Where The Wild Things Were: Re-wilding and the Sixth Extinction - Biodiversity Conservation and Environmental Change - page 30

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Where The Wild Things Were:
Re-wilding and the Sixth Extinction
Biodiversity is currently in the midst of an extinction crisis, the rate and magnitude of which
ranks alongside only five other similar events in the past 540 million years of life on Earth
(Barnosky et al. 2011, Braje and Erlandson 2013). At the same time, we face unprecedented
levels of landscape transformation and climate change (Barnosky et al. 2014). These changes
undermine the biosphere's ability to provide the ecosystem services and resilience that are
essential to human well-being, and furthermore degrades opportunities for current and
future generations to experience wild nature (Rockström et al. 2009, Monbiot 2013a, b). There-
fore, there is growing interest in re-wilding, variously defined as the restoration of keystone
species or the restoration of ecosystem function through re-introduction or replacement of
species (Seddon et al. 2014).
Over 300 terrestrial vertebrates have been lost since 1500 ce, while many others are locally
extinct, and this has had cascading effects on ecosystem structure and function (Estes et al.
2011, Dirzo et al. 2014, Seddon et al. 2014). This current pulse of extinctions began when
explorers and colonists brought guns, steel traps and diseases that allowed the slaughter of
animals on an unprecedented scale. Carnivores were particularly badly affected, due to the
value of their fur and their impacts on domestic livestock, though herbivores were not
immune to the carnage, both through direct killing and the spread of modern farming tech-
nologies, which converted habitat to croplands, rangelands, and plantations.
The loss of large carnivores has caused dramatic changes in herbivore populations and
vegetation; for example, the extirpation of wolves from Yellowstone National Park in the 1920s
led to cascading effects on elk, beaver, mesopredators, and riverine vegetation (Smith et al.
2003, Ripple and Beschta 2004). Island ecosystems have also been hard hit, with the loss of
unique large animals and flightless birds, which were poorly adapted to human hunting and
the introduction of predators. Their extinction disrupted crucial ecosystem services like pol-
lination and seed dispersal (Hansen et al. 2010).
Loss of megafauna began long before the recent pulse of Anthropocene extinctions, how-
ever (Braje and Erlandson 2013). Beginning in the cold, arid conditions of the Pleistocene
and continuing into the warmer climates of the Holocene, 97 out of 150 genera of megafauna
(animals >44kg) became extinct (Barnosky et al. 2004). It is likely that human impact played
a role, alongside changing climate (Koch and Barnosky 2006). One of the more extreme