Robert Brodman

Multivariate Analyses of the Influences of Water Chemistry and Habitat Parameters on the Abundances of Pond-Breeding Amphibians

ABSTRACT We surveyed 104 potential amphibian-breeding sites in northwest Indiana for the presence and abundance of amphibians, habitat parameters, and water chemistry. Linear regression was used as an exploratory analysis, and stepwise multiple regression and ANOVA were used to model factors that best explained amphibian species richness, abundance, and number of years with breeding populations. The most important breeding site factors among those studied were wetlands with semi-permanent hydrology, levels of dissolved chloride, silica, hardness and alkalinity, standing waters that were not ditches, wetlands without agriculture within 200 m, the number of hydrology types within one kilometer, the number of wetlands within 400 m, and biotic interactions within the amphibian community. Minor factors included the presence of ammonia, turbidity, low phosphates, low detergents and pH level; wetlands with wooded upland habitats <200 m, palustrine wetland habitats, surface area of the wetland, and percentage of the wetland covered by emergent vegetation.

ANNUAL VARIATION IN BREEDING SUCCESS OF TWO SYNTOPIC SPECIES OF AMBYSTOMA SALAMANDERS

Some pond-breeding salamander populations are declining because of high embryonic and larval mortality rates (Pough and Wilson, 1977; Freda et al., 1991; Pechmann et al., 1991; Peterson et al., 1991). Embryonic mortality among egg masses is often variable and may depend upon the distribution of egg masses (Harris, 1980; Stangel, 1988). Ambystoma opacum nesting sites affect embryonic mortality and females choose optimal locations for nest placement (Petranka and Petranka, 1981; Jackson et al., 1989; Petranka, 1990). However, A. opacum is atypical of most pond-breeding salamanders because it lays eggs on the dry pond bed in autumn and guards the eggs until rains fill the pond (Petranka and Petranka, 1981). Little is known about the effect of oviposition site on egg mortality when eggs are attached to submerged substrates. This study reports four years of monitoring the effects of temperature and egg mass distribution on breeding success in two populations of pond-breeding salamanders.

ACTIVITY AND MICROHABITAT USE DURING INTERACTIONS AMONG FIVE SPECIES OF POND-BREEDING SALAMANDER LARVAE

We evaluated five species of the genus Ambystoma in laboratory aquaria to quantify the effect of other larvae on microhabitat use and activity. We studied microhabitat use by partitioning containers into microhabitats that either contained or lacked refuges and recorded movement to determine activity. All five species altered microhabitat preferences and activity levels when they shared tanks with larvae of most species. The smallest species (A. laterale and A. maculatum) spent the most time in the vegetated chamber, used the vegetated chamber more often, and decreased activity in the presence of potential predators. When species were paired, both species usually changed their activity and use of microhabitat in opposite directions. These behaviors may be important in maintaining coexistence among species by reducing interspecific aggression and intraguild predation.

Historical Changes of Reptiles and Amphibians of Northwest Indiana Fish and Wildlife Properties

Abstract We conducted the first formal quantitative study of the herpetofauna of the Jasper-Pulaski, Willow Slough and LaSalle Fish and Wildlife areas (FWA) in northwest Indiana from 1994–1996 to gather baseline data necessary to determine distribution and status of species and to monitor long-term population trends. We compared our results with those of earlier collectors Chapman Grant, Paul Swanson and Sherman Minton. A total of 339 populations of 13 amphibian species and 78 populations of 22 reptile species were encountered from 1994–1996. Only 9 species were found at all three FWAs and only 11 were commonly encountered. Sixteen new site records and new county records were made while at least 7 species with validated records before 1972 were not found during this survey and may be locally extirpated. The relative abundance of species at Jasper-Pulaski FWA has changed between the 1930s and 1990s with declines of the thirteen most abundant species and increases in some formerly overlooked or rare species. Large-scale changes in habitat may be partly responsible for changes in species abundance. All of the state-listed species (Acris crepitans blanchardi, Rana blairi, R. pipiens, Thamnophis p. proximus, Clemmys guttata, Emydoidea blandingii, Kinosternon s. subrubrum, Terrapene o. ornata, Opheodrys vernalis and Sistrurus c. catenatus), except Ambystoma laterale, have clearly declined.

The Effectiveness of Pond-Breeding Salamanders as Agents of Larval Mosquito Control

ABSTRACT Frogs and salamanders are well known predators on insects; however, the benefits of pest control attributed to them are usually based on anecdotes. Tiger salamander (Ambystoma tigrinum) larvae were collected from eight sites in northern Indiana and analyzed for stomach contents. The larval and pupal stages of mosquitoes made up the third largest component of the diet and were found in the stomachs of 26% of the tiger salamander larvae. During controlled feeding experiments in the laboratory, mosquito larvae were a preferred prey, and tiger salamander larvae were able to eat a mean of 144 mosquito larvae per day. An extrapolation of this figure suggests that a typical tiger salamander population could be an effective natural agent in the biological control of larval mosquito populations.

Interaction of an aquatic herbicide and predatory salamander density on wetland communities.

Abstract Pesticides can be important conservation tool, but they could have unintended impacts on amphibians. The commercial glyphosate-based herbicide Accord is approved for use in wetlands and ponds because it is designed to be safer to aquatic wildlife than other herbicide formulations (e.g., Roundup or Atrazine); however, field experiments are needed to determine whether there are direct, indirect, or sublethal effects on amphibians or effects on wetland community structure. We conducted a replicated field experiment in constructed ponds to test for both the effects of Accord and predator (Tiger Salamanders, Ambystoma tigrinum) density on amphibians and aquatic invertebrates. Herbicide treatment had significant density-dependent effects on Tiger Salamander growth, development, and survival. The survival of anurans and aquatic invertebrates was also affected by herbicide treatment and predator density. At certain Tiger Salamander densities, the community structure was altered such that some species became more common with herbicide treatment, whereas others became less common. Behavior assays of salamander larvae suggest that herbicide treatment alters predator-prey relationships in the experimental pond communities. These results suggest that competition and predation may mediate indirect effects of this herbicide on the aquatic fauna. We conclude that exposure to Accord poses less of a risk to the ecology of amphibians than do other formulations of glyphosate-based herbicides.

HOW BLUE-SPOTTED AND SMALL-MOUTHED SALAMANDER LARVAE COEXIST WITH THEIR UNISEXUAL COUNTERPARTS

Species of pond-breeding salamanders in the Great Lakes region often coexist with unisexual (all-female) populations that compete with larvae and are sexual parasites on adult males. We evaluated the effects of interactions with the larvae from unisexual salamander (Ambystoma laterale-complex) populations on blue-spotted (A. laterale) and small-mouthed salamander (A. texanum) larvae. We coupled observations in natural ponds with mesocosm and laboratory approaches to investigate the roles of competition, predation, microhabitat partitioning, and behavior on the coexistence of these populations. Unisexual salamander larvae increased mortality, reduced growth, and were observed to attack and bite small-mouthed and blue-spotted salamander larvae in mesocosms. Unisexual larvae were competitively superior to blue-spotted salamander larvae, but competitively equal to small-mouthed salamander larvae. Laboratory experiments confirmed field observations that both species increased their use of refuges in the presence of unisexual larvae and that this behavior resulted in niche partitioning. Blue-spotted salamander larvae were less active in the presence of unisexuals; however, small-mouthed larvae increased activity and use of refuges in the presence of larger intraguild predators. The hypothesis that microhabitat partitioning and altered activities minimize the effects of competition and predation was supported.