May 10 2012

5:00 pm 154 BSRB

EcoEvoPub Series

Graduate Student Presentations


Department of Ecology and Evolutionary Biology

“The Royale Treatment: dental indicators of elevated stress in an island moose population”

Interruptions in tooth formation due to metabolic stress leave permanent marks in tooth tissues that can be easily diagnosed. Such marks are prevalent in the teeth of moose(Alces alces) dwelling on Isle Royale, Michigan. This population has been known to experience periodic overpopulation and island-wide starvation, as well as stunted growth and high incidence of arthritis. In this exploratory study, I surveyed moose from times of high and low density for signs of interrupted bone and enamel formation. Incidents of defective enamel formation have been prevalent since the 1970’s, implying that even following a population crash, moose are insufficiently nourished. Arthritis and short metatarsal length have previously been linked to malnutrition, but the total number of enamel defects does not correlate with these factors. Some of these observed defects may instead correspond to the stress imposed on juveniles during birth rather than starvation. I will analyze enamel defects against daily incremental growth within the teeth, revealing the time of birth and the effects of known environmental stresses on tooth formation. I will ultimately apply these data to determining the health of ungulates of unknown environment and population density, most notably animals closely predating the end-Pleistocene extinction event.

Department of Ecology and Evolutionary Biology

“Dietary behavior and resource partitioning among large carnivorans of late Pleistocene rancho La Brea”

The processing of food causes distinct patterns of microscopic wear on tooth enamel, patterns that represent indirect evidence of tooth use and diet. We examined dental microwear features of seven species of carnivorans from the late Pleistocene asphalt seeps at Rancho La Brea(Los Angeles, California, United States) to infer dietary resource use in the large-carnivoran assemblage. For a comparative database, we documented microwear features for seven species of extant North American carnivorans in order to characterize microwear differences among five dietary categories: hypercarnivore + bone, hypercarnivore, carnivore, omnivore, and herbivore/omnivore. Counts of total scratches, total pits, coarse scratches, fine scratches, large pits, small pits, and gouges were documented on light-microscopy photomicrographs of the anterior shearing facet of the lower first molar (carnassial). Length and direction of scratches were also recorded for the modern species. Among modern carnivorans, greater densities of microwear features, as well as greater length and consistent directionality of scratches, characterized more carnivorous versus more omnivorous diets. Among the Rancho La Brea carnivorans, Smilodon fatalis, the saber-tooth cat, was distinct in having a markedly low density of all features; Panthera atrox, the American lion, exhibited a high density of all features; and the remaining carnivorans clustered together in the intermediate range for most microwear variables. Discriminant analysis based on microwear variables of modern species classified Smilodon; the short-faced bear, Arctodus simus; the coyote, Canis latrans; the gray wolf, Canis lupus; and the cougar, Puma concolor, as omnivores. Like modern omnivores, these five Rancho La Brea carnivorans had more gouges and fewer fine scratches, large pits, and small pits. This surprising result may be the effect of the small size of the comparative database or an indication that the diet of the large carnivorans of Rancho La Brea, because of this locality's unique faunal composition and taphonomy, is not well described by the dental microwear of modern analogs.

THURSDAY, MAY 10, 2012











































































































































































































































































































































































































































































































































































































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