Diurnal foraging ant–tree co‐occurrence networks are similar between canopy and understorey in a Neotropical rain forest

Discovery-defense strategy as a mechanism of social foraging of ants in tropical rainforest canopies

Many hypotheses have been proposed to explain the coexistence of ants sharing similar food resources, including ecological trade-offs, however, these hypotheses have mostly been tested in ground-dwelling ant communities. For instance, the discovery-dominance trade-off hypothesis states that species with overlapping food resources differ in their ability to find and dominate resources. However, ant species may use different strategies to share food resources, including discovery-defense, in which the first species to arrive at a food resource maintains control of it. Here, we evaluated whether the discovery-dominance trade-off hypothesis, or the discovery-defense strategy could be a mechanism that promotes coexistence of ant species in the canopy of highly diverse tropical forest canopies. We evaluated the succession of ant species on 72 baits exposed on 24 trees during 13 observation periods (15–195 min) in the canopy of a tropical rain forest in Mexico. In general, we observed little variation in ant species composition (i.e., low β-diversity values) during the 195 min of bait exposure. Moreover, we found that ant species with the greatest ability to discover new food resources were those that dominated them. These findings empirically show that the discovery-defense strategy can be a social foraging strategy in rain forest canopy ants and reject the discovery-dominance trade-off. In short, our results highlight the importance of the discovery of a food resource in the canopy of a tropical rain forest, allowing it to be dominated.

Distance–decay patterns differ between canopy and ground ant assemblages in a tropical rainforest

Both decreases in compositional similarity with increasing geographic distances between sites (i.e. distance–decay relationship) and vertical stratification of species composition are key issues in ecology. However, the intersection between these two trends has scarcely been investigated. Here we use identical sampling methods in the canopy and at ground level in a tropical rainforest remnant on the coast of the Gulf of Mexico to evaluate, for the first time, a distance–decay relationship within vertical strata in insect assemblages. We found that the ant assemblage was vertically stratified; ant species richness was higher at ground level than in the canopy, and the species composition differed between the two vertical strata. Moreover, we observed that β-diversity increased with geographic distance at ground level, but not in the canopy strata. However, contrary to our prediction, there was less species turnover (lower β-diversity) between vertical strata than between trees. These findings may reflect differences in the dispersal capacity and nest habit of ants from each vertical stratum, and also habitat heterogeneity on the horizontal scale, e.g. the species of sampled trees. Our results illustrate the importance of sampling more than one vertical stratum to understand the spatial distribution patterns of biological diversity in tropical rainforests.