Conservation Issues

To estimate a predator's vulnerability, three main points should be considered. First, due to the top position in the food chain, predators get only a fraction of the energy circulating through the ecosystem. Second, the average size of individual predators is generally quite higher than the size of their average prey. Third, a trait shared by a majority of predators is a good-high mobility (Table 2). This set of characters or properties of predators has two consequences, both of relevance in terms of conservation. On the one side, the average density of individual predator species is often low; on the other, their geographical distribution is often large. As a consequence, local populations of predatory species are often readily threatened, by any of the usual causes of species decline such as habitat modification, pollution, and hunting. On the other hand, the species as a whole can still survive, owing to better conditions experienced by some populations within its overall range. In assessing the criticality of such a condition, it becomes thus important to consider how different the populations of the predator species are, either in genetic terms, or in their external characters and

Table 2 Size (weight), individual home range and average density of a sample of top predators, the big cats

Cat

Weight

Individual home

Density (animals

species

(kg)

range (km2)

per 100 km2)

Puma

35-100

up to 1800

0.2-5

Lynx

5-18

10-300

2.5-10

Bobcat

6.5-31

1-40

5-40

Snow

25-75

12-40

5-10

leopard

Tiger

65-300

10-10000

3-5

Leopard

28-90

8-400

3-100

Jaguar

60-120

10-400

4-10

Lion

120-240

20-4000

6-40

Cheetah

35-65

50-130 (up to at

Main sources of data: Kingdon J (1977) East African Mammals: An Atlas of Evolution in Africa, Vol. III A: Carnivores. Chicago, IL: The University of Chicago Press; Novak RM (1991) Walker's Mammals of the World, 5th edn. Baltimore, MD: Johns Hopkins University Press; and Skinner JD and Smithers RHN (1990) The Mammals of the Southern Africa Subregion. New Edition Pretoria: University of Pretoria.

least 1500)

Main sources of data: Kingdon J (1977) East African Mammals: An Atlas of Evolution in Africa, Vol. III A: Carnivores. Chicago, IL: The University of Chicago Press; Novak RM (1991) Walker's Mammals of the World, 5th edn. Baltimore, MD: Johns Hopkins University Press; and Skinner JD and Smithers RHN (1990) The Mammals of the Southern Africa Subregion. New Edition Pretoria: University of Pretoria.

behavior. Thus, the dramatic decline of the tiger is not completely described by comparing the estimated 100 000 specimens still living in 1900 with the estimated 7000 of 1990 and the 2000 likely surviving at the beginning of this century. Due to the conspicuous racial differences within the species, additional concern is provided by the estimate that no more than 400 Siberian tigers survive in the wild, while three other subspecies (the Bali tiger, the Caspian tiger, and the Javan tiger) already went extinct between the 1940s and the 1980s.

Many studies have been performed on the effects that removing a top predator from an ecosystem may cause on other species. Often, but not always, further species loss has been reported, that is, a series of cascading extinctions in the food web, where the top predator originally performed a stabilizing role. Relationships between food web complexity and effect of top predator removal have been suggested, but the point is still mooted.

See also: Coevolution. Further Reading

Barbosa P and Castellanos I (eds.) (2005) Ecology of Predator-Prey

Interactions. New York: Oxford University Press. Finke DL and Denno RF (2004) Predator diversity dampens trophic cascades. Nature 429: 407-410.

Kingdon J (1977) East African Mammals:An Atlas of Evolution in Africa, Vol. III A: Carnivores. Chicago, IL: The University of Chicago Press.

Korpimaki E, Norrdahl K, Huitu O, and Klemola T (2005) Predator-induced synchrony in population oscillations of coexisting small mammal species. Proceedings of the Royal Society of London, Biological Science 272: 193-202.

Krivan V (1996) Optimal foraging and predator-prey dynamics. Theoretical Population Biology 49: 265-290.

Krivan V and Eisner J (2003) Optimal foraging and predator-prey dynamics. Part III. Theoretical Population Biology 63: 269-279.

Krivan V and Sikder A (1999) Optimal foraging and predator-prey dynamics. Part II. Theoretical Population Biology 55: 111-126.

Lass S and Spaak P (2003) Chemically induced anti-predator defences in plankton: A review. Hydrobiologia 491: 221-239.

Lotka AJ (1925) Elements of Physical Biology. Baltimore: Williams and Wilkins (Reprinted in 1956 as Elements of Mathematical Biology. New York: Dover).

Norrdahl K (1995) Population cycles in northern small mammals. Biological Reviews 70: 621-637.

Novak RM (1991) Walker's Mammals of the World, 5th edn. Baltimore, MD: Johns Hopkins University Press.

Quince C, Higgs PG, and McKane AJ (2005) Deleting species from model food webs. Oikos 110: 283-296.

Shultz S, Noe R, McGraw WS, and Dunbar RI (2004) A community-level evaluation of the impact of prey behavioural and ecological characteristics on predator diet composition. Proceedings of the Royal Society of London, Biological Sciences 271: 725-732.

Sinclair AR, MdumaS, and Brashares JS (2003) Patterns of predation in a diverse predator-prey system. Nature 425: 288-290.

Skinner JD and Smithers RHN (1990) The Mammals of the Southern Africa Subregion. New Edition. Pretoria: University of Pretoria.

Taylor RJ (1984) Predation. New York: Chapman and Hall.

Vermeij G (1987) Evolution and Escalation: An Ecological History of Life. Princeton, NJ: Princeton University Press.

Volterra V (1926) Fluctuations in the abundance of a species considered mathematically. Nature 118: 558-560.

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