Invasive species are one of the main threats to biodiversity worldwide and the processes enabling their establishment and persistence remain poorly understood. In generalist consumers, plasticity in diet and trophic niche may play a crucial role in invasion success. There is growing evidence that invasive ants, in particular, occupy lower trophic levels in their introduced range compared to the native one, but evidences remain fragmented. We conducted stable isotope analysis at five locations distributed on two continents to infer the trophic position of the invasive ant Formica paralugubris in the native and introduced part of the range. This species forms large colonies and can be a voracious predator while feeding on sugar‐based resources as well. Whereas native populations had trophic positions comparable to that of an omnivore, the introduced populations varied from being honeydew specialists to top predators, or omnivore. Where other ant species co‐occurred, there was no overlap in their trophic niches, and F. paralugubris occupied the lower position, suggesting that trophic displacement may enable the coexistence of different ant species. Taken together, our results suggest that shifts in diet associated with changes in the trophic niche of introduced species might mediate invasion success and enable long‐term coexistence with native species.

Current global challenges call for a rigorously predictive ecology. Our understanding of ecological strategies, imputed through suites of measurable functional traits, comes from decades of work that largely focussed on plants. However, a key question is whether plant ecological strategies resemble those of other organisms. Among animals, ants have long been recognised to possess similarities with plants: as (largely) central place foragers. For example, individual ant workers play similar foraging roles to plant leaves and roots and are similarly expendable. Frameworks that aim to understand plant ecological strategies through key functional traits, such as the ‘leaf economics spectrum’, offer the potential for significant parallels with ant ecological strategies. Here, we explore these parallels across several proposed ecological strategy dimensions, including an ‘economic spectrum’, propagule size‐number trade‐offs, apparency‐defence trade‐offs, resource acquisition trade‐offs and stress‐tolerance trade‐offs. We also highlight where ecological strategies may differ between plants and ants. Furthermore, we consider how these strategies play out among the different modules of eusocial organisms, where selective forces act on the worker and reproductive castes, as well as the colony. Finally, we suggest future directions for ecological strategy research, including highlighting the availability of data and traits that may be more difficult to measure, but should receive more attention in future to better understand the ecological strategies of ants. The unique biology of eusocial organisms provides an unrivalled opportunity to bridge the gap in our understanding of ecological strategies in plants and animals and we hope that this perspective will ignite further interest. Read the freePlain Language Summaryfor this article on the Journal blog.

The study of ecological networks has progressively evolved from a mostly descriptive science to one that attempts to elucidate the processes governing the emerging structure of multitrophic communities. To move forward, we propose a conceptual framework using trait‐based inference of ecological processes to improve our understanding of network assembly and our ability to predict network reassembly amid global change. The framework formalizes the view that network assembly is governed by processes shaping the composition of resource and consumer communities within trophic levels and those dictating species’ interactions between trophic levels. To illustrate the framework and show its applicability, we (1) use simulations to explore network structures emerging from the interactions of these assembly processes, (2) develop a null model approach to infer the processes underlying network assembly from observational data, and (3) use the null model approach to quantify the relative influence of bottom‐up (resource‐driven) and top‐down (consumer‐driven) assembly modes on plant–frugivore networks along an elevational gradient. Simulations suggest that assembly processes governing the formation of pairwise interactions have a greater influence on network structure than those governing the composition of communities within trophic levels. Our case study further shows that the mode of network assembly along the gradient is mainly bottom‐up controlled, suggesting that the filtering of plant traits has a larger effect on network structure relative to the filtering of frugivore traits. Combined with increasingly available trait and interaction data, the framework provides a timely toolbox to infer assembly processes operating within and between trophic levels and to test competing hypotheses about the assembly mode of resource–consumer networks along environmental gradients and among biogeographic regions. It is a step toward a more process‐based network ecology and complete integration of multitrophic interactions in the prediction of future biodiversity.

Biologists have long been fascinated by the processes that give rise to phenotypic complexity of organisms, yet whether there exist geographical hotspots of phenotypic complexity remains poorly explored. Phenotypic complexity can be readily observed in ant colonies, which are superorganisms with morphologically differentiated queen and worker castes analogous to the germline and soma of multicellular organisms. Several ant species have evolved ‘worker polymorphism', where workers in a single colony show quantifiable differences in size and head-to-body scaling. Here, we use 256 754 occurrence points from 8990 ant species to investigate the geography of worker polymorphism. We show that arid regions of the world are the hotspots of superorganism complexity. Tropical savannahs and deserts, which are typically species-poor relative to tropical or even temperate forests, harbour the highest densities of polymorphic ants. We discuss the possible adaptive advantages that worker polymorphism provides in arid environments. Our work may provide a window into the environmental conditions that promote the emergence of highly complex phenotypes.