Seasonal And Habitat-based Prey Diversity Of Bobcats, Lynx Rufus, In Big Bend National Park, Texas
Browning, Ellen Stringer
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The bobcat (Lynx rufus) population in Big Bend National Park (BIBE) provides an excellent opportunity for study due to the varied arid habitat in which they exist, the dynamic nature of their environment, and the paucity of scientific documentation on this unexploited population. As an abundant carnivore, the bobcat is crucial to BIBE's community ecology and trophic structure, emphasizing the need to investigate, in depth food habits in relation to environmental factors. Bobcats feed on a variety of small vertebrates, primarily lagomorphs and rodents, and are also known to take down large prey, such as mule deer and white tailed deer. Previous research found bobcat diet within BIBE in relation to a reduction in the mule deer abundance in the park from 1972-74 to 1980-81. Their findings suggest that bobcats increase consumption of lagomorphs, a primary prey item when mule deer populations decline. However, they did not address habitat type or seasonality. Taking into account the five major ecosystems of BIBE (floodplain arroyo, desert scrub, sotol grassland, pinion-juniper-oak forest, cypress-pine-oak forest) and seasonal variation from winter to summer, I investigated differences in bobcat diet based on time of year and habitat type. I hypothesized that while lagomorphs and rodents would make up the majority of bobcat diet, ratios and species would vary by season and location, with significant differences between 1) cooler months following monsoon season (January) and the hottest, driest time of year (May/June) and 2) high elevation woodland/grassland, low desert, and riparian floodplain. My findings support the assumption that bobcats in BIBE primarily consumed lagomorphs and rodents, with lagomorphs consumed at a higher percentage for all samples combined (44%). Rodents comprised 28% of prey found in scat collected. Differences between seasons included an increase in number of taxa from May/June to January, including carnivores and deer. Seasonal changes also included a reduction in lagomorph occurrence (51% - 39%) and an increase in rodent occurrence (26% - 33%). Prey diversity did not differ significantly across ecosystem type and was quite low; May/June H' = 0.22, January H' = 0.20 (P > 0.1), and increasing sample size by combining both seasons resulted in a lower diversity measure (H' = 0.18) in other words, a lower evenness in prey species. Dietary niche breadth was higher in the summer (Bs = 0.53) than in the winter (Bs = 0.35), and overall dietary niche breadth was Bs = 33. Both diversity and niche breadth measures followed a similar trend, with summer being the highest and combined measures being lowest. Because diversity and dietary niche breadth are measures of the relationship between species richness and relative abundance, an increase in species diversity alone does not increase diversity, especially if those species exist in low relative abundance.