||Hearn, A., Sanderson, J., Ross, J., Wilting, A. & Sunarto, S.
The Bornean Clouded Leopard is forest-dependent, and forest cover on the island of Borneo, if current deforestation rates continue, is projected to decline from 50% to less than one-third by 2020 (Rautner et al. 2005). A decline of >20% in the Bornean Clouded Leopard population is thus projected over the next 16 years (= two generations) (IUCN Cats Red List Workshop 2007).
As a first working hypothesis Wilting et al. (2006) extrapolated, based on their densities from Tabin Wildlife Reserve (about 9 per 100 m²), the potential number of clouded leopards in Sabah to be 1,500-3,200 individuals. However, they pointed out that this number most likely overestimates the true number. Based on a different methodology (camera traps), Andrew Hearn and Joanna Ross (unpubl. 2007) obtained a lower density in a different area of Sabah of 6.4 adults per 100 km². This suggests the Sabah population could be at the low end or even below the above population estimates.
IUCN Guidelines (IUCN 2006) define population as the number of mature individuals, defined as “individuals known, estimated or inferred to be capable of reproduction.” While in general this refers to all reproductive-age adults in the population, the Guidelines also “stress that the intention of the definition of mature individuals is to allow the estimate of the number of mature individuals to take account of all the factors that may make a taxon more vulnerable than otherwise might be expected.” Two factors which increase felid vulnerability to extinction are their low densities (relative to other mammals, including their prey species) and relatively low recruitment rates (where few animals raise offspring which survive to join the breeding population, which has been documented in a number of felid populations). Low densities means that relatively large areas are required for conservation of viable populations; it has long been recognized that many protected areas are too small to conserve viable felid populations (Nowell and Jackson 1996). Low recruitment rates also require larger populations and larger areas to conserve viable populations, as well as mortality reduction in non-protected areas to maintain population size through connectivity. High mortality rates can be offset by an abundant prey base, but such conditions are rarely the norm for cats, particularly big cats, for which prey base depletion is often identified as a leading threat across their range. The IUCN Guidelines advise that “mature individuals that will never produce new recruits should not be counted.” Low recruitment rates indicate that fewer adults than would be expected produce new recruits. Defining population size as the total estimated number of reproductive age adults in the taxon would also not take into account that many occur in subpopulations which are too small or too threatened for long-term viability. Instead, the number of mature individuals is defined as equivalent to the estimated effective population size.
Effective population size (Ne) is an estimator of the genetic size of the population, and is generally considered representative of the proportion of the total adult population (N) which reproduces itself through offspring which themselves survive and reproduce. Ne is usually smaller than N, and based on four felid demographic studies, it is roughly estimated at 50% (Nowell et al. 2007).
At densities of 6.4 (A. Hearn and J. Ross unpubl. 2007) or higher (Wilting et al. 2006), with only about 6.9% of Borneo's forests protected in national parks (Rautner et al. 2005), its effective population size is probably less than 2,500 mature individuals, with no subpopulation having an effective population size greater than 250 mature individuals (IUCN Cats Red List Workshop 2007).