Does a Frog Change its Diet along a Successional Forest Gradient? The Case of the Shovel-Nosed Treefrog (Diaglena spatulata) in a Tropical Dry Forest in Western Mexico
Biologists have increasingly recognized the importance of secondary forests as facilitators of passive landscape restoration and recovery of faunal communities in landscapes fragmented by farming. To evaluate the role of secondary forests as providers of food resources for anurans, we studied the diet of the Shovel-Nosed Treefrog (Diaglena spatulata) from five vegetation stages of tropical dry forest (pasture, early forest, young forest, intermediate forest, and old-growth forest) on the coast of Jalisco, Mexico. We examined the stomach content of 97 individuals using a stomach-flushing method. We found 14 different types of prey (Class or Order) in the frog's diet. Araneae, Lepidoptera, and Orthoptera occurred in frogs from all five vegetation stages. We recorded the highest number of prey types (11) in the young and intermediate forest stages, and the highest prey volume and prey frequency in stomachs from frogs inhabiting the old-growth forest. We found no difference in size or body condition of frogs among vegetation stages, but there was a positive relation between size and body condition with the volume of stomach content. Our results suggest that D. spatulata presents high dietary plasticity and that secondary stages of dry tropical forest contribute to the persistence of this species in human-modified landscapes. La importancia de los bosques secundarios como facilitadores de la restauración del paisaje, así como de la recuperación de las comunidades faunísticas en paisajes fragmentados por actividades agropecuarias es cada vez más reconocida. Para evaluar la importancia de los bosques secundarios como proveedores de recursos alimenticios para los anuros, estudiamos la dieta de la rana pico de pato (Diaglena spatulata) en cinco estados de sucesión del bosque tropical caducifolio (pastizal, bosque temprano, bosque inicial, bosque intermedio y bosque maduro) en la costa de Jalisco, México. Examinamos el contenido estomacal de 97 individuos mediante lavado estomacal, encontrando 14 tipos de presas (Clase u Orden). Los órdenes Araneae, Lepidoptera y Orthoptera se encontraron en ranas de los cinco estados de sucesión. Registramos el mayor número de tipos de presa (11) en el bosque inicial y en el intermedio, mientras que en el bosque maduro encontramos el mayor volumen y frecuencia de presas por contenido estomacal. Aunque no encontramos diferencias en la talla o condición corporal de los individuos entre los estados de sucesión, si registramos una relación positiva entre talla y condición corporal con el volumen del contenido estomacal. Nuestros resultados sugieren que D. spatulata presenta una alta plasticidad dietaria y que los estados secundarios del bosque tropical caducifolio contribuyen a la persistencia de esta especie en paisajes modificados por actividades humanas.Abstract
Resumen
Study area location in the region of Chamela, Jalisco, Mexico. Black dots are sampling sites. Pasture = Z0-0, R0-0, SC0-0; early forest = Z5-6, SC5-6, SM5-6; young forest = C8-10, SC8-10, R8-10; intermediate forest = C15-17, R15-17, SC15-17; old-growth forest = T1, T2, G.
Average of prey volume (a) and prey frequency (b) of D. spatulata in tropical dry forest vegetation stages (pasture P, 0 yr since abandonment; early forest EF, 5–6 yr since abandonment; young forest YF, 8–10 yr since abandonment; intermediate forest IF, 15–17 yr since abandonment; old growth forest OGF, no signs of human disturbance). Bars represent the 95% confidence intervals.
Average body condition (A) and SVL (B) in females and males of D. spatulata. MIBC = mass index of body condition. Bars represent the 95% confidence intervals.
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