RUGGERA roman alberto
congresos y reuniones científicas
Spatiotemporal variation in diet-niche overlap of frugivorous birds in a subtropical montane forest
Campos do Jordao
Congreso; 25th International Ornithological Congress; 2010
Analyses on niche overlap can provide insights on processes affecting interspecific relationships in a community. Usually, niche overlap is assumed to be inversely related to competition intensity for resources. Resource scarcity would lead to a low niche overlap by increasing interspecific competition. Resource availability and its spatiotemporal variation are often ignored, however, and alternative explanations are overridden. We studied spatiotemporal variation in diet-niche overlap of frugivorous birds in a subtropical montane forest in NW Argentina. Six sites in four altitudinal strata were monitored during the main fruit period. One of those, was bi-monthly visited for a year. Pianka´s index was calculated including fruit availability data and compared against null models. Geographically, diets always overlapped more than expected by chance. Sites with more bird species had lower overlap levels, which would be related to specialization in few preferred fruit species rather than to competition, since fruit density and diversity in these sites were the highest. Temporally, diets overlapped less than expected by chance only in the month with the highest fruit scarcity, which would have increased the interspecific competition. Remaining months showed higher overlap than expected by chance, but months with the highest fruit abundance had the lowest absolute overlap indices. Thus, low overlap levels were reached in fruit scarcity periods by increasing interspecific competition, but also in resource abundance periods by consumption of preferred fruits. Hence, resource availability data were useful to distinguish two processes causing the same pattern.