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The upper part of the logistic growth curve shows where a population is impacted by density-dependent factors. What is meant by density-dependent factors? How do they differ from density-independent factors?

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The upper part of the logistic growth curve shows where a population is impacted by density-dependent factors. Provide an examples each of density-dependent and density-independent factors

Part 1)

Density dependent factors are those that affects growth of a population according to the density of the population. the density dependent growth rate factors may include competition between the population, predation, diseases, parasite or pest attack. For example, when the growth rate increases, the density of the population increases making the resources limited and problem in predation.

Three example of density dependent factors,

it can either be positive effect or negative effect.

density increase - positive effect on Schistosomias worm or any worm that is dioecious. The mating of female worm completes only after meeting the male one and vice versa. So increase in density can increase their chance of mating.

disease - When the density increases, the transmission of disease also increase due to more number of hosts for the pathogen. For ex- the antharax disease caused by Bacillus anthracis is easily communicable and has killed more than 80 hippos in Uganda (BBC)

parasites - The ecto- and endoparasites survive greater when they have many hosts.For ex- The moose population in Isle Royale decreases in high temperatures due to the parasite attack on them. they suck the blood and cause malnutrition ad some parasites cause deadly diseases too.

Other than this competition - intra and inter specific, migration are factors that influence the density dependent growth rates.

Part 2)

The density independent growth rates are those which are not affected due to the density of the population. The density has no influence in this. It includes natural disasters, predation, pollution and weather changes (global warming )

For example, the recent incident of forest fire in Australia has reported death of over millions of animals including koalas, kangaroos, etc. This natural disaster has no relation with the density of the animal population. Even it its one animal of a species or thousands of animal of a species, animals die to this massive disaster.

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Density-dependent factors are limiting factors whose frequency is related to density of population; and the growth in genetic variation seems to be limited. Population growth slows and gradually ends as population density rises, birth rates fall, and death rates rise.

A population size may be regulated by biotic, abiotic, and population size aspects. Density-dependent control can be affected by factors influencing birth and death levels, such as competition (intraspecific and inter-specific) for food (increasing nutritional and resource population density competition, resulting in lower birth rates), health (disease is more easily transmitted in dense populations),habitat loss (predators consume more food as prey population increases).

Density-independent regulation can be affected by factors that affect birth and death rates, such as abiotic factors and environmental factors, for example, floods, droughts, earthquakes, natural disasters, severe  weather conditions.