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Populations, communities and ecosystems
are all regulated by various factors. These can
be biological (biotic factors) or non biological
(abiotic factors).
Biotic factors: competition,
predation, mortality (death) rates, fecundity
(birth) rates and parasitism.
Abiotic factors: climate, water
currents and temperature.
Here we will look at two important biotic factors:
competition and predation.
Competition is defined as the interaction
between two organisms for a necessary resource
that exists in short supply. This competition
can exist between individuals of the same species
(intraspecific) or between individuals of different
species (interspecific). Organisms compete for
many reasons including one or more of the following:
light, space, mates, food, nutrients and water.
The outcome of any competition is either: competitors
manage to share the resource (which can limit
their individual needs), OR; one of the competitors
elimnates the other.
Predation is defined as the consumption
of one species by another. The consumer is the
predator and the consumed is the prey. Herbivores
are predators too, they consume autotrophic organisms,
this type of predation is called grazing.
Predation can be the only factor controlling a
prey population or it can have little or no affect
on the population. The ability to regulate a prey
population depends on the predator and prey relationship
and their species.
The image above shows quite a complex food web
where competition and predation would be occurring.
Organism |
Competition |
Predation |
|
Interspecific |
Intraspecific |
Predator |
Prey |
Phytoplankton |
Y |
Y |
N |
Y |
Zooplankton |
Y |
Y |
Y |
Y |
Fish |
Y |
Y |
Y |
Y |
Seabird |
Y |
Y |
Y |
NOT SHOWN |
Shark |
Y |
Y |
Y |
N |
Seal |
Y |
Y |
Y |
NOT SHOWN |
The table above tell us which biotic interactions
are occurring in the scenario above. For example,
phytoplankton will be competing with individuals
of the same species and other species for light,
nutrients and space. Being autotrophs they are
not predators, but they are prey for grazers such
as copepods.
Similarly the seabird will be competing intra-
and interspecifically, it is a predator of fish
and although none are shown here it may have at
least one predator.
Why not try out our
Competition and
Predation questions?
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