Black Bears, Palms, and Giant Palm Weevils: An Intraguild Mutualism

Abstract

In peninsular Florida, USA, the palm-feeding guild is dominated by the black bear (Ursus americanus floridanus, Pallas) and the giant palm weevil (Rhynchophorus cruentatus, Fabricius). Bears damage palms by consuming their hearts, allowing the weevil to reproduce within the exposed palm tissue. The giant palm weevil reproductively benefits from bear-damaged palms, and bears gain a valuable fat-rich food supply from consuming the insects, an apparent intraguild mutualism. We analyzed a natural experiment across widely distributed sites based on presence or absence of bear populations to test the hypothesis that the presence of bears increases the abundance of the giant palm weevil. Results support the hypothesis; data also show greater attraction of females than males to pheromone traps and indicate a predominance of activity by the insect during the day and at lower summer temperatures. This interaction closely resembles one previously documented involving indigenous humans in Amazonia.