Slave-maker ant competition for a shared host and the effect on coevolutionary dynamics

Competition is an important evolutionary force behind population regulation and community structures. The degree of competition symmetry ( competition hierarchies) between species determines coexistence, exclusion, or niche differentiation. Intraspeci. c competition, however, is an important component in dictating levels of symmetry/ asymmetry between species and should be accounted for when attempting to understand interspeci. c evolutionary or ecological outcomes. Some social parasites compete for access to a common host and, thus, adhere to both parasite - host and predator - prey coevolutionary and ecological dynamics. Here I examine tripartite evolutionary dynamics with respect to intraspeci. c competition of two sympatric slave- making social parasites in the family of ants that conduct `` brood raids'' on a shared host species and use the captured brood as a functional work force. Slave- makers were challenged with either a conspeci. c or heterospeci. c parasite and the impact on hosts and parasites was evaluated. Within- species raiding occurred frequently in the `` prudent'' slave- maker but was almost nonexistent in the `` virulent'' slave- maker. Although intraspeci. c raiding led to larger single prudent slave- maker colonies, the preservation of two independent virulent slavemaker colonies had an early and a more devastating effect on the host. However, in response to synchronized raiding phenologies, the prudent slave- maker emerged as the better direct competitor against the virulent slave- maker. Sex ratios were male biased in the virulent slavemaker colonies but numerically equal ( hence female biased) in prudent slave- maker colonies. Combined, these results suggest that interspeci. c parasite interactions have produced ecological shifts in both slave- makers and attenuated the coevolutionary arms race between the prudent slave- maker and the shared host in sympatric populations.