When trade‐offs interact: balance of terror enforces dominance discovery trade‐off in a local ant assemblage

Abstract

Summary 1.Trade-offs underpin local species coexistence. Trade-offs between interference and exploitative competitive ability provide a mechanism for explaining species coexistence within guilds that exploit overlapping resources. 2. Omnivorous, leaf litter ants exploit a shared food base and occur in species-rich assemblages. In these assemblages, species that excel at usurping food items from other species are poor at finding food items first. In assemblages where some members are attacked by phorid fly parasitoids, host species face an additional trade-off between defending themselves against parasitic attack and maximizing their competitive abilities. Host species thus face two trade-offs that interact via the trait-mediated indirect interaction generated by phorid defence behaviour. 3. In this study we test for the existence of these trade-offs and evaluate the predictions of a model for how they interact in an assemblage of woodland ants in which two behaviourally dominant members are attacked by phorid fly parasitoids as they attempt to harvest food resources. 4. The major findings are that unparasitized species in the assemblage follow a dominancediscovery trade-off curve. When not subject to attack by phorid flies, host species violate that trade-off by finding resources too quickly for their level of behavioural dominance. In contrast, when attacked by their phorid parasitoids, the host species dominance drops such that they fall into the assemblage trade-off. 5. These results match the predictions of the balance of terror model, which derives the optimal host response to parasitism, indicating that the host species balance the competing fitness costs of reduced competitive dominance and loss of workers to parasitism. This result supports the view that understanding the structure of ecological communities requires incorporating the indirect effects created by trait plasticity.

Temperature-mediated coexistence in temperate forest ant communities

“…One problem with assessing dominance rank is that not every species pair interacts in nature. In a recent study, LeBrun and Feener (2007) used a mathematical algorithm developed for rating American college football teams which takes into consideration non-interacting species to assess ranks in transitive dominance hierarchies (because not every football team plays every other football team). Although using a different dominance metric could slightly alter the order of dominance ranks, it is unlikely to make species such as A. rudis and P. faisonensis appear dominant, since both of these species are almost always submissive in interspecific encounters.…”

“…2 ? ÁÁÁ) and multiplied by the number of pitfall traps in which species x was recorded (see LeBrun and Feener, 2007 for details).…”

“…Specifically, we examine the possibility of a dominance-thermal tolerance tradeoff whereby differences in foraging temperature regimes allow behaviorally dominant and subordinate ant species to coexist. We also consider the alternative hypothesis that the ability of subordinate species to discover and exploit food resources allows them to coexist with dominant species (Fellers, 1987;LeBrun and Feener, 2007).…”

Variation in resource size distribution around colonies changes ant–parasitoid interactions

“…Behavioral responses to the threat of parasitoid attack usually consist of foragers returning immediately to the nest or hiding under leaf litter. In some cases this leads to loss of resources to competitors and reorganization of community dominance hierarchies (Orr et al, 1995;LeBrun and Feener, 2002;LeBrun, 2005;Adler et al, 2007;LeBrun and Feener, 2007;Wilkinson and Feener, 2007). Consequently, the large resources that dominant ant species are best suited to compete for may ultimately lead to increased mortality risk from parasitoids.…”

Exploitative Competition and Risk of Parasitism in Two Host Ant Species: The Roles of Habitat Complexity, Body Size, and Behavioral Dominance

“…Psyche Ant communities are not traditionally considered to be structured by top-down forces from predators. However, community composition can be influenced by specialist Dipteran parasitoids (Apocephalus: Phoridae) that attack host ant species, induce behavioral responses in their hosts, and alter the outcome of interspecific competition in the community [26][27][28][29][30][31][32]. Habitat complexity has been shown to benefit the host ant species Pheidole diversipilosa and P. bicarinata during interference competition with nonhost ant species by providing refuge from parasitoids.…”