24.2 Competition
Organisms compete for resources including food, shelter, space and light. As a result, competition between organisms has a significant effect on the number of organisms present in a particular area.
Types of competition
Competition is a biotic limiting factor - it is as a result of the interactions between living organisms.
Interspecific - competition between different species
Intraspecific - competition between members of the same species
Interspecific competition
This occurs when two or more different species of an organisms compete for the same resource. This interaction results in a reduction of the resources available to both populations.
If both species compete for the same food source, there will usually be less available for organisms of each species. As a result of less food, organisms will have less energy for growth and reproduction, resulting in smaller populations than if only one of the species had been present.
If two species of an organism, are both competing for the same food source but one is better adapted, the less well adapted species is likely to be outcompeted. If conditions remain the same, the less well adapted species will decline in numbers until it can no longer exist in the habitat alongside the better adapted species. This is known as competitive exclusion principle.
competitive exclusion principle - when two species are competing for limited resources, the one that uses the resources more effectively will ultimately eliminate the other.
Red and grey squirrels in the UK
In 1870’s, grey squirrel was introduced into the wild in the UK, its population quickly increase in numbers and resulted in the native red squirrel disappearing from many areas.
This is primarily because the grey squirrel can eat a wider range of food than a red squirrel and as it is larger is can store more fat. This increases its chance of survival and therefore its ability to reproduce thus increasing the population. An increasing population of grey squirrels further reduces the food supply available to the red squirrels, reducing their ability to survive and reproduce.
To explain how a limiting factor affects population
must link to its effect on the birth rate and death rates of an organism, increase in food can result in larger individuals survival change and therefore reproductive success.
Intraspecific competition
Intraspecific competition occurs when members of the same species compete for the same resource.
The availability of the resource determines the population size - the greater the availability the larger the population that can be supported. This results in fluctuations in the number of organisms present in a particular population time.
INSERT IMAGE
Stage 1 - when a resource is plentiful in a habitat (such as food or space) all organisms have enough of the resource to survive and reproduce. This results in an increase in population size.
Stage 2 - As a result on the increased population, there are many more individuals that share the food or space available. Resources are now limited; not enough is available for all organisms to survive, the population then decreases.
Stage 3 - less competition exists as the smaller population means less organisms are competing for the same resources. This means more organisms survive and reproduce, resulting in population growth.