Amphibian Distributions in a Landscape of Forests and Agriculture: an Examination of Landscape Composition and Conf iguration

: 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 = −0.13, nisolated = 64, nconnected = 52, p = 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 pond-forest 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 pond-forest 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. Resumen: Los paisajes pueden ser descritos por dos caracteristicas esenciales: la composicion y la disposicion de fragmentos. Consideramos la funcion de estos descriptores basicos de paisaje analizando como se asocio la presencia de nueve especies de anfibios en estanques de reproduccion con el area de habitat boscoso y la cercania de estanques a habitat boscoso. Utilizamos registros visuales y auditivos para comparar la composicion de comunidades de anfibios en 116 estanques adyacentes a un bosque o separados del mismo y rodeados de diferentes cantidades de terreno boscoso. El area de bosque y la distancia de los estanques del al bosque no estuvieron asociados ( t = −0.13, naislado= 64, nconectado = 52, p = 0.21) lo que significa que estos factores pueden manifestar sus efectos por separado. Utilizamos regresion logistica para probar predicciones referentes a asociaciones entre cada especie y el area de bosque y para comprobar si las asociaciones si relacionaban con la adyacencia de los estanques al bosque. asociaciones con la adyacencia de estanques - bosque. Siete de nueve especies se asociaron con el area de bosque. Ranas de bosque ( Rana sylvatica), ranas verdes ( Rana clamitans), tritones del este ( Notopthalmus viridescens), salamandras manchadas (Ambystoma maculatum) y salamandras del complejo manchas azules/Jefferson (Ambystoma laterale/A. jeffersonianum) ocuparon mas estanques en areas mas boscosas, mientras que ranas leopardo ( Rana pipiens) y sapos americanos ( Bufo americanus) se asociaron negativamente con el area de bosque. Tres especies se asociaron con la adyacencia al bosque. Salamandras manchadas y salamandras del complejo manchas azules/Jefferson tenian mayor probabilidad de ocupar estanques adyacentes a bosque. En areas con poco bosque, ranas leopardo ocurrieron en estanques adyacentes, pero lo contrario sucedio en areas con bosques extensos. Nuestros resultados sugieren que la composicion del paisaje que rodea a los estanques de reproduccion se asocia con la probabilidad de ocurrencia de la mayoria de las especies analizadas y que la configuracion del paisaje tambien es importante para un subconjunto de especies mas pequeno.