mesopredator control. Because of the effects apex predators have on an ecosystem,
their presence benefits the ecosystem as a whole. To revisit the previous example,
when populations of sea otters began to increase in the Aleutian archipelago, sea
urchin numbers dropped, the kelp forest grew and the number of fish increased.
10.3 Impacts on Preys
Large carnivores control prey populations by direct and indirect means. Carnivores
directly reduce the number of preys through predation (Terborgh 1988; Terborgh
et al. 1997; Estes et al. 1998; Miller et al. 2001). Their impact on populations of prey
species is a form of biological control. Apex predators limit the number of herbivores
and reduce pressure on plants (first and third trophic levels). For example, the wolf
(Canis lupus) and the lynx (Lynx sp.) prey on ungulate populations (Jedrzejewski
et al. 1993; Okarma 1995; Valdmann et al. 2005). The brown bear preys on ungulates to a lesser degree (Vulla et al. 2009), but in Northern Europe, it preys heavily on
the calves of reindeer (Rangifer tarandus) and moose (Alces alces) (Swenson et al.
2007) and in North America, the brown bear and black bear are major predators of
neonatal ungulates (Zager and Beecham 2006). In Bialowieza, Poland, the wolf and
lynx prey significantly on small ungulates, but less on wild boar (Sus scrofa), moose
and bison (Bison bison) since their numbers are limited by food availability and
weather conditions such as snow (Jedrzejewska and Jedrzejewski 2005). In
Norwegian forests, roe deer (Capreolus capreolus) density declined predators were
present in the habitat (Melis et al. 2009). The population went from 1485 roe deer
individuals per 100 km
2 when there were no predators to 605 with one predator
(European lynx or wolf) and 167 with both predators.
Carnivores’ indirect control has effects on resources, preys behaviour and diseases. It causes prey species to alter their behaviour to reduce their vulnerability
(McLaren and Peterson 1994; Fitzgibbon and Lazarus 1995; Schmitz 1998; Brown
1999; Miller et al. 2001). The prey chooses different habitats, food sources, group
sizes and activity times, and reduces the amount of time used for feeding (Miller
et al. 2001). If a predator selects from a wide range of prey species, the predator’s
presence may cause all prey species to reduce their respective niches, thus reducing
competition among these species. Prey species compete for limited resources and
decrease the diversity through competitive exclusion (Paine 1966; Terborgh et al.
1997). The control on preys also becomes a sanitary control because it prevents the
proliferation of infectious diseases among prey populations (Miller et al. 2001).
Predation risk by wolves affects the number and behaviour of moose on Isle Royale
(McLaren and Peterson 1994), as well as elk (Cervus elaphus) behaviour in
Yellowstone National Park (Ripple and Beschta 2006). This herbivore control, in
turn, mainly affects the balsam fir forest by regulating seedling establishment,
sapling recruitment, sapling growth rates, litter production in the forest and soil
nutrient dynamics (Pastor et al. 1988; Post et al. 1999, 2000; Miller et al. 2001). In
Shark Bay, Australia, a prey species of the tiger shark (Galeocerdo cuvier) altered
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S. Palazón
their presence benefits the ecosystem as a whole. To revisit the previous example,
when populations of sea otters began to increase in the Aleutian archipelago, sea
urchin numbers dropped, the kelp forest grew and the number of fish increased.
10.3 Impacts on Preys
Large carnivores control prey populations by direct and indirect means. Carnivores
directly reduce the number of preys through predation (Terborgh 1988; Terborgh
et al. 1997; Estes et al. 1998; Miller et al. 2001). Their impact on populations of prey
species is a form of biological control. Apex predators limit the number of herbivores
and reduce pressure on plants (first and third trophic levels). For example, the wolf
(Canis lupus) and the lynx (Lynx sp.) prey on ungulate populations (Jedrzejewski
et al. 1993; Okarma 1995; Valdmann et al. 2005). The brown bear preys on ungulates to a lesser degree (Vulla et al. 2009), but in Northern Europe, it preys heavily on
the calves of reindeer (Rangifer tarandus) and moose (Alces alces) (Swenson et al.
2007) and in North America, the brown bear and black bear are major predators of
neonatal ungulates (Zager and Beecham 2006). In Bialowieza, Poland, the wolf and
lynx prey significantly on small ungulates, but less on wild boar (Sus scrofa), moose
and bison (Bison bison) since their numbers are limited by food availability and
weather conditions such as snow (Jedrzejewska and Jedrzejewski 2005). In
Norwegian forests, roe deer (Capreolus capreolus) density declined predators were
present in the habitat (Melis et al. 2009). The population went from 1485 roe deer
individuals per 100 km
2 when there were no predators to 605 with one predator
(European lynx or wolf) and 167 with both predators.
Carnivores’ indirect control has effects on resources, preys behaviour and diseases. It causes prey species to alter their behaviour to reduce their vulnerability
(McLaren and Peterson 1994; Fitzgibbon and Lazarus 1995; Schmitz 1998; Brown
1999; Miller et al. 2001). The prey chooses different habitats, food sources, group
sizes and activity times, and reduces the amount of time used for feeding (Miller
et al. 2001). If a predator selects from a wide range of prey species, the predator’s
presence may cause all prey species to reduce their respective niches, thus reducing
competition among these species. Prey species compete for limited resources and
decrease the diversity through competitive exclusion (Paine 1966; Terborgh et al.
1997). The control on preys also becomes a sanitary control because it prevents the
proliferation of infectious diseases among prey populations (Miller et al. 2001).
Predation risk by wolves affects the number and behaviour of moose on Isle Royale
(McLaren and Peterson 1994), as well as elk (Cervus elaphus) behaviour in
Yellowstone National Park (Ripple and Beschta 2006). This herbivore control, in
turn, mainly affects the balsam fir forest by regulating seedling establishment,
sapling recruitment, sapling growth rates, litter production in the forest and soil
nutrient dynamics (Pastor et al. 1988; Post et al. 1999, 2000; Miller et al. 2001). In
Shark Bay, Australia, a prey species of the tiger shark (Galeocerdo cuvier) altered
234
S. Palazón