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Population Ecology – Definition, Characteristics, Importance, Effects

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  • Last Updated : 22 Aug, 2022
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Ecologists study how organisms interact with their surroundings on earth. Population ecology is a more specific field of study of how and why the populations of those organisms transform over time. As the human population rises in the 21st century, the information gleaned from population ecology can help with planning. It can also help with measures to preserve other species.

Population Ecology 

In population biology, the term population means a group of individuals of the same species living within a given area.

Population ecology is the study of how various factors impact population growth, rates of survival and reproduction, and risk of extinction. Population ecology has its most profound historical roots and development in the study of population growth, regulation, dynamics, or demography. The population can be open or closed population.

Closed Population

A closed population is not able to exchange with other people after a while. The population can grow through the birth of new people. This circumstance is usually seen on islands as a population might be laid out during a storm or any other influence but no additional members will be added over time. When a brief period of time is over, a population is bound to be closed. A storm event where more turtles are added during a single year than 100 years is less likely to happen on an island. Animals will not be able to cross the river during a normal year if the river stays at its full level. The population can grow through birth and decline through death, making it easier to project growth rates. The growth rate is not determined by the number of organisms or the rate of reproduction.

The population will be diminished by the death rate. population growth can be influenced:

  • space
  • hereditary qualities
  • age of individuals
  • resources

Open Population

An open population can acquire and lose different populations over time. The population isn’t geographically isolated. The longer the period of time, the more probable it is that the population will open. The typical changes in an environmental system are the reason for this.

After some time, we expect that rivers will experience times of dry weather, mountain passes will open and close, and bridges will be destroyed. The capacity of new individuals to join an existing population will be influenced by these things.

Characteristics of Population Ecology

Ecologists use diverse terms while understanding and examining populations of organisms. A population is all of one sort of species living in a particular location. Population size describes the total number of individuals in a habitat. Population density refers to how many individuals live in a specific area.

Population size is represented by the letter N, which refers to the total number of individual organisms in a population. The bigger a population is, the greater its generic variation and thus its potential for long-term survival. Increased population size can, however, lead to further issues, such as overuse of resources leading to a population crash. 

Population Density refers to the number of individual organisms in a particular area. A low-density region would have more organisms spread out. High-density regions would have more individuals residing closer together, leading to greater resource competition.

Population Dispersion: Hauls helpful information regarding how species interact with each other. Researchers can discover more about populations by studying how they are distributed or dispersed.

Population distribution describes how individual organisms of a species are spread out, whether they live close or far apart or massed into groups.

  • Uniform dispersion means the organisms that live in a distinct territory. One example would be penguins. Penguins live in parts; within those territories, the birds space themselves reasonably uniformly. 
  • Random dispersion means the spread of individual organisms, such as wind-dispersed seeds, which fall randomly after transiting.
  • Clustered or clumped dispersion means a drop of seeds straight to the ground, instead of being carried, to groups of animals living together, such as herds or schools. Schools of the fish show this manner of dispersion.

How Population Size and Density are Calculated

Quadrat method

A quadrat method is an ideal tool for the study of ecology, particularly biodiversity. Generally, a sequence of squares (quadrats) of a set size are arranged in a habitat of interest, and the species within those quadrats are pinpointed and recorded.

The passive quadrat method (accomplished without removing the organisms found within the quadrat) can be either done by hand, with researchers carefully sorting through each particular quadrat or, efficiently, can be done by taking a picture of the quadrat for future analysis.

Mark and recapture

A quadrat would not function for animals moving around. So to define the population size of more migrating organisms, scientists use a method called mark and recapture.

In this situation, individual animals are captured and labeled with a tag, band, paint, or something similar. The animal is released back into its environment. Then, another group of animals is captured, which may contain those already marked and unmarked animals.

The result of capturing both marked and unmarked animals provides researchers with a ratio to use, and from that, they can estimate the estimated population size.

Population Ecology Theory

  • Thomas Malthus, who published a report that described the population’s relationship to natural resources, formed the earliest theory of population ecology. Charles Darwin extended this with his “survival of the fittest” concepts.
  • In history, ecology depended upon the concepts of other areas of study. One scientist, Alfred James Lotka, changed the science practice when he came up with the origins of population ecology. Lotka pursued the formation of a new field of “physical biology” in which he included a systems strategy for studying the relationship between organisms and the environment.
  • Biostatistician Raymond Pearl took note of Lotka’s work and united with him to discuss predator-prey interactions.
  • Vito Volterra, an Italian mathematician, started investigating predator-prey relationships in the 1920s. This would lead to the Lotka-Volterra equations that acted as a springboard for mathematical population ecology.
  • Australian entomologist A.J. Nicholson led the earlier fields of study about density-dependent mortality factors. H.G. Andrewartha and L.C. Birch would go on to explain how abiotic factors impact populations. Lotka’s systems method to ecology still influences the field to this day.

Density-dependent population regulation

When population ecologists examine the growth of a population, it is via the lens of factors that are density-dependent or density-independent. Density-dependent population regulation represents a strategy in which a population’s density impacts its growth rate and mortality. Density-dependent regulation manages to be more biotic. For example, competition within and between species for resources, diseases, predation, and waste buildup represents density-dependent factors. The density of available prey would also impact the population of predators, causing them to move or potentially starve.

Density-independent population regulation

Density-independent population regulation refers to natural (physical or chemical) factors that impact mortality rates. In other words, mortality is affected without considering density.
These factors, such as natural disasters (e.g., wildfires and earthquakes), lead to being catastrophic. Anyway, Pollution is a man-made density-independent factor that affects many species. The Climate Crisis is another instance.

Population cycles

Populations grow and fall in a cyclic manner relying on the resources and competition in the environment. For instance harbour seals, are influenced by pollution and overfishing. Decreased prey for the seals shows the increased death of seals. If the number of births increased, that population size would stay stable. But if their deaths outpaced births, the population would fall.
As climate change persists to impact natural populations, the use of population biology standards becomes more crucial. The many aspects of population ecology aid scientists in better understanding how organisms interact and aid in species management, conservation, and protection strategies.

Effects of Population size

Genetic variation is more easily supported in large populations than in small ones. Random genetic drift can cause a genetic characteristic to be lost in a small population. Many people have at least two forms of a gene. A specific phenotype will be produced if an individual acquires any of the alleles. If populaces stay small for a long time, they might lose everything except one type of gene.

Sampling error leads to the loss of alleles. They exchange genes when they mate. 50% of the population has one type of a specific gene, and the other 50% have another type of gene. In a small population, the exchange of genes could bring about all of the cutting edge having the same allele. The main way for this populace to have a variety of this gene again is through a change of the genes from another population.

Minimizing the loss of genetic variation in small populations is one of the major issues faced by biologists. Natural selection constantly sorts out the genetic variation found within each population and chooses the most appropriate ones for the current environment. Populations risk extinction without the genetic variation that allows them to respond to changes in the physical environment, diseases, and competitors.

Frequently Asked Questions

Question 1: What is the meaning of Population Ecology?


Population ecology is the study of how various factors impact population growth, rates of survival and reproduction, and risk of extinction. Population ecology has its most profound historical roots and development in the study of population growth, regulation, dynamics, or demography.

Question 2: What defines population ecology accurately? 


The study of environmental factors that influence the growth and density of a group of organisms.

Question 3: Who discovered population ecology?


Thomas Robert Malthus was an effective writer on the subject of population and population limits in the early 19th century. His works were very influential in shaping the ways in which Darwin saw the world worked.

Question 4: What are the factors impacting population in ecology?


Food, water, shelter, predation, and density are the things that let the population grow or cause it to fall. Limiting factors like food and water are essential resources for all organisms; without them, they will die so these factors instantly affect population size.

Question 5: What are the principles of population ecology?


Population size is controlled by factors that are dependent or independent of population density. Biological and non-biological factors can impact population size. Biological factors contain interspecific interactions like predation, competition, parasitism, mutualism, as well as disease.

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