4 INTRASPECIFIC COMPETITION AND SPECIES RICHNESS
INTRASPECIFIC COMPETITION
If we look at early succession (annual plants), there is a larger species richness than in the tree
vegetation. This is because there are a lot of niches that can be used.
If we look at late succession, we see that there are some species that are very competitive for the
environment. They will start to dominate the community and out-compete other species, and there
will be a loss of species richness in that environment. This is why there are fewer species than in the
annual plants.
There are two types of competition:
• Intraspecific competition: individuals of the same species compete for or exclude each other
from the use of resources, resulting in reduced growth, survival or fitness.
• Interspecific competition: individuals of different species compete for or exclude each other
from the use of resources, resulting in reduced growth, survival or fitness.
Interspecific competition is one of the most fundamental processes in ecology and partly determines
the dispersion and success of a species, as well as the evolution of a species. The result is that
interspecific competition is decisive for the species composition of an ecological community.
What competition can potentially do? The effects of competition are powerful. For example,
species completely out-compete each other, so it can cause to have fewer species in an
environment.
What is the actual effect of competition? Competition does not always reach the point in which
we’re losing species, there are other factors that reduce the competition effects.
INTRA à An environment has a particular amount of resources, and individuals (same population)
will start to compete with each other for these resources. Eventually, they will stop growing in
number because it has been reached the carrying capacity of the environment.
INTER àif a new species is released in the same environment, this new species, depending on what
it eats, will start to take away resources to the other species, which means that the other population
of the first species cannot grow to its carrying capacity. Depending on how strong the inter-specific
effect is on species one, will determine if these two species can live together or whether one is going
to out-compete the other.
1
, Why depends on their niche. Their niche is defined by different elements of the environment that
they use.
Species look for places in which there is a good combination of food sources and abiotic condition.
Observation in the field:
- Competing species live together on a larger scale but have clear differences in distribution on
a small scale. Fish live in the same river, but are limited in dispersion to their own zone that is
related to a resource or environmental condition (temperature).
- Species are excluded for areas they could populate if interspecific competition was not a
factor. The fish could also live in the zone ordinarily occupied by another species, but are kept
out by competition.
We see that if the resources that they compete for are abundant, there is not limitation, and both
species can happily live together.
If one of the resources becomes a limiting factor, so is not abundant, then we will see that the species
that adapted to the more limiting resource is more likely to survive. This species is more competitive
because it can use that limited resource more efficiently.
Principle of competitive exclusion of Gause:
In a stable environment, two species can only live together sustainably (coexist) when they occupy
different niches.
If there is no niche differentiation, one competing species will drive the other species out.
Interspecific competition: Lotka-Volterra model
Logistic population growth with intraspecific competition (in the absence of species 2):
N1/dt = r1 N1 (K1 – N1 )
K1
Population growth with intraspecific and interspecific competition (in the presence of species 2):
dN1/dt = r1 N1 (K1 – ( N1 + α12 N2 )
K1
Competition coefficient α12 : the effect of species 2 on species 1
Fundamental niche: the combination of conditions and resources that allow the species to exist,
grow, and reproduce when considered in isolation from any other species that might be harmful (no
interspecific competition)
Realized niche: the combination of conditions and resources that allow the species to exist, grow,
and reproduce in the presence of other species that limit survival (interspecific competition)
Competing species can coexist when both are provided with a realized niche by their habitat.
Niche differentiation (differentiation in realized niches of the species) or different resources
utilization, allows species to coexist.
Example of niche complementarity:
same amount of food, but different coastal zone; same zone but different amount of food.
2
INTRASPECIFIC COMPETITION
If we look at early succession (annual plants), there is a larger species richness than in the tree
vegetation. This is because there are a lot of niches that can be used.
If we look at late succession, we see that there are some species that are very competitive for the
environment. They will start to dominate the community and out-compete other species, and there
will be a loss of species richness in that environment. This is why there are fewer species than in the
annual plants.
There are two types of competition:
• Intraspecific competition: individuals of the same species compete for or exclude each other
from the use of resources, resulting in reduced growth, survival or fitness.
• Interspecific competition: individuals of different species compete for or exclude each other
from the use of resources, resulting in reduced growth, survival or fitness.
Interspecific competition is one of the most fundamental processes in ecology and partly determines
the dispersion and success of a species, as well as the evolution of a species. The result is that
interspecific competition is decisive for the species composition of an ecological community.
What competition can potentially do? The effects of competition are powerful. For example,
species completely out-compete each other, so it can cause to have fewer species in an
environment.
What is the actual effect of competition? Competition does not always reach the point in which
we’re losing species, there are other factors that reduce the competition effects.
INTRA à An environment has a particular amount of resources, and individuals (same population)
will start to compete with each other for these resources. Eventually, they will stop growing in
number because it has been reached the carrying capacity of the environment.
INTER àif a new species is released in the same environment, this new species, depending on what
it eats, will start to take away resources to the other species, which means that the other population
of the first species cannot grow to its carrying capacity. Depending on how strong the inter-specific
effect is on species one, will determine if these two species can live together or whether one is going
to out-compete the other.
1
, Why depends on their niche. Their niche is defined by different elements of the environment that
they use.
Species look for places in which there is a good combination of food sources and abiotic condition.
Observation in the field:
- Competing species live together on a larger scale but have clear differences in distribution on
a small scale. Fish live in the same river, but are limited in dispersion to their own zone that is
related to a resource or environmental condition (temperature).
- Species are excluded for areas they could populate if interspecific competition was not a
factor. The fish could also live in the zone ordinarily occupied by another species, but are kept
out by competition.
We see that if the resources that they compete for are abundant, there is not limitation, and both
species can happily live together.
If one of the resources becomes a limiting factor, so is not abundant, then we will see that the species
that adapted to the more limiting resource is more likely to survive. This species is more competitive
because it can use that limited resource more efficiently.
Principle of competitive exclusion of Gause:
In a stable environment, two species can only live together sustainably (coexist) when they occupy
different niches.
If there is no niche differentiation, one competing species will drive the other species out.
Interspecific competition: Lotka-Volterra model
Logistic population growth with intraspecific competition (in the absence of species 2):
N1/dt = r1 N1 (K1 – N1 )
K1
Population growth with intraspecific and interspecific competition (in the presence of species 2):
dN1/dt = r1 N1 (K1 – ( N1 + α12 N2 )
K1
Competition coefficient α12 : the effect of species 2 on species 1
Fundamental niche: the combination of conditions and resources that allow the species to exist,
grow, and reproduce when considered in isolation from any other species that might be harmful (no
interspecific competition)
Realized niche: the combination of conditions and resources that allow the species to exist, grow,
and reproduce in the presence of other species that limit survival (interspecific competition)
Competing species can coexist when both are provided with a realized niche by their habitat.
Niche differentiation (differentiation in realized niches of the species) or different resources
utilization, allows species to coexist.
Example of niche complementarity:
same amount of food, but different coastal zone; same zone but different amount of food.
2
