Amphibians and aquatic invertebrates have complex life histories that link aquatic and terrestrial food webs. It has been suggested that amphibian reproduction is an important source of carbon to some aquatic systems. This process of energy flow may be shaped by shifts in habitat selection in response to predators. We hypothesized that predators decrease colonization and oviposition of prey, reducing active inputs. Thus predation risk is expected to shift the relative amounts of active and passive subsidies. We manipulated the presence of fish predators in aquatic mesocosms. Results suggest hylid treefrog eggs and hydrophilid beetles were less abundant in predator treatments. This difference in oviposition and colonization translated into small reductions in calories and ash free dry mass of active inputs. However, passive allochthonous inputs were more than double active amounts and variable, therefore relative amounts of active and passive inputs did not differ across the levels of predation risk.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Habitat loss and fragmentation are some of the causes of biodiversity decline. Naturally fragmented landscapes serve as analogues to anthropogenically fragmented landscapes. Recent studies have shown that the matrix between patches has an important role in the dynamics of patch-dwelling species. I studied phenology and habitat utilization of Hyla cinerea and Hyla squirella, the two most common yet understudied frogs, in two patchy landscapes of the Big Cypress National Preserve. Frogs were sampled in five domes and in their adjacent matrix, monthly, between 2006 and 2008. Using nighttime visual encounter surveys, specimens encountered were identified to species, and perch type, perch height and capture location were recorded. Analysis showed differences in abundance and habitat use patterns between patches and matrices for the two species across the two landscapes. These differences indicate that the matrix is important in shaping patterns of abundance and habitat use in fragmented landscapes.

In animal communication, individuals within a species often vary widely in their behavioral responses to species-typical signals. These variations in behavior may be due to differences in the sensory processing of communication signals. Sensory processing of behaviorally relevant stimuli is likely to be influenced by reproductive hormones. Here I report investigations on the influence of sex and reproductive condition on auditory processing in the green treefrog, Hyla cinerea. I conducted electrophysiological experiments that tested how sex and reproductive condition influence the neural representation of sounds in the auditory midbrain, the torus semicircularis. I found differences between and within the sexes that were both frequency-dependent (low vs. high frequency) and stimulus-dependent (tones vs. calls). For sex differences at auditory threshold, females were less sensitive to frequencies outside the spectral range of the male advertisement call and were not different from males inside the range. Sex differences were also stimulus-dependent with females more sensitive to the advertisement call than males. For stimuli consistent with close-range communication, I tested whether or not sex differences in response strengths to advertisement call and noise stimuli depended on the reproductive state of the female. I found that in response to low frequency stimuli postmated females had significantly reduced response strengths compared to males and unmated females. Additionally, I tested whether circulating reproductive hormones influenced auditory processing by manipulating androgen levels and assessing neural thresholds and response strengths to auditory stimuli. Elevated androgen levels in females resulted in increased thresholds and reduced response strengths but only in response to stimuli that are consistent with species-typical communication. Together the evidence from these studies suggest that sex and reproductive hormones influence auditory processing in a way that shapes the filtering properties of the auditory system for the detection of communication signals.

Thesis (Ph. D.)--Ohio State University, 2005. / Available online via OhioLINK's ETD Center; full text release delayed at author's request until 2008 Nov 30

Submitted by Alberto Vieira (martins_vieira@ibest.com.br) on 2018-06-15T17:48:25Z No. of bitstreams: 1 277981.pdf: 12888297 bytes, checksum: 20f87c643971ee0c951748d6f08233fb (MD5) / Made available in DSpace on 2018-06-15T17:48:25Z (GMT). No. of bitstreams: 1 277981.pdf: 12888297 bytes, checksum: 20f87c643971ee0c951748d6f08233fb (MD5) Previous issue date: 1996-12-11 / CAPES / Foram estudados e ilustrados os girinos das cinco espécies do grupo "albosignata", e com base nisso caracterizado o grupo. Os girinos do grupo foram associados a ambientes de água corrente e altitudes superiores a 800m. Dois conjuntos de girinos foram distinguidos morfologicamente: o primeiro constituído por H. albosignata e H. cavicola, e o segundo por H. callipygia, H. fluminea e H. leucopygia. Foi feita uma chave para a identificação dos girinos do grupo, baseada em padrão de colorido, diferença nas estruturas bucais e outros caracteres morfológicos. Considerações quanto a aspectos ecológicos e preferências ambientais foram feitas, relacionando ainda algumas, como duração do período reprodutivo e altitude, aos conjuntos de girinos. Foi observado que esses girinos atingem seu maior tamanho em torno do estágio 38, e que dependendo da espécie a cor verde surge em diferentes estágios e diferentes lugares no girino (cauda ou corpo). H. cavicola é a espécie em que a cor verde surge mais cedo (cauda), no estágio 36, e H. albosignata é a espécie em que surge mais tarde (corpo), no estágio 41. Foi ampliada a distribuição geográfica de H. callipygia, H. cavicola e H. Fluminea. / Tadpoles of the five Hyla species belonging to the "albosignata" group were studied and illustrated, and their shared characters used to define the group. Tadpoles of the "albosignata" group were shown to be associated with mountain streams from 800m to higher elevation. Two groups of tadpoles have been distinguished, the first involving H. albosignata and H. cavicola and the second H. callipygia, H. fluminea, and H. leucopygia. A key to the tadpoles of the group was elaborated taking into consideration color pattern, oral features and some other morphological traits. Some remarks on ecological aspects and environmental prefferences were made, associating some of them as a wider reproductive period and lower altitude streams occupation with the first group of tadpoles. It was observed that the tadpoles of the "albosignata" group get to their maximum size by stage 38, and that the green collor typical of all adults appears at different developmental stages and on different body parts depending on the species considered. Among the five species of the group it was found that H. cavicola shows the green color at the earliest stage (36) and H. albosignata at the later ( 41 ). The known geographic range for H. callipygia, H. cavicola, and H. fluminea was extended.

Amphibian populations are rapidly declining worldwide. Although individual factors may have large local influences, worldwide declines are attributed to interacting global stressors including rising temperatures and environmental pollutants. Globally, water temperatures closely track rising air temperatures and increase the metabolic rates of aquatic ectotherms, changing the rates of uptake, biotransformation, and excretion of contaminants, such as metals. To test how interactions of multiple, chronic stressors affect amphibian growth, I exposed Cope's gray treefrogs (Hyla chrysoscelis) in an outdoor mesocosm facility to three temperature regimes (ambient, ambient +1.5 oC, ambient +2.5 oC) in filtered lake water amended with mixtures of cadmium, copper, and lead ranging from 3.7 to 26.7 risk quotients (relative to the chronic concentration criteria protective of freshwater organisms). Temperature shifts and sublethal metals concentrations significantly affected the energetics of tadpoles as assessed by non-parametric and parametric analyses. Regression analyses indicated no significant relationship between temperature and time to forelimb emergence at the three lowest metals concentrations, but the relationship was parabolic at the three highest concentrations, indicating a differential effect of temperature across a gradient of water quality. The concept that tadpoles increase developmental rates to escape unfavorable aquatic conditions was supported at each temperature by shortened time to forelimb emergence (Gosner Stage 42) at the second highest metals concentration. This response, however, was overwhelmed by the energetic costs associated with the highest concentration and the highest temperature. Moreover, these parabolic relationships match predictions based on species specific thermal windows and pejus temperatures. My findings indicate that global warming may affect contaminated waters to a greater extent than pristine aquatic ecosystems, and that the primary effect may be diminished pejus and critical thermal maximum temperatures, and a narrowing of the species' thermal window.

No description available.

Researchers at the GFS, Washington County, Tennessee through the wet screening of nearly 100%of the sediment excavated at the site, recovered an extensive collection of anuran fossil elements. Until recently, these specimens have not been analyzed. The purpose here is the examination, description, and identification of all non-ranid anuran (frogsand toads) material using the following elements: ilium, urostyle, maxilla, frontoparietal, and last sacral vertebra. Anurans identified include Scaphiopus wardorum(extinct spadefoot toad), Bufo terrestris(southern toad), B. cf. B. marinus(giant neotropical toad), three morphotypes of Hyla(tree frogs), and Pseudacris cf. P. brachyphona(mountain chorus frog). Occurrence of these Anura support a paleoecological environment described as warm, moist, and wooded.