Top 9 Density Dependent and Density Independent Factors

Density Dependent and Density Independent Factors

Demography is the study of all the possible statistics that affect the size of a population. Some biotic and abiotic factors limit the size of a population. These factors are broadly categorized into density dependent and density independent factors.

Density Dependent Factors

A factor that affects the size of a population in response to the density of the population is called density dependent factors. These are also known as regulating factors as they regulate the size of a population in a certain range. These are the result of some biological phenomena thus also referred to as biological factors. As the density of the population decreases, the influence of these factors also decreases. Such as, if the plants affected by viral infection are removed from the field (population decreases), there are fewer chances of surviving plants getting that particular viral disease. Such factors are called density-dependent factors and they came into action when the population rises above a certain level. These factors include;

Disease

There are more chances of disease spread in a dense population. Populations, where individuals are near one another, have more chances of disease spread (especially of viral diseases). For example, if a plant of the cotton crop is affected by the cotton leaf curl virus (CLCV), it is recommended to uproot that plant and deep burry to avoid the spread of its spores to nearby plants.

Competition

Competing different individuals (plants or animals) for limited available resources is called competition. Competition among individuals increases within a dense population. This competition might be inter-specific or intraspecific.

Inter-specific competition

Competition for limited available resources among individuals of different specifies is called interspecific competition. This type of competition is not drastic as different species have different needs and preferences for a specific resource. For example, shade-loving plants can easily be grown under the shade of higher plants. Intercropping and mixed cropping can also be done on a single farm without any reluctance.

Intra-specific competition

Competition for limited available resources among individuals of the same specifies is called intraspecific competition. This type of competition is more strong and more drastic as plants belonging to the same species have an equal preference for a specific resource. For example crop plants (community of plants) or trees of the same species will resist the growth of other plants nearby them.

There is another plant-plant interaction called facilitation. The stress gradient hypothesis stated that unpalatable plants called benefactors (biotic refuges) protect neighboring plants from being eaten by herbivores. The balance between competition and facilitation largely depends upon the density of the benefactor. If in an ecosystem, there is an increased density of large-sized plants (shelter effect), this will result in a humped-shaped pattern of facilitation. However, unpalatable plants can also affect different ecological processes by changing the small-scale heterogeneity of the pasture and grazing pressure.

Parasitism and Predation

With the word parasite, the image of a bug or worm may pop into one’s head. Like all other parasites, plants also obtain their food from a host (other plants). They have specialized roots called haustoria. These haustoria are penetrated into the tissues of the host to get water and nutrients. The corpse flower, Thurber’s stem sucker, and Dodder are examples of parasitic plants. All these plants are angiosperms.

Venus flytrap, sundew, and pitcher plants are examples of plants showing the predation phenomenon.

Density Independent Factors

A factor that affects the size of a population irrespective of its density is called density-independent factors. These factors are the result of some physical or chemical phenomenon (abiotic in nature) rather than a biological phenomenon as in the case of density-dependent factors. Density independent factors are also known as limiting factors. These factors include unavailability of oxygen, wildfire, floods, landslide, earthquakes, etc.

Oxygen availability

Limiting the supply of oxygen as a result of flooded conditions negatively affects the population of plants and animals who cannot survive in such anoxic conditions. Despite its abundant availability in the atmosphere, oxygen as a limiting factor, frequently limit germination, growth, and survival of plants. A various metabolic phenomena like glycolytic rate, alcohol dehydrogenase (ADH) induction, and end–products of glycolysis are concerning the oxygen supply.

Wildfire

Another abiotic phenomenon that affects the density of plants is wildfire. Among all the abiotic factors, wildfire is the most drastic and profound phenomenon that alters the density and diversity of species in an ecosystem. Wildfire can subsequently affect the interaction of plants and their pollinators (bees) as well. If a wildfire is controlled and it covers grasses, herbs, and shrubs while tall trees survive, taller trees being more visible would be more attractive for pollinators thus their density will be boosted. Fire is an ecological factor.

Floods

A temporary overflow of water into dry land is called a flood. This abiotic factor can destroy vegetation on large scale irrespective of its density and stratification. It has a devastating effect on the existing plantation however may bring fertile soil and (alluvial soils) for the plants in coming years.

Landslides

The upper crust of the earth is unconsolidated and unstable. Sometimes the mass of rocks, soil, debris, or earth moves down the slope (landslip). This abiotic factor proves hurtful for all types of plantations and is much more common in sloppy areas.

Earthquake

An earthquake of high magnitude may have a devastating and long-term deleterious impact on vegetation and the ecosystem. This physical factor is a density-independent factor. It destroys all types of terrestrial vegetation. These are most common in tectonically active regions. They have a strong impact and can also cause land sliding.

Conclusion

The population of plants is affected by multiple factors. These are density dependent and density independent factors in nature (Biological, Physical or chemical). The size of one species may affect the size of other species of the same population positively or negatively. Thus these factors (density dependent and density independent factors) are closely related. Diseased, pathogenic, and off-type plants adversely affect the population of competing species. The other component of the ecosystem i.e. physical or chemical (abiotic) elements limit the size of a population irrespective of the density of the population (e.g. forest vegetation) thus termed density-independent factors.

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