Ants on the Move: Resource Limitation of a Litter‐nesting Ant Community in Costa Rica¹

Abstract

The leaf litter of tropical wet forests is replete with itinerant ant nests. Nest movement may help ants evade the constraints of stress and disturbance and increase access to resources. I studied how nest relocation and environmental factors may explain the density, size, and growth of leaf litter ant nests. I decoupled the relationships among litter depth, food abundance, and nest availability in a 4-mo manipulation of food and leaf litter in a community of litter-nesting ants in a lowland wet forest in Costa Rica. Over 4 mo, 290 1 m 2 treatment and control plots were sampled without replacement. Nest densities doubled in response to food supplementation, but did not decrease in response to litter removal or stress (from litter trampling). The supplementation of food increased the utilization of less favored nesting materials. In response to food supplementation and litter trampling, arboreal ants established nests in the litter, and growth rates of the most common ants (Pheidole spp.) increased. Colony growth was independent of colony size and growth rates of the most abundant ants. In general, I conclude that litter-nesting ant density is driven primarily by food limitation, that nest relocation behavior significantly affects access to resource and the demographic structure of this community, and that nest fission may be a method to break the growth-reproduction trade-off. RESUMENLa hojarasca de bosques húmedos tropicales está repleta de nidos itinerantes de hormiga. El movimiento de nido puede ayudar a las hormigas a evadir las limitaciones producidas por tensión y perturbación y a la vez aumentar el acceso a recursos. lLas relaciones entre la profundidad de la hojarasca, la abundancia de alimento y la disponibilidad de nido fueron desconectadas durante 4 meses debido a la manipulación de hojarasca y de alimento en un bosque húmedo bajo en Costa Rica. Durante 4 meses, 290 parcelas de tratamiento y control de 1 m 2 fueron muestreadas sin reemplazo. Las densidades de nido doblaron en respuesta al alimento suplementario, pero no disminuyeron en respuesta a la eliminación de la hojarasca y la tensión (causada al pisotear la hojarasca). El alimento suplementario aumentó la utilización de materiales menos favorecidos para anidar. Debido al alimento suplementario y la tensión en la hojarasca, las hormigas arbóreas establecieron nidos en la hojarasca y las tasas de crecimiento de las hormigas más comunes (Pheidole spp.) aumentaron. El crecimiento de la colonia era independiente del tamaño de la colonia, y de las tasas de crecimiento de las hormigas más abundantes. En terminos generales, se concluye que la densidad de las hormigas en la hojarasca es gobernada primordialmente por la limitación de alimento, que la conducta de transladar nido afecta significativamente el acceso a recursos y a la estructura demográfica de esta comunidad, y que la fisión de nido puede ser un método para romper el intercambio entre crecimiento y reproducción.

Differential response of ants to nutrient addition in a tropical Brown Food Web

“…One of the main goals of this study was to study the response of leaf-litter ants to an increased availability of prey, by adding resources without modifying the habitat (in contrast with litter addition experiments, see Ponge et al, 1993;McGlynn, 2006). However, the manipulations of our study ultimately also resulted in alterations of habitat volume.…”

“…Three resource addition experiments conducted in the tropics (McGlynn, 2006;McGlynn et al, 2010;Shik and Kaspari, 2010) have been performed by adding dead insects to the plots, but not all the ants are predators. Few BFW studies include ants (but see Milton and Kaspari, 2007;Shik and Kaspari, 2010), and neither nutrient addition experiments nor BFW studies have ever distinguished trophic groups among litter ants.…”

A comparison of the leaf-litter ant fauna in a secondary atlantic forest with an adjacent pine plantation in southeastern Brazil

“…The leaf-litter ant communities in tropical rain forests are characterized by a patchy distribution of colonies, due to both biotic (nest availability, food abundance, food distribution, frequent colony fi ssion, small home ranges) and abiotic constraints (microclimate and disturbance). All these factors may lead to nest aggregations in suitable zones (Soares & Schoereder 2001, Theunis et al 2005, McGlynn 2006.…”

Leaf-litter amount as a factor in the structure of a ponerine ants community (Hymenoptera, Formicidae, Ponerinae) in an eastern Amazonian rainforest, Brazil

“…Moreover, the leaf-litter ant communities presents a dynamic of re-colonization and nest relocation according to this environmental variability, especially due to preferences for some resources (nests or food) (McGlynn 2006;Campos et al 2007;Blüthgen & Feldhaar 2010). Therefore, the high faunistic dissimilarity found at small scales strongly suggests that local scattering of leaflitter density is highly heterogeneous.…”

“…As ants forage and nest according to local nutrient limitation and resource availability (McGlynn & Kirksey 2000;McGlynn et al 2007), and since leaves, small twig sticks, seeds and other special components are unequally distributed in the leaflitter, ants of different kinds or functional groups should also be heterogeneously distributed on the forest floor. For instance, when a species exploits immature ants in its diet, it is more probable to occur (foraging) in leaf-litter patches with high density of ant nests, where this resource abounds (McGlynn 2006). In order to understand the presence or absence of an ant species or functional group, we must also take into account the species biology and community interactions.…”