Digging Deeper into the Ecology of Subterranean Ants: Diversity and Niche Partitioning across Two Continents

Soil fauna is generally understudied compared to above-ground arthropods, and ants are no exception. Here, we compared a primary and a secondary forest each on two continents using four different sampling methods. Winkler sampling, pitfalls, and four types of above- and below-ground baits (dead, crushed insects; melezitose; living termites; living mealworms/grasshoppers) were applied on four plots (4 × 4 grid points) on each site. Although less diverse than Winkler samples and pitfalls, subterranean baits provided a remarkable ant community. Our baiting system provided a large dataset to systematically quantify strata and dietary specialisation in tropical rainforest ants. Compared to above-ground baits, 10–28% of the species at subterranean baits were overall more common (or unique to) below ground, indicating a fauna that was truly specialised to this stratum. Species turnover was particularly high in the primary forests, both concerning above-ground and subterranean baits and between grid points within a site. This suggests that secondary forests are more impoverished, especially concerning their subterranean fauna. Although subterranean ants rarely displayed specific preferences for a bait type, they were in general more specialised than above-ground ants; this was true for entire communities, but also for the same species if they foraged in both strata

Digging Deeper into the Ecology of Subterranean Ants: Diversity and Niche Partitioning across Two Continents

Soil fauna is generally understudied compared to above-ground arthropods, and ants are no exception. Here, we compared a primary and a secondary forest each on two continents using four different sampling methods. Winkler sampling, pitfalls, and four types of above- and below-ground baits (dead, crushed insects; melezitose; living termites; living mealworms/grasshoppers) were applied on four plots (4 × 4 grid points) on each site. Although less diverse than Winkler samples and pitfalls, subterranean baits provided a remarkable ant community. Our baiting system provided a large dataset to systematically quantify strata and dietary specialisation in tropical rainforest ants. Compared to above-ground baits, 10–28% of the species at subterranean baits were overall more common (or unique to) below ground, indicating a fauna that was truly specialised to this stratum. Species turnover was particularly high in the primary forests, both concerning above-ground and subterranean baits and between grid points within a site. This suggests that secondary forests are more impoverished, especially concerning their subterranean fauna. Although subterranean ants rarely displayed specific preferences for a bait type, they were in general more specialised than above-ground ants; this was true for entire communities, but also for the same species if they foraged in both strata

Trophic and temporal specialization in tropical ants and its relation to species coexistence and ecosystem functioning

Niche differentiation is thought to be one of the main mechanisms how species avoid competitive exclusion. However, to assess differentiation in several niches, a multifactorial approach enabling several niche dimensions to be measured simultaneously is necessary. In this way, the relative effects of several factors can be quantitatively compared in a single ecological context. Tropical ecosystems represent an especially interesting study system where invertebrates in general show high species density and diversity, and consequently high interspecific competition. This is particularly the case in ants where a few dominant species usually displace others from food resources. In view of these factors, we used a new sampling method to simultaneously assess dietary and temporal specialisation of all common ants in a community. We assessed niche position as well as niche breadth (degree of specialisation), for food and for differences between night and day in the paleotropics and neotropics in forests with differing status. Determinants of ecosystem stability have been under intense scrutiny during the last decades. Among these, temporal asynchrony is now recognised as one important factor enhancing stability and has been thoroughly studied on large scales such as seasons or years. However, in order to evaluate the merits of functional asynchrony, it seems fundamental to investigate its role across heteroclite temporal scales in order to properly assess its explanatory power on the diversity-stability relationship

Host-plant dissections reveal contrasting distributions of Crematogaster ants and their symbionts in two myrmecophytic Macaranga species

Here we compared two myrmecophytic systems, Macaranga trachyphylla with Crematogaster captiosa (Mt+Cc) and M. beccariana with C. decamera (Mb+Cd), using a fine-scale dissection of the stems. For the two plant species, for each internode we recorded both contents (ants, coccids, refuse piles) and structure (internode height, numbers of open and occluded ant holes

Host-plant dissections reveal contrasting distributions of Crematogaster ants and their symbionts in two myrmecophytic Macaranga species

1. Ant–plant mutualisms are among the most widespread and ecologically important insect–plant interactions in the tropics. The multitrophic mutualism involving Macaranga plants (Euphorbiaceae) and Crematogaster ants (Formicidae) is the most diverse in Southeast Asia. This interaction also includes trophobiotic scale insects (Coccidae) and nematodes inhabiting ant refuse piles. 2. Here two myrmecophytic systems were compared, Macaranga trachyphylla with Crematogaster captiosa (Mt + Cc) and Macaranga beccariana with Crematogaster decamera (Mb + Cd), using a fine‐scale dissection of the stems. For the two plant species, for each internode, both contents (ants, coccids, refuse piles) and structure (internode height, numbers of open and occluded ant holes) were recorded. 3. There were significant patterns in the vertical distribution of ant colonies and their symbionts in the plant stems. Most coccids were kept in the highest sections of both systems, although Mb + Cd hosted a broader range of coccid species than Mt + Cc. Three nematode species were recorded, but with a rather low specificity to plant or ant species. Furthermore, the fine‐scale distribution showed aggregation of closed holes with ant brood and separation of nematode‐infested refuse piles from eggs. 4. The results of this study indicate that ants manipulate spatial colony structure via distribution of brood, holes and the symbionts. It is suggested that ants optimise the location of refuse piles and occluded holes via spatial heterogeneity in their distribution among internodes. This paper discusses the protective role of occluded holes and demonstrates some general interactions with other symbiotic fauna

Ant-mediated ecosystem processes are driven by trophic community structure but mainly by the environment

The diversity and functional identity of organisms are known to be relevant to the maintenance of ecosystem processes but can be variable in different environments. Particularly, it is uncertain whether ecosystem processes are driven by complementary effects or by dominant groups of species. We investigated how community structure (i.e., the diversity and relative abundance of biological entities) explains the community-level contribution of Neotropical ant communities to different ecosystem processes in different environments. Ants were attracted with food resources representing six ant-mediated ecosystem processes in four environments: ground and vegetation strata in cropland and forest habitats. The exploitation frequencies of the baits were used to calculate the taxonomic and trophic structures of ant communities and their contribution to ecosystem processes considered individually or in combination (i.e., multifunctionality). We then investigated whether community structure variables could predict ecosystem processes and whether such relationships were affected by the environment. We found that forests presented a greater biodiversity and trophic complementarity and lower dominance than croplands, but this did not affect ecosystem processes. In contrast, trophic complementarity was greater on the ground than on vegetation and was followed by greater resource exploitation levels. Although ant participation in ecosystem processes can be predicted by means of trophic-based indices, we found that variations in community structure and performance in ecosystem processes were best explained by environment. We conclude that determining the extent to which the dominance and complementarity of communities affect ecosystem processes in different environments requires a better understanding of resource availability to different species

AMF Raw data

Species-Abundance-Matrix from all five sites: NPF (Neotropical Primary Forest); NSF (Neotropical Secondary Forest); PPF (Paleotropical Primary Forest); PSF (Paleotropical Secondary Forest) and AMF (Australian monsoonal forest). We sampled ants on 64 grid points (A1-A8, B1-B8, C1-C8, D1-D8). We used six different types of baits (bird feces, large prey, small prey, crushed insects, seeds, melezitose, and sucrose). Each bait was placed on each grid point at daytime and nighttime. Pitfall traps were operated for three 10-hr periods between 20h00 to 6h00 (nocturnal traps) or 7h00 to 17h00 (diurnal traps) over three consecutive days when no food resources were presented, such that we obtained a total of 30h of pitfall sampling per grid point and per time of day

Data from: Niche differentiation in rainforest ant communities across three continents

A central prediction of niche theory is that biotic communities are structured by niche differentiation arising from competition. To date, there have been numerous studies of niche differentiation in local ant communities, but, little attention has been given to the macroecology of niche differentiation, including the extent to which particular biomes show distinctive patterns of niche structure across their global ranges. We investigated patterns of niche differentiation and competition in ant communities in tropical rainforests, using different baits reflecting the natural food spectrum. We examined the extent of temporal and dietary niche differentiation and spatial segregation of ant communities at five rainforest sites in the neotropics, paleotropics, and tropical Australia. Despite high niche overlap, we found significant dietary and temporal niche differentiation in every site. However, there was no spatial segregation among foraging ants at the community level, despite strong competition for preferred food resources. Although sucrose, melezitose, and dead insects attracted most ants, some species preferentially foraged on seeds, living insects or bird feces. Moreover, most sites harboured more diurnal than nocturnal species. Overall niche differentiation was strongest in the least diverse site, possibly due to its lower number of rare species. Both temporal and dietary differentiation thus had strong effects on the ant assemblages, but their relative importance varied markedly among sites. Our analyses show that patterns of niche differentiation in ant communities are highly idiosyncratic even within a biome, such that a mechanistic understanding of the drivers of niche structure in ant communities remains elusive