Abstract
Fire plays a key role in ecosystem dynamics worldwide, altering energy flows and species community structure and composition. However, the functional mechanisms underlying these effects are not well understood. Many ground-dwelling animal species can shelter themselves from exposure to heat and therefore rarely suffer direct mortality. However, fire-induced alterations to the environment may change a species' relative trophic level within a food web and its mode of foraging. We assessed how fire could affect ant resource utilization at different scales in a Mediterranean forest. First, we conducted isotopic analyses on entire ant species assemblages and their potential food resources, which included plants and other arthropods, in burned and unburned plots 1 year postfire. Second, we measured the production of males and females by nests of a fire-resilient species, Aphaenogaster gibbosa, and analyzed the differences in isotopic values among workers, males, and females to test whether fire constrained resource allocation. We found that, in spite of major modifications in biotic and abiotic conditions, fire had little impact on the relative trophic position of ant species. The studied assemblage was composed of species with a wide array of diets. They ranged from being mostly herbivorous to completely omnivorous, and a given species' trophic level was the same in burned and unburned plots. In A. gibbosa nests, sexuals had greater δ15N values than workers in both burned and unburned plots, which suggests that the former had a more protein-rich diet than the latter. Fire also appeared to have a major effect on A. gibbosa sex allocation: The proportion of nests that produced male brood was greater on burned zones, as was the mean number of males produced per nest with the same reproductive investment. Our results show that generalist ants with relatively broad diets maintained a constant trophic position, even following a major disturbance like fire. However, the dramatically reduced production of females on burned zones compared to unburned zones 1 year postfire may result in considerably reduced recruitment of new colonies in the mid to long term, which could yield genetic bottlenecks and founder effects. Our study paves the way for future functional analyses of fire-induced modifications in ant populations and communities.
Highlights
Wildfires constitute a major disturbance force in forest ecosystems worldwide and cause profound alterations in habitat structure, energy flow, and species community composition (Bengtsson et al 2000; Moretti et al 2004, 2010)
Ecology and Evolution published by John Wiley & Sons Ltd
Whereas the unburned plots were covered by a dense canopy of P. nigra (83%), the burned plots were characterized by a higher proportion of bare ground
Summary
Wildfires constitute a major disturbance force in forest ecosystems worldwide and cause profound alterations in habitat structure, energy flow, and species community composition (Bengtsson et al 2000; Moretti et al 2004, 2010). 2008; Westerling et al 2011), their effects on biodiversity and ecosystem functioning are still debated (Gill et al 1999; Copelan et al 2002). Numerous studies have shown that the composition of animal communities and/or the abundance of animals therein vary greatly between burned and unburned areas, yet the functional mechanisms responsible for these patterns are still not well understood, in invertebrate communities (Anderson et al 1989; Gill et al 1999; Arnan et al 2006, 2007; Cobb et al 2007; Gillette et al 2008; Parr and Andersen 2008; Andersen and Hoffmann 2011)
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