Long-Term Impacts of Poaching on Relatedness, Stress Physiology, and Reproductive Output of Adult Female African Elephants

摘要

Widespread poaching prior to the 1989 ivory ban greatly altered the demographic structure of matrilineal African elephant (Loxodonta africana) family groups in many populations by decreasing the number of old, adult females. We assessed the long-term impacts of poaching by investigating genetic, physiological, and reproductive correlates of a disturbed social structure resulting from heavy poaching of an African elephant population in Mikumi National Park, Tanzania, prior to 1989. We examined fecal glucocorticoid levels and reproductive output among 218 adult female elephants from 109 groups differing in size, age structure, and average genetic relatedness over 25 months from 2003 to 2005. The distribution in group size has changed little since 1989, but the number of families with tusked old matriarchs has increased by 14.2%. Females from groups that lacked an old matriarch, first-order adult relatives, and strong social bonds had significantly higher fecal glucocorticoid values than those from groups with these features (all females R-2 = 0.31; females in multiadult groups R-2 = 0.46). Females that frequented isolated areas with historically high poaching risk had higher fecal glucocorticoid values than those in low poaching risk areas. Females with weak bonds and low group relatedness had significantly lower reproductive output (R-2[U] = 0.21). Females from disrupted groups, defined as having observed average group relatedness 1 SD below the expected mean for a simulated unpoached family, had significantly lower reproductive output than females from intact groups, despite many being in their reproductive prime. These results suggest that long-term negative impacts from poaching of old, related matriarchs have persisted among adult female elephants 1.5 decades after the 1989 ivory ban was implemented.La caceria furtiva generalizada antes de la prohibicion del comercio de marfil en 1989 altero la estructura demografica de grupos familiares matrilineales de elefante africano (Loxodonta africana) en muchas poblaciones por la disminucion del numero de hembras adultas, viejas. Evaluamos los impactos a largo plazo de la caceria furtiva investigando correlaciones geneticas, fisiologicas y reproductivas de una estructura social perturbada resultante de la caceria furtiva intensiva de una poblacion de elefante africano en el Parque Nacional Mikumi, Tanzania, antes de 1989. Examinamos los niveles de glucocorticoides fecales y la productividad de 218 hembras adultas de 109 grupos de diferente tamano, estructura de edades y relacion genetica promedio durante 25 meses entre 2003 y 2005. La distribucion del tamano de los grupos ha cambiado poco desde 1989, pero el numero de familias con matriarcas viejas con colmillos ha incrementado en 14.2%. Las hembras de grupos que carecian de una matriarca vieja, parientes adultos de primer orden y lazos sociales estrechos tenian valores de glucocorticoides significativamente mayores que los grupos con esas caracteristicas (todas las hembras R-2 = 0.31; hembras en grupos multiadultos R-2 = 0.46). Las hembras que frecuentaban lugares aislados con riesgo historicamente alto de caza furtiva tuvieron niveles de glucocorticoides mas altos que en las areas con bajo riesgo de caza furtiva. Las hembras con relaciones debiles y un bajo grado de relacion entre grupos tuvieron una productividad significativamente menor (R-2[U] = 0.21). Las hembras de grupos desestabilizados, definidas con base en un grado observado de relacion entre grupos 1 DS debajo de la meia esperada para una familia no cazada simulada, tuvieron una productividad significativamente menor que las hembras de grupos intactos, no obstante que muchas estaban en su mejor momento reproductivo. Estos resultados sugieren que los impactos negativos a largo plazo de la caceria de matriarcas viejas emparentadas han persistido entre las hembras adultas jovenes 1.5 decadas despues de la prohicion del comercio de marfil.