The interaction between the aphid Aphis coreopsidis (Thomas) (Hemiptera, Aphididae) and the ant Camponotus sp.1 (Hymenoptera, Formicidae) on the plant Bidens pilosa L. (Asteraceae) was studied. We manipulated the presence of ants and other insects to understand the effects of this aphid-ant interaction on: (a) the growth of A. coreopsidis population, (b) the seed production of B. pilosa, (c) the density of predator spiders. The growth of the A. coreopsidis population was positively affected by attending ants, showing greater increase on ant-present control plants than on ant-excluded plants. The density of aphids on control plants was positively correlated with the density of attending ants, while the density of aphids on ant-excluded plants was positively correlated with the density of spiders. Plants with ants had a significantly lower quantity of viable seeds than those without ants. These results show that: (a) the presence of Camponotus ants reduces the number of predator spiders on B. pilosa, (b) the population of A. coreopsidis increases when attended by the ants, (c) this increase in aphid density as a result of ant attendance reduces the number of viable seeds of B. pilosa, and thus (d) an interspecific interaction between two species can have an indirect negative fitness effect on other partners.

The expansion of agriculture has led to forest loss and fragmentation, resulting in dramatic biodiversity impoverishment. Surprisingly, few studies have assessed forest fragmentation effects on leaf‐cutting ant assemblages, and none has dealt with effects on their community richness and composition, despite their known role as key herbivores and ecosystem engineers. We analysed forest area and edge effects on leaf‐cutting ant abundance, richness and assemblage composition, by recording and identifying colonies along edge and interior transects in 12 Chaco Serrano forest remnants of different sizes, in Central Argentina. We also explored leaf‐cutting ant presence in the adjacent soybean matrix. We recorded five leaf‐cutting ant species, in the genus Acromyrmex. In the soybean matrix, colonies of three species were observed, which were also found at the forest edge. Within the forest, edges sustained more species and colonies than interior habitats, whereas forest area was linked positively to colony abundance. Taxonomic composition of leaf‐cutting ant assemblages reflected both area and edge effects. Our results revealed overall positive edge and area effects on leaf‐cutting ant communities, highlighting differential species‐specific responses and a possible role for Acromyrmex crassispinus as a forest status indicator. According to our findings, an increase in edge habitats may favour most leaf‐cutting ant species, providing a suitable interface for access to the cultivated matrix, but hindering species associated with undisturbed forest conditions. As leaf‐cutting ants are acknowledged as cornerstones of ecosystem functioning, the consequences of these trends may be far reaching.

Context Small fragments of natural habitats with an increased proportion of edges are common landscape traits following agricultural expansion. Consequences of habitat fragmentation are widely documented. However, functional and mechanistic approaches are still needed in order to understand these changes. Objectives We studied habitat loss and edge effects on ant communities, addressing changes in species and functional group diversity, and the relative importance of b-diversity components. Methods In an endangered Neotropical forest, we sampled ants in edge and interior habitats using pitfall traps, during three summers (28 sites). We calculated taxonomic, phylogenetic and functional diversity and partitioned taxonomic and functional b-diversity into replacement and loss/gain components. Results We found more species and functional groups at edge than interior habitats, and four species were edge indicators. Habitat loss negatively affected total abundance and that of particular functional groups (fungus-growers and cryptic species) but had a positive effect on taxonomic, phylogenetic and functional diversity as well as abundance of opportunists and predators. Species and functional group replacement drove b-diversity, being linked to habitat loss. However, interactions between habitat loss and edges explained the loss/gain of taxonomic and functional composition. Conclusions Fragmentation led to enriched ant communities at edges, possibly resulting from a higher influx of matrix species as edges become pervasive. This highlights the need to assess the spillover between habitats to understand its influence. Moreover, species replacement and the decrease of functional groups due to habitat loss could have an impact on ecosystem processes in which ants play an important role.

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