The Ecological Niche and the Competitive Exclusion Principle
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The Ecological Niche and the Competitive Exclusion Principle

Welcome again today we begin on the Caribbean island of Tobago looking at hermit crabs these animals have very unusual
lifestyles they seek out empty shells of snails and other animals as potential homes as the crab grows it needs to seek out
larger shells apart from house hunting hermit crabs must escape predators seek food for themselves and fight off other crabs for food and for potential
homes and mates in some marine crabs sea anemones attach themselves
to the shell and can assist the crab in scaring off its predators while
benefiting by consuming fragments from the hermit
crabs real here you can see a hermit crab with its
claw visible as it is poised to defend itself against
potential predators what you just heard is a description
of an ecological niche students often confuse the niche with the
habitat the niche is a species share of a habitat
and the resource is in it an organism’s ecological niche depends
not only on where it lives but also on what it does whereas the habitat is simply
an environment in which a species normally lives such
is the uniqueness of a species Niche that biologists often refer to a
competitive exclusion principle if two competitors exist in the same niche one will out-compete the other alternatively a compromise is made and each competitor retreats into a part of the niche and concedes the remainder to its
competition this can take the form of changing its behavior and reducing its range these two lizards
of the Iguanidae family provide a good example the green iguana and the Green Basilisk both are endemic to the rain forests of Central America
in the course of evolution each species developed distinct
behaviors that confined them to what is termed a realized niche in the absence of a similar competitor a possible
extension at the niche can occur and this is termed the fundamental niche this green basilisk better known as the Jesus Christ lizard is omnivorous surviving on a diet of plant material and fruit but mainly on a diet of insects like moths and dragonflies they are excellent climbers and as their
name suggests excellent swimmers able to walk on water green iguanas have a very similar job description or niche but in keeping with the
competitive exclusion principle each species although they can potentially
occupy the niche of the other has specialized into a
distinct or realized niche green iguanas are known to feed on the
occasional insect but their diet is comprised
primarily of plant material and fruit according to
the principle of competitive exclusion two similar species cannot occupy the same niche what can and
does occur in the course of evolution is that species concede parts of their potential niche also known as the fundamental niche and in time the retreat into a more
specialized or realized niche in the case of the green basilisk although it is capable of living in the treetops it tends to confine itself to the undergrowth and the water feeding on a diet that includes mainly
insects and small invertebrates although it is
known to feed on plant material and fruit on the other hand for the iguana although it is a good swimmer it tends to spend a lot of its time in
the treetops foraging for plant material and fruit and although iguanas have been
observed consuming insects their diet is primarily vegetarian it is possible that in the absence of competition from
a similar species the Green Basilisks may have expanded their Niche to occupy the full fundamental niche a similar situation
could have possibly occurred for the iguanas in the absence at the Green Basilisk this extension at the niche or the
space in which the organism generally occupies and the functions
that it carries out is known as its Fundamental Niche

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