The distribution and interaction of red imported fire ants and native ants across ecotones in a Post Oak Savanna

Abstract

Native ants play a vital role in forested landscapes. Since their invasion in the 1930's, red imported fire ants (Solenopsis invicta Buren) have displaced many native ant species and, consequently, have reduced native arthropod biodiversity. While many studies have examined S. invicta population effects within habitat patches, none have focused on the interface, or ecotones, between these habitats. The objectives of this project are (1) to compare species diversity among seven ecotone types, (2) to characterize the distribution and abundance of native ants across the ecotones, and (3) to identify ecotones with a high abundance of S. invicta. A total of 227 pitfall traps, arranged along 63 transects, was used to capture insects across seven different ecotone types. Species count, Shannon and Simpson diversity indices, and two multiple comparison tests were used to quantify species diversity, abundance, and distribution. Sixteen native ant genera and S. invicta were found within the seven ecotone types. Wood-Grass was the most diverse ecotone; all 17 ant genera were found. The other ecotones contained from 9 to 5 ant genera. The most abundant native ant genera were Forelius, Hypoponera, Monomorium, and Pheidole. Solenopsis invicta was found to be significantly greater in abundance then all native ant genera for all seven ecotones. Solenopsis invicta abundance was greatest within the Grass-Pond and Wood-Cultivated field ecotone types and least abundant within the Wood-Pond, Cleared Wood-Pond, and Wood-Cleared Wood ecotones. The high abundance of S. invicta across all 7 ecotones allowed this study to quantify the ability of this exotic species to outcompete native species within this landscape element.