Are vultures birds, and do snakes have venom, because of macro- and microscavenger conflict?

Abstract

I outline models that describe vertebrate and microbial competition for carrion resources and help explain the resultant morphologies observed in extant vertebrate scavengers. Odors from microbial decomposition signal the presence of a carcass to vertebrate scavengers. Therefore, microbes must consume carcasses rapidly or evolve toxic defenses to protect themselves and their resource from their vertebrate competitors. Similarly, macroscavengers must evolve traits that allow rapid detection of carcasses or develop chemical defenses against microbial toxins. My modeling suggests that the most efficient macroscavenger adaptations increase the probability of carcass detection, which explains why highly vagile species, such as vultures, are the most obligate of vertebrate scavengers. Empirical data from vultures and from a scavenging snake species suggest that evolutionary pressures favor detection maximizers relative to toxification minimizers in competitive interactions for carcasses. However, detoxification mechanisms allow safe consumption of carrion and may have influenced the development of the complex digestive enzymes and delivery systems now seen in minimally vagile scavenging snakes. © 2006 American Institute of Biological Sciences.