Amphibians commonly use wetlands for breeding habitat, and given the concern about their ongoing global declines, the effects of urbanization on the breeding distribution of amphibians need to be quantified. Thus, we conducted a survey of the larval amphibian community in central Pennsylvania (U.S.A.) wetlands along an urbanization gradient. Wetlands in urban areas had less surrounding forest and wetlands and greater road density than rural wetlands. Urbanization was also associated with increases in hydroperiod (i.e., wetland permanency) and the presence of fish predators. Moreover, urban wetlands had lower larval amphibian species richness than rural wetlands. This decrease in richness was attributable to a decrease in occurrence of wood frogs ( Rana sylvatica) and ambystomatid salamanders (Ambystoma maculatum and A. jeffersonianum) in urban sites. Wood frogs and ambystomatid salamanders were positively associated with the amount of forest surrounding sites and negatively associated with hydroperiod. As a result, we hypothesize that these species are sensitive to the effects of urban development. The remaining species in this study appear fairly resilient to the effects of urbanization. These data demonstrate the importance of quantifying both local and landscape attributes when describing the factors that limit the breeding distribution of amphibians. We recommend that to preserve amphibian biodiversity in urbanized landscapes, it is best to focus on regional diversity, which protects a variety of sites that encompass various hydroperiods, have adequate buffer habitat, and are connected by dispersal routes. Distribución de la Reproducción de Anfibios en un Paisaje UrbanizadoResumen: Los anfibios comúnmente utilizan humedales como hábitat de reproducción, y dada la preocupación por sus declinaciones globales, existe la necesidad de cuantificar los efectos de la urbanización sobre la distribución de la reproducción de anfibios. Por lo tanto, examinamos la comunidad larvaria de anfibios en humedales de Pennsylvania central (E, U. A.) a lo largo de un gradiente de urbanización. Los humedales enáreas urbanas tenían menos bosque y humedales en los alrededores y mayor densidad de caminos que los humedales rurales. La urbanización también se asoció con incrementos en el hidroperíodo (i. e permanencia del humedal) y con la presencia de peces depredadores. Más aun, los humedales urbanos tenían menor riqueza de especies de larvas de anfibios que los humedales rurales. Este decremento en riqueza se debió al decremento en la ocurrencia de ranas ( Rana sylvatica) y de salamandras ambistómidas (Ambystoma maculatum y A. jeffersonianum) en sitios urbanos. Las ranas y salamandras ambistómidas se asociaron positivamente con la cantidad de bosque alrededor de los sitios y negativamente con el hidroperíodo. Como resultado, planteamos la hipótesis de que estas especies son sensibles a los efectos del desarrollo urbano. Las especies restantes en este estudio parecen medianamente resistentes a los efectos de la urbanización. Estos ...

The temperate deciduous forest of the northeastern United States is believed to be undergoing a shift from domination by mixed oak (Quercus sp.) to red maple (Acer rubrum); a shift termed ''The Red Maple Paradox.'' This shift in the composition of the forest has the potential to affect ecosystems within the forest that use leaf litter as an energy source. To assess the impact of the red maple paradox on detrital food webs, we conducted a mesocosm experiment investigating the influence of red maple litter on the food web of temporary woodland ponds. Amphibian biomass and survival were significantly lower in experimental ponds that contained only maple litter. The negative effects of maple litter were most pronounced in larval wood frogs (Rana sylvatica). We hypothesize that this effect resulted from a temporary shift from a grazing-based food web in oak mesocosms to a microbial-based food web in maple mesocosms, as oak mesocosms initially had higher levels of phytoplankton biomass and lower levels of bacterial production than maple mesocosms. This bottom-up effect of maple litter on wood frogs then appeared to affect other amphibians and zooplankton through a complex series of interactions. These data suggest that litter composition impacted the performance of most trophic groups by altering the processing of energy in this system, thereby destabilizing species interactions throughout the food web. Therefore, ''subtle'' compositional shifts in the forest have the potential to influence communities that rely upon leaf litter inputs as a primary source of energy.

Social and cultural institutions influence how societies organize themselves to extract resources, affecting the ways in which resources are used and ultimately managed. In Papua New Guinea, marine tenure rights largely determine how individuals and communities use inshore marine resources. Whether institutions of customary marine tenure can play a role in resource conservation or are simply mechanisms to avoid conflict and maximize exploitation is a matter of debate. In the Manus Province, an unusual marine tenure and trade arrangement has resulted in the community of Andra producing the majority of lime powder used for consumption with betel nut. A socioeconomic and ecological assessment revealed that more than 90% of Andra's community was engaged in lime production, an industry contributing an estimated US$102,000 ± 28,000 to the village annually. The main source of material used in lime production at Andra is live branching coral (primarily Acropora spp.). The annual removal of approximately 2,113 ± 660 m 3 of coral appears to have produced significant changes in coral cover in Andra's reefs, resulting in a lower percent cover of hard corals (24 ± 2% SE) compared with neighboring reefs with little harvesting (33 ± 3% SE). Existing common-property regimes may provide incentives for individuals to sustainably use their own reef area. A lapse in supply, however, could threaten the community's virtual monopoly and provide other villages with an opportunity to gain a market share of lime production. Thus, the marine tenure and trade arrangements that facilitated Andra's position as the dominant supplier of lime to the province may result in incentives for the overexploitation of coral in ways that are paradoxical to an open-access scenario. Management interventions that aim to reduce the ecological impacts of coral harvesting should reflect the community's economic dependence on the practice and the sociocultural institutions that influence resource use.Resumen: Las instituciones sociales y culturales influyen en la forma en que las sociedades se organizan para extraer recursos, afectan a la manera en que los recursos son utilizados y manejados finalmente. En Papua Nueva Guinea, los derechos de posesión marina en gran medida determinan la manera en que individuos y comunidades utilizan los recursos marinos costeros. Es motivo de debate si las instituciones de posesión marina convencional pueden jugar un papel en la conservación de recursos o si son simples mecanismos para evitar conflictos y maximizar la explotación. En la comunidad de Andra, Provincia de Manus, donde se produce la mayor parte de polvo de cal utilizado para el consumo de nuez de betel, hay una forma de posesión marina y de organización de comercio poco usual. Una evaluación socioeconómica y ecológica reveló que más de 90% de los habitantes de Andra estaba ocupado en la producción de cal, una industria que anualmente aporta alrededor de US$102,000 ± 28,000 a la comunidad. El coral vivo (principalmente Acropora spp.) es la fuente principal del mater...

Recent research suggests that secondary production in aquatic systems can be driven by inputs of energy from terrestrial sources. Temporary forest ponds appear to be unproductive ecosystems that are reliant upon allochthonous inputs of energy to support secondary production, but the functioning of these systems has not been well quantified. To assess the metabolic state of this type of ecosystem as well as to quantify the importance of terrestrial subsidies of carbon to ecosystem function, we conducted an experiment in which we manipulated the amount of leaf litter in ponds. Litter was either removed or removed and replaced (that is, control) from the dry basins of ponds immediately after leaf abscission. Once the ponds filled, we monitored net ecosystem production (NEP) on a biweekly basis from 9 April to 27 May 2002. All ponds were consistently net heterotrophic; however, NEP was significantly less negative in removal ponds. Furthermore, removal ponds also had lower levels of respiration (R) and higher dissolved oxygen levels than control ponds. The removal of litter had no effect on gross primary production, indicating that the difference in NEP between treatments was driven by the change in R. Therefore, it appears that terrestrial inputs of organic carbon support heterotrophic respiration in these ponds, and that the endogenous production of carbon is insufficient to support secondary production.

Terrestrial support of aquatic food webs is becoming well established in the science of ecology. However, while terrestrial subsidies of energy have been shown to exert strong effects on aquatic food webs, it is less clear how variations in these subsidies, via natural or anthropogenic factors, will affect recipient ecosystems. To assess the influence of variations in terrestrial subsidies on an aquatic food web, we manipulated leaf-litter inputs in artificial ponds. Decreasing litter inputs did not affect any of the response variables in artificial ponds. This may be because the minimal amount of terrestrial carbon present combined with autochthonous production was enough to sustain the food web and/or the food web was altered in ways not detected by the experimental design. However, increasing leaf-litter inputs increased the percent survival and developmental rate of larval wood frogs (Rana sylvatica). Conversely, increasing litter input appeared to have no influence on zooplankton or salamander larvae. Increasing litter inputs also increased the dissolved organic carbon content and decreased the percent saturation of dissolved oxygen in artificial ponds. As system respiration in aquatic systems is frequently dominated by microbial respiration, we hypothesize that the effects of increasing litter input on wood frogs were the result of an increase food resources (i.e., microbes) for tadpoles. The lack of a response by salamander larvae and zooplankton may be due to the densities of zooplankton in tanks providing enough food for salamanders in all treatments, variation among specific zooplankton species in their ability to exploit these resources and transfer energy to salamanders, or omnivory among zooplankton offsetting the affects of leaf-litter inputs. Additional work is needed to determine the influence of litter inputs on zooplankton and salamanders in this community. These data demonstrate that variations in leaf-litter inputs can influence food web structure; however, the importance of these variations will likely be dependent upon the trophic position of various consumers.