Susan Claire Walls

United States Geological Survey | USGS · Wetland and Aquatic Research Center

1. One of the primary ways in which climate change will impact coastal freshwater wetlands is through changes in the frequency, intensity, timing, and distribution of extreme weather events. Disentangling the direct and indirect mechanisms of population‐ and community‐level responses to extreme events is vital to predicting how species composition...

Rockland habitat in South Florida, USA, is a threatened ecosystem that has been lost, fragmented, or degraded because of urbanization or other anthropogenic disturbance. Furthermore, low‐lying islands and coastal areas are experiencing sea level rise (SLR) and an increased frequency and intensity of tidal flooding, putting rockland habitats there a...

Occurrence data used to build species distribution models often include historical records from locations in which the species no longer exists. When these records are paired with contemporary environmental values that no longer represent the conditions the species experienced, the model creates false associations that hurt predictive performance....

The salamander chytrid fungus (Batrachochytrium salamandrivorans [Bsal]) is causing massive mortality of salamanders in Europe. The potential for spread via international trade into North America and the high diversity of salamanders has catalyzed concern about Bsal in the U.S. Surveillance programs for invading pathogens must initially meet challe...

Environmental change associated with anthropogenic disturbance can lower habitat quality, especially for sensitive species such as many amphibians. Variation in environmental quality may affect an organism's physiological health and, ultimately, survival and fitness. Using multiple health measures can aid in identifying populations at increased ris...

Managing spatially structured populations of imperiled species presents many challenges. Spatial structure can make it difficult to predict population responses to potential recovery activities, and learning through experimentation may not be advised if it could harm threatened populations. Adaptive management provides an appealing framework when e...

The amphibian decline crisis has been challenging to address because of the complexity of factors—and their multitude of interactive effects—that drive this global issue. Dissecting such complexity could benefit from strategies that integrate multiple disciplines and address the mechanistic underpinnings of population declines and extirpations. We...

Climate change is anticipated to exacerbate the extinction risk of species whose persistence is already compromised by habitat loss, invasive species, disease, or other stressors. In coastal areas of the southeastern United States (USA), many imperiled vertebrates are vulnerable to hurricanes, which climate models predict to become more severe in t...

Temporary wetlands have value to both ecological and social systems. Interactions between local climate and the surrounding landscape result in patterns of hydrology that are unique to temporary wetlands. These seasonal and annual fluctuations in wetland inundation contribute to community composition and richness. Thus, predicting wetland community...

Changing climate will impact species' ranges only when environmental variability directly impacts the demography of local populations. However, measurement of demographic responses to climate change has largely been limited to single species and locations. Here we show that amphibian communities are responsive to climatic variability, using >500,00...

A research priority can be defined as a knowledge gap that, if resolved, identifies the optimal course of conservation action. We (a group of geographically distributed and multidisciplinary research scientists) used tools from nominal group theory and decision analysis to collaboratively identify and prioritize information needs within the context...

Conservation resources have become increasingly limited and, along with social, cultural and political complexities, this shortfall frequently challenges effectiveness in conservation. Because conservation can be costly, efforts are often only initiated after a species has declined below a critical threshold and/or when statutory protection is mand...

The development and use of automated species-detection technologies, such as acoustic recorders, for monitoring wildlife are rapidly expanding. Automated classification algorithms provide a cost- and time-effective means to process information-rich data, but often at the cost of additional detection errors. Appropriate methods are necessary to anal...

Plasticity in life history strategies can be advantageous for species that occupy spatially or temporally variable environments. We examined how phenotypic plasticity influences responses of the mole salamander, Ambystoma talpoideum, to disturbance events at the St. Marks National Wildlife Refuge (SMNWR), FL, USA from 2009 to 2014. We observed peri...

We evaluated the current literature, coupled with our collective research expertise, on surface-water connectivity of wetlands considered to be “geographically isolated” (sensu Tiner Wetlands 23:494–516, 2003a) to critically assess the scientific foundation of grouping wetlands based on the singular condition of being surrounded by uplands. The mos...

At least one-third of all amphibian species face the threat of extinction, and current amphibian extinction rates are four orders of magnitude greater than background rates. Preventing extirpation often requires both ex situ (i.e., conservation breeding programs) and in situ strategies (i.e., protecting natural habitats). Flatwoods salamanders (Amb...

A comprehensive view of population declines and their underlying causes is necessary to reverse species loss. Historically, in many cases, a narrow view may have allowed species declines to continue, virtually undetected, for long periods of time (perhaps even decades). We suggest that extinction debt is likely responsible for numerous (perhaps mos...

Small, seasonal pools and temporary ponds (<4.0 ha) are the most numerous and biologically diverse wetlands in many natural landscapes. Thus, accurate determination of their numbers and spatial characteristics is beneficial for conservation and management of biodiversity associated with these freshwater systems. We examined the utility of a topogra...

Disentangling the role that multiple interacting factors have on species responses to shifting climate poses a significant challenge. However, our ability to do so is of utmost importance to predict the effects of climate change on species distributions. We examined how populations of three species of wetland breeding amphibians, which varied in li...

The US Endangered Species Act of 1973 (ESA) affords many potential benefits to species threatened with extinction. However, most at-risk amphibians—one of the most imperiled vertebrate groups—remain unlisted under the provisions of the ESA, and many impediments to recovery exist for those species that have been listed. Of the 35 US amphibian specie...

Section 6 funds were used to conduct surveys to determine the status and distribution of three rare and imperiled pond-breeding amphibians: striped newt (Notophthalmus perstriatus), frosted flatwoods salamander (Ambystoma cingulatum), and reticulated flatwoods salamander (A.bishopi). This report summarizes the results of surveys for these species f...

Since amphibian declines were first proposed as a global phenomenon over a quarter century ago, the conservation community has made little progress in halting or reversing these trends. The early search for a “smoking gun” was replaced with the expectation that declines are caused by multiple drivers. While field observations and experiments have i...

Geographically isolated wetlands (GIWs), those surrounded by uplands, exchange materials, energy, and organisms with other elements in hydrological and habitat networks, contributing to landscape functions, such as flow generation, nutrient and sediment retention, and biodiversity support. GIWs constitute most of the wetlands in many North American...

We explore the category “geographically isolated wetlands” (GIWs; i.e., wetlands completely surrounded by uplands at the local scale) as used in the wetland sciences. As currently used, the GIW category (1) hampers scientific efforts by obscuring important hydrological and ecological differences among multiple wetland functional types, (2) aggregat...

1.With ongoing climate change, many species are expected to shift their spatial and temporal distributions. To document changes in species distribution and phenology, detection/non-detection data have proven very useful. Occupancy models provide a robust way to analyze such data, but inference is usually focused on species spatial distribution, not...

I review the primary literature to ascertain the status of amphibian monitoring efforts in the southeastern USA, a “hotspot” for biodiversity in North America. This effort revealed taxonomic, geographic and ecological disparities in studies of amphibian populations in this region. Of the species of anurans and caudates known to occur in the Southea...

A fundamental goal of wetland restoration is to reinstate pre-disturbance hydrological conditions to degraded landscapes, facilitating recolonization by native species and the production of resilient, functional ecosystems. To evaluate restoration success, baseline conditions need to be determined and a reference target needs to be established that...

We measured amphibian habitat use to quantify the effectiveness of conservation practices implemented under the Wetland Reserve Program (WRP), an initiative of the U.S. Department of Agriculture’s Natural Resources Conservation Service. From February to June 2007, we quantified calling male anurans in cultivated cropland, former cultivated cropland...

We scored 48 Malaclemys terrapin nests destroyed by raccoons on Fisherman Island, Virginia, for the presence or absence of tree canopy, shrub canopy, no canopy, bare sand, grass cover, and herbaceous cover. Significantly more nests than expected were found in the open with no vegetation cover and observed distances of predator-destroyed nests from...

Amphibians in freshwater coastal wetlands periodically experience acute exposure to salinity from hurricane-related overwash events, as well as chronic exposure associated with rising sea levels. In a comparative experimental approach, we examined whether seven species of anuran amphibians vary in their tolerance to changes in salinity. In a labora...

Though a third of amphibian species worldwide are thought to be imperiled, existing assessments simply categorize extinction risk, providing little information on the rate of population losses. We conducted the first analysis of the rate of change in the probability that amphibians occupy ponds and other comparable habitat features across the Unite...

Comparison of instantaneous trend estimates derived from linear and log-linear models of change in amphibian occupancy at ARMI monitoring areas, 2002–2011. (DOC)

Trends in the probability of site occupancy by species for ARMI monitoring areas, 2002–2011. The estimated trend effects are annual proportional changes in occupancy and are conditional on a random effect for a variable coding species that was included in the statistical model. Caution should be taken in interpreting results for individual species...

In the southeastern U.S., changes in temperature and precipitation over the last three decades have been the most dramatic in winter and spring seasons. Continuation of these trends could negatively impact pond-breeding amphibians, especially those that rely on winter and spring rains to fill seasonal wetlands, trigger breeding, and ensure reproduc...

The Class Amphibia is one of the most severely impacted taxa in an on-going global biodiversity crisis. Because amphibian reproduction is tightly associated with the presence of water, climatic changes that affect water availability pose a particularly menacing threat to both aquatic and terrestrial-breeding amphibians. We explore the impacts that...

Background/Question/Methods Agricultural cultivation is a major contributor to wetland loss and alteration and may impact wetland-dependent species such as many aquatic-breeding amphibians. Historically, the Lower Mississippi Valley (LMV) was the largest bottomland hardwood forest (BLH) ecosystem in North America and provided extensive wetland hab...

Effective monitoring programs are designed to track changes in the distribution, occurrence, and abundance of species. We developed an extension of Royle and Kéry's (2007) single species model to estimate simultaneously temporal changes in probabilities of detection, occupancy, colonization, extinction, and species turnover using data on calling an...

We investigated the mechanisms of competition between two species of larval salamanders, Ambystoma talpoideum and Ambystoma maculatum. A laboratory experiment revealed that A. maculatum suffered higher mortality during early periods of larval growth when raised with its congener, A. talpoideum, than it did when combined with conspecifics. Ambystoma...

Restoration of wetland ecosystems is an important priority for many state and federal agencies, as well as nongovernmental conservation organizations. The historic conversion of wetlands in the Mississippi Alluvial Valley (MAV) has resulted in large-scale implementation of a variety of conservation practices designed to restore and enhance wetland...

Models currently used to estimate patterns of species co-occurrence while accounting for errors in detection of species can be difficult to fit when the effects of covariates on species occurrence probabilities are included. The source of the estimation problems is the particular parameterization used to specify species co-occurrence probability. W...

As part of an overall decline in biodiversity, populations of many organisms are declining and species are being lost at unprecedented rates around the world. This includes many populations and species of amphibians. Although numerous factors are affecting amphibian populations, we show potential direct and indirect effects of climate change on amp...

I examined the potential influence of climate change on the dynamics of a previously studied hybrid zone between a pair of terrestrial salamanders at the Coweeta Hydrologic Laboratory, U.S. Forest Service, in the Nantahala Mountains of North Carolina, USA. A 16-year study led by Nelson G. Hairston, Sr. revealed that Plethodon teyahalee and Plethodo...

El consumo de partes del cuerpo de reptiles, como ser la propia muda o la de un individuo coespecífico (keratofagia) se ha documentado en 248 saurios de 16 familias y 19 ofidios de cuatro familias. No se conocen casos en tortugas o cocodrilos. Una revisión previa basada en records de zoológicos reportó keratofagia en 160 especies de saurios, de los...

From 1999 to 2006, we sampled > 1200 amphibians for the fungal pathogen Batrachochytrium dendrobatidis (Bd) at 30 sites in the southeastern USA. Using histological techniques or PCR assays, we detected chytrid infection in 10 species of aquatic-breeding amphibians in 6 states. The prevalence of chytrid infection was 17.8% for samples of postmetamor...

We quantified deformities in the marginal papillae, tooth rows, and jaw sheaths of tadpoles from 13 population samples representing three families and 11 sites in the southeastern United States. Oral deformities were observed in all samples and in 13.5- 98% of the specimens per sample. Batrachochytrium dendrobatidis (chytrid) infections were detect...

Amphibian populations have declined worldwide. To pursue conservation efforts adequately, land managers need more information concerning amphibian habitat requirements. To address this need, we examined relationships between anurans and habitat characteristics of wetlands in the Lower Mississippi River Alluvial Valley (LMAV). We surveyed chorusing...

Most research to assess amphibian declines has focused on local-scale projects on one or a few species. The Amphibian Research and Monitoring Initiative (ARMI) is a national program in the United States mandated by congressional directive and implemented by the U.S. Department of the Interior (specifically the U.S. Geological Survey, USGS). Program...

Most research to assess amphibian,declines has focused on local-scale projects on one or a few species. The Amphibian Research and Monitoring Initiative (ARMI) is a national program,in the United States mandated,by congressional directive and implemented,by the U.S. Department of the Interior (specifically the U.S. Geological Survey, USGS). Program...

Fundamental issues in the study of predator-prey interactions include addressing how prey coexist with their predators and, moreover, whether predators promote coexistence among competing prey. We conducted a series of laboratory experiments with a freshwater assemblage consisting of two predators that differd in their foraging modes ( a crayfish,...

We examined whether the species composition of a community influences the persistence of larval Ambystoma maculatum in assemblages composed of two larger intraguild predators (A. opacum and A. jeffersonianum) and an alternative prey species (tadpoles of Rana sylvatica). We predicted a priori that A. maculatum would have higher survival in more dive...

I examined the roles of food limitation and aggressive interference in density-dependent growth and survival in larvae of the spotted salamander, Ambystoma maculatum. In a laboratory experiment, I raised larvae at a low density, low food level; high density, low food level; and high density, high food level. An increased density of larvae fed low f...

Co-existence in a species-pair of pond-breeding salamanders has been attributed to a trade-off in the competitive abilities of their larvae: the mole salamander,Ambystoma talpoideum, is aggressively superior to the spotted salamander,A. maculatum. Conversely,A. maculatuminhibits the growth of both conspecifics andA. talpoideum, yet the mechanism of...

We examined whether kinship and familiarity influenced the agonistic behaviour of larvae From three different populations of the Northwestern salamander, Ambystoma gracile. We tested for differential behaviour (1) between individuals within each population; (2) among the three populations; and (3) between non-siblings originating from the same, ver...

The context=dependent nature of kin discrimination was examined in larvae of the marbled salamander,Ambystoma opacum. In a graphical analysis, relationships between aggression and social and ecological factors were explored. Increasing relatedness between individuals was predicted to reduce aggressive encounters, except when correlates of fitness (...

The context-dependent nature of kin discrimination was examined in larvae of the marbled salamander, Ambystoma opacum. In a graphical analysis, relationships between aggression and social and ecological factors were explored. Increasing relatedness between individuals was predicted to reduce aggressive encounters, except when correlates of fitness...

The effect of kinship on larval cannibalism was examined in the marbled salamander. In separate behavioural trials, cannibalistic larvae were presented with two smaller conspecifics (a ‘prey group’), matched for size, that were (1) siblings of the cannibal, (2) non-siblings and (3) one sibling and one non-sibling (i.e. a mixture of two sibling grou...

The aquatic larvae of two species of salamanders coexist as a result of differences in their competitive abilities: Ambystoma talpoideum is a superior aggressor, whereas A. maculatum is a superior forager. I examined the behavioral mechanisms that permit these species to coexist with their predatory congener, A. opacum. I asked whether the two prey...

Reviews the territorial behaviour of salamanders, with sections based on fundamental life history strategies: completely terrestrial; species that are terrestrial as adults but have complex life cycles (ie aquatic larvae); species with complex life cycles and predominantly semi-aquatic adults; and predominantly or completely aquatic species. After...

Reviews the social factors which influence associations between amphibians. Social behaviour is defined as all behaviour directly related to potential or actual encounters between individuals, regardless of whether or not the behaviour is gregarious or cooperative. It is divided into three main sections. The first reviews aggregative behaviour in a...

We examined the effects of variation in larval density, genetic relatedness and their interaction in the marbled salamander, Ambystoma opacum. In a factorial experiment, we reared larvae in artificial ponds at low and high densities and in groups comprised of either a single sibship (all siblings) or an equal mixture of six different sibships. Afte...

When distributional assumptions for analysis of variance are suspect, and nonparametric methods are unavailable, ecologists frequently employ rank transformation (RT) methods. The technique replaces observations by their ranks, which are then analysed using standard parametric tests. RT methods are widely recommended in statistics texts and in manu...

The populations of many amphibian species, in widely scattered habitats, appear to be in severe decline; other amphibians show no such declines. There is no known single cause for the declines, but their widespread distribution suggests involvement of global agents--increased UV-B radiation, for example. We addressed the hypothesis that differentia...

We examined diet-dependent plasticity in head shape in larvae of the eastern long-toed salamander, Ambystoma macrodactylum columbianum. Larvae in some populations of this species exhibit trophic polymorphism, with some individuals possessing exaggerated trophic features characteristic of a cannibalistic morphology in larval Ambystoma; e.g. a dispro...

Although numerous studies of the ontogeny of kin recognition behaviour have been conducted, large gaps in our knowledge remain concerning the dynamics of the individual components of the recognition system. A series of laboratory experiments were conducted to investigate the signal/perception system in tadpoles of the red-legged frog, Rana aurora,...

We studied the competitive interactions of two species of larval salamanders (Ambystoma maculatum and A. talpoideum) which occur either syntopically or allotopically in parts of their common geographic range (Mississippi and South Carolina, respectively). Larvae from both geographic regions were reared alone and combined at two total densities in a...

We document morphological variation and its association with larval cannibalism in a population of long-toed salamanders, Ambystoma macrodacrylum columbianum. Larvae observed in a natural pond engaged in cannibalism. Additionally, these larvae possessed significantly longer and wider heads, as well as larger vomerine teeth, than did conspecifics of...

The amphibian fauna of the Pacific Northwest includes several species that are found nowhere else. A significant proportion of Northwest amphibians possesses relatively specific ecological requirements and have extremely limited distributions, which increases their risk of local extinction. Five species are candidates for the US endangered species...

Aggresssive interference may be an important mechanism of competition in species-assemblages of caudate amphibians. The larvae of two pond-breeding salamanders, Ambystoma maculatum and A. talpoideum, exhibit several behavioral displays that are employed during interspecific competitive interactions. Biting (BITE), lunging (LUNGE, unsuccessful bite...