Population Regulation

The population is influenced and regulated by various abiotic and biotic factors including population size. The regulation can be density dependent or density independent.

Density dependent

The factors involved in density dependent regulation are generally biotic (biological). Density dependent regulation affects the birth and death rate of population via factors such as predation and competition. Other factors are diseases (especially caused by parasitism), waste accumulation and both type of negative interaction i.e. interspecific and intraspecific competition. The high density population usually depicts high mortality rates.

Predation affects regulates the density of population by regulating the prey population density. As the population density of prey increases the predation increases and thus regulates the density.

Competitions either intraspecific or interspecific influence the fecundity rate of population and also limit the availability of food resources thereby limiting the growth in population density.

Independent dependent factor

This type of regulation is independent on population size and affects the whole population in similar way and mainly involves chemical or physical factors (abiotic). Density independent factors affecting the death and birth rate of population are regulated by environmental factors such as climatic conditions (weather), natural disaster such as fire, and pollution in air, water, land and Human interference such as deforestation.

Population Interactions

Population is a group of species living independently of other species. Ecosystems consist of group of different species population where the interacting species of one population has major effects on other populations. Various interactions are affecting growth of interacting populations. Among all the three major interactions are Competition, mutualism and predation.

Competition is when members of population limit the growth of same or different species and the members belong to same trophic levels. Mutualism and predation involves members of adjacent trophic levels. One species affects the other in either negative way or positive ways and sometimes has no effect on each other. These interactions can be presented in signs of “+” or “-“or “0” means positive effect, negative effect and no effect of one population on another.

Competition: Competition can be between individuals of same species or different species and termed as intraspecific competition and interspecific competition respectively. In this type of interaction both the interacting population has negative effect on each other and thus, inhibits each other’s growth. Hence, it’s a -/- type of interaction. 

Figure 13: Interspecific competition for food between Lion and hynae

Figure 14: Intraspecific competition for territory

Mutualism: Mutualism is a type of interaction where both the interacting populations benefit each other and there is no negative effect. It’s a +/+ type of interaction between populations. For example lichens, Mycorrhizae etc.

Figure 15: Lichens as an example of mutualism

Predation: Predation is an interaction between prey and predation population constituting a prey-predator system. The predator has negative effect on prey population while prey has no effect on predator population density. Thus, it’s a +/- type of interaction. For example grazing, browsing etc.

Figure 16: Grazing by cows showing predation (Herbivory)

Other types of interactions are Amensalism, parasitism, commensalism, cleaning symbiosis etc.

In Amensalism one population secrete some allelochemicals inhibiting the growth of others while other population has no effect on it. It’s a -/0 type of interaction. For example bacteria, fungi etc.

In Commensalism type of interaction one population is benefitted while the other is unaffected. It’s a +/0 type of interaction. For example lianas, Epiphytes etc.

The interspecific competition that is the competition between different species of population relates to a classical mathematical model called as Lotka-Volterra equations. If the population dynamics follow logistic model the outcomes of Lotka-Volterra equations will be:

a.     When the intraspecific competition is more intense than interspecific competition the species may coexist. Neither population reaches their intrinsic growth rate.

b.     The species with intense negative effect on its competition species will survive and other is eliminated.

c.      When both the interacting species have equal negative effects and when the interspecific competition is more intense than intraspecific competition than the species with high density of population persist while the other is eliminated.