streams

Riparian areas are known for their high species richness and their influence on ecological processes. However, riparian zones are difficult to define because of their ambiguous borders. Defining riparian zones by examining habitat use of species that require both terrestrial and aquatic environments is one method that has not been thoroughly examined. We sampled amphibians in Maine, USA, with pitfall traps located at five distances (1, 8, 18, 28, and 33 m) from 15 headwater streams. We captured 1897 amphibians of 10 species over 73 536 trap-nights. We used a repeated-measures analysis of variance to determine if species' capture rates varied among pitfall-trap locations. The highest numbers of three species, spring salamander (Gyrinophilus porphyriticus), two-lined salamander (Eurycea bislineata), and dusky salamander (Desmognathus fuscus), were captured in trap locations closest to the streams. Total species richness and average species richness were highest in the trap location located closest to the stream. We conclude that the riparian zone along headwater streams, as defined by amphibian species richness and abundance, is relatively narrow (7–9 m).