Quantitative variation in ecological and hormonal variables correlates with spatial organization of pronghorn (Antilocapra americana) males |
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Authors: | C R Maher |
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Institution: | (1) Department of Biological Sciences, University of Southern Maine, Portland, ME 04104, USA e-mail: cmaher@usm.maine.edu Tel.: +1-207-7804612, Fax: +1-207-2288116, US |
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Abstract: | Whereas variation in pronghorn (Antilocapra americana) spatial organization is well documented, underlying ecological or physiological explanations are not well understood. This
study quantitatively describes spacing systems of pronghorn males and correlates of their spatial organization. I collected
behavioral data from two populations in South Dakota (Wind Cave) and Montana (Bar Diamond) to determine if males differed
in space use, response to intruders, and behavior patterns indicative of area defense. I measured sex ratio and population
density, and I examined characteristics of food resources, including forb species diversity, richness, coverage, biomass,
and nitrogen content, and how they changed during the growing season. I also collected and analyzed fecal samples to determine
if males differed in testosterone concentrations. Pronghorn males at Wind Cave were more territorial than males at Bar Diamond,
although males at Bar Diamond became more territorial during the second year. The forb community at Wind Cave was more diverse,
contained greater amounts of forbs later in summer, and had a higher nitrogen content later in summer. Population density
was lower at Wind Cave, although density dropped at Bar Diamond during the second year, and sex ratios were skewed toward
males at Bar Diamond. Finally, males at Wind Cave had higher testosterone concentrations than did Bar Diamond males, although
differences were not statistically significant. With lower population density and higher forb abundance and quality, food
resources were more economically defensible at Wind Cave, and males were more territorial there. Analyses using these and
other pronghorn populations revealed that population density and sex ratio correlated weakly with spatial organization, whereas
precipitation correlated most strongly, which suggests plant productivity has a powerful role in determining pronghorn territoriality.
Received: 16 June 1999 / Received in revised form: 21 September 1999 / Accepted: 31 December 1999 |
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Keywords: | Territoriality Ecological correlates Intraspecific variation Testosterone Pronghorn |
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