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1.
Understanding metapopulation dynamics in large carnivores with naturally fragmented populations is difficult because of the large temporal and spatial context of such dynamics. We coupled a long-term database of visitor sighting records with an intensive 3-year telemetry study to describe population dynamics of recolonization by black bears (Ursus americanus) of Big Bend National Park in Texas during 1988-2002. This population, which occurs within a metapopulation in western Texas and northern Mexico, increased from a single pair of known breeding-age animals in 1988 to 29 bears (including 6 females of breeding age) in March 2000 (λ = 1.25/year). A migration and dispersal event in August-December 2000 reduced the population to 2 adult females and as few as 5-7 individuals. One-way movement distances from the study area during this event averaged 76 km for females (n = 7) and 92 km for males (n = 4), and 3 animals conducted migrations of at least 154, 178, and 214 km, respectively. Our observations exemplify the importance of stochastic events on demographics of small populations and highlight the potential scale of bear movement among montane islands of southwestern North America. They also provide insight into the use of dispersal data in parameterizing metapopulation models for large carnivores.  相似文献   

2.
This study investigates the dynamics and viability of a marsh fritillary butterfly Euphydryas aurinia metapopulation in a Belgian successional landscape. Based on capture-mark-recapture and winter nest census data, we first estimated demography (survival and recruitment rates, population size, density dependence) and dispersal parameters (emigration rate, effect of patch connectivity on dispersal, mortality during dispersal). Then using RAMAS/GIS platform, we parameterised a population viability analysis (PVA) model with these parameters to simulate the future of this metapopulation under different scenarios.The metapopulation does not seem viable even if natural reforestation is controlled by adequate management. In its present state, the patch system is not able to sustain enough individuals: due to the large temporal fluctuations in demographic parameters, a carrying capacity far higher than currently would be necessary to limit extinction risk to 1%, suggesting the existence of an extinction debt for the species in Belgium. The situation of E. aurinia appears much worse compared to two other fritillary species threatened in Belgium, for which similar PVA are available. It is therefore urgent to increase the carrying capacity of the patch system. How and where it is achieved are of secondary importance for the gain in viability: improvement of habitat quality through restoration, or increase of habitat quantity via enlargement of existing patches and/or creation of new habitat in the matrix. A regime of management based on regular re-opening and maintenance of habitat patches may be the only guarantee of long-term persistence for this critically endangered species in Belgium.  相似文献   

3.
Many orchids are currently red-listed due to changes in land use, and their future persistence will depend on management. Traditional land use like mowing is believed to favour orchids through increased survival and reproduction of established individuals, but the lack of data connecting their complex life cycle presently limits our ability to evaluate effects of management. Here we used data from 16 years of demographic monitoring to study how mowing affects population dynamics in two populations of the rare orchid Dactylorhiza lapponica. Both populations were characterized by long-lived individuals, low adult mortality and high seedling mortality. The traditional regime of mowing every second year strongly increased recruitment and reduced seed production in both populations, but had moderate effect on adult survival, growth rate and flowering probability. Population growth rate was positive for all population × treatment combinations. Traditional mowing significantly increased growth rate in both populations, and LTRE-analyses revealed that this primarily was a result of increased recruitment. The results indicate that demographic rates commonly associated with orchid persistence may be insensitive to traditional management, and underscores the importance of seed production and recruitment to maintain population growth in this long-lived species. The combination of low establishment success and no seed bank makes D. lapponica dependent on high seed input. Our results suggest that D. lapponica would benefit most from traditional mowing performed after seed dispersal in the study areas, but also suggest a high probability of future survival in the absence of mowing.  相似文献   

4.
Most turtle species require high adult survivorship to maintain stable populations. Translocations are often implemented to conserve turtle populations but may cause demographic disturbance as a result of increased mortality or dispersal of released animals. The gopher tortoise (Gopherus polyphemus) is one of the most frequently translocated turtle species. Short-term monitoring indicates that dispersal by released tortoises is common, but few long-term data are available to determine if losses of translocated animals continue for multiple years. We used 12 years of mark-recapture data to investigate long-term apparent survival of two groups of gopher tortoises translocated during separate periods to St. Catherines Island, Georgia, USA. We analyzed capture histories in program MARK to compare apparent survival of newly released tortoises and previously established translocated tortoises and also to determine whether apparent survival varied with sex or maturity. Apparent annual survival did not vary between adult males and females (0.98 ± 0.01), but was lower in sexually immature tortoises (0.84 ± 0.05). We documented a temporary reduction in apparent survival of newly released adult (0.75 ± 0.06) and immature tortoises (0.45 ± 0.26) during the first year after release that may be attributed in part to permanent dispersal. However, for both maturity classes, apparent survival of newly released tortoises was consistently high and matched that of previously established animals during the remainder of the study. Additional long-term studies of both translocated and naturally-occurring populations are needed to improve management of remaining tortoise populations.  相似文献   

5.
Although population declines of grassland songbirds in North America and Europe are well-documented, the effect of local processes on regional population persistence is unclear. To assess population viability of grassland songbirds at a regional scale (∼150,000 ha), we quantified Savannah Sparrow Passerculus sandwichensis and Bobolink Dolichonyx oryzivorus annual productivity, adult apparent survival, habitat selection, and density in the four most (regionally) common grassland treatments. We applied these data to a female-based, stochastic, pre-breeding population model to examine whether current grassland management practices can sustain viable populations of breeding songbirds. Additionally, we evaluated six conservation strategies to determine which would most effectively increase population trends. Given baseline conditions, over 10 years, simulations showed a slightly declining or stable Savannah Sparrow population (mean bootstrap λ = 0.99; 95% CI = 1.00-0.989) and severely declining Bobolink population (mean bootstrap λ = 0.75; 95% CI = 0.753-0.747). Savannah Sparrow populations were sensitive to increases in all demographic parameters, particularly adult survival. However for Bobolinks, increasing adult apparent survival, juvenile apparent survival, or preference by changing habitat selection cues for late-hayed fields (highest quality) only slightly decreased the rate of decline. For both species, increasing the amount of high-quality habitat (late- and middle-hayed) marginally slowed population declines; increasing the amount of low-quality habitat (early-hayed and grazed) marginally increased population declines. Both species were most sensitive to low productivity and survival on early-hayed fields, despite the fact that this habitat comprised only 18% of the landscape. Management plans for all agricultural regions should increase quality on both low- and high-quality fields by balancing habitat needs, nesting phenology, and species’ response to management.  相似文献   

6.
The monophagous flightless weevil Hadramphus spinipennis causes the frequent local extinction of its host plant Aciphylla dieffenbachii through overexploitation. Both species are endemic and restricted to the Chatham Islands group (New Zealand). The weevil is classified as endangered and the plant as a threatened species. As this herbivore-plant system is locally unstable long-term persistence only appears possible via a metapopulation structure in which subpopulations are connected by dispersal. This paper investigates this hypothesis using a spatially explicit model of a consumer population whose resource is patchily distributed. The parameters are adapted to the H. spinipennis-A. dieffenbachii system. Our model includes local population dynamics and dispersal of the consumer, the destruction of host plant patches due to foraging and their regeneration. The results show that the key factor for long-term persistence is the short-range dispersal of the consumer with high mortality during dispersal. Only this highly inefficient dispersal prevents the synchronisation of local dynamics while ensuring sufficient colonisation of regenerated patches. We also show that although synchronisation through spatially correlated environmental fluctuations may be critical for long-term persistence, it cannot replace the strong effects of dispersal. Thus, in a consumer-resource metapopulation with deterministic local extinction, the strength and spatial scale of consumer dispersal in relation to the spatial and temporal scales of the resource patch dynamics (patch destruction and regeneration, number, size and distance of patches) play a vital role for long-term persistence. The consequence for conservation management is that such metapopulations could in fact profit rather than suffer from decreasing connectivity of resource patches.  相似文献   

7.
Many seabird populations are currently decreasing, especially albatrosses for which the primary threat is recognised to be mortality in fisheries. Introduced predators, climate change and other factors such as diseases can also have large impacts on seabirds. Here, we assessed the relative effect of three potential threats: climate, fisheries and diseases on the demography of an endangered marine predator and modelled its population dynamics to project its size under different scenarios. We based our study on a long-term monitoring of a colony of individually marked Indian yellow-nosed albatrosses at Amsterdam Island, subtropical Indian Ocean, that has declined during the past twenty years. We found no evidence for an impact of legal tuna longlining on demographic parameters. Hatching success was lower during El Niño years but survival (0.902 ± 0.011) was not affected by climatic factors. Avian cholera caused high chick mortality (0.808 ± 0.181) which in turn probably triggered the high emigration rate (0.038 ± 0.011) through dispersal of failed breeders. This colony has a high risk of extinction. However, the rest of the population at Amsterdam Island seemingly not affected to the same extent, declined but stabilised since 1998. Matrix models indicated that lowered adult survival and the very low breeding success, resulting in low recruitment, have both contributed to the decline of the yellow-nosed albatross colony until the mid-1990s, but that more recent decline was primarily caused by low fledging success. Our results highlight that potential threats such as fisheries, diseases or climate have to be considered simultaneously to disentangle their roles when assessing the conservation status of a marine predator species.  相似文献   

8.
We used reverse time capture-mark-recapture models to describe associations between rate of population change (λ) and climate for northern spotted owls (Strix occidentalis caurina) at six long-term study areas in Washington and Oregon, USA. Populations in three of six areas showed strong evidence of declining populations, while populations in two additional areas were likely declining as well. At four areas, λ was positively associated with wetter-than-normal conditions during the growing season, which likely affects prey availability. Lambda was also negatively associated with cold, wet winters and nesting seasons, and the number of hot summer days. The amount of annual variation in λ accounted for by climate varied across study areas (3-85%). Rate of population change was more sensitive to adult survival than to recruitment; however, there was considerable variation among years and across study areas for all demographic rates. While annual survival was more closely related to regional climate conditions, recruitment was often associated with local weather. In addition to climate, declines in recruitment at four of six areas were associated with increased presence of barred owls. Climate change models predict warmer, wetter winters and hotter, drier summers for the Pacific Northwest in the first half of the 21st century. Our results indicate that these conditions have the potential to negatively affect annual survival, recruitment, and consequently population growth rates for northern spotted owls.  相似文献   

9.
Tropical forest trees that produce large fruits and/or large seeds are believed to be dependant on a few and often rare large vertebrates for dispersal. However, little is known about the population dynamics of such trees when they lose their specialised dispersers. This study examines the juvenile spatial distribution of Balanites wilsoniana, Dawe & Spraque, which is believed to be dependant solely on elephants for dispersal, in forests with and without elephants. Using camera traps, elephants were confirmed to be the only frugivores feeding and thus dispersing Balanites wilsoniana fruits. There was a high density of seedlings beneath adult trees in one forest without elephants, which was attributed to low seed and seedling predation in this forest. Nevertheless, it was only in the forest with elephants that juveniles were established away from adult trees. Analysis of the spatial distribution of these juveniles by size revealed that saplings and poles are more likely to be found away from adult trees thus providing evidence that dispersal enhances juvenile survival. This study underlines the importance of seed dispersal for trees that cannot maintain their populations through seedlings germinating and surviving beneath adult conspecifics. The study also demonstrates that loss of vertebrates has ramifications for tree species dynamics above and beyond loss of seed dispersers.  相似文献   

10.
Forest clearcutting is a form of habitat alteration that drastically alters the landscape and may contribute to declines in amphibian populations. Indeed, many studies have documented decreases in amphibian abundances and species richness in clearcuts. The development of effective conservation strategies to reduce the effects of timber harvesting has been hindered by lack of knowledge of the mechanisms underlying these changes in abundance. To better understand the potentially negative consequences of forest clearcutting, we used field enclosures in forested and clearcut habitats to examine changes in the survival and growth of juvenile southern toads (Bufo terrestris) over a two-month period. We also conducted a comparative monitoring study using drift fences and pitfall traps in forests and clearcuts to determine the effect of clearcutting on the abundance of juvenile southern toads. We found no significant effect of habitat on the number of juvenile southern toads captured in forests or clearcuts. In contrast, the average survival of toads in clearcut enclosures was significantly reduced compared to that of toads in forested enclosures (17 ± 5% versus 61 ± 3%). Toads surviving in clearcuts were also significantly smaller than those surviving in forested enclosures (27.9 ± 0.1 mm versus 30.3 ± 0.8 mm SVL). Our results highlight the difficulty in interpreting abundance patterns as a sole metric for habitat comparison. Because there is much interest in studying the effects of habitat alteration on amphibian populations, we recommend that future studies place more emphasis on determining changes in vital rates of populations following habitat alteration.  相似文献   

11.
The northern aplomado falcon (Falco femoralis septentrionalis) has been the subject of a large-scale reintroduction effort conducted by The Peregrine Fund since 1993. Intensive monitoring during 2002-2004 revealed approximately 38 breeding pairs and numerous non-territorial individuals in two study areas centered on Matagorda Island National Wildlife Refuge (NWR) and Laguna Atascosa NWR. Continued releases (“hacking”) of captive-bred young after pair establishment and successful wild breeding provided an opportunity to compare survival and recruitment histories of wild-reared and hacked falcons hatched during 2001-2003. We used Program MARK to rank multi-state models of apparent survival and recruitment rates with Akaike’s Information Criterion scores, corrected for small samples. The top model candidate, with almost 3.5 times more support than the next best model, detected differences due to falcon origin (wild or captivity): although breeder survival was independent of origin, juvenile hacked falcons survived and recruited at lower rates than wild-reared falcons. Given the high density of territorial adult falcons in the study areas, the difference in apparent survival may reflect greater dispersal by hacked falcons, increased tolerance of wild falcons in territory margins due to prior socialization, or other factors effecting higher intrinsic fitness of wild falcons. However, natal dispersal did not differ between the two groups, strengthening the hypothesis of a difference in true survival. Disproportionately greater recruitment of wild falcons into the breeding population again suggests their higher intrinsic fitness. These findings show how close monitoring of population vital rates can efficiently guide adaptive management of recovering populations.  相似文献   

12.
Many amphibian species are plastic in their selection of breeding sites and use both short- and longer-hydroperiod wetlands. Understanding which wetland types are most important to amphibian production is critical for focusing conservation efforts. We compared reproduction of wood frogs (Rana sylvatica) and spotted salamanders (Ambystoma maculatum) and production of wood frog juveniles between seasonal (vernal pools) and semi-permanent (beaver-created ponds) wetlands in the central Adirondack region of the northeastern United States. In 65 seasonal wetlands and 37 semi-permanent wetlands over 3 years, densities of wood frog egg masses were similar, but seasonal wetlands contained 4× as many spotted salamander egg masses as did semi-permanent wetlands. For wood frogs, survival to metamorphosis and juvenile production were an order of magnitude higher in semi-permanent wetlands. Models of wood frog production linked to the climatic record predicted that, depending on annual variation in rainfall and survival to metamorphosis, semi-permanent wetlands may produce annually 1.2–23× the number of wood frogs that seasonal wetlands produce within the study area. Models incorporating variation in demographic traits throughout the range of wood frogs suggest that higher survival to metamorphosis in beaver ponds and higher clutch densities in vernal pools strongly influence metamorph production on a regional basis. Semi-permanent wetlands make major contributions to amphibian production in our region and may also be an important source of colonists to seasonal wetlands following periods of drought. Protection of wetlands along the landscape-level continuum of hydroperiod therefore may be critical for maintaining and restoring amphibian populations.  相似文献   

13.
We used size-structured Lefkovitch projection matrix analysis to predict future trends in the survival of Aquilaria crassna (Thymelaeaceae), a tropical evergreen forest tree that has been highly sought after for its valuable aromatic wood (agarwood) for millennia. Data on growth, damage to trees by poachers, fruit production, seed dispersal and seedling recruitment were collected from a 30-ha plot in Khao Yai National Park, central Thailand that had seen moderate poaching. The population asymptotic growth rate, λa, and transient growth rate, λtr, found from using the matrix to project the observed population 48 years, were 1.002 and 1.005, respectively, with 95% confidence intervals of [0.985, 1.016] and [0.985, 1.023]. The stable size distribution obtained from the matrix was reasonably similar to the observed size distribution, suggesting that at the time of the study the population was not far from equilibrium. Sensitivity analysis and simulations of poaching on adult trees indicate that both λ’s are very sensitive to the removal of adult trees and the growth of preadult trees. In particular, the increase in tree mortality and decrease in preadult growth rate caused by agarwood collection seen in some areas could cause extirpation of the population. While in such cases the population appears to be poised on the brink of decline, several factors that we could not evaluate could alter its fate. First, adult deaths could stimulate recruitment of young under the parent trees; second, there is marked year-to-year variation in fruiting success and possibly recruitment; third, there is considerable spatial variation in tree density and recruitment, suggesting that attempts to evaluate future success need to encompass larger spatial and time scales.  相似文献   

14.
Evidence for disease-related amphibian decline in Colorado   总被引：8，自引：0，他引：8  
The recent discovery of a pathogenic fungus (Batrachochytrium dendrobatidis) associated with declines of frogs in the American and Australian tropics, suggests that at least the proximate cause, may be known for many previously unexplained amphibian declines. We have monitored boreal toads in Colorado since 1991 at four sites using capture–recapture of adults and counts of egg masses to examine the dynamics of this metapopulation. Numbers of male toads declined in 1996 and 1999 with annual survival rate averaging 78% from 1991 to 1994, 45% in 1995 and 3% between 1998 and 1999. Numbers of egg masses also declined. An etiological diagnosis of chytridiomycosis consistent with infections by the genus Batrachochytrium was made in six wild adult toads. Characteristic histomorphological features (i.e. intracellular location, shape of thalli, presence of discharge tubes and rhizoids) of chytrid organisms, and host tissue response (acanthosis and hyperkeratosis) were observed in individual toads. These characteristics were indistinguishable from previously reported mortality events associated with chytrid fungus. We also observed epizootiological features consistent with mortality events associated with chytrid fungus: an increase in the ratio of female:male toads captured, an apparent spread of mortalities within the metapopulation and mortalities restricted to post metamorphic animals. Eleven years of population data suggest that this metapopulation of toads is in danger of extinction, pathological and epizootiological evidence indicates that B. dendrobatidis has played a proximate role in this process  相似文献   

15.
Introduced pests threaten many species and their control is generally beneficial for conservation, particularly on islands where complete eradication is possible. Unfortunately on ‘nearshore’ islands neighbouring source populations exist and unaided reinvasion is likely. Pest control programmes at these sites thus require a metapopulation context to adequately manage movements between source and sink populations. We investigated the ecology of introduced ship rats (Rattus rattus) on a nearshore island, and gene flow with adjacent mainland populations, in order to understand the metapopulation dynamics and relative levels of pest control required within the landscape. We sampled the entire population by trapping (n = 30), achieving eradication, and found a low rat density (3.2 ha−1) indicative of a sink population. Seed and other plant material constituted the major dietary component of rats. Despite its proximity to mainland source populations, the island population was genetically distinct with reduced allelic diversity caused by a recent reinvasion founder effect. Genetic analyses also detected recent migrants between the populations. In contrast, two mainland populations separated by a similar distance displayed complete genetic mixing. The small water gap therefore provides a sufficient barrier to lower the migration rate to the island and delay reinvasion, which nonetheless eventually happens. In order to maintain nearshore islands pest-free, conservation management will require a metapopulation approach simultaneously focusing on both island and source population pest control.  相似文献   

16.
Previous in situ studies of orchid population dynamics with conservation relevance have focused on one or a few populations in a limited area. Many species of orchids occur as hyperdispersed populations in ephemeral habitats (epiphytic, twig epiphytes, short lived or vulnerable host). In this contribution, we show that orchid populations that are patchily distributed and that exist in disturbance-prone environments may act somewhat like a metapopulation with high turnover and low correlation in population dynamics. We tested for evidence of metapopulation dynamics in the riparian orchid Lepanthes rupestris by sampling over 1000 sites (250 initially occupied, 750 initially unoccupied) in biannual surveys for 5 years. Extinction and colonization of groups of orchids on a single substrate or patch (either trees or boulders) was common and more or less consistent across different time periods, and asynchronous subpopulation dynamics were evident among the populations. From this we predict non-zero equilibrium values for site occupancy () of L. rupestris. Nevertheless, this study species differed from a typical Levins’ metapopulation system in that small populations were more likely to go extinct than large populations, and that colonization of previously occupied sites was more common than colonization of initially unoccupied sites suggesting that site quality may influence population persistence and colonization. A major difficulty applying the metapopulation approach to orchid conservation is identifying empty sites suitable for colonization. In spite of this limitation, our study highlights the necessity of following multiple orchid subpopulations (e.g., an entire orchid “metapopulation” in the broad sense) may provide a more accurate basis for predicting persistence in epiphytic orchids.  相似文献   

17.
Even among widespread species with high reproductive potentials and significant dispersal abilities, the probability of extinctions should be correlated both with population size variance and with the extent of population isolation. To address how variation in demographic characteristics and habitat requirements may reflect on the comparative risk of species decline, I examined 617 time series of population census data derived from 89 amphibian species using the normalized estimate of the realized rate of increase, ΔN, and its variance. Amphibians are demonstrably in general decline and exhibit a great range of dispersal abilities, demographic characteristics, and population sizes. I compared species according to life-history characteristics and habitat use. Among the populations examined, census declines outnumbered increases yet the average magnitudes for both declines and increases were not demonstrably different, substantiating findings of amphibian decline. This gives no support for the idea that amphibian population sizes are dictated by regimes featuring relatively rare years of high recruitment offset by intervening years of gradual decline such that declines may outnumber increases without negative effect. For any given population size, those populations living in large streams or in ponds had significantly higher variance than did populations of completely terrestrial or other stream-dwelling amphibians. This could not be related to life-history complexity as all the stream-breeding species examined have larvae and all of the wholly terrestrial species have direct development without a larval stage. Variance in ΔN was highest amongst the smallest populations in each comparison group. Estimated local extinction rates averaged 3.1% among pond-breeding frogs, 2.2% for pond-breeding salamanders, and negligible for both stream-breeding and terrestrial direct-developing species. Recoveries slightly exceeded extinctions among European pond-breeding frogs but not among North American pond-breeding frogs. Less common species had greater negative disparities between extinctions and recoveries. Species with highly fluctuating populations and high frequencies of local extinctions living in changeable environments, such pond- and torrent-breeding amphibians, may be especially susceptible to curtailment of dispersal and restriction of habitat.  相似文献   

18.
The wild population of the palm Ptychosperma macarthurii near Darwin, in monsoonal northern Australia, is regionally endangered and provides a focus to illustrate a range of issues pertinent to conservation of rainforest habitat. Surveys in 1990 found that several populations exhibited a polarised size class structure typified by large adults and small juvenile plants. Over the following decade, in the absence of wildfire and in a period of reduced disturbance from introduced buffalo (Bubalus bubalis), cattle (Bos indicus) and pig (Sus scrofa), sufficient small juvenile plants survived and grew so as to infill the intermediate size classes. Three stage (bifid, juvenile and adult) transition matrix models characterised the population as declining under all observed conditions (intrinsic rate of increase: unburnt + few animals 0.9850; unburnt + many animals 0.9584; burnt <1 year 0.8737; burnt 1-2 years 0.9146; burnt >2 years 0.9937). In the absence of fire, simulations conducted to explore management options revealed a positive rate of increase with exclusion of introduced animals. With only partial introduced animal control or supplementation with juvenile plants, the median rate of increase remained negative. The regional population is at risk by more frequent and more intense fire due to the invasion of exotic grass species and land use changes in the catchment which result in an increased drying of the rainforest habitat. Ongoing decline is the most likely outcome in the absence of effective management intervention.  相似文献   

19.
In this study, the effectiveness of management measures aimed at promoting recruitment in the last large Flemish juniper population at Heiderbos is evaluated. We resurveyed demographic plots 23 years after their establishment in 1980 and linked the population changes with detailed records of the intensive management during the same period. Between 1980 and 2003 the population size has decreased by 36% and has changed from a relatively immature to a mature population with very few young individuals. Based on a simple model that simulated height growth between 1980 and 2003, the recruitment and mortality rates were estimated to be 5 and 24 ha−1 yr−1, respectively. Intensive management has thus not been able to promote recruitment and the population might go extinct within 40 years if these rates remain unchanged. Furthermore, some measures, notably the working of the soil, have increased mortality of established junipers. The reasons for the limited recruitment are not entirely clear yet, but it may be due to a combination of the limited availability of bare ground for germination and the extremely low viability of juniper seeds. The latter fact may be a common characteristic of many threatened juniper populations in northwestern Europe.  相似文献   

20.
The persistence of amphibian populations in fragmented landscapes requires dispersal and recolonization of habitat patches after local extinction. These processes entail individuals crossing habitat edges. Edge permeability integrates the behavior of individuals with the vegetative structure of the habitat edge and may influence the dispersal rates between habitat patches. We used drift fences, radio telemetry, and an experimental displacement to examine the movement behavior of juvenile and adult spotted salamanders (Ambystoma maculatum) at a pond located in continuous forest and a pond located on a distinct forest-grassland edge. At the pond on the habitat edge, adult salamanders migrated to and from the forested side of the pond. Resident adults with transmitters migrated to forested habitat without approaching the habitat edge. Displaced adults with transmitters halted emigration movements when they approached the habitat edge. None of the radio-tagged adults were observed more than a few meters into the grassland. Recently metamorphosed juveniles exiting the grassland side of the pond changed their direction of movement and migrated into the forested habitat. We conclude that salamanders oriented movements with respect to features in the terrestrial habitat, detected the habitat edge, and behaviorally avoided the grassland. Exploring the permeability of habitat edges will improve our understanding of dispersal within fragmented landscapes and enhance efforts to conserve regional populations of amphibians.  相似文献   

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