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Interactions between branchiate mole salamanders (Ambystoma talpoideum) and lesser sirens (Siren intermedia): Asymmetrical competition and intraguild predation
Abstract
Using field sampling and experiments in natural and artificial ponds, I studied interactions between branchiate adult mole salamanders (Ambystoma talpoideum) and lesser sirens (Siren intermedia), two top predators in temporary ponds of the southeastern United States. The abundance and distribution of these two salamanders were independent among ponds, with A. talpoideum more numerous and widespread than S. intermedia. Both species were more likely to be found in ponds near other intermittent wetlands. Within a pond, captures of these two species were negatively correlated, and a field experiment showed that paedomorphic A. talpoideum avoided traps containing S. intermedia. An experiment in artificial ponds confirmed that interactions between these two species were highly asymmetrical; S. intermedia reduced the growth and recruitment of A. talpoideum without experiencing reciprocal. positive or negative effects. These results suggest that S. intermedia competes with and is an intraguild predator of A. talpoideum, limiting its growth and controlling its recruitment.
... This group is potentially vulnerable to cannibalism from older age cohorts of mole salamanders and IGP from several guild members (e.g., Ambystoma opacum; Boone et al., 2002), while still in the egg mass and in the free-swimming hatchling stage. Paedomorphosis in A. talpoideum has been well-studied experimentally in some ecological contexts (e.g., Semlitsch, 1987a; Ryan and Semlitsch, 2003; Doyle and Whiteman, 2008), yet the functional role paedomorphs play as a top predator via cannibalism or IGP on either smaller classes of conspecifics or guild members, has not been addressed despite their importance in community dynamics (Fauth, 1999aFauth, , 1999b). Overwintering ecology of larval mole salamanders has also received little attention, although such individuals have the potential to be superior IG predators and cannibals, similar to other ambystomatid species (Wissinger et al., 1999Wissinger et al., , 2010). ...
... Predator values for both size classes are mean values based on five replicates for each treatment. * indicates treatments that had significantly higher mortality., 1983; Fauth, 1999b; Wissinger et al., 2010 ). In regions where multiple species cooccur in ponds, such as the southeastern United States, few studies have examined IGP and cannibalism across age cohorts, though the importance of these interactions has been documented for some species (e.g., Morin, 1983; Fauth, 1999b). ...
... * indicates treatments that had significantly higher mortality., 1983; Fauth, 1999b; Wissinger et al., 2010 ). In regions where multiple species cooccur in ponds, such as the southeastern United States, few studies have examined IGP and cannibalism across age cohorts, though the importance of these interactions has been documented for some species (e.g., Morin, 1983; Fauth, 1999b). In this study we assessed how predation by two larger size classes of mole salamanders that are also an older age cohort affected the survival of early life history stages of conspecific and congeneric prey, which were predicted to be highly susceptible to predation by guild members. ...
Predation risk is an important contributor to community structure that varies in response to abiotic and biotic factors. In aquatic habitats, predation risk is often linked to hydroperiod as the latter directly influences predator identity within these ecosystems. For pond-breeding salamanders, intraguild predation (IGP) and cannibalism are prevalent interactions in larval communities, but the frequency of each type of agonistic interaction, as well as changes in their pervasiveness along hydroperiod gradients are not well understood. Size-structured populations of aquatic life stages (paedomorphic adults and overwintered larvae) of mole salamanders (Ambystoma talpoideum) have the potential to be dominant IG predators and cannibals in permanent ponds because of large size advantages over successive cohorts, but the species exists as only a single larval cohort in temporary ponds with reduced predatory abilities on guild members. Thus, both the potential for and intensity of predation by this species is linked to hydroperiod; yet, the predatory abilities of aquatic life stages of mole salamanders have not been evaluated. This study examined the extent to which larger size classes (paedomorphs and overwintered larvae) of mole salamanders preyed upon conspecifics and a congeneric competitor, the spotted salamander (Ambystoma maculatum). Predation trials occurred in indoor microcosms and were executed under two habitat treatments that included pseudo-natural conditions containing alternate prey and refugia, as well as simplified environments (no alternative food or cover). Embryos or hatchlings of mole and spotted salamanders were exposed either separately or concurrently to paedomorphic and overwintered larval mole salamanders in each habitat treatment. Additionally, overwintered larvae were offered as prey to paedomorphic adults. No significant differences in mortality were observed between habitat treatments (complex versus simple) for either embryo or hatchling predation experiments. Mortality of mole and spotted embryos did not differ when they were offered separately or together, but paedomorphs caused significantly higher mortality among mole embryos compared to spotted embryos. Hatchlings of both species were heavily preyed upon (nearly 100% in all trials), but overwintered larvae exhibited 100% survival with paedomorph predators, indicating size-thresholds of predation risk that were not species specific. Paedomorphs and overwintered larvae therefore are most likely generalist predators that feed equally and effectively on hatchlings of co-occurring species, but are more likely to consume egg masses that do not incur significant handling costs. When present, paedomorphs or overwintered larvae have the potential to alter population dynamics of both guild members and conspecifics by being dominant predators on early life stages. As the prevalence of overwintering and paedomorphosis varies along hydroperiod gradients, predation risk from this species is likely to occur discontinuously and thereby may be an important, yet variable, structuring force.
... Both species overwinter in ponds and subsequently are in ponds before A. maculatum breeds in the spring, though via different ontogenetic processes (Petranka 1998). Paedomorphic A. talpoideum, individuals that retain their gills and become reproductively mature adults, stay in ponds year-round and can be the dominant predators in permanent ponds without fish (Semlitsch 1985a;McAllister and Trauth 1996;Fauth 1999aFauth , 1999bRudolf and Van Allen 2017). Ambystoma opacum, however, gains a size advantage over spring-breeding amphibians by breeding in the fall, with larvae overwintering in ponds (Stenhouse 1985;Cortwright and Nelson 1990). ...
... This suggests that the top-down effects of A. talpoideum are so strong that any size variability within a population of prey, no matter what generates that variability, will be eradicated by A. talpoideum predators. Ambystoma talpoideum can be voracious top predators in pond communities (Fauth 1999a(Fauth , 1999bPintar and Resetarits 2017) with almost complete eradication of prey in some experiments (Anderson et al. 2013). Similar effects were observed in natural populations of A. maculatum co-occurring with A. annulatum, another fall-breeding species that heavily predates on A. maculatum Semlitsch 2014, 2016). ...
Variability in phenological shifts (seasonal changes in biological events) has become more common with climate change. As phenological variability increases due to climatic factors, species interactions within diverse communities can be affected. Shifts in hatching phenology can lead to body size variability that can alter species interactions, especially within and across trophic levels in complex food webs. To understand the effects of hatching phenology and food web complexity on prey communities, we conducted an experiment with ectotherms from ponds by manipulating hatching synchrony of a prey species across three dates and food web complexity. We hypothesized that predation on prey would be highest in the lowest synchrony treatment due to predator satiation effects in high synchrony additions. Food webs with top predators present had the lowest survival rates for prey compared to other food webs. Prey size at metamorphosis was also highest in the top predator food webs, suggesting a thinning effect. Hatching synchrony treatments did not have a significant impact on prey survival or size at metamorphosis except in treatments where intermediate and top predators were absent. Overall, our results show that top-down effects of predators may be enough to suppress the influence of phenological shifts in prey.
... Exceptions to the "juvenile dispersal" hypothesis for wetland-breeding amphibians are the genera Siren, Amphiuma, and Pseudobranchus, which have fully aquatic adults that are generally restricted to permanent wetlands, and also have the ability to persist in seasonal wetlands by aestivating for prolonged periods when a wetland dries (Gelbach et al. 1973;Moler 2008). When siren and amphiuma occur in seasonal wetlands, they can function as keystone predators (Fauth 1999) with strong effects on the amphibian and invertebrate communities. Due to their diminutive limbs, all three genera are thought to be poor overland dispersers (Snodgrass et al. 1999). ...
... Due to their diminutive limbs, all three genera are thought to be poor overland dispersers (Snodgrass et al. 1999). Distributional studies show that siren and amphiuma occur in longer hydroperiod seasonal wetlands and can apparently recolonize wetlands up to 0.7 km from other aquatic habitats (Fauth 1999;Snodgrass et al. 1999); thus, there is evidence of biological connectivity between seasonal wetlands and nearby more permanent waters even for these poor dispersers. ...
Many species that inhabit seasonally ponded wetlands also rely on surrounding upland habitats and nearby aquatic ecosystems for resources to support life stages and to maintain viable populations. Understanding biological connectivity among these habitats is critical to ensure that landscapes are protected at appropriate scales to conserve species and ecosystem function. Biological connectivity occurs across a range of spatial and temporal scales. For example, at annual time scales many organisms move between seasonal wetlands and adjacent terrestrial habitats as they undergo life‐stage transitions; at generational time scales, individuals may disperse among nearby wetlands; and at multigenerational scales, there can be gene flow across large portions of a species’ range. The scale of biological connectivity may also vary among species. Larger bodied or more vagile species can connect a matrix of seasonally ponded wetlands, streams, lakes, and surrounding terrestrial habitats on a seasonal or annual basis. Measuring biological connectivity at different spatial and temporal scales remains a challenge. Here we review environmental and biological factors that drive biological connectivity, discuss implications of biological connectivity for animal populations and ecosystem processes, and provide examples illustrating the range of spatial and temporal scales across which biological connectivity occurs in seasonal wetlands. Research Impact Statement: Seasonal wetlands are connected biologically to surrounding ecosystems through the movements of animals. This connectivity is critical to species conservation and ecosystem functioning.
... Greater siren (Siren lacertina, Linnaeus) and two-toed amphiuma (Amphiuma means, Garden) are large, fully aquatic salamanders that occur in a variety of shallowwater habitats throughout much of the Southeastern Coastal Plain (Petranka 1998). Although studies have revealed their importance as predators and competitors in some aquatic systems (Fauth and Resetarits 1991, Resetarits and Fauth 1998, Fauth 1999a, Snodgrass et al. 1999), much is unknown about their life history. Their conservation status is uncertain due to lack of systematic population surveys (Petranka 1998). ...
... Minnow traps, usually constructed of plastic, have been the tool of choice for recent ecological studies involving S. /acertina, S. intermedia, and A. means. (Fauth and Resetarits 1991, Resetarits and Fauth 1998, Fauth 1999a, b, Snodgrass et al. 1999, Eason and Fauth 2001). We have shown that VexarTM-lined traps are superior to plastic minnow traps at capturing S./acertina andA. ...
We describe a commercially-available funnel trap for sampling aquatic vertebrates. The traps can be used in heavily vegetated wetlands and can be set in water up to 60 cm deep without concern for drowning the animals. They were especially useful for capturing the aquatic salamanders Siren lacertina and Amphiuma means, which have been difficult to capture with traditional sampling methods. They also were effective for sampling small fishes, particularly centrarchids, and larval anurans. In total, 14 species of amphibians, nine species of aquatic reptiles, and at least 32 fish species were captured. The trap we describe differs significantly from traditional funnel traps (e.g., minnow traps) and holds great promise for studies of small, aquatic vertebrates, in particular Siren and Amphiuma species.
... The richness of amphibian species decreases significantly with increasing distance to nearest intermittent or permanent wetlands (Schurbon & Fauth, 2003 ). Evidence suggests that several amphibian species have difficulty dispersing more than a few hundred meters from their natal ponds (Semlitsch, 1998; Fauth, 1999). Based on the statistical distribution of distances to nearest– neighbor, we found at least four types of relationships in amphibians of Alabama. ...
... The richness of amphibian species decreases significantly with increasing distance to nearest intermittent or permanent wetlands (Schurbon & Fauth, 2003). Evidence suggests that several amphibian species have difficulty dispersing more than a few hundred meters from their natal ponds (Semlitsch, 1998; 2000; Fauth, 1999). Based on the statistical distribution of distances to nearest– neighbor, we found at least four types of relationships in amphibians of Alabama. ...
Large-scale biodiversity conservation is urgently needed due to increasing habitat loss and fragmentation. Understanding topological perspectives of species' distribution patterns can provide useful information for linking conservation studies at larger scales. We studied topological properties of localities in Alabama where 60 species of 12 families of amphibians were present. Analysis included a clustering coefficient which measures the strength of a population group, the relationship between occurrence localities and species number, the fractal dimension of occurrence localities (which emphasizes spatial irregularity), and distance to nearest-neighbor. The results indicate that the clustering coefficients of most amphibian species were low, but were higher for species with few occurrence localities, such as Rana sylvatica and Limnaoedus ocularis. The general relationship between species number and occurrence localities was that the majority of species held few localities in their distribution, while the remaining species occupied a greater number of localities. The fractal dimension (FD) for all amphibian localities was about 1.58, although FD was low for most individual species. We identified four relationships in the distribution of distance to nearest-neighbor: linear, logarithmic, power and polynomial. These topological properties may indicate intrinsic features about amphibians in Alabama and provide useful information for regional planning. Enhancing landscape linkages across a large area using undisturbed areas, such as 300-500 km in diameter may be a good approach to conservation practice in this region. Steps needed for biodiversity conservation planning in Alabama include creating or conserving small habitats across agricultural and urban land, and maintaining suitable spatial complexity and distance to nearest neighbors.
... We stocked each mesocosm with the same number of an assortment of tadpole prey that co-occur in natural ponds. Previous studies have used 150-650 larval amphibian prey in each mesocosm (Fauth and Resetarits, 1991;Fauth, 1999;Chalcraft and Resetarits, 2003a). Thus, we used a total of 540 tadpoles per mesocosm for this experiment, according to availability: 100 American toads (Anaxyrus americanus), 160 southern leopard frogs (Rana sphenocephala), 140 wood frogs (Rana sylvatica), 15 upland chorus frogs (Pseudacris feriarum), and 125 spring peepers (Pseudacris crucifer; Morin, 1983;Wilbur, 1997;Alford, 1999). ...
Functional redundancy occurs when different predator species have similar effects on the diversity, abundance, and composition of a prey community. When multiple predators coexist, their interactions can alter prey survival and ultimately diversity through emergent multiple-predator effects (MPEs). MPEs can be exacerbated by differences in predator behavior; however, little is known about the magnitude of MPEs when predators compete for the same prey or have similar behavioral traits. To understand functional redundancy and the interactions of multiple predators in similar niches, as well as their impacts on the composition of a prey community, we conducted two experiments using two ambystomatid salamander predators (Ambystoma opacum and Ambystoma annulatum). We exposed a suite of tadpole prey (Anaxyrus americanus, Rana sphenocephala, Rana sylvatica, Pseudacris feriarum, and Pseudacris crucifer) to different experimental food webs in a mesocosm experiment, and a single prey species (R. sphenocephala) in microcosm experiment with substitutive and additive designs to test for MPEs. We found no evidence for functional redundancy between the two predators: A. annulatum selectively preyed on competitively dominant prey species (A. americanus) and did not alter community diversity. Ambystoma opacum decreased prey diversity relative to the control because of natural phenological mismatch with A. americanus. Interactions between the two predators (e.g., predator inference) were lacking, indicating that predation risk from each predator was independent for the one prey species we tested. A better understanding of community and ecosystem-level effects by A. annulatum can inform future conservation efforts and management decisions regarding this endemic species.
... The richness of amphibian species decreases significantly with increasing distance to nearest intermittent or permanent wetlands (Schurbon & Fauth, 2003). Evidence suggests that several amphibian species have difficulty dispersing more than a few hundred meters from their natal ponds (Semlitsch, 1998;Fauth, 1999). Based on the statistical distribution of distances to nearest– neighbor, we found at least four types of relationships in amphibians of Alabama. ...
Background/Question/Methods
Biodiversity conservation at large scales is urgently due to increasing habitat loss and fragmentation. Understanding topological and geometric perspective of species distribution pattern may provide useful information for linking conservation studies to larger scales. Some topological and geometric properties of the occurred locations of amphibians in
Alabama, including 60 species of 12 families, are analyzed by the metrics including clustering coefficient which measures the strength of a group, relationship between occurred locations and species number, fractal dimension of occurred locations which emphasizes spatial irregularity, and distance of nearest-neighbor.
Results/Conclusions
The results indicate that the clustering coefficients of most amphibian species were lower, but the species with limited occurred locations had higher ones, such as Ranta sylvatica and Limnaoedus ocularis. The general relationship between species number and their occurred locations is that most species had less occurred locations, while limited number of species had more occurred locations. The fractal dimension (FD) of all occurred locations of amphibians was about 1.58, while FD for most species was low. Based on the distribution of the distance of nearest-neighbor, there were four types of relationships: linear, logarithmic, power and polynomial. These topological and geometric properties may indicate some intrinsic features about amphibians in
Alabama and provide useful information for regional planning. Properly enhancing the landscape linkages across a large area, such as 300-500 km, may be a good regulatory for conservation practice in this region. Some steps need to be included into the planning of biodiversity conservation in Alabama, such as creating or conserving small habitats across agricultural or urban land and maintaining suitable spatial complexity and the nearest neighbors.
... Amphibian species richness decreased significantly with increasing distance to the nearest intermittent and manent wetlands, suggesting that movement between aquatic habitats is important for maintaining local populations . Independent evidence suggests that several amphibian species have difficulty dispersing more than a few hundred meters from their natal ponds ( Semlitsch 1998 Semlitsch , 2000 Fauth 1999b ). Differential colonization ability also may explain why evenness was low when a temporary wetland was nearby: weak dispersers are generally good competitors and often dominate the communities they colonize (Hubbell 2001). ...
Fire alters the abundance and diversity of many species, but its effects on amphibians are poorly known. We tested whether prescribed burning affected amphibian abundance and diversity within the Francis Marion National Forest, South Carolina, by monitoring assemblages at 15 temporary ponds with five different burn histories: 0, 1, 3, 5, and 12 years after burns. We also monitored terrestrial and aquatic environmental variables likely to influence amphibian diversity, such as leaf-litter depth, pond water chemistry, and distance to neighboring ponds. Fire had significant negative effects. Immediate effects ( burning during the study ) explained 12.8% and 10.8% of the variation in anuran and amphibian abundance, respectively, whereas short-term effects explained 31.8% and 24.6% of variation in amphibian species richness and evenness, respectively. Species richness increased and evenness decreased with time since burn, primarily because salamanders were rarely encountered at sites burned within 2 years. These sites had the shallowest leaf litter and highest soil temperature variances. Environmental factors unrelated to burning also significantly influenced amphibian diversity. Water chemistry explained 31.1% of variation in species richness, 32.2% of evenness, and>25% of anuran, salamander, and total amphibian abundances. Salamanders were most sensitive to water chemistry factors, particularly pH. Our results suggest that decreasing the frequency of prescribed burns from the current 2–3 years to 3–7 years will better maintain diverse amphibian and plant assemblages. Substituting growing-season burns for the current practice of winter and spring burns would avoid repeatedly interrupting amphibian breeding and would maintain the desired longleaf pine community.
This benchmark volume documents in comprehensive detail a major environmental crisis: rapidly declining amphibian populations and the disturbing developmental problems that are increasingly prevalent within many amphibian species. Horror stories on this topic have been featured in the scientific and popular press over the past fifteen years, invariably asking what amphibian declines are telling us about the state of the environment. Are declines harbingers of devastated ecosystems or simply weird reflections of a peculiar amphibian world? This compendium-presenting new data, reviews of current literature, and comprehensive species accounts-reinforces what scientists have begun to suspect, that amphibians are a lens through which the state of the environment can be viewed more clearly. And, that the view is alarming and presages serious concerns for all life, including that of our own species. The first part of this work consists of more than fifty essays covering topics from the causes of declines to conservation, surveys and monitoring, and education. The second part consists of species accounts describing the life history and natural history of every known amphibian species in the United States.
Identifying keystone species is essential for understanding community dynamics and preserving species richness. However, few studies have used quantitative, a priori methods to identify potential keystone species. Species known to act as keystones in North Carolina (NC) temporary ponds (Notophthalmus viridescens, eastern newt, and Siren intermedia, lesser siren) were tested to see whether they played the same role in similar habitats in South Carolina (SC). Newts and sirens had no effect on anuran species richness in SC. Instead, another salamander (Ambystoma talpoideum, mole salamander) absent from the NC ponds was identified as a strong keystone in SC. It functioned independently of environmental factors and the densities of other predators. Larval dragonflies (Tramea carolina, Carolina saddlebag) were identified as weak, context-dependent keystones in SC, supporting anuran richness in isolated ponds with very low pH. The results suggest that the identity of keystone species varies, even in similar habitats within a physiographic region.
This study examines the mutual competitive effects among larvae of trio syntopic salamanders, Ambystoma macrodactylum rind Ambystoma gracile, Evidence for competitive equivalence and constant per capita effects,among these syntopic species could justify the use of simple models for describing competition. The species were raised alone and together at two densities in replicated artificial ponds. Hatchlings of Ambystoma macrodactylum were smaller than A. gracile, vet larger at the end of the experiment when A, macrodactylum began to metamorphose. Competition was detected as a decrease in grown rate with increasing, density, but competition was riot so strong as to influence the survival of either species. Ambystoma macrodactylum grew slowly relative to heterospecifics, and growth declined more with increasing conspecific density than with heterospecific density. In contrast, growth of A. gracile leas depressed more by increasing density. of the slower growing heterospecifics: These differences in effects of competition likely arise from differing breeding phenology-A. macrodactylum breeds earlier than A. gracile, and A. macrodae- was larger than A. gracile when the latter were added to the experimental ponds. The results provide no evidence for competitive differences or interaction at tire loo density used here. Assuming a coexistence mechanism exists to offset the competitive asymmetry at high density, I present a testable hypothesis on the mechanism of differential susceptibility of the species to predation.
Identifying the factors that limit species distributions and maintain patterns of diversity is a major goal of temporary pond ecologists, and an important pursuit for conservation biologists. We used multiple regression analysis to identify ecological correlates of anuran species richness in twenty-one temporary pools within the Francis Marion National Forest, South Carolina. Analysis of data collected in 19961997 revealed that anuran richness was limited by the multiplicative effects of pool acidity, hydroperiod, and fish species richness. Anuran species richness declined with decreasing pH and hydroperiod, and with colonization by more species-rich assemblages of predatory fish. Two species of frog (Hyla cinerea and Rana grylio) and a newt (Notophthalmus viridescens) were excluded from the most acidic pools, and three anurans (Bufo quercicus, Pseudacris ornata, and R. capito) were limited by fish. Two large-bodied frogs with tadpoles that overwinter prior to metamorphosis (R. catesbeiana and R. virgatipes) were restricted to pools with longer hydroperiods, and R. capito was more likely to breed in large than in small ponds. The results suggest that anuran richness at our study site is controlled by different factors than in similar ponds in North Carolina, where hydroperiod and the densities of tadpoles and two species of salamander were important. Identifying mechanisms likely to affect local anuran species richness allowed us to predict how subtle anthropogenic stresses could cause declines in amphibians to begin, in a region where few have been reported.
In this paper, we investigate the property of how color channels of a projector-camera system interact with each other, which is also called color mixing of the system. We propose a method to describe this property with a single color mixing matrix for the system, rather than a different matrix for every surface point. The matrix is independent of projection surface and ambient light. It can be measured just like response functions of projector-camera system. The matrix is helpful for color sensitive applications like radiometric compensation and scene reconstruction. By decoupling color channels with the matrix of the system, color images can be processed on each channel separately just like gray images. As most projector-camera systems have broad overlap color channels, it's improper to neglect their interactions. We will show the validity of describing color mixing of the system with a single matrix. In the end, some experiments are designed to verify our method. The result is convincing.
I conducted a mark-recapture study of Siren lacertina and Amphiuma means for one year at a lake in north Florida and documented average individual movement, size class distribution, seasonal activity patterns, survival rates, and density estimates. I captured Siren lacertina more frequently in winter and A. means more frequently in spring. Recapture probabilities of both species were low, whereas survival rates and density estimates (1.3 salamanders/m2 for S. lacertina, 0.28 salamanders/m2 for A. means) were high. I recorded no individual movement of over 10 m for either species. Sirens and amphiumas are large, predatory generalists that can have substantial biomass in wetlands (233 g/m2 and 44 g/m2, respectively, at this study site), and therefore can impact many other wetland species. Thus, more attention must be focused on evaluating and monitoring their populations.
The Lesser Siren (Siren intermedia) is a fully aquatic salamander with functionally limited overland dispersal. Details of the ecology of this species throughout its geographic range and diversity of habitats are limited. In this study, I investigated the ecology of a presumably isolated population of S. intermedia in eastern Texas. The conservative estimated population density was 0.33 sirens/m2 with a standing crop biomass of 9.66 g/m2. Growth rates averaged 0.022 mm/day in total length, slightly slower than other populations. Growth rate was not significantly different between males and females, nor was it correlated with size. The diet of the study population included at least 10 different taxa, of which tadpoles and snails (Order Basommatophora) were the most important prey. Like other populations, activity was highest during late winter and early spring, which coincides with the breeding season. The abundance of siren captures was weakly influenced by water temperature but not correlated with precipitation. Bite marks are hypothesized to be a result of siren courtship behavior. The abundance of males and females captured with fresh bite marks was significantly correlated with the number of gravid females. Because sirens are predatory generalists and represent a significant proportion of biomass in many aquatic environments, it is important to understand siren ecology throughout its geographic range and broad use of habitat types.
Printout. Thesis (M.S.)--University of Florida, 2003. Vita. Includes bibliographical references.
We used a replicated field experiment to determine the relative intensity of intraspecific and interspecific competition between larvae of Siren intermedia and Notophthalmus viridescens. These two salamanders possess markedly different morphologies and life histories and belong to distantly related salamander families, but feed on similar prey. Each species was raised in artificial ponds, alone at either low density (3 larvae per pond, 1.95 m-2) or high density (6 larvae per pond, 3.90 m-2) or together in a 3:3 ratio for a combined density of 6 larvae per pond. These 5 treatments were each replicated 4 times in a total of 20 ponds. The experimental design allowed us to explicitly compare the relative intensities of intra- and interspecific competition under realistic conditions. Competition affected different components of fitness in each species. Both intraspecific and interspecific competition caused a decline in survival of Notophthalmus, but had no detectable effect on body size or length of larval period. Negative density-dependent mortality may regulate Notophthalmus populations in the larval stage of their complex life cycle. Intraspecific competition caused a decline in both the survival and growth of larval Siren, but interspecific competition caused only growth to decline. Decreased growth rates may increase the vulnerability of larval Siren to desiccation and to predation. We found no evidence to reject the null hypothesis that larvae of these two species are equal competitors at the densities we employed. Our results indicate that, despite dissimilarities in life history and morphology, and a distant phylogenetic relationship, larval Siren and larval Notophthalmus compete as equals.
The relationships among timing of metamorphosis, size at metamorphosis, and traits related to adult fitness were studied for 8 yr in the salamander Ambystoma talpoideum at a temporary pond. Among years, the modal time of metamorphosis and mean body size at metamorphosis were positively correlated with the date the pond dried. In years that the pond dried late, one group of larvae metamorphosed well before the pond dried, whereas the other group metamorphosed just before pond drying. Mean body size of late-metamorphosing individuals was not greater than that of individuals metamorphosing early. Early-metamorphosing males and females were larger at first and second reproduction than were late-metamorphosing individuals. Independent of timing of metamorphosis, larger juveniles at metamorphosis were also larger adults at first reproduction. Age at first reproduction for males was not associated with timing of or size at metamorphosis but large early-metamorphosing females reproduced at a younger age than did small early-metamorphosing females. Neither time of metamorphosis nor size at metamorphosis was associated with survival to first reproduction. These results demonstrate a direct relationship between phenotypic variation generated in the larval stage and adult traits closely associated with an individual's fitness.
Siren lacertina is capable of surviving long periods of drought by estivating in burrows. -from Author
Experimental manipulations of densities of the predatory salamanders Notophthalmus viridescens dorsalis and Ambystoma tigrinum significantly altered relative abundances of six species of larval anurans in 22 artificial-pond communities. One competitively inferior anuran, Hyla crucifer, was virtually excluded from predator-free control communities but survived best and occurred at greater relative abundances in communities containing high densities of Notophthalmus. A second competitively inferior species, Hyla gratiosa, survived best at intermediate intensities of predation. Each of four competitively superior species (Scaphiopus holbrooki, Rana sphenocephala, Bufo terrestris, and Hyla chrysocelis) exhibited inverse relationships between relative abundance and Notophthalmus density. Ambystoma eliminated the entire anuran guild from tank communities and had a much greater per capita impact on anuran guild composition than did Notophthalmus. In most anuran species, maximum and mean mass at metamorphosis were positively correlated with predator density, suggesting an inverse relationship between intensities of predation and competition among tadpoles. Low growth rates of most anuran species in the absence of predators were correlated with high abundances of superior competitors. These results indicate that predators mediated interspecific competition among larval anurans. Intermediate values of Notophthalmus density maximized the total production of anuran metamorph biomass. Biomass of metamorphs of each species varied in a species-specific manner with predation. The propensity of Rana sphenocephala for overwintering as tadpoles following a season of growth was also related to predator density. Laboratory feeding experiments demonstrated that at least two competitively superior anurans, Scaphiopus holbrooki and Bufo terrestris, were especially vulnerable to predation by salamanders. This suggested that Notophthalmus may preferentially remove competitively superior anurans from pond communities, allowing competitively inferior anurans to persist and to complete development successfully at moderate to high predator densities.
The annual cycle of residence in water differed considerably among the three syntopic newts Triturus vulgaris, T cristatus and T. alpestris at a pond in northern Italy. T. vulgaris were resident in water for only short periods, which were used exclusively for reproduction. Adult T cristatus were present in the water for 3-4 months after reproduction, and regained weight during autumn. T. alpestris were present throughout the year; branchiate juveniles and neotenics were more abundant than adults.
In a community where broken-striped newt Notophthalmus viridescens dorsalis acts as a keystone predator on larval anurans, the authors independently manipulated the initial density of adult Notophthalmus (2 or 4) and the presence or absence of one adult Siren intermedia. At low newt density Siren had no effect on survival, but at high newt density competition reduced the survival and growth rates of Notophthalmus. Density of Notophthalmus and presence of Siren interacted to determine the fecundity of Notophthalmus. At low newt density Siren reduced Notophthalmus reproductive success by preying on larvae. At high newt density Siren indirectly enhanced reproductive success by reducing survival of adults, thus releasing larvae from intraspecific competition and cannibalism. Notophthalmus density had no effect on adult Siren survival or growth but other evidence indicates that competition with Notophthalmus reduces growth rates of Siren. Notophthalmus acted as a keystone predator on the assemblage of spring-breeding anurans; it increased the number of metamorphs of the weak competitor Pseudacris crucifer by releasing them from interspecific competition. Siren preyed on tadpoles in a nonselective manner. -from Authors
Reports of declining amphibian populations in many parts of the world are numerous, but supporting long-term census data are generally unavailable. Census data from 1979 to 1990 for three salamander species and one frog species at a breeding pond in South Carolina showed fluctuations of substantial magnitude in both the size of breeding populations and in recruitment of juveniles. Breeding population sizes exhibited no overall trend in three species and increased in the fourth. Recent droughts account satisfactorily for an increase in recruitment failures. These data illustrate that to distinguish between natural population fluctuations and declines with anthropogenic causes may require long-term studies.
When drought occurs, sirenids burrow into the substratum and remain inactive until the habitat is reflooded. Resting metabolic rates are 60-70% lower in estivators than in aquatic animals. At these low metabolic rates, adult S. lacertina (>500 g body mass) could survive 2-3 yr on stored energy. Smaller S. lacertina and P. striatus have higher mass-specific metabolic rates during estivation, but even a 1 g sirenid could survive for several months. -from Author
A "common garden" experiment using artifical ponds was performed to test if differences in frequency of paedomorphosis and metamorphosis among six natural populations of the salamander Ambystoma talpoideum resulted from the drying regime of the aquatic habitat acting as an agent of selection. Our experiment supports the hypothesis of genetic differentiation in the propensity to metamorphose among the populations, but gave mixed evidence that pond-drying regime is the selective force directing evolution of this trait. Some populations appear to have evolved phenotypic plasticity whereas others may have a genetic polymorphism in their propensity to metamorphose as ponds dry.
The diel pattern of migratory activity for five species of salamanders (Eurycea quadridigitata, Notophthalmus viridescens, Ambystoma talpoideum, A. tigrinum and A. opacum) was monitored by terrestrial drift fences with pitfall traps surrounding two breeding sites. Individuals captured (N = 1,124) in pitfall traps were censused at 6-hour intervals during nine 24-hour periods from 1981 to 1983. Census days were selected non-randomly in order to equalize the amount of rainfall and mean air temperature between day and night periods. This design allowed the separation of environmental effects other than photoperiod from species differences in diel activity. There were significant species differences in the number of individuals censused among time intervals and between day and night. N. viridescens and E. quadridigitata were equally active night and day. A. talpoideum and A. tigrinum were significantly more active at night. There were no significant differences in either mean air temperature or amount of rainfall among time intervals or between day and night periods. The results indicated distinct differences among species in the diel pattern of migratory activity that were not explicable by variation in air temperature and amount of rainfall. Species patterns probably reflect adjustments produced by natural selection to avoid predation and desiccation.
Siren intermedia nettingi Goin is unique among salamanders in combining high density $(0.9-1.3\ \text{sirens}/\text{m}^{2})$ through high net productivity $(29\text{g}/\text{m}^{2}/\text{year})$ with large size (x̄ 42 g) to attain a standing crop biomass of $38-57\ \text{g}/\text{m}^{2}$ . Characteristics that contribute to the high productivity include great fecundity (151-226 eggs/female/year) and rapid growth (0.42%/day) to sexual maturity in one year. The standing crop of S. intermedia alone may be 1.1-1.3 times that predicted for all seven species of insectivorous fishes in the same beaver pond community in Texas. Siren intermedia is unusual among vertebrates in being both an early colonizer and dominant species in at least two different successional stages of a single community.
A lesser siren (Siren intermedia) may burrow into the bottom of its drying pond and aestivate for several weeks to more than a year. During aestivation it secretes a mucous cocoon, its, oxygen consumption and heart rate drop significantly and duration of its righting response increases. The gills atrophy and the body shrinks as fat is metabolized at one-fifth the rate of aquatic sirens after 16 weeks of aestivation. Large individuals store more fat and consume less oxygen per unit weight than small ones; hence, they can survive much longer periods of aestivation. Upon inundation, lesser sirens become active within a day but do not reach pre-aestivational metabolic levels until feeding begins. Then they may require only 8-11 weeks to regain the weight lost during 16 weeks of aestivation.
Two spent female Siren intermedia were found attending eggs in early February in a S Florida water hyacinth community. Embryos from both nests tended to hatch synchronously, averaged 11.5 mm in total length and showed more advanced development than those reported from Arkansas. The two attendant females had several distinct epidermal marks, which closely matched the cornified beaks and vomerine teeth of conspecifics, and possibly were made by courting males. Examinations of 487 additional S. intermedia collected from this site indicated that bite-marks were restricted to breeding females. The larger body size and enlarged masseter muscles of male S. intermedia probably are related to social interaction and sexual activity.
Phenotypic variation in metamorphosis and paedomorphosis in the salamander Ambystoma talpoideum was examined to determine its environmental or genetic basis. Eight artificial ponds were maintained, four at each of two environmental treatments: constant water level, to simulate fish-free permanent breeding ponds, and gradual drying out, to simulate temporary breeding ponds. Two populations of salamanders were used, derived from two breeding ponds having different frequencies of paedomorphosis. The water level in the drying treatment was lowered during the last 10 wk of the experimental period with no apparent differences in water chemistry parameters between treatments and only a slight change in water temperature during the last 2 wk. The effects of water level were potentially confounded by those of water temperature, density of larvae, and amount food. Population differences in the frequency of metamorphosis and paedomorphosis could potentially represent genetic differences resulting from the different selective regimes that individuals encounter in breeding ponds varying in drying frequency. 35 references, 3 figures, 4 tables.
The expression of metamorphosis and paedomorphosis in the salamander Ambystoma talpoideum was examined in a three-factor experiment using artificial ponds. This experiment was designed to measure simultaneously the effects of initial larval density, food level, pond drying regime, and their interactions on the percentage of individuals metamorphosing or becoming paedomorphic. A higher percentage of individuals metamorphosed from drying low-density, and high-food ponds than from constant water level, high-density, and low-food ponds. A higher percentage of individuals became paedomorphic in constant water-level and low-density ponds than in drying and high-density ponds. Food level had no effect on the expression of paedomorphosis. Initial density, food level, and drying regime all had significant effects on the mean snout-vent length of larvae in ponds. The percentage of paedomorphic individuals in a pond was positively correlated with mean snout-vent length in the population. Analysis of covariance using snout-vent length as the covariate removed density and food level effects on the percentage of metamorphic individuals but did not remove the effects of drying regime. Use of snout-vent length as covariate in an analysis of covariance for the percentage of paedomorphic individuals failed to remove significant effects of density or drying regime. Only initial density affected the survival of larvae. The factors manipulated in this experiment affected the expression of paedomorphosis both directly through the physical environmental conditions that they created and indirectly through the growth and body size of larvae. These results suggest that differences in environmental factors among populations can affect the life-history pathways of individuals and lead to a predominance of paedomorphosis in permanent aquatic habitats with favorable growth environments.
A food web graphically represents the paths of nutrients and energy through the living components of an ecosystem and the context in which individuals exploit their prey and avoid their enemies. Temporary ponds are excellent arenas for the study of food webs because they are discrete communities that can be mimicked in containers that approach the realism of natural habitats. Artificial ponds permit repeatable initial con- ditions and sufficient replication of independent experimental units in complex experi- ments to test hypotheses about the control of structure and function in natural commu- nities. I used a combination of observations of natural ponds, ''experimental natural history'' of artificial ponds in my study area, and controlled experiments in an array of 144 replicate ponds to develop, then test, hypotheses about how the structures of food webs are regulated. Understanding food webs begins with population biology. Amphibians use the aquatic larval stage of their biphasic life cycle to exploit ephemeral opportunities for growth and development in temporary ponds. The regulation of population density and the fitness of individuals are determined by complex interactions among competition, predation, and uncertainty in the length of the time ponds retain water. Exponential models of density- dependent recruitment relate the number of metamorphs to the input of eggs into ponds without predators. Extensions of these models include interspecific competition and pre-
Effects of egg size on growth, survival, and metamorphosis of larval salamanders (Ambystoma talpoideum) were examined in varying environments. Pond drying regime and presence vs. absence of an interspecific competitor were manipulated in a factorial experiment using artificial ponds to measure the responses of larvae. Females that were 4 yr old produced larger eggs and hatchlings than 1-yr-old females. Differences in body size at hatching persisted through day 49 of the experiment but disappeared by day 129. Drying regime also affected body size at day 49 but not at day 129. Larvae from large eggs, and larvae in constant water level ponds, had higher survival to day 129 than larvae from small eggs, and in drying ponds. There was also a significant interaction between egg size and drying regime. Larvae from large eggs survived better than larvae from small eggs in the constant water level ponds, but not in drying ponds. Interspecific competitors did not affect growth or survival to day 129. More individuals metamorphosed from drying ponds than from constant water level ponds. The growth advantages conferred by larger body size at hatching are transient and may disappear during compensatory growth later in the larval period. Body size advantages early in the larval period, however, probably account for increased survival through size-specific mechanisms at a time when newly hatched larvae are most vulnerable.
Laboratory experiments were conducted to evaluate the effects of temperature, water evaporation rate, and food availability on the incidence of neoteny in Ambystoma gracile and to assess the nature of its genetic control. Larvae hatched from six clutches of eggs from ponds in British Columbia were reared until they were about to metamorphose. Six experiments were then initiated, each involving larvae from a single distinct clutch. Results indicated that at 12 °C larvae metamorphosed later and the incidence of neoteny was higher than at 19 °C; similarly, larvae fed once per week transformed more slowly and were more frequently neotenic than larvae fed three times per week. The rate at which water evaporated, and associated changes in salinity and depth appeared to have no effect. With one exception, under standard conditions there were no differences in the timing of metamorphosis of larvae from different clutches and different populations. It appears that populations of A. gracile are highly polymorphic, comprising some individuals which always metamorphose, some which never do, and others which may or may not transform, depending on the nature of the habitat.