10.6 What Happens When Large Predators Disappear?
Since the Late Pleistocene, over-exploitation, hunting, agriculture, livestock, habitat
loss and destruction have had a major impact on the populations of large carnivores
living in terrestrial and marine habitats. As human civilisation has progressed, human
density has massively increased, and the populations of large carnivores have
decreased or been eliminated. As a result, large predators have been entirely removed
from the system in many areas, or their numbers have been severely reduced (Weber
and Rabinowitz 1996; Terborgh et al. 1999; Woodroffe 2000; Miller et al. 2001).
The loss of large carnivores has long-term effects on ecosystem stability (Miller
et al. 2001). Because they have disappeared from large territories where they once
lived, top-down processes previously regulated by them have been considerably
altered (Rosenblatt et al. 2013). Trophic chains and cascades shorten, and animal
and plant populations suffer alterations in their numbers and dynamics. Without top
predators, populations of prey species increase; the increase of herbivores leads to
greater pressure on plants, reducing vegetation cover and increasing the prevalence
of diseases. Changes in animal and plant populations, also alter nutrient and biogeochemical cycles (soil and water) (Estes et al. 2011, Ritchie and Johnson 2009).
In the absence of top predators, mesopredator populations increase, thus leading to
so-called “mesopredator release” (Soulé et al. 1988) and a decline in populations of
smaller prey species. Summarising, the loss of predators limits the ecosystem’s
ability to restore the process of top-down control.
Apex predators have disappeared from different ecosystems. The extirpation of
large top predators in Northern Arizona in the early twentieth century led to the
irruption (sudden and rapid increase) of the mule deer (Odocoileus hemionus)
population, which caused over-browsing, a reduction in woody browse cover and
eventually famine among the deer (Rosenblatt et al. 2013; Binkley et al. 2006). In
Yellowstone National Park, the extirpation of wolves in the early twentieth century
led to an increase in the elk (Cervus elaphus) population, a concomitant decrease in
the recruitment of deciduous tree species and related effects on ecosystem structure
and function (Ripple and Beschta 2012; Rosenblatt et al. 2013). In the Aleutian
archipelago, the arctic fox (Alopex sp.) limits the number of sea birds, thus
decreasing the amount of nutrients transported from sea to land and maintaining the
herbaceous structure of the tundra (Croll et al. 2005). When sea otters (Enhydra
lutris) were overexploited by the fur trade in the North Pacific, marine invertebrate
herbivores increased in number, especially sea urchins (Strongylocentrotus spp.)
and devastated kelp forests. This fact produced a cascade of indirect effects that
reduced diversity in fish, shorebirds, invertebrates and raptors (Estes 1996; Estes
and Duggins 1995; Miller et al. 2001; Estes et al. 2003). After 7 years of isolation in
the recently formed Lago Guri reservoir in Venezuela, nearly 75% of the vertebrate
species have disappeared from the scattered islands that are too small to hold the
jaguar (Panthera onca) or the puma (Puma concolor). The few species that remain
are hyper-abundant and have gross effects on the plant community. There is also
little regeneration of the canopy trees (Terborgh et al. 1997).
10 The Importance of Reintroducing Large Carnivores …
237
Since the Late Pleistocene, over-exploitation, hunting, agriculture, livestock, habitat
loss and destruction have had a major impact on the populations of large carnivores
living in terrestrial and marine habitats. As human civilisation has progressed, human
density has massively increased, and the populations of large carnivores have
decreased or been eliminated. As a result, large predators have been entirely removed
from the system in many areas, or their numbers have been severely reduced (Weber
and Rabinowitz 1996; Terborgh et al. 1999; Woodroffe 2000; Miller et al. 2001).
The loss of large carnivores has long-term effects on ecosystem stability (Miller
et al. 2001). Because they have disappeared from large territories where they once
lived, top-down processes previously regulated by them have been considerably
altered (Rosenblatt et al. 2013). Trophic chains and cascades shorten, and animal
and plant populations suffer alterations in their numbers and dynamics. Without top
predators, populations of prey species increase; the increase of herbivores leads to
greater pressure on plants, reducing vegetation cover and increasing the prevalence
of diseases. Changes in animal and plant populations, also alter nutrient and biogeochemical cycles (soil and water) (Estes et al. 2011, Ritchie and Johnson 2009).
In the absence of top predators, mesopredator populations increase, thus leading to
so-called “mesopredator release” (Soulé et al. 1988) and a decline in populations of
smaller prey species. Summarising, the loss of predators limits the ecosystem’s
ability to restore the process of top-down control.
Apex predators have disappeared from different ecosystems. The extirpation of
large top predators in Northern Arizona in the early twentieth century led to the
irruption (sudden and rapid increase) of the mule deer (Odocoileus hemionus)
population, which caused over-browsing, a reduction in woody browse cover and
eventually famine among the deer (Rosenblatt et al. 2013; Binkley et al. 2006). In
Yellowstone National Park, the extirpation of wolves in the early twentieth century
led to an increase in the elk (Cervus elaphus) population, a concomitant decrease in
the recruitment of deciduous tree species and related effects on ecosystem structure
and function (Ripple and Beschta 2012; Rosenblatt et al. 2013). In the Aleutian
archipelago, the arctic fox (Alopex sp.) limits the number of sea birds, thus
decreasing the amount of nutrients transported from sea to land and maintaining the
herbaceous structure of the tundra (Croll et al. 2005). When sea otters (Enhydra
lutris) were overexploited by the fur trade in the North Pacific, marine invertebrate
herbivores increased in number, especially sea urchins (Strongylocentrotus spp.)
and devastated kelp forests. This fact produced a cascade of indirect effects that
reduced diversity in fish, shorebirds, invertebrates and raptors (Estes 1996; Estes
and Duggins 1995; Miller et al. 2001; Estes et al. 2003). After 7 years of isolation in
the recently formed Lago Guri reservoir in Venezuela, nearly 75% of the vertebrate
species have disappeared from the scattered islands that are too small to hold the
jaguar (Panthera onca) or the puma (Puma concolor). The few species that remain
are hyper-abundant and have gross effects on the plant community. There is also
little regeneration of the canopy trees (Terborgh et al. 1997).
10 The Importance of Reintroducing Large Carnivores …
237