Species in natural ecosystem are connected through food webs. In natural ecosystems, food chains are present as part of the food webs only. These food webs are very much complex. They are the routes of energy and matter transfer in an ecosystem. Food webs contain large number of large food chains. So usually an elimination of few species won’t stop the transfer of energy and matter through food webs, as their rare alternate routes for that in a food web. That is why the food webs bring more stability to the ecosystem.
All species are important in an ecosystem, as each species perform some particular function, commonly called niche of a species. There are some species in ecosystems which are more important than the other species, as the ecological niche of these species can’t be filled by other species native to the area. Such species are called keystone species. In absence of keystone species, the ecosystem would either be dramatically different or collapses altogether.
Any species may be a keystone species. They may not be the largest or the most abundant species in an ecosystem. However, mostly the animal species are the keystone species as they have large influence on the food webs. Among the animals, often the predator species are keystone species, as few predators can control the distribution and population of large prey species.
Identifying the keystone species of ecosystems is essential for maintaining the sustainability of an ecosystem. The mere re-introduction of the keystone species could lead to restoration of the whole ecosystem. This was successfully done in the Yellowstone National Park, USA.
The grey wolf used to roam over the whole of North America. It is estimated that between 1850 and 1900, 2 million grey wolves were shot, trapped and poisoned by ranchers, hunters and govt. employees. The idea was to make the area safe haven for livestock and big game animals. So the area was almost made wolves free, with only few hundred wolves remained in the area.
In absence of the grey wolves, the population of the bison, elk, Coyote etc. increased tremendously. The herds of elk, moose, dear and antelope devastated the vegetation such as willow and aspen trees. This increased soil erosion. The coyotes attacked the cattle in surrounding ranches. So both the degradation of the ecosystem and the attacks on the livestock actually increased more in absence of the grey wolves.
Ecologists realized the importance of this keystone predator species in the area. In 1987, the US Fish and Wildlife services proposed the re-introduction of grey wolves as keystone species in the Yellowstone National Park, USA to sustain the biodiversity of the ecosystem and prevent it’s further degradation. The proposal met with angry protests, some from ranchers who feared wolves would attack their livestock, from hunters who feared wolves would kill large game animals and from logging companies who feared govt would stop logging operations on wolf populated areas.
The government went ahead with the proposal and captured the grey wolves in Canada and relocated them in Yellow Stone National Park in 1995. The estimated carrying capacity of the Park is 110 to 150 grey wolves. By 2006, the park had 136 grey wolves.
Re-introduction of the grey wolves sent ecological ripples through the park’s ecosystem. The population of the ilk, bison, Coyote etc. starts reducing. This spurred the growth of aspen, cottonwoods and willow trees. This helps in stabilization of the soil and water temperature decreased, which is better for the growth of trout. The leftovers of preys killed by wolves are an important source of food for scavengers like Ravens and bald eagles.
The coyote’s population reduced to half, which results in lesser attacks on cattle in surrounding ranches. The population of smaller animals such as ground squirrels, mice and gophers increased which are hunted by coyotes, eagles and hawks. So with the re-introduction of the grey wolves the Park has returned to its pristine glory.