Population ecology is a division of ecology that deals with the dynamics of species populations and how these populations interact with the environment. This is a study of how the size of a population of species changes in time and space. This term is often used interchangeably with population biology or population dynamics. He also often describes types of struggles for existence. Due to natural selection, the number of individuals maximally adapted increases.
In biology, a population is the degree of distribution of a particular species or a certain number of its representatives living in the same territory.
History
How it all began? The development of population ecology is largely connected with demography and current life tables. This section is very important in the current environmental conditions.
Population ecology is important in conservation biology, especially when developing a population viability analysis (PVA) that predicts the long-term likelihood of species conservation at a given habitat. Although this ecology is a subspecies of biology, it poses interesting problems for mathematicians and statisticians who work in the field of demographic dynamics. In biology, a population is one of the central terms.
Models
Like any science, ecology uses models. Simplified patterns of population change usually begin with four key variables (four demographic processes), including death, birth, immigration, and emigration. Mathematical models used to calculate changes in the demographic situation and the evolution of the population, suggest the absence of external influence. Models can be more mathematically complex when "... several competing hypotheses collide with data at the same time."
Any model of population development can be used to mathematically derive certain properties of geometric populations. A population with a geometrically increasing size is a population where breeding generations do not overlap. In each generation, there is an effective size (and territory) of populations, designated as Ne, which is the number of individuals in a population that can and will reproduce in any reproductive generation. What is causing concern.
Theory of selection r / K
An important concept in population ecology is the r / K selection theory. The first variable is r (the internal rate of natural increase in population size, it does not depend on density), and the second variable is K (population throughput, depends on density). Intraspecific relationships play a role in this.
An R-selected species (for example, many insect species such as aphids) is one that has high fertility rates, low parental investment in juveniles, and high mortality rates before individuals reach maturity. Evolution promotes productivity in r-selected species. In contrast, K-selected species (such as humans) have low fertility rates, high levels of parental investment at a young age, and low mortality rates as individuals grow older.
Evolution in K-selected species contributes to efficiency in turning more resources into fewer descendants. As a result of unproductive interspecific relationships, these descendants can die out, becoming the last representatives of their population.
History of theory
The terminology of r / K selection was coined by ecologists Robert MacArthur and E.O. Wilson in 1967 based on their work on island biogeography. This theory allows us to identify the causes of fluctuations in the population size.
The theory was popular in the 1970s and 1980s when it was used as a heuristic device, but lost value in the early 1990s when it was criticized by several several empirical studies. The life history paradigm has replaced the r / K choice paradigm, but continues to include many of its important topics. The craving for reproduction is the main driving force of evolution, therefore this theory is extremely useful for its study.
Thus, r-selected species are those that emphasize high growth rates, usually use less crowded ecological niches and produce many offspring, each of which has a relatively low probability of surviving into adulthood (i.e. high r, low K). A typical species of r is dandelion (genus Taraxacum).
In unstable or unpredictable environments, r-selection predominates due to the ability to multiply rapidly. There are few advantages in adaptations that can successfully compete with other organisms because the environment is likely to change again. Among the traits that are believed to characterize r-selection are: high fecundity, small body size, early onset of maturity, short generation time, and the ability to widely disperse offspring.
Organisms whose life story undergoes r-selection are often called r-strategists. Organisms that exhibit r-selected traits can range from bacteria and diatoms to insects and grasses, as well as various seven-petalled cephalopods and small mammals, especially rodents. The differential theory of K has an indirect relationship with the natural selection of animals.
Species selection
K-selected species show traits associated with life in densities close to bearing capacity, and, as a rule, are strong competitors in such crowded niches that invest more in fewer descendants. Each of which has a relatively high probability of surviving into adulthood (i.e. low g, high K). In the scientific literature, r-selected species are sometimes called “opportunistic”, while K-selected species are described as “equilibrium”.
Under stable or predictable conditions, K-selection prevails, since the ability to compete successfully for limited resources is crucial, and populations of K-selected organisms are usually very constant in number and close to the maximum that the medium can withstand. Unlike r-selected ones, where the population size can change much faster. Low abundance leads to incest, which is one of the causes of mutations.
Specific traits
Traits that are believed to be characteristic of K-selection include large body size, longer life spans, and fewer offspring that often require careful parental care until they become mature. Organisms whose life story is subjected to K-selection are often called K-strategists or K-selected. Organisms with K-selected traits include large organisms such as elephants, humans, and whales, as well as smaller, longer-lived organisms such as Arctic terns, parrots, and eagles. Population growth is a type of struggle for existence.
Classification of organisms
Although some organisms are identified primarily as r- or K-strategists, most organisms do not follow this pattern. For example, trees have traits such as longevity and high competitiveness that characterize them as K-strategists. However, when propagated, trees usually produce thousands of offspring and scatter them widely, which is typical for r-strategists.
Likewise, reptiles, such as sea turtles, have both r- and K-characteristics: although sea turtles are large organisms with a long lifespan (provided that they reach adulthood), they produce a large number of undetected offspring.
Other expressions
The r / K dichotomy can be re-expressed as a continuous spectrum using the economic concept of discounted future returns with an r-choice corresponding to large discount rates and a K-choice corresponding to small discount rates.
In areas with severe environmental disruption or sterilization (for example, after a violent volcanic eruption, such as Krakatau or Mount St. Helens), r and K strategists play different roles in the ecological sequence that restores the ecosystem. Because of their higher reproductive rates and environmental opportunism, primary colonizers are usually strategists, and they are followed by a series of growing competition between flora and fauna. The ability of the environment to increase energy content through photosynthetic capture of solar energy increases with increasing complex biodiversity, as r-species reproduce, reaching the maximum possible using strategies K.
New balance
In the end, a new equilibrium sets in (sometimes called the climax community), when r-strategists are gradually replaced by K-strategists, which are more competitive and better adapt to emerging microecological changes in the landscape. Traditionally, biodiversity was considered maximized at this stage with the introduction of new species, which led to the replacement and local extinction of endemic species. Nonetheless, the intermediate disturbance hypothesis states that intermediate levels of disturbance in the landscape stain at different levels of sequence, contributing to the coexistence of colonialists and competitors on a regional scale.
Although r / K selection theory is usually applied at the species level, it is also useful for studying the evolution of ecological and life differences between subspecies. For example, the African honey bee A. m. scutellata and the Italian bee A. m. ligustica. At the other end of the scale, it was also used to study the evolutionary ecology of entire groups of organisms, such as bacteriophages.
Opinions of researchers
Some researchers, such as Lee Ellis, J. Philip Rushton, and Aurelio Jose Figueeredo, have applied r / K selection theory to various human behaviors, including crime, sexual licentiousness, fertility, and other traits related to life history theory. Rushton’s work led him to develop a “differential K theory” to try to explain the many differences in human behavior in different geographical areas. And this theory has been criticized by many other researchers. The latter suggested that the evolution of human inflammatory responses is associated with the choice of r / K.
Although r / K selection theory began to be widely used in the 1970s, it also began to attract more and more attention. In particular, a review by environmentalist Stephen S. Sterns drew attention to the gaps in theory and the ambiguities in interpreting empirical evidence to validate it.
Further research
In 1981, a review of the literature on r / K selection by Parry showed that there was no agreement among researchers using the theory of determining r- and K-selection, which made him doubt the assumption about the relationship between the costs of reproductive function.
A study by Templeton and Johnson in 1982 showed that in a Drosophila mercatorum (fly subspecies) population subjected to K-sampling, it actually yields a higher frequency of traits typically associated with r-sampling. Several other studies, contrary to the predictions of r / K selection theory, were also published between 1977 and 1994.
When Stearns reviewed the status of theory in 1992, he noted that from 1977 to 1982, the BIOSIS literature search service averaged 42 references to theory per year, but from 1984 to 1989 the average dropped to 16 per year and continued to decline. He concluded that the r / K theory was once a useful heuristic that no longer serves a purpose in life history theory.
More recently, the theories of the panarchy of adaptive abilities and sustainability, promoted by S. S. Holling and Lance Gunderson, have revived interest in theory and use it as a way to integrate social systems, economics, and ecology.
Ecology of metapopulation
Ecology of metapopulation is a simplified landscape model for sites of different quality levels. Migrants moving between sites are structured in metapopulations as sources or sinks. In the terminology of metapopulation, there are emigrants (people who leave the site) and immigrants (people who move to the site).
Metapopulation models examine the dynamics of sites over time to answer questions about spatial and demographic ecology. An important concept in the ecology of metapopulation is the rescue effect, in which small areas of lower quality (i.e. sinks) are supported by a seasonal influx of new immigrants.
The metapopulation structure evolves from year to year, where some sites are shells, such as dry years, and become sources when conditions are more favorable. Environmentalists use a mixture of computer models and field studies to explain the structure of metapopulation. The age structure of the population is the presence in the population of representatives of certain ages.
Autoecology
The older term autoecology (from the Greek: αὐτο, auto, “self”; οίκος, oikos, “household” and λόγος, logos, “knowledge”) refers to approximately the same field of study as the ecology of the population. It follows from the division of ecology into autecology - the study of individual species in relation to the environment - and synecology - the study of groups of organisms in relation to the environment - or the ecology of the community. Odum (an American biologist) believed that synecology should be divided into population ecology, community ecology, and ecosystem ecology, defining autoecology as “species ecology”.
However, for some time, biologists have recognized that the population is a more significant level of organization of the species, because at this level the species gene pool is the most consistent. In fact, Odum considered "autoecology" as the "current trend" in ecology (that is, an archaic term), although it included "species ecology" as one of the four divisions of ecology.
The first publication of the journal "Ecology of the Population" (originally called "Studies on the Ecology of the Population") was released in 1952.
Scientific articles on population ecology can also be found in animal ecology journals.
Population dynamics
Population dynamics is a branch of the life sciences that studies the size and age composition of the population as dynamic systems, as well as the biological and environmental processes that trigger them (for example, fertility and mortality rates, as well as immigration and emigration). Examples of scenarios are population aging, growth or decline.
Exponential growth describes unregulated reproduction. It is very unusual to see in nature. Over the past 100 years, population growth has been exponential.
Thomas Malthus believed that population growth would lead to overpopulation and hunger due to lack of resources, including food. In the future, people will not be able to feed large populations. The biological assumption of exponential growth is that the growth rate per capita is constant. Growth is not limited to resource scarcity or predation.
Population dynamics has been widely used in several applications of control theory. Using evolutionary game theory, population games are widely used for a variety of industrial and everyday contexts. It is mainly used in systems with multiple inputs and multiple outputs (MIMO), although they can be adapted for use in systems with single input and single output (SISO). Some examples of applications are military campaigns, distribution of resources for water distribution, dispatch of distributed generators, laboratory experiments, problems with transport, communication problems. In addition, with adequate contextualization of production problems, population dynamics can become an effective and easy to use solution to problems associated with control. Numerous scientific studies have been and are ongoing.
Overpopulation
Overpopulation occurs when the population of a species exceeds the carrying capacity of an ecological niche. ( ), , . , , , . .
In the wild, overpopulation often causes an increase in predator populations. This has the effect of controlling the prey population and ensuring its evolution in favor of genetic characteristics that make it less vulnerable to predators (and a predator can co-develop).
In the absence of predators, species are linked by resources that they can find in their environment, but this does not necessarily control overpopulation. At least in the short term. An abundant supply of resources can lead to a demographic boom, followed by a demographic crisis. Rodents, such as lemmings and voles, have such cycles of rapid population growth and subsequent contraction. The snowshoe hare population also changes dramatically cyclically, as in one of the predators hunting them - lynx. Tracing this trend is much easier than identifying the genome of a population.