PARENT SESSION
Oral Session #32: Animal Community Ecology. Presiding: M. Weiss.
Tuesday, August 7, 2001. 1:00 PM to 4:45 PM. Hall of Ideas P&Q.
Short-term interactions among species for a discrete resource, cavities in living pines.
Walters, Eric1, 1
ABSTRACT- This study examined the interactions among species that use a discrete resource, cavities in living pine trees excavated by red-cockaded woodpeckers (Picoides borealis). I tested the following hypotheses: (i) cavity availability is a limiting resource to the red-cockaded woodpecker and the other species that use cavities created by red-cockaded woodpeckers; (ii) occupants have hierarchical preferences for cavities; and (iii) usurpation of cavities is contributing to the population decline of the red-cockaded woodpecker. I increased the number of suitable cavities by 25% in treatment sites (n=12) and compared response variables with control sites (n=12). Within 18 months, over 90% of the new cavities were occupied. The number of red-cockaded woodpeckers produced increased in sites where cavities had been added. To examine hierarchical preferences, individual red-cockaded and red-bellied woodpeckers (Melanerpes carolinus) were occluded from their respective cavities. Eighty-seven percent (n=39) of red-cockaded woodpeckers and 73% (n=26) of red-bellied woodpeckers did not move to another cavity when occluded. Within 2 days of a red-cockaded woodpecker being removed from a cavity, the cavity was occupied by another red-cockaded woodpecker 15% (n=47) of the time (red-bellied 13%, empty 72%). Red-bellied woodpeckers were removed from treatment sites (n=11) over 4 years. Red-cockaded woodpecker group size decreased and they switched nest trees more frequently in removal sites (compared with control sites) because of interference competition with red-bellied woodpeckers. Cavities appear to be a limiting resource, occupants do exhibit hierarchical preferences, and competition between red-bellied woodpeckers and red-cockaded woodpeckers may be contributing to the population decline of the latter.
KEY WORDS: competition, woodpecker, species interactions