HARVEST RATES AND PATCH-USE STRATEGY OF EGYPTIAN FRUIT BATS IN ARTIFICIAL FOOD PATCHES

FOOD SELECTION AND USE OF SPACE BY DIDELPHIS PERNIGRA (DIDELPHIDAE: MAMMALIA) IN AN ANDEAN SUBURBAN ENVIRONMENT

Cities have grown throughout the Andes and we know little about the ecology of those species that tolerate them, limiting our options to do conservation. We applied optimal foraging theory to examine the behavior of the Andean White-eared Opossum (Didelphis pernigra), in a suburban area in Bogotá, Colombia. We used the giving-up density technique, which uses the amount of food left in a feeding patch, to evaluate whether the opossum’s foraging costs were affected by the height of food from the ground, and the quality and quantity of food. We also evaluated whether the spatial heterogeneity of the study site affected the opossum’s foraging. We used an artificial feeding patch to test these ideas. When food was either concentrated and, in less amount, (concentrated food) or diluted and more amount (diluted food), the opossums preferred to forage at 2 m than at 0.5 m, but concentrated food at 0.5 m was not significantly different from diluted food at 2 m. The opossums’ habitat use was affected by the spatial heterogeneity at the study site and animals preferred foraging along metal fences than on live fences made of trees. When a cable allowed connection between the metallic and live fences, the value of food patches at the live fence appeared to increase.  Thus, although the opossums need resources associated with natural environments, our results suggest that there are human modifications that can benefit them, such as those that reduce the risk of predation and favor their mobility in suburban environments.

Sugars are complementary resources to ethanol in foods consumed by Egyptian fruit bats

Food resources are complementary for a forager if their contribution to fitness is higher when consumed together than when consumed independently,e.g. ingesting one may reduce the toxic effects of another. The concentration of potentially toxic ethanol, [EtOH], in fleshy fruit increases during ripening and affects food choices by Egyptian fruit bats, becoming deterrent at high concentrations (⩾1%). However, ethanol toxicity is apparently reduced when ingested along with some sugars; more with fructose than with sucrose or glucose. We predicted (1) that ingested ethanol is eliminated faster by bats eating fructose than by bats eating sucrose or glucose, (2)that the marginal value of fructose-containing food (food+fructose) increases with increasing [EtOH] more than the marginal value of sucrose- or glucose-containing food (food+sucrose, food+glucose), and (3) that by increasing [EtOH] the marginal value of food+sucose is incremented more than that of food+glucose. Ethanol in bat breath declined faster after they ate fructose than after eating sucrose or glucose. When food [EtOH] increased, the marginal value of food+fructose increased relative to food+glucose. However,the marginal value of food+sucrose increased with increasing [EtOH] more than food+fructose or food+glucose. Although fructose enhanced the rate at which ethanol declined in Egyptian fruit bat breath more than the other sugars, the bats treated both fructose and sucrose as complementary to ethanol. This suggests that in the wild, the amount of ethanol-containing fruit consumed or rejected by Egyptian fruit bats may be related to the fruit's own sugar content and composition, and/or the near-by availability of other sucrose- and fructose-containing fruits.