a comparison of density dependent and density independent factors
A Comparison of Density-dependent and Density-independent Factors
Various factors are employed to chart the population growth of species in order to ensure that it doesn't have any untoward effect on the ecosystem. These determining factors are classified into density-dependent and density-independent factors. In this Buzzle article, we compare the two in a bid to find out what they are responsible for.
Liebig's Law of the Minimum
In agricultural science, the Liebig's law states that the growth of a plant is controlled by the availability of the scarcest resource, and not by the total amount of resources available.How Nature Limits Population Growth
Well, it simply resorts to limiting factors. In population ecology, a limiting factor can be any resource or environmental condition that limits the growth, abundance, or distribution of the population. Based on the Liebig's law of the minimum, it implies that even if all other factors are favorable, the one that is least favorable will dictate the growth, abundance, or distribution of the population of a species. As you can see, it doesn't just restrict the population growth, but also determines which species will survive in a particular ecosystem.
If reptiles or herbivores are not found in Antarctica, it's because of the limiting factors that come into play in that region. For reptiles, the limiting factor in Antarctica is the freezing temperature, as they being cold-blooded, depend on ambient temperature to stay warm. Similarly, for herbivores, the limiting factor on the southernmost continent is the lack of vegetation ... for obvious reasons.
Density-dependent Vs. Density-independent Factors
A limiting factor can be biotic (related to living organisms) or abiotic (some non-living component of the environment). Further, these factors are classified into two types: density-dependent limiting factors and density-independent limiting factors.
Density-dependent Factors
Density-dependent factors are those that depend on the population density. These are the factors whose effects on the population vary depending on the density of population. These include availability of food, competition, predation, parasitism, diseases, etc.
Examples
Competition: If the density of population is high, there will be more competition for food and other resources. It will eventually result in starvation, low reproduction rate, and even migration, with species looking for favorable conditions in other regions.
Diseases: If the density is high, diseases will spread faster and more individuals will be affected.
What to Infer
Density-dependent factors only come into play when the population reaches a certain level. Larger the population, stronger the impact.Density-independent Factors
Density-independent factors are the ones that are not dependent on the population density. They affect the species regardless of how dense the population is. These include natural disasters, like floods, drought, tornadoes, etc., climate, and even human activities.
Examples
Extreme weather: When the weather changes drastically, even native species bear its brunt. If, for instance, temperatures spike in the tropics, then it will cause lakes to evaporate, and that, in turn, will spell disaster for aquatic species.
Climate: In deserts and polar areas, where climate is far from favorable, the number of species is low.
What to Infer
Density-independent factors do not have size constraint. They are effective in the case of both, large populations and small populations.