Conservation strategies have now shifted focus to the keystone species whose presence and diversity affects the community dynamics, stability and diversity.

Ecological systems are the more prone to disturbances. The effects may sometimes further accelerate a series of events in a wave like fashion affecting the stability of the system as a whole. Extinction of a single species can sometimes lead to loss of many other species in the ecosystem. Such species are called as keystone species

The term 'keystone species' was introduced by T.Paine in1969. Since then, identification and conservation efforts of keystone species have been evident in ecological studies.

The main features of a keystone species are listed below.
1. The activity of the species determines the community structure.
2. They can create or modify habitats and can influence the interspecific interactions among the community.
3. They maintain the organization and diversity of their communities.
4. The effects are disproportionate to the biomass or relative abundance of the species.
5. The species need not be dominant always.
6. Removal of keystone species causes loss in biodiversity of the community.

History

The original finding of the keystone species was by Paine. He experimentally removed some carnivorous species which inhabits the intertidal zone. He chose the starfish Pisaster for the experiment. The removal affected the prey of Pisaster (mussels) increasing their dominance and drastically reducing the biodiversity. The mussel population in fact exploded but it soon led the other species to decline in number and gradually loss of biodiversity. Almost half of the species which were originally present at the start of the experiment soon became absent once the Pisaster was removed from the ecosystem.

The methodology adopted by Paine was soon followed by ecological researches and the list of keystone species became longer.

Categories of keystone species

1. Predator species:
Their removal or increase affects the prey species. The subsequent effects create a change in diversity of the prey as well as competitor species. Most of the keystone species are predators. Eg: Starfish Pisaster, Sea Otters (Enhydra lutris), fire ants (Solenopsis
geminata) etc.


2. Prey species:
When the key stone species is one of the prey species, then their removal affect the other species which are sensitive to predation and lead them to extinction. Subsequently, the predator population decline. Some keystone prey species were found to increase the diversity of other species also. One such example is the snowshoe hares. African elephants are a classic example of keystone species which affect the species diversity of the community by their extensive destructive habits of the ecosystem.

3. Plant species:

When certain plants act as keystone species, removal/increase of such species results in change of diversity of dependent herbivore animals, pollinators and insects which are involved in dispersal of seeds.

4. Modifier:
Some keystone species are habitat modifiers. When they are removed or increased in the ecosystem, they cause depletion of materials which affect the typical flow of energy within the ecosystem. The process affects the other species which depend on these resources and hence succession. These keystone species does not have a direct effect on the food chain, but their activity typically changes the vegetation or habitat to such an extent that it modifies the species diversity of the entire ecosystem.
e.g. The North American beaver, Brazilian termite etc.

5. Links:
The key stone species can also be a link between the different trophic levels of the community. Any great changes in the species abundance will cause a cascade of effects which causes the entire food web to collapse and subsequent loss of habitat for the entire community. In short, they form a critical structural link in the ecosystem and their removal results in change of ecosystem function and species density.

6. Keystone mutualists:
These keystone species function to maintain the mutualistic relationships. They are also termed as 'mobile links' which connect the food webs which are otherwise separated from each other. Mostly pollinators and seed dispersers act as keystone mutualists.
e.g. humming birds(pollinators), mammals which disperse the mycorrhiza.


7. Keystone hosts:
The plant species which are critical in sustaining the mobile links are also considered to be keystone species since the population of these mobile links are dependent on the host plants. Plants supporting the generalist species of pollinators and dispersers are included in this category. These pollinators and dispersers should be keystone species. These plants offer the keystone resources such as nectar, figs, nuts etc which are essential to maintain the keystone species.


Major roles in conservation

1. These species can be targeted for conservation approaches to maintain diversity.
2. Used to retain the community structure intact.
3. Reestablishment of ecosystems. For example, restoration of forest lands after fire hazards.
4. Support the viable populations of other species in the community which otherwise needs expensive methods of conservation.
5. Creation of habitat which can be inhabited by species prone to extinction. E.g. Coral introduced into the coastal lines branch up and provide shelter for other species of marine invertebrates such as fishes. Many of the species having the corals as their habitat are facing extinction; hence the introduction of corals into newer coasts will augment the preservation of these species indirectly.

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