TERRITORIAL NEEDS OF THE WORLD’S LOWEST-DENSITY TERRESTRIAL ANIMALS

Space needs vary enormously among animals. The mountain top of Montaña Uyuca in Honduras (House, at all 2002) is just a bit under 1000 ha and it is home to about a dozen of endemic plants that have been present on only that small location for who knows how many thousands of years, as they may have developed there on the spot and/or have been left behind as glacial relicts. In the Nevada’s Mojave Desert, USA, 16 species of Pupfish and another 16 species in Mexico live in regions that tens of thousands of years ago contained interconnected rivers and lakes, but where (semi-)desert conditions now prevail. Being isolated from each other, "in their islands of water in an ocean of desert", these pupfish have drifted off into different species, one of them, the Devils Hole pupfish, Cyprinodon diabolis, has been clinging onto life with numbers varying between 200 and 700 individuals (Chen 2002). On the other hand, a number of animals need very large areas, like the big cats and the large birds of prey albeit not necessarily of only one specific ecosystem class. They may happily survive in large protected areas of mixed ecosystem composition.

Literature data on the world’s most territory demanding species, large endothermic predators¹ are scarce, unreliable and vary greatly. Population densities of animals are poorly known for almost any species and their needs vary greatly, depending on habitat – which for several of the cited species may vary from closed forest to semi-desert conditions. The numbers are not the result of extensive literature revision and only serve as an indication for the order of magnitude required to maintain complete ecosystems with all trophic levels in different parts of the world, but it is expected that only a few birds of prey need to be added to the twenty-some very low density species cited in this box.

Particularly in areas with low organic production levels, like semi-deserts and tundras, indicated densities may be considerably lower than the figures cited and sometimes much larger areas are needed under such extreme conditions. Large areas are usually not determined by criteria of composition of ecosystems but rather by mere availability. In the future more and better data may be published on:

http://www.birdlist.org/nature_management/national_parks/national_parks_systems_development.htm , as they become available. It is recommanded that all species in need of more that 100,000 ha be monitored in protected areas to assess the compliance with a minimum effective population of 500 individuals.

Jaguars, Panthera onca, whose densities have only recently become slightly better observed with camera traps (WCS 2002) are found to have densities of 1 territorial adult per 2500 ha (effective population) in Brasil² (Nowak 1999), while in Cockscomb³, Belize a density of 1 per 200 ha (total population) was found (Garman 1997), with probably an under-censused population in the case of Brasil. Still, assuming the low density to be the rule, an effective population should be able to survive in 1,500,000 ha. If the density in Belize is any indication, considerable smaller areas might suffice if hunting can be as effectively controlled as in Belize. For Pumas Felis concolor, densities in the USA are found to vary from 1 per 2,000 – 20,000 ha, while a case has been reported of 1 per 1,400 in Patagonia, Argentina. Total population density of lions, Panthera leo, for the Serengeti ecosystem have been reported 1 per 1.200 ha and other areas up to 1 per 5,000 ha, which in the Serengeti would require about 2,500,000 ha and 10,000,000 ha under less favorable conditions. With tigers, Panthera tigris, no longer finding natural conditions in most of its remaining distribution (except Russia, de K. Korte, pers. com.) it is hard to approximate natural population densities, although Nowak reports a density of 1 per 1,900-15,100 ha for males and 1,000-5,100 ha for females from a study in Nepal, from which an effective population density may be deducted. Population densities of Leopards have been recorded from 1 per 100 ha under exceptionally favorable conditions to 1 per 3000 ha. Cheetahs, Acinonyx jubatus, lives at densities between 1 per 2,000 to 10,000 ha, but may decrease to 1 per 25,000 in semi-desert conditions. Other cats living at densities whose MVPs require special attention are: Snow Leopard (Panthera uncia), Clouded Leopard (Neofelis nubulosa), Asian Golden Cat, Felis Temminck, Caracal, Felis caracal, Eurasian Lynx, Felis Lynx, and Canada Lynx, Felis Canadensis.

Bears usually live in considerably higher densities, for which Nowak (1999) reports total population densities: e.g. American Black Bear, Ursus americanus, 1 per 70-260 ha; Brown or Grizzly Bear, Ursus arctos, 1 per 150 – 6,000 ha, (which is obviously heavily influenced by hunting pressure and habitat conditions), Asian Black Bear, Ursus thibetanus, 1 per 10 – 130 ha; Sloth Bear, Ursus ursinus, 1 per 10 ha and appear to be able to maintain an MVP in areas somewhere between 100,000 and 500,000 ha. The Spectacled Bear is not listed, but given its size, it is expected to have ranges comparable to those of the Asian and American Black Bear.

Canines are often heavily persecuted and low population densities listed are no doubt the result of a combined effect of less favorable habitat conditions and hunting: Grey Wolf, Canis lupus, 1 per 2,000-27,300 ha; African Hunting Dog, Lycaon pictus, 1 per 3,000-50,000 ha (which is obviously heavily influenced by hunting pressure and habitat conditions), Maned Wolf ,Chrysocyon brachyurus, 1 territorial adult per 1,300 ha (effective population). The Red Wolf, Canis rufus, appears to need areas in the range of 1,000,000 to 2,000,000 ha, provided that hunting be effectively stopped in those areas, although no data exist on natural population densities, as the animal has just started its recovery from the brink of extinction as it is being reintroduced at a few locations. Of the Hyena’s, only the Brown Hyena, Hyaena brunnea, which primarily lives in arid regions, appears to live in very low densities that may vary from 1 per 500 to 1 per 13,000 ha.

Of the large herbivores, only a few species live in low densities similar to those of mammalian predators, like elephants and ungulates that live in desserts, like the Oryx and Addax, Addax nasomaculatus. All other herbivores live in much higher population densities than mammalian predators. Nowak (1999) reports that a relatively undisturbed population of 500 elephants lives in about 350,000 ha in Amboseli National Park in Kenya, suggesting a total population density of 1 per 700 ha, which would require a minimum area of 1,400,000 ha for a viable population. Frequently Elephant densities are much higher (S. van Wieren, pers. com.). Tapirs, Tapirus, who mainly live secluded solitary lives, may reach densities of 8 per 1,000 ha in very lush vegetation, which would require 250,000 ha for their MVPs. However, as for Jaguars, Panthera onca, this estimate is probably a strong underestimate of the natural population density, as observation in the jungle is extremely difficult. For most ungulates areas of 100,000 ha suffice to maintain MVPs.

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