Intraspecific competition affects population size and resource allocation in an ant dispersing by colony fission

Abstract

Abstract. Intraspecific competition is a pervasive phenomenon with important ecological and evolutionary consequences, yet its effect in natural populations remains controversial. Although numerous studies suggest that in many cases populations across all organisms are limited by density-dependent processes, this conclusion often relies on correlative data. Here, using an experimental approach, we examined the effect of intraspecific competition on population regulation of the ant Aphaenogaster senilis. In this species females are philopatric while males disperse by flying over relatively long distances. All colonies were removed from 15 experimental plots, except for one focal colony in each plot, while 15 other plots remained unmanipulated. After the first reproductive season, nest density in the experimental plots returned to a level nonsignificantly different from that in the control plots, which was not expected if the populations were indeed regulated by density-independent phenomena. In both the control plots and the experimental plots colonies remained overdispersed throughout the experiment, suggesting colony mutual exclusion. Nests outside the plots rapidly extended their foraging span, but we did not detect any significant inward migration into the experimental plots. Experimental reduction in density did not significantly affect the focal colonies' biomass, measured just before the first reproductive season. However, the ratio of males to workers-pupae biomasses was smaller in experimental plots, suggesting that colonies there had redirected part of the resources normally allocated to male production to the production instead of new workers. Microsatellite analysis indicated that, after the reproductive season, many colonies in the experimental plots were headed by a young queen that was the mother of the brood but not of the old workers, indicating that reduction in colony density stimulated fission of the remaining colonies. Finally, at the end of the experiment, 14 months after experimental reduction in density, colonies that derived from fission were smaller in the experimental than in the control plots, suggesting that the former had undergone fission at a smaller size than in control plots, which presumably allowed them to colonize the emptied areas. We conclude that colonies adjust resource allocation and colony fission to the degree of intraspecific competition.

Colony life history and lifetime reproductive success of red harvester ant colonies

“…Foitzik, Strätz & Heinze ; Molet, Van Baalen & Peeters ; Foitzik, Achenbach & Brandt ; Boulay et al . ) or nest site availability (Frederickson ). But as Keller () points out, reproductive output, in numbers of reproductives, is not a measure of realized reproductive success, since not all reproductives mate and not all mated queens survive to found new colonies.…”

Are the spatio-temporal dynamics of soil-feeding termite colonies shaped by intra-specific competition?

“…Levings & Traniello, 1981;Ryti & Case, 1986;Folgarait et al, 2007;Boulay et al, 2010), although sometimes, competition does not lead to this pattern (Pielou, 1960;Gordon, 1997). In ants, individuals from different colonies of the same species generally interact agonistically, often resulting in nest overdispersion (e.g.…”

Recognition of caste and mating status maintains monogyny in the ant Aphaenogaster senilis

“…This colony fission strategy guarantees both high foundation success and monogyny. In ants, colony fission occurs, for example, in army ants (Godwald 1995), in desert ants Cataglyphis floricola (Amor et al 2011) and Cataglyphis cursor (Chéron et al 2011) and in the gipsy ant Aphaenogaster senilis (Boulay et al 2010;Galarza et al 2012). Several species of bees, including the honeybee Apis mellifera (Seeley 1985), and the Polybiine wasps (Ross and Mathews 1991) also disperse through fission.…”