BI SC 002 LECTURE 10—COMMUNITY ECOLOGY
Draft: December 2, 2010
deals with how different populations of organisms interact with each other.
The possible types of interaction include
, in which two or organisms are trying to
utilize the same resources,
, in which organisms lives are linked to each other, and
, in which one organism consumes another organism.
These interactions affect the
population biology of a particular species because they all influence dN/dt (the rate of growth of
Two hypotheses exist about how community interactions take place.
H.A. Gleason developed
individualistic concept of communities
This idea states that the community is nothing
more than an aggregation of species that happen to coexist in one place.
This is opposed by F.E.
holistic concept of communities
, in which communities are integrated units.
Clements saw the community as a “super-organism” whose constituent species have coevolved
to specific functions (like various organs in a body).
Most ecologists tend to prefer Gleason’s
individual concept because in reality, organisms tend to respond independently of each other to
Before we can discuss competition, we must first define the term
A niche is the sum total
of all of the ways an organism utilizes the resources of its environment.
Basically, the niche is
the “role” an organism plays in the environment.
The niche can include space utilization, food
consumption, temperature range, mating conditions, moisture, and other environmental
Competition is an important factor in defining the niche of an organism.
is competition between individuals of different species, while
is competition between individuals of the same species.
An organism may be capable of using many, many resources in the environment.
organism is capable of using is called the organism’s
may compete for some of those resources and another organism may be a better competitor, thus
making the original’s niche smaller.
The actual niche an organism occupies in the environment
is called the organism’s
The classic example of realized and fundamental niches is J.H. Connell’s work with barnacles.
On the seaside cliffs of England grow two types of barnacles—
which is found
above the low tide line, and
which is found below the low tide line.
If you remove
is capable of growing in its place below the low tide line.
’s fundamental niche is the entire cliff.
is a better competitor
below the low tide line, so
’s realized niche is just that area that is sometimes
exposed to air.
If you remove
will not expand its range above the tide
line (it cannot survive the exposure to air).
Thus, for this organism, the realized niche and
fundamental niche are the same.