Biology Reference
In-Depth Information
be made however the models assume seasonal stability of time and thus this introduces
inaccuracies. There is however the seasonal oscillations that need to be introduced in
calculations for an environmental space since populations can rapidly rise and fall and the
idea of an area reaching equilibrium is a fallacy. Rather populations vary widely with in wide
range with some corrective effects to slow down the swings. It is within this realm that man
can help regulate populations and mitigate the swings because Mother Nature left to her own
ends, decimates populations if allowed to rise to maximums that cannot not be maintained in
the long - term due to environmental oscillations. The exception appears to be elephants. We
never say to patients that Nature needs to takes its course with disease nor should we say that
in the restricted habitats that wildlife has been forced into, should we say Nature should take
its course.
Based his experience with managing the ecology of the Zimbabwean Game Reserves, Don
Heath commented on the practical aspects of implementation:
“The math's and concept behind it looks good BUT…The 'definitive' paper on carrying
capacity is 'carrying capacity and related slippery shibboleths' by Graeme Caughley. I
developed the technique to set hunting quotas based as far as possible on herd/pride structure
rather than as a % of the population, and where that wasn't viable, on trophy quality.
Popular and traditional quota setting as used by WWF and extensively promoted by the Du
Toit brothers (Roul and Johann) Russel Taylor et all is that a population that is below carrying
capacity will increase by x% per year - What the % growth is depends on how close to
carrying capacity you hold the population and the impact of predators. The basic work from
which all modern revisions of this concept is based is Grame Caughley's 'Analysis of
Vertebrate Populations'
Our counting methods were too inaccurate for anything other than elephant so saying you
could sustainably harvest 2% per annum of a buffalo population stocked at 80% of carrying
capacity and exposed to normal predatory pressures or 3% per annum if the population was at
50% of carrying capacity was just an unscientific wild ass guess. We don't actually know the
carrying capacity of an area for buffalo; we don't really know the numbers so you are setting a
human off take based on a 'best guestimate'. Caughley advocated the trophy quality analysis
method back in 1975 and it was actively implemented by National Parks in Matetsi but for
some obscure reason it never caught on in the rest of Parks let alone Africa- Sure- it needed
refinement but by 1991 when I was redoing our quota setting manual for parks we had found by
hard experience the obvious flaws and modified the techniques as appropriate to Africa.
It is certainly true that getting a reasonable estimate of carrying capacity is a vital tool to the
manager of any area- the problem for wildlife is that so many species are involved- cattle are
easy and stocking rates have been worked out empirically for each region/vegetation type, and
active predator controls implemented.
We found for example (Bowler 1991) that when leopard density fell below 80% of
estimated carrying capacity you couldn't get them to readily come to baits in daylight. They
had sufficient food that there was no need for them to take risks and/or scavenge. This
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