DOI: 10.5061/dryad.vf1gq0q
title: Data from: Do an ecosystem engineer and environmental gradient act independently or in concert to shape juvenile plant communities? Tests with the leaf-cutter ant Atta laevigata in a Neotropical savanna

description: Background. Ecosystem Engineers are species that transform habitats in
 ways that influence other species. While the impacts of many engineers
 have been well described, our understanding of how their impact varies
 along environmental gradients remains limited. Although disentangling the
 effects of gradients and engineers on biodiversity is complicated – the
 gradients themselves can be altered by engineers – doing so is necessary
 to advance conceptual and mathematical models of ecosystem engineering. We
 used leaf-cutter ants (Atta spp.) to investigate the relative influence of
 gradients and environmental engineers on the abundance and species
 richness of woody plants. Methods. We conducted our research in South
 America's Cerrado. With a survey of plant recruits along a canopy
 cover gradient, and data on environmental conditions that influence plant
 recruitment, we fit statistical models that addressed the following
 questions: (1) Does A. laevigata modify the gradient in canopy cover found
 in our Cerrado site? (2) Do environmental conditions that influence woody
 plant establishment in the Cerrado vary with canopy cover or proximity to
 A. laevigata nests? (3) Do A. laevigata and canopy cover act independently
 or in concert to influence recruit abundance and species richness?
 Results. We found that environmental conditions previously shown to
 influence plant establishment in the Cerrado varied in concert with canopy
 cover, but that ants are not modifying the cover gradient or cover over
 nests. However, ants are modifying other local environmental conditions,
 and the magnitude and spatial extent of these changes is consistent across
 the gradient. In contrast to prior studies, we found that ant-related
 factors (e.g., proximity to nests, ant changes in surface conditions),
 rather than canopy cover, had the strongest effect on the abundance of
 plant recruits. However, the diversity of plants was influenced by both
 the engineer and the canopy cover gradient. Discussion. Atta laevigata in
 the Cerrado modify local conditions in ways that have strong but spatially
 restricted consequences for plant communities. We hypothesize that ants
 indirectly reduce seedling establishment by clearing litter and reducing
 soil moisture, which leads to seed and seedling desiccation. Altering soil
 nutrients could also reduce juvenile growth and survivorship; if so these
 indirect negative effects of engineering could exacerbate their direct
 effects of harvesting plants. The effects of Atta appear restricted to
 nest mounds, but they could be long-lasting because mounds persist long
 after a colony has died or migrated. Our results support the hypothesis
 that leaf-cutter ants play a dominant role in Cerrado plant demography. We
 suggest the ecological and economic footprint of these engineers may
 increase dramatically in coming decades due to the transformation of the
 Cerrado by human activities.
description: Spp_ID_HabitData on the growth habit of plant species that were recorded in a survey of woody plants associated with leaf-cutter ant nests conducted at Estação Ecológica do Panga (Uberlandia, Minas Gerais, Brazil).EnvData_ActiveNestsEnvironmental data collected in plots at different distances from Atta laevigata nests at the Estação Ecológica do Panga (Uberlandia, Minas Gerais, Brazil).PlantCensus_ActiveNestsData on the identity and height of seedlings found in survey plots located at three different distances from Atta laevigata nest mounds.