PARENT SESSION
Poster Session #31: Animal Population and Community Ecology I.
Wednesday, August 7. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC
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Facilitation-inhibition: Burrowing owls and their hosts in central Argentina.
Machicote, Marcela1,2, Branch, Lyn*,1,2, Villarreal, Diego2, 1 University of Florida, Gainesville, FL2 Universidad Nacional de La Pampa, Santa Rosa, La Pampa, Argentina
ABSTRACT- Interactions between pairs of species can vary with environmental conditions and population characteristics of participants, resulting in a range of outcomes from facilitation to inhibition. However, evidence of conditional outcomes and knowledge of the factors that change these outcomes are limited. We examined interactions between burrowing owls (Athene cunicularia) and two ecosystem engineers, hairy armadillos (Chaetophractus villosus) and plains vizcachas (Lagostomus maximus). We evaluated whether these two species are interchangeable as hosts for owls, and then examined how changes in environmental conditions induced by a host can shift the outcome of the interaction from facilitation to inhibition. Owls nested in armadillo and vizcacha burrows, but no fledglings were produced in armadillo burrows. Thirty-five percent of the nests in vizcacha burrows were successful. A habitat model constructed with logistic regression indicated that the location of owl nests could be predicted successfully using cover and height of grasses and height and density of shrubs (all variables negatively correlated with the presence of owls). Vizcacha grazing facilitates owls by maintaining open understory. Armadillos do not alter vegetation; their burrows are suitable for nest sites only in burned or other disturbed areas. Fire constitutes a key process that switches habitat for owls from unsuitable to suitable. Vizcachas increase fire intervals and inhibit owls indirectly by facilitating shrub persistence. Eradication of vizcachas and fire suppression in shrublands could have strong negative consequences for burrowing owls.
KEY WORDS: positive interactions, conditional outcomes, burrowing owls, habitat model