title: Ecological interactions in dinosaur communities: influences of small offspring and complex ontogenetic life histories.
abstract: Because egg-laying meant that even the largest dinosaurs gave birth to very small offspring, they had to pass through multiple ontogenetic life stages to adulthood. Dinosaurs' successors as the dominant terrestrial vertebrate life form, the mammals, give birth to live young, and have much larger offspring and less complex ontogenetic histories. The larger number of juveniles in dinosaur as compared to mammal ecosystems represents both a greater diversity of food available to predators, and competitors for similar-sized individuals of sympatric species. Models of population abundances across different-sized species of dinosaurs and mammals, based on simulated ecological life tables, are employed to investigate how differences in predation and competition pressure influenced dinosaur communities. Higher small- to medium-sized prey availability leads to a normal body mass-species richness (M-S) distribution of carnivorous dinosaurs (as found in the theropod fossil record), in contrast to the right-skewed M-S distribution of carnivorous mammals (as found living members of the order Carnivora). Higher levels of interspecific competition leads to a left-skewed M-S distribution in herbivorous dinosaurs (as found in sauropods and ornithopods), in contrast to the normal M-S distribution of large herbivorous mammals. Thus, our models suggest that differences in reproductive strategy, and consequently ontogeny, explain observed differences in community structure between dinosaur and mammal faunas. Models also show that the largest dinosaurian predators could have subsisted on similar-sized prey by including younger life stages of the largest herbivore species, but that large predators likely avoided prey much smaller than themselves because, despite predicted higher abundances of smaller than larger-bodied prey, contributions of small prey to biomass intake would be insufficient to satisfy meat requirements. A lack of large carnivores feeding on small prey exists in mammals larger than 21.5 kg, and it seems a similar minimum prey-size threshold could have affected dinosaurs as well.
authors.affiliation: Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zürich, Zürich, Switzerland ; Florisbad Quaternary Research, National Museum, Bloemfontein, South Africa ; School of Biological and Conservation Sciences, University of KwaZulu-Natal, Pietermaritzburg, South Africa ; Department of Anthropology, University of Colorado at Boulder, Boulder, Colorado, United States of America.
authors.forename: Daryl
authors.initials: D
authors.lastname: Codron
authors.forename: Chris
authors.initials: C
authors.lastname: Carbone
authors.forename: Marcus
authors.initials: M
authors.lastname: Clauss
mesh_terms: D000818:Animals; D049628:Body Size / Q000502:physiology*; D060435:Carnivory / Q000502:physiology*; D025061:Dinosaurs / Q000502:physiology*; D017753:Ecosystem; D005260:Female; D020387:Food Chain; D005580:Fossils; D060434:Herbivory; D008297:Male; D008322:Mammals / Q000502:physiology; D015233:Models, Statistical; D011157:Population Dynamics; D011235:Predatory Behavior / Q000502:physiology*; D012098:Reproduction; D015053:Zygote