Species-level predation network uncovers high prey specificity in a Neotropical army ant community.

Army ants are among the top arthropod predators and considered keystone species in tropical ecosystems. During daily mass raids with many thousand workers, army ants hunt live prey, likely exerting strong top-down control on prey species. Many tropical sites exhibit a high army ant species diversity (>20 species), suggesting that sympatric species partition the available prey niches. However, whether and to what extent this is achieved has not been intensively studied yet. We therefore conducted a large-scale diet survey of a community of surface-raiding army ants at La Selva Biological Station in Costa Rica. We systematically collected 3,262 prey items from eleven army ant species (genera Eciton, Nomamyrmex and Neivamyrmex). Prey items were classified as ant prey or non-ant prey. The prey nearly exclusively consisted of other ants (98%), and most booty was ant brood (87%). Using morphological characters and DNA barcoding, we identified a total of 1,103 ant prey specimens to the species level. One hundred twenty-nine ant species were detected among the army ant prey, representing about 30% of the known local ant diversity. Using weighted bipartite network analyses, we show that prey specialization in army ants is unexpectedly high and prey niche overlap very small. Besides food niche differentiation, we uncovered a spatiotemporal niche differentiation in army ant raid activity. We discuss competition-driven multidimensional niche differentiation and predator-prey arms races as possible mechanisms underlying prey specialization in army ants. By combining systematic prey sampling with species-level prey identification and network analyses, our integrative approach can guide future research by portraying how predator-prey interactions in complex communities can be reliably studied, even in cases where morphological prey identification is infeasible.

Hoenle PO ，Blüthgen N ，Brückner A ，Kronauer DJC ，Fiala B ，Donoso DA ，Smith MA ，Ospina Jara B ，von Beeren C ... -  《-》

Detection of prey odours underpins dietary specialization in a Neotropical top-predator: How army ants find their ant prey.

Deciphering the mechanisms that underpin dietary specialization and niche partitioning is crucial to understanding the maintenance of biodiversity. New world army ants live in species-rich assemblages throughout the Neotropics and are voracious predators of other arthropods. They are therefore an important and potentially informative group for addressing how diverse predator assemblages partition available prey resources. New World army ants are largely specialist predators of other ants, with each species specializing on different ant genera. However, the mechanisms of prey choice are unknown. In this study, we addressed whether the army ant Eciton hamatum: (a) can detect potential prey odours, (b) can distinguish between odours of prey and non-prey and (c) can differentiate between different types of odours associated with its prey. Using field experiments, we tested the response of army ants to the following four odour treatments: alarm odours, dead ants, live ants and nest material. Each treatment had a unique combination of odour sources and included some movement in two of the treatments (alarm and live ants). Odour treatments were tested for both prey and non-prey ants. These data were used to determine the degree to which E. hamatum are using specific prey stimuli to detect potential prey and direct their foraging. Army ants responded strongly to odours derived from prey ants, which triggered both increased localized recruitment and slowed advancement of the raid as they targeted the odour source. Odours from non-prey ants were largely ignored. Additionally, the army ants had the strongest response to the nest material of their preferred prey, with progressively weaker responses across the live ant, dead ant and alarm odours treatments respectively. This study reveals that the detection of prey odours, and especially the most persistent odours related to the prey's nest, provides a mechanism for dietary specialization in army ants. If ubiquitous across the Neotropical army ants, then this olfaction-based ecological specialization may facilitate patterns of resource partitioning and coexistence in these diverse predator communities.

Manubay JA ，Powell S 《-》

Are tiny subterranean ants top predators affecting aboveground ant communities?

Ants are a widespread group of ecologically important insects. Therefore, ants that are important predators of other ants are likely to play key roles by changing the abundance and impacts of their prey. Familiar arthropod predators, like army ants, are known for their overwhelming raids on invertebrate prey but are limited to mostly tropical systems. Thief ants (Genus: Solenopsis Westwood) are a cosmopolitan group of mostly subterranean ants found in a wide variety of ecosystem types. They are known for their extremely small sizes and their specialized predation where they stealthily tunnel into the nests of other larger ant species to capture and consume only immature ants (larvae and pupae). Predation of ant colonies by other ants, and specialized predatory behaviors of presumed top ant predators (e.g., army ants) are well known. However long-term predation effects, such as across several seasons, are still poorly understood because of a lack of experimental studies. Here we report results of a ~1.5-year press field experiment where thief ants were reduced in natural ant communities. Potential impacts, such as predator-release, were quantified by sampling the co-occurring ant community. Compared to control plots, overall worker abundance and biomass increased where thief ants were reduced, and effects varied among ant species. Results suggest predator release as select aboveground foraging ant species increased in abundance and that thief ants may act as significant predators. Because thief ants are abundant and widespread, similar predatory effects may occur in many ant communities, and our understanding of important predators may need to adjust to include thieving species as well as army ants. Thief ants are very abundant, tiny, specialized to consume immature life stages, equipped with powerful venom, eusocial, and subterranean. This suite of adaptive traits seems unique to eusocial predators compared to animals, where "thieving" predators are usually larger in size compared to their adult-sized prey. Future work quantifying top-down regulation of prey and cascading consumptive and non-consumptive effects will help to understand thief ant predation and potential effects on ecosystem processes.

Ohyama L ，King JR ，Jenkins DG 《-》

Influence of the hypogaeic army ant Dorylus (Dichthadia) laevigatus on tropical arthropod communities.

Berghoff SM ，Maschwitz U ，Linsenmair KE 《OECOLOGIA》

Cryptic diversity, high host specificity and reproductive synchronization in army ant-associated Vatesus beetles.

Army ants and their arthropod symbionts represent one of the most species-rich animal associations on Earth, and constitute a fascinating example of diverse host-symbiont interaction networks. However, despite decades of research, our knowledge of army ant symbionts remains fragmentary due to taxonomic ambiguity and the inability to study army ants in the laboratory. Here, we present an integrative approach that allows us to reliably determine species boundaries, assess biodiversity, match different developmental stages and sexes, and to study the life cycles of army ant symbionts. This approach is based on a combination of community sampling, DNA barcoding, morphology and physiology. As a test case, we applied this approach to the staphylinid beetle genus Vatesus and its different Eciton army ant host species at La Selva Biological Station, Costa Rica. DNA barcoding led to the discovery of cryptic biodiversity and, in combination with extensive community sampling, revealed strict host partitioning with no overlap in host range. Using DNA barcoding, we were also able to match the larval stages of all focal Vatesus species. In combination with studies of female reproductive physiology, this allowed us to reconstruct almost the complete life cycles of the different beetle species. We show that Vatesus beetles are highly adapted to the symbiosis with army ants, in that their reproduction and larval development are synchronized with the stereotypical reproductive and behavioural cycles of their host colonies. Our approach can now be used to study army ant-symbiont communities more broadly, and to obtain novel insights into co-evolutionary and ecological dynamics in species-rich host-symbiont systems.

von Beeren C ，Maruyama M ，Kronauer DJ 《-》