Demographic Effects of Reproductive Resource Supplementation in a Territorial Frog, Dendrobates Pumilio

Abstract

To determine whether tadpole—rearing sites (bromeliads) or oviposition substrates (leaf litter) were the objects of male defense in the position—dart frog Dendrobates pumilio, I experimentally increased the availability of these two resources in a complete two—factor factorial design for variance analysis and examined the demographic response of the frogs. I also examined the effects of resource addition on sex ratio and age—structure. Mark—recapture data were collected on experimental and control plots during the 7 mo of the treatment period, during which 4754 observations were made on 1208 marked individuals. I used a three—factor repeated measures analysis of variance to determine if resource addition affected density. The addition of oviposition substrate did not result in increased density, but the addition of bromeliads led to an increase in the density of adult males and females on treatment plots relative to the controls. To document which demographic variables were affected, animals were classified as immigrants, recruits, or survivors; all losses were assumed to be the result of emigration. The demographic variables were analyzed with three—factor repeated measures ANOVA. The increases in males resulted from increased survival on treatment plots, whereas the increase in females resulted from increased immigration, recruitment, and the accumulation of survivors. Sex ratio was not affected by resource supplementation but age—structure was; litter addition increased the proportion of juveniles on treatment plots. The population—level response suggests that bromeliad availability is limited and this resource is defended by males.