Wednesday 4 March 2009

Low Wildcat Populations

I constantly read about low wildcat populations. Nearly all the numbers that I read about in relation to a specific area are often in single or double figures and sometimes in treble figure but they always seem shockingly low and no one seems to recognize this as a problem in its own right.

With low wildcat populations in an isolated and cut off habitat there will be, at least, the possibility of inbreeding depression but how real is the risk? Lets take an example. I recently read that in Cameron County in southern Texas, near the Mexico border that there may be the greatest number of wild cat species in the United States. The area boasts sightings of cougars, jaguarundis, ocelot and bobcat. Fantastic news for people like me. But how big are these populations?

The report in the Brownsville Herald quotes these figures:
  • Jaguarundis (uncertain number but if they saw one it was a success).
  • Ocelot -- 10 to 25 ocelots live at or near to Laguna Atascosa National Wildlife Refuge in eastern Cameron County with 100 ocelots remaining in the United States in total and as a maximum it seems (src: U.S. Fish & Wildlife Service biologist Jody Mays) - see Ocelot habitat.
  • Bobcats -- about 100 in Cameron County.
The book Wildlife Ecology, Conservation, and Management by Anthony R. E. Sinclair, John M. Fryxell, Graeme Caughley, states that inbreeding depression is seldom reported for population less that "a couple of dozen individuals". On that basis inbreeding depression could take hold in the Cameron Ocelot population. Inbreeding depression is a decline in fitness due to the recessive defective genes coming to the fore (this is my layperson's language). As the frequency in mating between close relatives increases so random genetic drift decreases. This leads to reduced heterozygosity which in turn leads to an exposure of the effect of semi-lethal recessive alleles. This leads to increased mortality which leads to lower populations and the cycle restarts until the population dies out. The Iberian Lynx is subject to this phenomenon as her habitat is fragmented.

Many wild cat species in areas of heavy or growing human population are subject to habitat erosion and habitat fragmentation which threatens survival of the species by inbreeding. Another classic case is the Florida Cougar, enclosed as it is on a "habitat island".

But what upsets me is the blaise way in which reports quote such low number when the adjacent human population can be counted in tens of thousands or more. Humans certainly have killed off wildlife by sheer force of numbers. The same story can be told all over the world, India being a particular case in point. There are 1.1 billion Indians. It is a large country but when you drive through it you barely ever get out into the open country as it simply doesn't exist. There the tiger (see Bengal tiger) suffers the same fate as the wildcats of the United States.

Low Wildcat populations to Wild Cat Species

Low Wildcat Populations - Photo: of Jaguarundi cat, published under Wikimedia® creative commons license license = Attribution-ShareAlike License

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