The Processes of Niche Differentiation
Brady Boyer
The process of niche differentiation, also referred to as niche partitioning, is a
phenomenon that occurs whenever two competing species limit their resource
intake in order to avoid interaction with their competitors. This process is
important for understanding the ecological interactions that occur within
environments throughout the world.
Niches
In every environment, any given species is limited to its own niche. A niche can be
defined as an n-dimensional hypervolume, where the dimensions are the
environmental conditions and resources that the species needs in order to survive.
For example, some conditions could be temperature and humidity and some
resources could be water, food, or sunlight. Almost always, an individual is unable to
experience its fundamental niche, which is everything the species needs that is
currently available in the environment. Since individuals rarely acquire everything
that they need, they are often considered to occupy their realized niche. A realized
niche is the sum of required conditions and resources that the species is actually
obtaining, but not everything that is available in the environment.
Competition
So why would an individual not be able to obtain all its needs from the
environment? There are two common reasons for this issue. First, every individual
in a population of a certain species will experience some degree of competition with
members of their own species. The biggest competitors are the ones that need the
exact same conditions and resources as you do, and this competition comes from
members of your own species. This type of competition is referred to as intraspecific
competition. Also, an individual may have to compete for resources with a different
species. This other species may not require the exact same resources as the
individual, however it could be more or less efficient at obtaining said resource. This
type of competition is referred to as interspecific competition.
Competitive Exclusion
If one species is able to exploit a resource more effectively than another species, it
will be able to dominate that resource and procure more of it. This idea leads us to
the competitive exclusion principle. This principle states that if two species require
the same resource, then they will have to compete with the other species to obtain
it. More often than not, one species will be better than the other at obtaining the
resource. If the two species are competing long enough, one species will eventually
be driven out of the environment or be driven to extinction. Of course, if this were
the only factor effecting species then there would be very few species in the world.
Lotka-Volterra Model
The entire idea of competitive exclusion can be very vague and it is possible for us to
refine it further with the Lotka-Volterra Model. This model uses the carrying
capacities of the environment for both species as well as the competitive effect for
both species. The carrying capacity is represented by K and is the maximum number
of individuals of a species that the environment can support. The competitive effect
of one species on another is normally represented by α12 or α21, but in this figure the
α seems to be replaced by a box (an error from when the authors copied it to their
website). Finally, N1 and N2 refer to the population sizes of both species. Based on
this model there are four possible outcomes whenever two species compete for a
resource.
Lotka-Volterra Model
Three of these outcomes (a,b, and d) result in competitive exclusion and extinction
of one (a, b) or both (d) species. However, it is possible for two species to coexist
without adaptation if conditions are absolutely perfect, as shown in c. The circles
show where a species would eventually end up. The arrows within each figure
represent the movement a point would take over time. For example, in a, if a point
was in the middle of the graph it would eventually move down and to the left until it
was between the two lines and then move down and to the right. If a point ends up
on one of the axes of a graph then it represents the extinction of the species because
there are none left. In d, both species are excluded, while in a and b, either species
Image from http://tc.wangchao.net.cn/baike/detail_1606477.html.
one or species two is excluded. Graph c within the figure is the only graph that has a
point where all arrows guide each species to a central location. This means that the
two species will coexist, even if they are competing with each other. While this
model does show that extinction is not always the final result, it fails to fully
describe how species continue to coexist.
Niche Differentiation
One of the main reasons that species do not go extinct due to competitive exclusion
is niche partitioning. If two species are competing for a resource, it is possible for a
physiological or behavioral adaptation to evolve so that both species can coexist.
This process makes it so that each species can still obtain part of the resource they
need while also minimizing contact with the competing species. One great example
that is always used discusses birds in a tree. Say that you have two species of birds
that both feed within trees. If these two species live in the same area, then they will
both be entering the same trees to try to get the same food. Some birds have
developed behavioral adaptations to scavenge for food in only a certain part of the
tree. One species could scan for resources in the upper part of the canopy while the
other species searches for food in the lower canopy. There is actually a system like
this that exists where seven different species of birds search only a particular part of
each tree! Therefore, niche differentiation can allow species that have overlapping
fundamental niches to coexist in the same environment.
Conclusion
In conclusion, the processes that combine to cause niche partitioning to occur are
complex and numerous. Species-specific conditional and resource needs drive them
to live in certain environments that may lead them to competition with other
species of similar needs. This conflict can lead to extinction, but more often than not
it leads to coexistence due to the ability of species to alter their physiology or their
behavior in order to “share” the vital resource that each species requires. The
process of niche differentiation is one way for different species to deal with
competition, however there are several other methods. This phenomenon of niche
differentiation is just one of many facets of ecology that can be closely studied to
better understand the complexity of interactions between species.