COS 59-7 - Pasture management, the red imported fire ant (Solenopsis invicta) and dung beetle mediated ecosystem services

Tuesday, August 8, 2017: 3:40 PM
B112, Oregon Convention Center
Christen H. Steele, Ecology and Evolutionary Biology, Tulane University, New Orleans, LA

Grazing animals in Florida deposit over 20 million metric tons of dung per year, making dung a significant non-point source of pollution (extrapolated from Fincher, 1981). Degradation of this dung occurs naturally, primarily due to a diverse group of beetles (Order Coleoptera) primarily in the families Scarabaeidae and Geotrupidae(hereafter dung beetles). Dung that is not degraded becomes a non-point source of pollutants and may be leached into water bodies. Additionally, dung provides an incubation site for the pests and parasites of both humans and livestock. Thus, as dung beetles consume and degrade dung, they provide a multitude of ecosystem services by increasing the rate of dung decomposition in pasture ecosystems.

However, dung beetles are not alone in their colonization and use of dung as a food source. The non- native fire ant Solenopsis invicta has been observed to frequently utilize dung as a site to forage for the larvae of other insects. Based on the known food preferences of S. invicta, dung beetle adults and larvae fit the profile of a potential food source. Whether the ecosystem services provided by dung beetles are being reduced, un-impacted, or potentially increased through complementarity is unclear. Thus, this project sought to utilize a field experiment to test whether the interaction between S. invicta and native dung beetle communities impacts the provisioning of two ecosystem services: rate of dung degradation and parasite suppression.


Overall, parasite survival was significantly reduced in the presence of dung beetles, regardless of pasture conditions and fire ant treatments. The mechanism by which dung beetle activity results in this reduction is not entirely clear. However, the hypothesis that dung beetle activity reduces parasite survival indirectly through the burial of dung was not supported because the amount of dung in grams lost to dung beetle activity was not significant. No evidence was found to indicate that S. invicta presence impacts the activity of dung beetles or the survival of parasites in the absence of beetles. Because natural densities of ants were used in this experiment, it is possible that S. invicta densities were simply too low to detect an effect with this experimental design. Overall, S. invicta densities were found to be on average 70 mounds per hectare, which is relatively low in comparison to the highest densities recorded in Texas of 600 mounds per hectare (Steele unpublished, Vogt et al. 2003).