By Krista Ruppert, Texas A&M WFSC
‘16
Southern
Texas is home to two similar species of small wild cat: the ocelot, which is a
federally endangered habitat specialist, and the bobcat, a thriving habitat
generalist. Despite their similar size, environment, and food preferences, the
two are able to coexist. Competition between the two is poorly documented. While
the ocelot decline is most attributed to habitat loss and fragmentation, it is
possible that competition with bobcats is also a factor in their decline.
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A bobcat
captured on a game camera at the Rolling Plains Quail Research Ranch.
Photo from Texas A&M AgriLife Extension
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Ocelots and bobcats are sympatric,
meaning they occur in the same geographic range. Competitive exclusion theory
says that ecologically equivalent species cannot coexist, but ocelots and
bobcats have similar diets, size, and active times, and are still able to
coexist; habitat is the only major differing factor between the two. An
explanation for their coexistence could be in habitat partitioning. Bobcats are
habitat generalists, meaning they can live and be successful in a number of
habitats, while ocelots are habitat specialists, meaning they can only be
successful in a specific type of habitat. If ocelots remain in only the
closed-cover canopy (their preferred habitat), and bobcats select any remaining
habitat, competition for space, and potentially food, may not occur as
frequently. Horne et al. (2009) found a distinct boundary in habitat selection
between the two, with ocelots selecting for dense thornshrub and bobcats
selecting mixed and open cover. Bobcats are able to survive in dense
thornshrub, however, and it is likely that they avoid it due to ocelot presence
and competitive interactions. Even so, it is possible that ocelots are being
negatively affected by this competition with bobcats, an effect which could be a
contributor to ocelot decline.
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Hispid cotton rats, Sigmodon hispidus, are a common prey
item for both bobcats and ocelots.
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Ocelots and bobcats occupy the same trophic level (meaning they perform the same function in the food chain) as they are both mesopredators, so it follows that they would share similar prey. Booth-Binczik et al. (2013) studied sympatric ocelots and bobcats, analyzing scat to determine whether they appear to be competing for food. They found that rodents were the most common prey for both species, and that the top three preferred rodents for each overlapped by one species, with bobcats consuming white-footed mice and southern plains woodrats, ocelots consuming Mexican spiny pocket mice and fulvous harvest mice, and both species of cat consuming hispid cotton rats. Bobcats were more likely to consume rabbits and large (more than 1.4-2.6 ounces) rodents, while ocelots were more likely to consume medium-sized (1-1.4 ounces) rodents. Despite this difference, the top rodents for both occupied the same habitat (edge, or the boundary between two types of habitat; in this case, dense and sparse brush), indicating that these two wild cats share some overlapping hunting grounds. Upon comparison to ocelots in Central and South America, ocelots in Texas consume much smaller prey. This difference could be attributed to overall habitat differences between Texas and Central/South America, but it also could be due to competition with bobcats. Bobcats are not found as far south as ocelots, so it is possible that ocelots consume larger prey when they are free of competition. Food competition between bobcats and ocelots cannot yet be confirmed, but some competition is likely; whether this competition is contributing to ocelot decline is currently unknown.
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Bobcats and
ocelots are sympatric in South Texas.
Photo from the US Fish and Wildlife
Service.
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Bobcats
are able to coexist with agricultural and urban development without losses to
genetic diversity, but ocelots are not as flexible to changing habitat.
Additionally, bobcats are more adaptable to changes in environment and have a
higher reproductive output as a whole when compared to ocelots. Bobcats have
been able to adapt to landscape and food source changes, while ocelots have not.
Habitat fragmentation is detrimental to ocelots, but much less so for bobcats,
as they are able to traverse and live in areas of various cover; as habitat
changes, the ability for bobcats to outcompete ocelots increases. With ocelots
already facing many threats to their continued survival in Texas, the
possibility for competition is important to consider, particularly during times
when resources are scarce, such as during drought.
Competition
between ocelots and bobcats is not the most pressing issue regarding ocelot conservation.
However, ongoing research on the East El Sauz Ranch in Willacy County will
provide biologists with a better understanding of how ocelots and bobcats live
together. Steps to ensure the success and conservation of ocelots in Texas
should focus on habitat restoration, efforts to increase genetic
variation, and strategies to reduce road mortality. The potential effects
of bobcat competition should be considered and further investigated, but
otherwise should not be considered an extreme threat to ocelot success.
Literature
Cited
Booth-Binczik, S.
D., R. D. Bradley, C. W. Thompson, L. C. Bender, J. W. Huntley, J. A. Harvey,
L. L. Laack, and J. L. Mays. 2013. Food habits of ocelots and potential for
competition with bobcats in southern Texas. The
Southwestern Naturalist 58(4):403-410.
Haines, A. M., M.
E. Tewes, and L. L. Laack. 2005. Survival and sources of mortality in ocelots. Journal of Wildlife Management 69(1):255-263.
Horne, J. S., A.
M. Haines, M. E. Tewes, and L. L. Laack. 2009. Habitat partitioning by
sympatric ocelots and bobcats: implications for recovery of ocelots in southern
Texas. The Southwestern Naturalist
54(2):119-126.
Janecka, J. E.,
M. E. Tewes, I. A. Davis, A. M. Haines, A. Caso, T. L. Blankenship, and R. L.
Honeycutt. 2016. Genetic differences in the response to landscape fragmentation
by a habitat generalist, the bobcats, and a habitat specialist, the ocelot. Conservation Genetics.
Laack, L. L., M.
E. Tewes, A. M. Haines, and J. H. Rappole. 2005. Reproductive life history of
ocelots Leopardus pardalis in
southern Texas. Acta Theriologica
50(4):505-514.
Walker, C. W.
1997. Patterns of genetic variation in ocelot (Leopardus pardalis) populations for South Texas and northern
Mexico. Dissertation, Texas A&M University–Kingsville, Kingsville TX.