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Impacts of red imported fire ants on gopher tortoises and their associated burrow commensal fauna.
Epperson, Deborah*,1, Allen, Craig2, 1 The Nature Conservancy, Camp Shelby, MS2 South Carolina Cooperative Fish and Wildlife Research Unit, Clemson, SC
ABSTRACT- We examined the potential impacts of red imported fire ants (Solenopsis invicta) on gopher tortoise (Gopherus polyphemus) hatchling survivorship and invertebrate burrow commensals. Red imported fire ants were introduced into the United States at the Port of Mobile in the 1930's and have spread throughout the southeastern United States. Throughout the range of the gopher tortoise red imported fire ants are now widespread. We experimentally manipulated fire ant densities using a fire ant bait (Fenoxycarb) on one randomly chosen member of each of five paired sites at Camp Shelby Training Site in southern Mississippi. Fire ant bait was applied in the spring of 1998, spring and fall of 1999, and in the spring of 2000. Sites were paired to reduce heterogeneity based on tortoise populations, S. invicta densities and overall habitat similarities. From 1997 - 2000, gopher tortoise hatchlings were fitted with radio-transmitters and followed until no longer extant. Cause of death was determined, and the number of days alive calculated for each individual. Of forty-one individuals confirmed dead, 27% of these mortalities were attributed to S. invicta. Comparison of survivorship between treated and untreated sites using the Kaplan-Meier method revealed higher survivorship on treated sites (Fisher's Exact Two Sided test P = 0.087). Invertebrate burrow commensals were sampled twice per year from 1998-2000 using a D-Vac suction apparatus. Ten burrows in each site were vacuumed and invertebrates identified to species when possible. Burrow species richness, Shannon Diversity indices, and abundance were compared between treated and untreated sites using a repeated measures randomized block ANOVA. We found significant treatment effects for species richness (P = 0.0016), diversity (P = 0.0186), and abundance (P = 0.0852).
Key words: Solenopsis invicta, Gopherus polyphemus, invasive species, commensal