Resource Partitioning in a Neotropical Necrophagous Scarab Guild

Abstract

Data collected from naturally occurring and artificially placed vertebrate carcasses were examined for the purpose of revealing mechanisms permitting the coexistence of carrion feeders in tropical forests. Studies concentrated on the necrophagous scarab guild and were conducted at three sites in the Panama Canal Zone during the periods January-June 1974, January-May 1975, and September-December 1975. Only mammalian carcasses were discovered at the principal study site, Barre Colorado Island (BCI). The seven species represented were among the 15 largest mammalian species known to occur on the island. Naturally occurring carcasses were most abundant late in the wet season, but the rate of utilization of carcasses was greatest in the dry season. Vertebrate scavengers appeared to be the most important consumers of carrion on BCI, and were the primary cause of high carcass utilization rates in the dry season. Invertebrate carrion consumers were rare in the dry season, but in the wet season probably consumed as much as 50% of the available vertebrate carrion. Field experiments demonstrated that mammalian carcasses were consumed by arthropods faster than bird carcasses, and that lizard carcasses were consumed very slowly, if at all. Consumption time by arthropods was directly proportional to carcass size, and fresh carcasses attracted many more species of arthropods than did older carcasses. Larval dipterans dominated carrion during the wet season. They could render a typical large (2 kg) vertebrate carcass unsuitable for other consumers in three days and consume 80% of the carcass in nine days. Larval dipterans also provided the food of a large group of predators. Potential competitors of larval dipterans (vertebrates, scarab beetles) were only successful if they arrived at the carcass quickly and removed portions of the carcass before larval dipteran populations rendered the food unsuitable. The necrophagous scarab guild on BCI contained 25 species and partitioned food along several dimensions. Differences in the techniques of removing food from a carcass for subsequent consumption or egg-laying appeared to be the most important in achieving species separation within this guild. Along temporal dimensions, both wet vs. dry season and day vs. night were important in species separation, Also of importance was the ability of species to consume a variety of foods, both carrion and other resources. Body size and trophic apparati were also of some importance. A linear dominance hierarchy, based on fighting ability, exists in the necrophagous scarab guild and is directly correlated with the type of food removal. Species biomass was also directly correlated with the dominance hierarchy. Ball-rolling species, for example, were always capable of taking food away from other species and represented the largest portion of the guild biomass.