Effects of agriculture and topography on tropical amphibian species and communities (original) (raw)
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Amphibian assemblages in dry forests: Multi-scale variables explain variations in species richness
Acta Oecologica, 2015
Pond-breeding amphibians depend on several habitats and scales throughout their complex life cycle. For pond-breeding amphibians inhabiting seasonal dry forests, landscape is composed of a set of scarce and ephemeral isolated ponds surrounded by a contrasting matrix. The Chaco ecoregion is one of the most extensive dry seasonal forests in South America. In the last four decades, agricultural expansion and transformation from subsistence livestock farming to commercial livestock production have triggered dramatic deforestation processes all across the region, changing landscape composition and configuration. We postulate that richness of pond-breeding amphibians in the Chaco dry forest is negatively associated with pond hydroperiod and isolation, and terrestrial matrix degradation. Pond attributes and landscape configuration and composition were used to fit a statistical model to predict amphibian species abundance and richness in Arid Chaco ponds. Our results show that amphibian abundance and species richness in Chaco ponds is related to local and landscape predictors. Isolated and ephemeral ponds located in degraded shrublands showed low species richness values in Chaco dry forests. These results suggest that present-day land-use changes in the Chaco will have important effects on amphibians assemblages from the region, because such changes imply not only the loss of native vegetation but also a reduction of rural people devoted to extensive livestock production, where the artificial ponds used for watering livestock are also used as breeding sites by Chaco amphibians.
Landscape use and habitat configuration effects on amphibian diversity in southern Brazil wetlands
Wetlands, 2024
In this study, we evaluated the effect of changes in natural wetlands on the amphibian diversity at differing spatial and temporal scales. We sampled 10 wetland sites along floodplains in southern Brazil. We classified the sites as reference or altered ponds according to the preservation degree and presence of human impact. The amphibian monitoring was conducted through calling surveys performed between 2015/2016 using an automated recording system that identified the calling male species. We identified 23 species, mainly distributed in the families Hylidae (43%) and Leptodactylidae (34.8%). The altered ponds had lower diversity and higher species dominance. Even ponds with the greatest landscape change revealed a high degree of resilience concerning the amphibian species composition. However, only Boana pulchella was dominant in altered ponds and B. pulchella and Pseudopaludicola falcipes were dominant in reference ponds. A reduction of amphibian richness was driven by the expansion of the urban area and loss of flooding areas. From 1999 to 2016 all sampled sites had their wetland area reduced as the surrounding urban area increased, contributing to the combined loss of habitat and reproductive sites of anurans in subtropical wetlands.
The Influence of Forest Management on Headwater Stream Amphibians at Multiple Spatial Scales
Ecological Applications, 2005
Understanding how habitat structure at multiple spatial scales influences vertebrates can facilitate development of effective conservation strategies, but until recently most studies have focused on habitat relationships only at fine or intermediate scales. In particular, patterns of amphibian occurrence across broad spatial scales are not well studied, despite recent concerns over regional and global declines. We examined habitat relationships of larval and neotenic Pacific giant salamanders (Dicamptodon tenebrosus), larval and adult Pacific tailed frogs (Ascaphus truei) (hereafter ''tailed frogs''), and torrent salamanders (Rhyacotriton spp.) at three spatial scales (2-m sample unit, intermediate, and drainage). In 1998 and 1999, we captured 1568 amphibians in 702 sample units in 16 randomly chosen drainages in the Oregon Coast Range. We examined species-habitat associations at each spatial scale using an information-theoretic approach of analysis to rank sets of logistic regression models developed a priori. At the 2-m sample unit scale, all groups were negatively associated with proportion of small substrate and positively associated with stream width or elevation. At the intermediate scale, Pacific giant salamanders, adult tailed frogs, and torrent salamanders were positively associated with presence of a 46-m band of forested habitat on each side of the stream, and larval tailed frogs were positively associated with presence of forest Ͼ105 years old. Aspect was important for Pacific giant salamanders and larval tailed frogs at the intermediate scale. At the drainage scale, all groups except torrent salamanders were positively associated with proportion of stream length having forested bands Ͼ46 m in width, but further analysis suggests narrower bands may provide adequate protection for some groups. Population-and community-level responses at broad spatial scales may be reflected in species-level responses at fine spatial scales, and our results suggest that geophysical and ecological characteristics, as well as measures of instream habitat, can be used together to prioritize conservation emphasis areas for stream amphibians in managed landscapes.
Landscape Ecology, 2011
Amphibians are an imperiled group of vertebrate animals that typically have biphasic life histories involving a shift from aquatic larval habitats to terrestrial adult habitats. Habitat loss is the greatest threat to amphibians and the importance of the spatial configuration of terrestrial and breeding habitats upon the landscape in determining amphibian persistence is poorly known. The information gap is particularly acute in tropical landscapes that simultaneously host the greatest and most imperiled amphibian fauna on Earth. We installed 125 artificial ponds at different distances from forest fragments embedded in an agricultural matrix in southeastern Brazil. Constructed ponds attracted 13 anuran species; ponds at the forest fragment-matrix transition hosted a greater abundance and higher species richness of frogs and toads than those installed either far from or well within forest fragments. Forest fragments larger than 70 ha in agricultural areas harbored more individuals than smaller fragments. Our results indicate that landscape configuration has an important influence on frog and toad distribution and abundance in tropical agricultural landscapes and we suggest guidelines for maintaining favorable configurations of aquatic and terrestrial habitats for conserving this rich and imperiled species suite.
Patch size matters for amphibians in tropical fragmented landscapes
Several factors may affect the persistence of amphibian species in tropical fragmented landscapes, including the size of remaining patches. While fragment size is considered the main factor acting on species diversity for most taxa, it is less clear how it affects amphibian diversity. A possible reason is that the scale at which previous studies were conducted was too small (only few forest fragments and/or a small range of fragment sizes considered) and/or the sampling method was not the most optimal one. We investigate whether amphibian diversity is affected by patch size in the largest study (in terms of number of fragments and range of fragment sizes) ever conducted in tropical forests. We predicted that larger forest remnants hold higher amphibian diversity compared to smaller patches, and that continuously forest sites were more diverse than forest fragments. We used the visual encounter survey method to collect data from 24 sites (21 forest fragments between 1.9 and 619 ha and three sites within a large continuous forest remnant) located in the Brazilian Atlantic Forest, a highly threatened biodiversity hotspot. We recorded a total of 2839 individuals from 50 species. In line with our predictions, larger fragments had more species, more integer communities and a larger diversity of reproductive modes than smaller ones. In addition, we found higher values for all diversity measures in continuous forest sites compared to fragments. These results indicate that continuous forests are irreplaceable for amphibian conservation, but also show that large forest fragments outside these areas are important for sustaining amphibian diversity. Our study provides robust empirical evidence for the importance of fragment size for amphibian persistence in tropical fragmented landscapes and highlights the need for an adequate sampling design and method that enable the detection of a higher number of species.
Conservation Biology, 2002
Landscapes can be described by two essential features: the composition and spatial arrangement of patches. We considered the roles of these basic landscape descriptors by examining how the occurrence of nine amphibian species in breeding ponds was associated with the area of forested habitat and the proximity of ponds to forested habitat. We used visual and call surveys to compare the composition of amphibian assemblages in 116 ponds adjacent to or separated from forest and surrounded by different amounts of forested land. The area of forest and pond adjacency to forest were not associated (t ϭ Ϫ 0.13, n isolated ϭ 64, n connected ϭ 52, p ϭ 0.21), which means these factors can manifest their effects separately. We used logistic regression to test predictions about associations between each species and forest area and to test for associations with pondforest adjacency. Seven of nine species were associated with forest area. Wood frogs (Rana sylvatica), green frogs (Rana clamitans), eastern newts (Notopthalmus viridescens), spotted salamanders (Ambystoma maculatum), and salamanders of the blue-spotted/Jefferson's complex (Ambystoma laterale/A. jeffersonianum) were more likely to occupy ponds in more forested areas, whereas leopard frogs (Rana pipiens) and American toads (Bufo americanus) were negatively associated with forest area. Three species were associated with pondforest adjacency. Spotted salamanders and salamanders of the blue-spotted/Jefferson's complex were more likely to occupy ponds that were adjacent to forest. In areas with little forest, leopard frogs were more likely to occur in adjacent ponds, but the reverse was true for areas with extensive forests. Our results suggest that the composition of the landscape surrounding breeding ponds is associated with the likelihood of occurrence of most of the species examined and that landscape configuration is also important for a smaller subset of species.
Basin-Scale Surveys of Stream-Associated Amphibians in Intensively Managed Forests
Journal of Wildlife Management, 2010
Conservation and management of native species on landscapes managed for intensive wood production represents an ongoing challenge to forest managers. Previous research suggests that impacts of forest practices on stream-associated amphibians (SAA; giant [Dicamptodon spp.], torrent [Rhyacotriton spp.], and plethodontid [Plethodon spp.] salamanders and coastal tailed frogs [Ascaphus truei]) in Oregon and Washington, USA, vary spatially and temporally as a result of biotic and abiotic factors, some of which can be influenced by management treatments. Although individual harvest units can encompass multiple stream reaches and entire second-order basins, nearly all published research studies used stream reaches of various lengths as sample units. To address this discrepancy between research and operational scales, we sampled first-, second-, and third-order streams in 70 randomly selected third-order basins in Oregon and Washington in 2007 and 2008 to estimate detection and occupancy parameters for SAA and to develop basin-level density estimates for different species and genera. We estimated occupancy probabilities of 0.99 (95% CL 5 0.96-1.00) for torrent and giant salamanders, 0.93 (95% CL 5 0.76-0.92) for Dunn's salamanders (Plethodon dunni), and 0.60 (95% CL 5 0.46-0.72) for tailed frogs. Our estimates can be compared with estimates for unmanaged third-order basins in Oregon and Washington to provide a relative measure of potential impacts of forest management on these taxa. In addition, our estimates provide baseline information with which to assess potential effects of future environmental changes on the 4 genera.