Metapopulation

Overview

Metapopulation is a term used in the field of ecology to denote populations of living things that are separate yet interrelated. Ecology is the broad study of the relationships between all living organisms and the environments in which they live. This means studying how countless living things interact with one another, as well as how they interact with the weather and various types of terrain. Additionally, the term “environment” within the context of ecology can refer to many different things. Some ecological researchers study microenvironments, which may include interactions between microscopic organisms and various types of soil. Other ecological researchers may study the interactions between entire continents and their inhabitants.

The field of ecology is concerned with the study of populations of organisms. Within this field, the term “population” refers to any group of interacting organisms of the same species. It includes individual members of that species of various age groups. Information on a given population can be beneficial for ecologists. For example, if ecologists can gather information on the ages of many of the members of a population, they can break it down into population demographics. This might give scientists insight into how long young individuals stay with their families, the typical male-to-female ratio of a population in a given group, or how often individuals of a specific species tend to live in the wild. It also shows the rate at which a population is growing or shrinking.

Additionally, through tracking members of a population, ecologists might discover the geographic range of its members. This can show ecologists the types of terrain preferred by a species and what objects, environmental changes, or other species might prevent their spread beyond a certain point. For example, a population of reptiles that prefers warm weather might grow gradually, moving in a specific direction, until temperatures become too low for the population to thrive.

Studying a population of a particular type of animal is a common practice for ensuring its survival. For this reason, ecologists commonly study populations of organisms that are endangered, threatened, or at-risk. They may observe the impact of habitat loss, which commonly occurs when humans claim new land for farms or settlements, and study how such a drastic change impacts a population. They may also study the effects of pollution, disease, and territoriality. Once ecologists are aware of the specific factors that threaten a population, they may work with local authorities or activist groups to address those factors.

In many cases, studying a single population provides a limited view of the overall health and habits of a species in a particular region. In order to gain greater insights, ecologists commonly broaden their studies to include metapopulations. Metapopulations are regional groupings of populations that interact with one another. Even distant biological relation is often enough of a connection to include otherwise separate populations in the same metapopulation.

Local populations are prone to growing and shrinking in size. If a specific population grows too quickly, it may create resource scarcity in a region. There may not be enough food or territory to allow that many animals to thrive in the population’s space. This has the potential to lead to a collapse of the entire population through the rapid depletion of the resources necessary for a species’ survival. However, because of the existence of a larger metapopulation, individuals in a single overpopulated region may migrate to other regions, joining existing populations that can support their greater numbers. If a large enough percentage of an overly large population breaks away altogether, it may form its own population.

Migration between population groups, even if limited, can help ensure the survival of a species by reinforcing struggling population groups. If a population has been significantly reduced, including by over-predation, disease, loss of territory, or other sudden change, it may also be prone to collapse. However, the area in which that population lives may now have an abundance of resources that is capable of supporting more members of the same species. This may encourage members of other populations to migrate, bolstering the size of the struggling population and ensuring that it will continue to exist.

In some cases, metapopulations consist of a single extremely large population surrounded by many smaller populations. These smaller populations are called satellite populations. If left unchecked, the primary population would quickly become too large for its given territory to support. Additionally, if left alone, the smaller satellite populations would be vulnerable to localized extinction. However, the satellite populations continually draw members away from the main population, benefiting both groups and increasing the odds of the species’ survival.

The creation and maintenance of a large metapopulation, as opposed to a single large population, insulates the species against sudden environmental changes. For example, should a forest fire destroy a significant portion of the woods, one population of herbivores may be unable to sustain itself, resulting in the collapse of that population. However, because other regional populations were located in other areas, the species as a whole will continue to survive. Over time, the metapopulation may re-inhabit that area, establishing a new population in place of the old.

Ecologists who study larger metapopulations for significant periods of time may be able to make complex predictions about their future. For example, they may note that species undergo long-term migration patterns, and predict when those migrations might occur. They might use past data to predict the outcome of a planned environmental change and whether a metapopulation will adapt to that change or wholly collapse.

Metapopulations also encourage genetic diversity within a species. Many members of a given population may interact with other populations for the express purpose of breeding. Though they may not permanently migrate to the other population, this process may spread beneficial gene mutations from one population to the others. Additionally, when populations within a larger metapopulation rarely interact, they may develop in different ways. As evolution allows species to adapt to changing circumstances, and different regions may place different demands on the same species, individual populations may develop different biological traits. This process is called divergent evolution. Over extended periods of time, separate populations of the same species may eventually become different species, losing their ability to create offspring with one another.

Applications

Metapopulation theory is typically paired with the study of the habitats of specific species. Ecologists work to attain a greater understanding of the movements and status of the entirety of a species by studying both individual populations and the means by which individuals travel between populations. In order to accomplish this, ecologists study the concept of habitat fragmentation.

Habitat fragmentation is the process in which a number of separate, self-contained, suitable habitats for a specific species are created. In many cases, these multiple habitats were once a single habitat. However, through natural change or through human development, the larger habitat is split into numerous smaller habitats. This reduces the total amount of resources available for a single population, encouraging it to split into several smaller populations.

Habitat fragmentation is particularly common in urban developments within forested areas. Newly constructed roads, town expansions, farms, and any other form of development that destroys the natural ecosystem and replaces it with terrain more suitable to humans breaks up natural habitats. Some species may easily be able to traverse fragmented terrain and may be able to adapt to their new environments. Others, however, may only be able to thrive in a very specific ecosystem. They may be unable to travel through modified terrain to find more suitable regions.

While researching this process and developing metapopulation theory, ecologists realized that habitat fragmentation had a significant effect on the overall health of a species. They noted that the size of the available fragments loosely correlated with the size of available populations. However, it should be noted that the relative habitat size needed to support a stable population differs significantly between species. Some species require only a very small amount of space in order to thrive, making them well-suited to habitat fragmentation. Other larger or more solitary species may require much more land, making them vulnerable to continued habitat fragmentation. However, overall, ecologists found that as the size of available habitat fragments increases, the risk of extinction of a species decreases.

Ecologists working with metapopulation theory and specific species may study the paths by which species move between their fragmented habitats. Some may routinely migrate between populations for breeding or in search of additional resources. Others may be carried by human forms of transportation, such as boats, automobiles, or planes. Understanding this process provides ecologists with a better understanding of the negative impacts of habitat fragmentation, which may allow them to limit the impact of the process in future human construction.

In some cases, ecologists use metapopulation theory and direct observation of populations to calculate the risk that a particular population will become extinct in the future. If that risk is significant, ecologists may work with other experts to aid that population. This may involve changing local laws or ordinances to reduce the number of unnecessary deaths caused to that population by humans. It may also include modifying or creating new habitats better suited to the species, allowing the region to support larger populations.

Additionally, by tracking the metapopulations of numerous species within a specific region, ecologists can better understand the interactions between different species. If populations of species overlap, ecologists may theorize that some form of relationship between the two species exists. One species may prey upon the other, following its migrations in order to secure food. Alternatively, the two species may hunt for the same food source. If the populations of two species in a region rarely overlap, it may show that they have significantly different environmental requirements. It may also show that the two species compete with one another for similar resources and thus struggle to coexist.

Issues

Metapopulation study is commonly used in the field of ecological conservation. Due to numerous hazards, including human destruction, habitat loss, pollution, and global warming, many species across the world are approaching extinction. Detailed knowledge of the metapopulations of various species allows ecologists to clearly see which species are in need of intervention and how future events might impact the distribution of a particular species. For example, if a species exists in a region with a single large population and numerous colony populations, ecologists might make local politicians aware of how disrupting the large population might lead to the overall extinction of the species. This might stop the development of construction projects in the region that would disrupt the important population.

Additionally, conservation efforts have worked to reconnect populations that have been isolated through changes to the environment. Because the isolation of a population tends to correlate with the eventual extinction of the population, and because humanity’s actions and development have resulted in widespread environmental change that has isolated many populations from other parts of their historic metapopulations, the construction of new pathways between populations within the same metapopulation may be a necessity. In reducing the isolation between metapopulations in urban regions or other fragmented landscapes, ecologists may increase the stability and population numbers of many species. It will also increase the genetic variation of the population, making it more resistant to disease and other potential extinction-causing events.

Metapopulation theory is sometimes criticized when applied to populations of large mammals. Ecologists have found significant supporting evidence for metapopulation theory in populations of small mammals, amphibians, and insects. However, large mammals typically have longer gestation periods and slower reproduction times. This leads to slower population growth and requires the researchers to investigate large mammal populations for longer timescales in order to observe the effects of metapopulation theory. For this reason, some critics of metapopulation theory argue that it should not be applied to the conservation of large mammals. They believe that over time, the remaining populations of large mammals may show different patterns of behavior than those predicted by metapopulation theory.

Metapopulation theory is also questioned in instances of colonization and extinction. According to metapopulation theory, extinctions and colonization are most commonly caused by unstable environments, resource shortages, overpopulation, or other problems that threaten a specific population. Despite these claims, population extinction and population colonization have been observed even in stable populations, where no threat to the population appears to be present. Critics of metapopulation theory assert that these extinctions and colonizations are evidence that the theory is inaccurate in this regard.

Despite these criticisms, metapopulation theory has been a useful tool for ecologists, allowing them a better understanding of the impacts of subpopulations and fractured habitats on species in a given environment. These insights enable ecologists to better identify species that might be at risk of collapse and provide them with new avenues for addressing the problems that threaten those species.

About the Author

Tyler Biscontini is a writer from Northeast Pennsylvania. He graduated from King’s College in Wilkes-Barre, PA, with a bachelor’s degree in professional writing. He then worked in educational book publishing.

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