Pseudacris Crucifer Research Articles

Firewood and Ashes

Firewood and Ashes Ben Howard (bio) Firewood becomes ashes, it does not become wood again. Don’t think that wood is first, ashes after. . . . Life is life, death is death and are each in their own place like winter and spring. Winter does not become spring, spring does not become winter. —Eihei Dogen We cut them, one by one. How else were we to fell maple, beech, and ash? One by one they dropped, were trimmed, sawed, and hauled to the yard beside the barn. One by one I split still-living limbs and trunks and stacked them loosely, letting fresh air circulate between their freshly split fibers. How else transform a breathing tree into a fuel which, for good or ill, the world calls firewood? 2 We sat beside your stove discussing this and that— Carruth’s adverse opinion of Walden and Thoreau, the merits of a life [End Page 24] lived, in part, alone. That was how you liked it, you claimed, though soon enough your talk turned from poets or mallards on your pond to gossip, kind or cruel— who said what to whom or who was leaving whom. And all the while your wood was turning into ashes. 3 Yes, we combust ourselves from morning until night. No action could be plainer, no truth more evident. But what particular loss, Need, or cherished value compelled you to combust your mind’s midnight oil perusing students’ journals, each intimate detail demanding your attention? Whole weekends you went at it, poring over stories of drinking, drugs, abuse, as though they were your own. 4 Silence, you once wrote, was what you craved the most. Why, then, did you subject your senses to the racket the spring peepers made [End Page 25] and why did you endure the self-imposed distractions of Scrabble, crossword puzzles, and always-answered calls? What you most enjoyed, I think, was listening, whether what you heard was a clear well-chosen word or, sometimes, a log falling with a thud. 5 Forty years of friendship. One by one they rise, these memories, as if they might resume a story or fashion out of fire a single breathing person. So let those sparks arise, and let that smoke disperse, knowing as we do that even firewood does and doesn’t turn to ashes. Here and now the flowers that you loved are blooming near your urn as if you still might listen. [End Page 26] Ben Howard Ben Howard is the author of eight books of poetry and prose. He has a special interest in Ireland and its literature. Copyright © 2012 University of the South

Varying Responses of Northeastern North American Amphibians to the Chytrid Pathogen Batrachochytrium dendrobatidis

Chytridiomycosis, caused by Batrachochytrium dendrobatidis (Bd), is widespread among amphibians in northeastern North America. It is unknown, however, whether Bd has the potential to cause extensive amphibian mortalities in northeastern North America as have occurred elsewhere. In the laboratory, we exposed seven common northeastern North American amphibian species to Bd to assess the likelihood of population-level effects from the disease. We exposed larval wood frogs (Lithobates sylvaticus) and postmetamorphic frogs of six other species to two different strains of Bd, a northeastern strain (JEL404) and a strain that caused die-offs of amphibians in Panama (JEL423), under ideal in vitro growth conditions for Bd. Exposed American toads (Anaxyrus americanus) all died; thus, this species may be the most likely to die from Bd-caused disease in the wild. Both Bd strains were associated with mortalities of wood frogs, although half the metamorphs survived. The Bd strain from Panama killed metamorphic green frogs (L. clamitans), whereas the northeastern strain did not, which means novel strains of Bd may lead to death even when local strains may not. No mortality was observed in four species (bullfrogs [L. catesbeianus], northern leopard frogs [L. pipiens], spring peepers [Pseudacris crucifer], and blue-spotted salamanders [Ambystoma laterale]) and in some individuals of green frogs and wood frogs that we exposed. This finding suggests these six species may be Bd vectors. Our results show that systematic exposures of amphibian species to Bd in the laboratory may be a good first step in the identification of species susceptible to Bd-caused declines and in directing regional conservation efforts aimed at susceptible species.

Biomass export of salamanders and anurans from ponds is affected differentially by changes in canopy cover

SUMMARY 1. Previous research shows that canopy-associated shifts from an algal to a detritus-based food web can affect anuran tadpoles negatively. This may not be true of salamander larvae, however, because they are predators. 2. To investigate the influence of canopy cover on the survival and growth of salamanders, and on the subsequent export of biomass from ponds, we conducted a mesocosm experiment examining effects of shading (high or low) and litter (leaves or grass) on Ambystoma maculatum (a forest specialist) and A. texanum (a habitat generalist). Additionally, we reanalysed data from Williams, Rittenhouse & Semlitsch (2008) to examine the effects of shading and litter on biomass export of three anurans: Rana sphenocephala, Pseudacris crucifer and Hyla versicolor. 3. In contrast to previous studies, we found that salamanders performed better in mesocosms with the characteristics of closed canopy ponds (high shade and leaf litter), whichresultedinagreaterexportof biomass.Salamandersgrewlargerunderclosedcanopy conditions, probably because of differences in prey abundance among treatments. Anurans responded differentlytocanopycoverthan caudates.The biomassexportofR. sphenocephala and P. crucifer was reduced under closed canopy conditions (although differently affected by litter and shading), while the biomass of H. versicolor was not affected. 4. This and other studies suggest that changes in canopy cover may induce a shift in the amphibians emerging from ponds, from primarily anurans in open canopy ponds to primarily salamanders in closed canopy ponds. Additional multispecies studies will determine whether these trends hold true for more diverse amphibian assemblages. Further investigation into the effects of canopy cover on salamanders will be important for understanding aquatic–terrestrial linkages.

Sex-Related Differences in Somatic Stored Energy Reserves of Pseudacris crucifer and Pseudacris triseriata during the Early Breeding Season

We examined how differences in the allocation of resources influence prebreeding somatic stored energy reserves (fat and glycogen) in males and females of the hylid frogs Pseudacris crucifer and Pseudacris triseriata. Males had shorter snout–vent lengths than did females but similar wet and dry carcass masses. Nonpolar lipid and glycogen contents of the carcass increased with carcass mass in males but not in females. Similarly, triglyceride and glycogen contents of the liver increased more acutely with increasing liver mass in males than in females. Ovarian mass in gravid females correlated with body size and in P. crucifer the gonadal-somatic index increased with increasing body size, indicating a greater than proportional increase in ovary mass with increasing body size. These findings suggest that, during the pre-reproductive period, larger males allocate more energy toward preparation for courtship activity than do smaller males, whereas larger females may allocate more energy toward production of eggs.

Factors Associated with Amphibian Detection and Occupancy in Southern Michigan Forests

Abstract Large-scale amphibian conservation often relies on remotely sensed data to describe spatial patterns in occupancy. Commonly used data include ownership, forest type, soil class, and proximity of wetlands. We evaluated the influence of these variables on terrestrial amphibian occupancy in southern Michigan. We trapped amphibians using drift-fence arrays in 82 forest patches and estimated detection probabilities for all captured species. Ten species were captured, but only three were detected at levels suitable for occupancy modeling. We concluded that drift-fence arrays alone were not sufficient for adequately detecting the majority of terrestrial amphibians. The best detection models for American Toad (Anaxyrus americanus), Wood Frog (Lithobates sylvaticus), and Spring Peeper (Pseudacris crucifer) consistently included a positive relationship with temperature and precipitation. Detection-adjusted occupancy models for the three anurans indicated relatively high occupancy (>0.43). Ownership, forest...

Carry-over effects of the larval environment on post-metamorphic performance in two hylid frogs

Life history theory and empirical studies suggest that large size or earlier metamorphosis are suitable proxies for increased lifetime fitness. Thus, across a gradient of larval habitat quality, individuals with similar phenotypes for these traits should exhibit similar post-metamorphic performance. Here we examine this paradigm by testing for differences in post-metamorphic growth and survival independent of metamorphic size in a temperate (spring peeper, Pseudacris crucifer) and tropical (red-eyed treefrog, Agalychnis callidryas) anuran reared under differing larval conditions. For spring peepers, increased food in the larval environment increased post-metamorphic growth efficiency more than predicted by metamorphic phenotype and led to increased mass. Similarly, red-eyed treefrogs reared at low larval density ended the experiment at a higher mass than predicted by metamorphic phenotype. These results show that larval environments can have delayed effects not captured by examining only metamorphic phenotype. These delayed effects for the larval environment link larval and juvenile life history stages and could be important in the population dynamics of organisms with complex life cycles.

Fatty acid analyses reveal high degrees of omnivory and dietary plasticity in pond‐dwelling tadpoles

Summary1. Understanding the trophic relationships of consumers is central to ecology, but constructing meaningful food webs is often difficult because of a lack of detailed information on consumption versus assimilation and high degrees of omnivory.2. We used fatty acid analyses to examine the trophic relationships of three common larval anurans (Pseudacris crucifer, Lithobates catesbeianus and Lithobates clamitans) that are often classified as grazers or detritivores. Tadpoles and potential food sources were sampled in four ponds in southern Illinois and analysed for fatty acid composition. Single linkage cluster analysis was then used to compare fatty acid profiles among tadpole gut contents, tadpole muscle tissues and available food resources.3. Diets varied among species and within species among ponds, but organic sediments consistently contributed most to the fatty acid composition of the gut contents of all species. Fatty acid profiles also indicated that larval insects and phytoplankton were consumed by both L. catesbeianus and L. clamitans in one pond, while L. clamitans and P. crucifer consumed mainly periphyton along with sediments in another pond, and these diet differences appeared linked to physical differences among ponds, with periphyton and/or phytoplankton contributing more to tadpole diets in less shaded ponds.4. The fatty acid composition of muscle tissues of L. clamitans, the dominant tadpole in these systems, indicated that plant detritus and bacteria, which were the dominant components of organic sediments in the ponds, were common components of the assimilatory diet.5. Results demonstrate the utility of fatty acid analyses for assessing both consumption and assimilation. The tadpole assemblages we examined derive much of their energy from heterotrophic and allochthonous sources and exhibit high dietary plasticity. This information will allow for more accurate and comprehensive assessments of trophic interactions in freshwater habitats, as well as aid in amphibian conservation, management and captive propagation efforts.

Preliminary Amphibian Health Survey in the Delaware Water Gap National Recreation Area

To detect aquatic animal diseases of national concern, 111 individual amphibians, including wood frogs Rana sylvatica (28), spring peepers Pseudacris crucifer (35), red-spotted newts Notophthalmus viridescens (41), and gray tree frogs Hyla versicolor (7), were sampled at seven different sites in the Delaware Water Gap National Recreation Area (DGNRA), Pennsylvania, from June 14 to July 19, 2007. These samples were screened for Batrachochytrium dendrobatidis and viral pathogens at the U.S. Fish and Wildlife Service's Fish Health Center in Lamar, Pennsylvania. Cell culture revealed cytopathic effect (CPE) in two cell lines (epithelioma papillosum cyprini and fathead minnow) inoculated with liver, kidney, and spleen samples from one sample pool of Notophthalmus viridescens (4 individuals). Polymerase chain reaction was conducted on cell culture supernatant exhibiting CPE. Sequencing revealed the resulting product to be identical to frog virus 3, a ranavirus in the family Iridoviridae. Upon gross examination, two Notophthalmus viridescens were found to exhibit dermal swelling and lethargy. Histological examination of these lesions revealed involvement by an Ichthyophonus sp. In summary, two pathogens of concern were found in amphibians in the DGNRA: a ranavirus with a major capsid protein sequence identical to that of frog virus 3 and a mesomycetozoan, Ichthyophonus sp. Although no epizootic die-offs were observed during this health survey, the results warrant further research into the distribution of these pathogens throughout the DGNRA because they have the potential to cause mass mortalities in amphibians.

The potential impact of simulated ground-water withdrawals on the oviposition, larval development, and metamorphosis of pond-breeding frogs

Wetland hydroperiod is a key factor for the reproductive success of pond-breeding amphibians. Ground-water withdrawals may cause intermittent ponds to dry prematurely, potentially affecting amphibian development. In three intermittent ponds, we monitored hydrology and tracked oviposition, larval development, and metamorphosis for three frog species that represented a range of breeding phenologies. The three species were the southern leopard frog (Lithobates sphenocephalus), spring peeper (Pseudacris crucifer), and Pine Barrens treefrog (Hyla andersonii). We simulated ground-water withdrawals by subtracting from 5 to 50 cm (in 5-cm increments) from the measured water-depth values at the ponds over a short-term (2-year) period and a long-term (10-year) period to estimate the potential impact of hydroperiod alterations on frog development. Short-term simulations indicated that 5 and 10 cm water-depth reductions would have resulted in little or no impact to hydroperiod or larval development and metamorphosis of any of the species. Noticeable impacts were estimated to occur for reductions ≥15 cm. Long-term simulations showed that impacts to the appearance of the first pre-metamorphs and metamorphs would have occurred at reductions ≥10 cm and impacts to initial egg deposition would have occurred at reductions ≥20 cm. For all simulations, successively greater reductions would have caused increasing impacts that varied by species and pond, with the 50-cm reductions shortening hydroperiods enough to practically eliminate the possibility of larval development and metamorphosis for all three species. Compared to the spring peeper and southern leopard frog, the estimated impacts of the simulations on the various life stages were the greatest for the Pine Barrens treefrog.

Anuran Calling Survey Optimization: Developing and Testing Predictive Models of Anuran Calling Activity

Amphibian populations, particularly anurans, are declining worldwide, and programs that use calling surveys have been established to monitor anuran populations. Models that describe the environment's influence on calling may be useful to increase detection allowing optimization of surveys. Using an automated recording system, we evaluated the calling activity of Pseudacris crucifer, Pseudacris feriarum, and Rana sphenocephala at an ephemeral wetland in the Piedmont of North Carolina. We used stepwise logistic regression to model environmental variables that significantly affected calling activity. Models revealed that, for P. crucifer, water and air temperature positively influenced calling, whereas day of year, barometric pressure, and light intensity negatively influenced calling. For P. feriarum, air temperature positively influenced calling, and day of year, relative humidity, wind speed, barometric pressure, and light intensity negatively influenced calling. Finally, air temperature positively influenced calling for R. sphenocephala, whereas water temperature, relative humidity, wind speed, and light intensity negatively influenced its calling. Using these results, we developed comprehensive as well as simpler, ''user-friendly'' models, predicting the best conditions under which to conduct anuran calling surveys. The user-friendly models were tested using previously collected data from calling surveys performed in the same region of North Carolina and found to accurately predict calling activity approximately 70% of the time. We discuss how weather forecast data may be applied to these models to determine the best times to conduct calling surveys and how models such as those developed in this study can be used to interpret data previously collected during amphibian calling surveys.

The toxicity of Roundup Original Max® to 13 species of larval amphibians

With the increased use of glyphosate-based herbicides (marketed under several names, including Roundup and Vision), there has been a concomitant increased concern about the unintended impacts that particular formulations containing the popular surfactant polyethoxylated tallowamine (POEA) might have on amphibians. Published studies have examined a relatively small number of anuran species (primarily from Australia and eastern North America) and, surprisingly, no species of salamanders. Using a popular formulation of glyphosate (Roundup Original Max), the goal of the present study was to conduct tests of lethal concentrations estimated to kill 50% of a population after 96 h (LC50(96-h)) on a wider diversity of species from both eastern and western North America. Tests were conducted on nine species of stage 25, larval anurans from three families (Ranidae: Rana pipiens, R. clamitans, R. sylvatica, R. catesbeiana, R. cascadae; Bufonidae: Bufo americanus, B. boreas; and Hylidae: Hyla versicolor, Pseudacris crucifer) and four species of larval salamanders from two families (Ambystomatidae: Ambystoma gracile, A. maculatum, A. laterale; and Salamandridae: Notophthalmus viridescens). For the nine species of larval anurans, LC50(96-h) values ranged from 0.8- to 2.0-mg acid equivalents per liter with relatively little pattern in differential sensitivity among the species or families. The four species of larval salamanders were less sensitive than the anurans, with LC50(96-h) values ranging from 2.7- to 3.2-mg acid equivalents per liter and no substantial differences among the species of salamanders. This work substantially increases the available data on amphibian sensitivity to glyphosate formulations that include either POEA surfactants or the equally moderately to highly toxic surfactants of Roundup Original Max and should be useful for improving future risk assessments.

Very highly toxic effects of endosulfan across nine species of tadpoles: Lag effects and family‐level sensitivity

Pesticides are commonly used for health and economic benefits worldwide, but increased use has led to increased contamination of aquatic habitats. To understand potential impacts on nontarget organisms in these habitats, toxicologists generally use short-term (4-d) toxicity tests on model organisms. For most pesticides, few amphibian tests have been conducted, but there is growing concern about the potential impact of pesticides to amphibian populations. For the insecticide endosulfan, previous studies have found that low concentrations can be very highly toxic to amphibians and have suggested that this mortality may exhibit important lag effects. To estimate the lethal concentration of endosulfan that would cause 50% mortality after 4 d (LC50(4-d)) across a diversity of amphibians and the presence of lag effects, LC50(4-d) experiments were conducted on nine species of tadpoles from three families (Bufonidae: Bufo americanus, B. boreas; Hylidae: Pseudacris crucifer, P. regilla, Hyla versicolor; and Ranidae: Rana pipiens, R. clamitans, R. cascadae, R. catesbeiana) and then held the animals for an additional 4 d in clean water. The LC50(4-d) values for endosulfan ranged from 1.3 to 120 ppb, which classifies endosulfan as highly toxic to very highly toxic. Moreover, holding the animals for an additional 4 d in clean water revealed significant additional mortality in three of the nine species. Leopard frogs, for example, experienced no significant death during the initial 4-d exposure to 60 ppb but 97% death after an additional 4 d in clean water. A phylogenetic pattern also appears to exist among families, with Bufonidae being least susceptible, Hylidae being moderately susceptible, and Ranidae being most susceptible. Results from the present study provide valuable data to assess the impact of endosulfan on a globally declining group of vertebrates.

Context-dependent plasticity of aggressive signalling in a dynamic social environment

Frog choruses are dynamic social environments in which males must balance the conflicting demands of attracting a female and defending their calling site. The optimal trade-off is probably one that adaptively tracks temporal and spatial changes in the local social environment. Previous studies have indicated that a male frog's propensity to interact aggressively with its nearby neighbours reflects patterns of plasticity that could allow for such tracking. We presently do not know the mechanisms underlying plasticity in aggressive signalling in frogs, nor do we understand how plasticity depends on variation in social context. In this field playback experiment with spring peepers, Pseudacris crucifer, we investigated how differences in the type of signalling interactions (a form of social context) experienced by calling males influence the plasticity of aggression directed towards nearby neighbours in the chorus. We used the habituation–discrimination experimental paradigm to present males with calls simulating a new neighbour that was initially either aggressive (producing a mixture of advertisement and aggressive vocalizations) or nonaggressive (producing only advertisement calls). We found that interacting with an initially aggressive versus nonaggressive neighbour had negligible effects on the plasticity of a male's aggressive response, but that subsequent changes in social context (e.g. a switch to aggressive calling by a previously nonaggressive neighbour) greatly influenced a male's aggressive responsiveness. We discuss our results in terms of short-term habituation as a mechanism for the plasticity and specificity of aggressive signalling behaviour in frog choruses.

Comparative landscape dynamics of two anuran species: climate‐driven interaction of local and regional processes

The dynamics of ecological communities emerge from the interplay of local and regional processes, but there are few long‐term data on multiple interacting species across multiple sites to evaluate these processes. We report the population dynamics of two species of treefrogs, the spring peeper (Pseudacris crucifer) and the chorus frog (P. triseriata), in 37 ponds over 11 years. We examined the relation between larval traits of these species and responses to environmental change (a severe drought) at the local (pond) level, and the consequences to regional dynamics of the species. Consistent with experimental evidence, predators limited abundances of both species, competitive effects were undetectable, and pond hydroperiod and forest canopy cover affected species' presences and population sizes. The drought caused strong reductions in pond hydroperiods and predator densities, which led to increases in colonization probability and decreases in extinction probability for the chorus frog. These habitat dynamics resulted in the colonization of 15 new ponds and exponential growth in regional population size of the chorus frog. Colonization probability was positively related to pond connectivity. Pond occupancy rates for the spring peeper were relatively constant, but important source ponds on the landscape changed with the drought. Ponds with extensive forest canopy cover were sink habitats for both species, and high pond connectivity appeared to be necessary to maintain species' presences in these habitats. Landscape dynamics were responsible for changes in the fundamental spatial structure of species' populations, e.g., the chorus frog transitioned between approximations of a classic metapopulation and a patchy population over the course of the study. Many of these results were driven by the interplay of climate variation and spatial food web structure, indicating the importance of incorporating this interaction into metacommunity theory. Our results further indicate the crucial role of habitat (pond) heterogeneity to species persistence, i.e., moderating the potential Moran effects of spatially correlated weather conditions. Overall this study illustrates: (1) how natural systems constantly transition between metapopulation/metacommunity states typically treated as static in the literature, (2) the extensive interconnection of phenomena at different scales in ecology, and (3) the importance of habitat heterogeneity and landscape context for amphibian conservation strategies.

Water molds of the genera Saprolegnia and Leptolegnia are pathogenic to the North American frogs Rana catesbeiana and Pseudacris crucifer, respectively

Water molds are commonly associated with amphibian mortality. Since water molds often act as saprophytes, it is important to test their effects on amphibians to determine whether they can also act as pathogens. In controlled experiments, the eggs of 2 amphibian species, the American bullfrog Rana catesbeiana and the spring peeper Pseudacris crucifer, suffered higher mortality when they were exposed to zoospores of water molds of the genera Saprolegnia and Leptolegnia, respectively. Water molds are important pathogens in many amphibian systems, yet their ecological impact on amphibians remains mostly unknown.

Wildlife use of back channels associated with islands on the Ohio River

The back channels of islands on the Ohio River are assumed to provide habitat critical for several wildlife species. However, quantitative information on the wildlife value of back channels is needed by natural resource managers for the conservation of these forested islands and embayments in the face of increasing shoreline development and recreational boating. We compared the relative abundance of waterbirds, turtles, anurans, and riparian furbearing mammals during 2001 and 2002 in back and main channels of the Ohio River in West Virginia. Wood ducks (Aix sponsa), snapping turtles (Chelydra serpentina), beavers (Castor canadensis), and muskrats (Ondatra zibethicus) were more abundant in back than main channels. Spring peepers (Pseudacris crucifer) and American toads (Bufo americanus) occurred more frequently on back than main channels. These results provide quantitative evidence that back channels are important for several wildlife species. The narrowness of the back channels, the protection they provide from the main current of the river, and their ability to support vegetated shorelines and woody debris, are characteristics that appear to benefit these species. As a conservation measure for important riparian wildlife habitat, we suggest limiting building of piers and development of the shoreline in back channel areas.

Toxicity of road salt to Nova Scotia amphibians

The deposition of chemical pollutants into roadside wetlands from runoff is a current environmental concern. In northern latitudes, a major pollutant in runoff water is salt (NaCl), used as de-icing agents. In this study, 26 roadside ponds were surveyed for amphibian species richness and chloride concentration. Acute toxicity tests (LC(50)) were performed on five locally common amphibian species using a range of environmentally significant NaCl concentrations. Field surveys indicated that spotted salamanders (Ambystoma maculatum) and wood frogs (Rana sylvatica) did not occupy high chloride ponds. American toads (Bufo americanus) showed no pond preference based on chloride concentration. Acute toxicity tests showed spotted salamanders and wood frogs were most sensitive to chloride, and American toads were the least. Spring peepers (Pseudacris crucifer) and green frogs (Rana clamitans) showed intermediate sensitivities. We concluded that chloride concentrations in ponds due to application of de-icing salts, influenced community structure by excluding salt intolerant species.

Coltsfoot, Spring Peepers, and New Potatoes

Coltsfoot, Spring Peepers, and New Potatoes

Phonotaxis to Amphibian Vocalizations in <I>Culex territans</I> (Diptera: Culicidae)

Culexterritans Walker (Diptera: Culicidae) acquires bloodmeals from amphibian hosts. Females overwinter as inseminated adults and exit diapause in New Jersey when spring peepers (Pseudacris crucifer) are calling. We tested the hypothesis that Cx. territans uses amphibian vocal- izations as a long-distance attractant. Two thirds of females oriented toward sound across all exper- iments. Females allowed to orient toward or away from a frog call, bird song, live frog, or control (a plugged in compact disc player) exhibited positive phonotaxis only to the frog call. Females exhibited positive phonotaxis to calls of P. crucifer, Hyla versicolor (northern gray tree frog), Bufo americanus (American toad), andRanaclamitans (green frog), but they were not attracted to calls ofR.catesbeiana (bullfrog),R.sylvatica (wood frog), or control. Multiple regression analysis showed that call frequency is the best predictor for phonotaxis, with pulse duration and call amplitude increasing the attrac- tiveness of the source. When exposed to P. crucifer calls at increasing sound intensity levels, females oriented to calls in the range of 50 Ð75 dB, with particle velocities of 0.02Ð 0.3 mm/s, indicating that phonotaxis occurs at distances 5 m from the source.

Are Anurans of Great Lakes Coastal Wetlands Reliable Indicators of Ecological Condition?

Frogs and toads (anurans) are sensitive to a variety of anthropogenic stressors and are widely suggested as indicators of ecological condition. We surveyed 220 coastal wetlands along the U.S. shores of the Laurentian Great Lakes and quantified relationships between presence of anuran species and degree of anthropogenic disturbance. Results were used to derive explicit, functional relationships between environmental condition and anuran occurrences. These functions were subsequently used to calculate a multi-species indicator of ecological condition at other (novel) wetlands. Of 14 anuran species observed, spring peeper (Pseudacris crucifer) exhibited the strongest and most consistent relationship with environmental condition across the entire study area. Other species exhibited significant relationships with the environmental gradient, but the direction of association varied geographically or the overall species abundance was very low (e.g., mink frog, Rana septentrionalis). Even if applied to separate ecological provinces (Laurentian Mixed Forest or Eastern Deciduous Forest), multi-species estimates of wetland condition based on anurans are not much better indicators of environmental condition based on human disturbance than are indices based solely on occurrence of spring peeper. Nevertheless, indicators grounded in explicit relationships with environmental stress are superior to traditional measures (e.g., species richness) that combine species with different responses to the stress gradient. At least one anuran species (spring peeper) can contribute meaningfully to the assessment of ecological condition in Great Lakes coastal wetlands; its value as an indicator will be improved if it can be combined with information from other wetland species such as birds, fishes, and vascular plants.