Title

Community Trophic Structure: The Roles of Diet, Body Size, and Activity Time in Vertebrate Predators

Document Type

NCA Publications/Journals & Book Chapters

Publication Date

5-1-1993

Journal Title/Publication Source

Oikos

Volume

67

Issue Number

1

Page Numbers

6-18

Abstract

We examined trophic structure in an assemblage of 17 vertebrate predators — two snakes (Pituophis catenifer and Crotalus viridis), six hawks (Circus cyaneus, Buteo jamaicensis, B. regalis, Aquila chrysaetos, Falco sparverius, and F. mexicanus), six owls (Tyto alba, Otus kennicottii, Bubo virginianus, Speotyto cunicularia, Asio otus, and Aegolius acadicus), one passerine (Corvus corax), and two mammals (Canis latrans and Taxidea taxus). These predators fed collectively on prey in nine taxonomic classes. Mammalian prey were numerically most important in 15 diets and contributed the most biomass to all 17 diets. Mean prey mass ranged from 2.2-711 g, and correlated with predator mass. No significant differences were apparent in food-niche breadth or mean prey mass between diurnal and nocturnal predators, but dietary overlap among predators with the same diel activity was significantly greater than that among asynchronously-active predators. Mean diet overlap was significantly greater among nocturnal predators than among diurnal predators. Four feeding guilds were defined by dietary similarity. A ground squirrel-eating guild contained one snake, three hawks, and a mammal. A jackrabbit-eating guild consisted of a hawk and a mammal. An arthropod/mammal-eating guild was composed of an owl and the raven. Four owls, one hawk, and one snake formed a small-rodent guild. One owl and one hawk were not members of guilds. Mass ratios of adjacent-sized predators were greater within guilds.

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Community Trophic Structure: The Roles of Diet, Body Size, and Activity Time in Vertebrate Predators

We examined trophic structure in an assemblage of 17 vertebrate predators — two snakes (Pituophis catenifer and Crotalus viridis), six hawks (Circus cyaneus, Buteo jamaicensis, B. regalis, Aquila chrysaetos, Falco sparverius, and F. mexicanus), six owls (Tyto alba, Otus kennicottii, Bubo virginianus, Speotyto cunicularia, Asio otus, and Aegolius acadicus), one passerine (Corvus corax), and two mammals (Canis latrans and Taxidea taxus). These predators fed collectively on prey in nine taxonomic classes. Mammalian prey were numerically most important in 15 diets and contributed the most biomass to all 17 diets. Mean prey mass ranged from 2.2-711 g, and correlated with predator mass. No significant differences were apparent in food-niche breadth or mean prey mass between diurnal and nocturnal predators, but dietary overlap among predators with the same diel activity was significantly greater than that among asynchronously-active predators. Mean diet overlap was significantly greater among nocturnal predators than among diurnal predators. Four feeding guilds were defined by dietary similarity. A ground squirrel-eating guild contained one snake, three hawks, and a mammal. A jackrabbit-eating guild consisted of a hawk and a mammal. An arthropod/mammal-eating guild was composed of an owl and the raven. Four owls, one hawk, and one snake formed a small-rodent guild. One owl and one hawk were not members of guilds. Mass ratios of adjacent-sized predators were greater within guilds.