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Title: Habitat and Grazing Influence on Terrestrial Ants in Subtropical Grasslands and Savannas of Argentina

item CALCATERRA, LUIS - South American Biological Control Lab(SABCL)
item CABRERA, SONIA - Universidad De Buenos Aires
item CUEZZO, FABIANA - Consejo Nacional De Investigaciones Científicas Y Técnicas(CONICET)
item JIMENEZ PEREZ, IGNACIO - Conservation Land Trusts
item BRIANO, JUAN - South American Biological Control Lab(SABCL)

Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2010
Publication Date: 9/1/2010
Citation: Calcaterra, L.A., Cabrera, S.M., Cuezzo, F., Jimenez Perez, I., Briano, J.A. 2010. Habitat and Grazing Influence on Terrestrial Ants in Subtropical Grasslands and Savannas of Argentina. Annals of the Entomological Society of America. Vol. 103, no. 5, pp. 1-12.

Interpretive Summary: Habitat degradation and biological invasion are the two greatest threats to global biodiversity. The Iberá Reserve in Northeastern Argentina protects one of the largest freshwater wetlands in the world. Natural and human disturbances such as floods, fires or grazing, affect the functioning of the reserve. The grazing effect has been widely studied on many biological components of wetlands; however, few studies investigated its effect on ants. The main objective of this work was to study the livestock grazing effect on ants that forage on the ground surface, with special attention to the invasive fire ants that were accidentally introduced into the U.S. from Argentina in the early 1900’s. We also wanted to confirm whether or not the red imported fire ant is more abundant in grazed areas, as reported in North America. Our results indicated that widespread livestock grazing impacted only some specific ants, including the red imported fire ant.

Technical Abstract: The maintenance of species diversity in modified and natural habitats is a central focus of conservation biology. The Iberá Nature Reserve (INR) protects highly diverse ecosystems in northeastern Argentina, including one of the largest freshwater wetlands in South America. Livestock grazing is one of the major disturbances to these ecosystems; however, its effect on ant diversity is poorly known. The objective of this work was to study the effect of savanna versus grassland and livestock grazing on the structure and composition of subtropical terrestrial ants focusing on the particular response of the native red fire ant, Solenopsis invicta Buren. Unbaited pitfall traps were used to capture worker ants in 25 grazed and 20 non-grazed sites. Fifty ant species were collected. The savanna showed more species, individuals, biomass and functional groups of ants than the grassland. S. invicta was the most frequently captured (61.4%) and numerically dominant species; however, Camponotus punctulatus punctulatus Mayr showed the highest biomass. Grazing simplified vegetation structure in both habitats, but its impact on vegetation seemed only to promote a higher total biomass especially in the grassland, and/or functional groups, favoring occurrence of hot-climate specialists in the savanna. This study revealed that habitat type strongly affected the organization of the terrestrial ant assemblages at the INR. However, as in other studies, we did not find clear evidence that habitat modification by grazing significantly affected terrestrial ant assemblages. The weak grazing influence could be the consequence of the short enclosure time as to recover the original ant communities, the differential response of ant species to habitat type, and/or the resilience of ants.