Origin
The idea of keystone
species is resulting from the
assumption that different
species are not equal in their
importance for the
functioning of communities.
The term keystone species
was first derived after
Robert T. Paine’s work on a rocky shore community in 1996. He
removed the top predator, starfish (Pisaster ocbraceous) from a
section of the shore. It results in reduction of 15-species assembly
to eight species. It shows that removal of a single species
drastically changes the community. These kinds of changes in any
community also effects the surrounding communities. As all
organisms in an ecosystem rely on each other.
Definition
Robert T. Paine defined it as:
“A species that feeds preferentially on the dominant competitor
among its prey species, such that the keystone predator’s feeding
prevents the dominant prey from excluding other species and
therefore maintains a higher species diversity in the system than
in the keystone’s absence”
The term keystone is originally applied to a predator in a rocky
intertidal zone whose presence or absence greatly influenced the
other species in the ecosystem. On the other hand, Power et al.
defined it as:
“A species whose effect is large, and disproportionately large
relative to its abundance”
This definition distinguishes the keystone species from dominant
species, so the role of keystone species in an ecosystem must be
great as compared to its relative abundance. Thus it is possible for
rare species to have a great impact on food webs of the ecosystem
than more common ones.
In simple words, a species on which other species in an ecosystem
largely depend, such that if it were removed the ecosystem would
change drastically.
There are two hallmarks of keystone species used by many
ecologists.
Presence of keystone species is essential in maintaining the
organization and diversity of the community.
These species are exceptional in their importance relative to
rest of the community.
Types of keystone species:
Keystone species are divided in to different types on the basis
of their functional role as keystones. Some predator species play
unique roles in their ecosystem by regulating the populations of
their prey. Their elimination can affect the abundance and presence
of other predators and lead to the removal of both prey and
competitors.
Some species play key roles in the maintenance of plant
populations by providing pollination services that maintain gene
flow and secure plant fecundity. Therefore, absence of these
pollinators can affect all species that depend on them directly.
Examples of Keystone species:
Wolves: (Canis lupus)
Being a top predator, wolves are important in many habitats.
Wolves prey on deer populations and keep their population in
check, because too many deer will eat small trees, which leads to
fewer trees. In turn, there would be fewer birds and beavers and the
whole ecosystem would change.
Wolves No of deer Fewer small Fewer
absent increases trees birds
Fewer
beavers
Impact of Wolves absence on the ecosystem.
Jaguars: (Panthera onca)
Jaguars are predators, as are many keystone species. The
jaguar has a preference for dense rainforest but is found
across a variety of forested and open territory. They have a
very diverse diet of about 87 different species i.e. monkey,
turtles, snake, birds, fishes, etc. Which contributes to their
importance by keeping the number of these species in
balance. Without the jaguar, herbivorous prey animals would
decimate the plants of their ecosystem. The jaguar is
considered near threatened and numbers are declining.
Tiger shark: (Galeocerdo cuvier)
As the top predator,
tiger sharks directly or
indirectly limit the
behavior and population
of other species in the
food web. Dugongs and
green sea turtles are
staples of the tiger shark
diet and the presence of
a shark intimidates these
two species to graze lower
quality sea grass near the patch edges and continually modifying
their distribution. This allows the sharks to prevent overgrazing of
the sea grass.Tiger sharks also influence the location and
distribution of bottlenose dolphins even though they are rarely
consumed by the sharks. In their presence, dolphins avoid feeding
in the productive shallow waters. Once the sharks leave, dolphins
and other species are free to feed in all habitat types. Not only do
they exert control on sea grass grazing, tiger sharks also influence
and limit feeding of the fish community. Removal of the keystone
species would lead to an imbalance in the food web by having
over-exploitation of sea grass and fish by uncontrolled populations
of turtles, dugongs, and dolphins.
American alligator:
(Alligator
mississippiensis)
They American
alligators are important
members of their
ecosystem, and are
regarded as keystone
species of the Southeast.
Many animals are affected by their existence. Young alligators are
prey for wading birds, turtles, snakes, mammals, etc. Alligators are
at the top of their food chain. As top predators, they are important
in controlling prey numbers. Alligators use their tails to make
burrows for nesting and to keep warm. When an alligator
abandons a burrow, the hole left behind fills with freshwater and is
utilized by other species for breeding and drinking. If alligators are
removed from their native ecosystem, it would affect countless
other species.
Prairie dog: (Cynomys)
It is one of keystone
species they make
burrows and provide
nesting areas for many
species. Prairie dog
tunnel systems also
help channel rainwater
into the water table to
prevent overflow and
erosion, and can also serve to change the composition of the soil in
a region by increasing aeration and reversing soil compaction that
can be a result of cattle grazing. By eating grass, prairie dogs keep
water in the soil instead of the water evaporating from the leaves of
plants.
Prairie dog’s
Home for Aerate the
burrows
Insects Soil
Home for Home for Home for
Rabbits Ferrets Owls
Prairie dog enable opportunities for other species.
Gopher tortoise: (Gopherus Polyphemus)
Gopher tortoises are so named because of their ability to dig large,
deep burrows. These burrows are widely used by more than 350
species throughout the ecosystem, making gopher tortoises a
keystone species with a pivotal role to play in their native
community. Other species that use the gopher tortoise burrows are
called commensals, and they include nearly 400 mammals, birds,
reptiles, amphibians and insects such as owls, snakes and frogs.
Red-naped sapsuckers: (Sphyrapicus nuchalis)
It plays two distinct keystone roles.
They dig nest cavities in
fungus-infected aspens
that are required as nest
sites by two species of
swallows and they drill
sap wells into willows
that provide abundant
nourishment for
themselves,
hummingbirds, orange-
crowned warblers,
chipmunks, and an array of other sap robbers. The swallows thus
depend on, and the sap robbers benefit from, a keystone species
complex comprised of sapsuckers, willows, aspens, and a
heartwood fungus. Disappearance of any element of the complex
could cause an unexpected separating of the community.
Noisy miner:
(Manorina
melanocephala)It has
been described as a
keystone species, as it is
colonizing an ever-
increasing range of
human-dominated
habitats, and aggressively
excluding smaller bird species from urban environments. This
phenomenon has been also observed in rural areas. The noisy
miner's presence linked with reduced numbers of insectivorous
birds such as fantails, whistlers, the restless flycatcher and other
honeyeater species, and that this decrease was most marked in sites
with better access to water and nutrients.
Snow geese: (Chen caerulescens)
If there are not enough snow geese in salt marshes, other harmful
plant species would take over. When the geese graze, it leaves
open areas for other varieties of plants to take root, thus adding to
the diversity of the habitat. They keep the population of plants.
Honey bees: (Anthophila)
honey bees are
involved in the
process of pollination
which is one of the primary ways plants reproduce. Honey bees are
responsible for the movement of pollen from one flower to another
as they gather nectar. The distribute of pollen can lead to the
process of cross-pollination. Cross-pollination helps to maintain
the genetic diversity of the plant community in the ecosystem.
Plants are shelter for insects, which are then eaten by other species,
like birds.
Woodpeckers: (Picidae)
They are the
master carpenters
of the bird world.
They're called
"keystone
species" for their
crucial role in
creating habitat
suited to other
woodland
wildlife.
Abandoned woodpecker nest-holes become nests or roosts for
small owls, cavity-nesting ducks, swifts, bluebirds, swallows,
wrens, and other birds, as well as many small mammals.
Benefits of keystone species:
Keystone species enhance their habitat. they maintain the
populations of other species in the ecosystem. Some keystone
species provide shelter to other species. They also participate in
recycling of different nutrients and waste material to keep the
balance in the ecosystem.
Regulate
Enhance animal
habitats papulaion
Keystone
Species
Recycle
nutrients, Pollination
wastes
References
Paine, Robert. T. (1995). A conversation on refining the
concept of keystone species. Conservation Biology 9, 962-964.
Paine, Robert T. (1966). Food web complexity and species
diversity. American Naturalist, 100, 65–75.
Mills, L. Scott; Soule, Michael E.; & Doak, Daniel F. (1993).
The
keystone-species concept in ecology and conservation
Bioscience.
Berger 2001, Hebblewhite, M., C. A. White, C. G. Nietvelt, J.
A. Mckenzie, T. E. Hurd, J. M. Fryxell, S. E. Bayley, P. C.
Paquet. 2005. Human Activity Mediates A Trophic Cascade
Caused By Wolves. Ecology, 86(8), 2005, pp. 2135-2144.
Ehrlich, P. R. and G. C. Daily. 1988. Red-naped sapsuckers
feeding at willows: possible key-stone herbivores. Am. Birds
42: 357-365.
Ashley, Lisa C.; Major, Richard E.; Taylor, Charlotte E. (2009).
"Does the Presence of Grevilleas and Eucalypts in Urban
Gardens Influence the Distribution and Foraging Ecology of
Noisy Miners?"
Assignment
Zoology
Submitted to
Rabiya Mukhtar
Submitted by
Sonia Javed
Roll No
96
Department Bs. Chemistry 3rd
Semester (Evening)
Topic
Animal
Keystone Species
