Population biology

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Events calendar powered by Trumba.Population ecologystudy of the processes that affect the distribution and abundance of animal and plant populations. A population is a subset of individuals of one species that occupies a particular geographic area and, in sexually reproducing species, interbreeds. The geographic boundaries of a population are easy to establish for some species but more difficult for others.

For example, plants or animals occupying islands have a geographic range defined by the perimeter of the island. In contrast, some species are dispersed across vast expanses, and the boundaries of local populations are more difficult to determine. A continuum exists from closed populations that are geographically isolated from, and lack exchange with, other populations of the same species to open populations that show varying degrees of connectedness. In sexually reproducing species, each local population contains a distinct combination of genes.

As a result, a species is a collection of populations that differ genetically from one another to a greater or lesser degree. These genetic differences manifest themselves as differences among populations in morphologyphysiologybehaviour, and life histories; in other words, genetic characteristics genotype affect expressed, or observed, characteristics phenotype.

Natural selection initially operates on an individual organismal phenotypic level, favouring or discriminating against individuals based on their expressed characteristics. The gene pool total aggregate of genes in a population at a certain time is affected as organisms with phenotypes that are compatible with the environment are more likely to survive for longer periods, during which time they can reproduce more often and pass on more of their genes.

The amount of genetic variation within local populations varies tremendously, and much of the discipline of conservation biology is concerned with maintaining genetic diversity within and among populations of plants and animals.

Population Biology

Some small isolated populations of asexual species often have little genetic variation among individuals, whereas large sexual populations often have great variation. Two major factors are responsible for this variety: mode of reproduction and population size. In sexual populations, genes are recombined in each generation, and new genotypes may result. Offspring in most sexual species inherit half their genes from their mother and half from their father, and their genetic makeup is therefore different from either parent or any other individual in the population.

In both sexually and asexually reproducing species, mutations are the single most important source of genetic variation. New favourable mutations that initially appear in separate individuals can be recombined in many ways over time within a sexual population.

In contrast, the offspring of an asexual individual are genetically identical to their parent. The only source of new gene combinations in asexual populations is mutation. Asexual populations accumulate genetic variation only at the rate at which their genes mutate. Favourable mutations arising in different asexual individuals have no way of recombining and eventually appearing together in any one individual, as they do in sexual populations.

Over long periods of time, genetic variation is more easily sustained in large populations than in small populations. Through the effects of random genetic drifta genetic trait can be lost from a small population relatively quickly see biosphere: Processes of evolution.

For example, many populations have two or more forms of a gene, which are called alleles. Depending on which allele an individual has inherited, a certain phenotype will be produced. If populations remain small for many generations, they may lose all but one form of each gene by chance alone. This loss of alleles happens from sampling error. As individuals mate, they exchange genes.

Imagine that initially half of the population has one form of a particular gene, and the other half of the population has another form of the gene. By chance, in a small population the exchange of genes could result in all individuals of the next generation having the same allele. The only way for this population to contain a variation of this gene again is through mutation of the gene or immigration of individuals from another population see evolution: Genetic variation in populations.

Minimizing the loss of genetic variation in small populations is one of the major problems faced by conservation biologists. Environments constantly change, and natural selection continually sorts through the genetic variation found within each population, favouring those individuals with phenotypes best suited for the current environment. Natural selection, therefore, continually works to reduce genetic variation within populations, but populations risk extinction without the genetic variation that allows populations to respond evolutionarily to changes in the physical environment, diseasespredators, and competitors.

Population ecology. Article Media. Info Print Print. Table Of Contents.Populations are groups of individuals belonging to the same species that live in the same region at the same time.

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Populations, like individual organisms, have unique attributes such as growth rate, age structure, sex ratio, and mortality rate. Populations change over time due to births, deaths, and the dispersal of individuals between separate populations.

When resources are plentiful and environmental conditions appropriate, populations can increase rapidly. A population's ability to increase at its maximum rate under optimal conditions is called its biotic potential. Biotic potential is represented by the letter r when used in mathematical equations. In most instances, resources are not unlimited and environmental conditions are not optimal. Climate, food, habitat, water availability, and other factors keep population growth in check due to environmental resistance.

The environment can only support a limited number of individuals in a population before some resource runs out or limits the survival of those individuals. The number of individuals that a particular habitat or environment can support is referred to as the carrying capacity.

Carrying capacity is represented by the letter K when used in mathematical equations. Populations can sometimes be categorized by their growth characteristics. Species whose populations increase until they reach the carrying capacity of their environment and then level off are referred to as K -selected species. Species whose populations increase rapidly, often exponentially, quickly filling available environments, are referred to as r -selected species. Characteristics of K -selected species include:.

Characteristics of r -selected species include:. Some environmental and biological factors can influence a population differently depending on its density. If population density is high, such factors become increasingly limiting on the success of the population. For example, if individuals are cramped in a small area, the disease may spread faster than it would if population density were low.

Factors that are affected by population density are referred to as density-dependent factors. There are also density-independent factors which affect populations regardless of their density. Examples of density-independent factors might include a change in temperature such as an extraordinarily cold or dry winter.

population biology

Another limiting factor on populations is intra-specific competition which occurs when individuals within a population compete with one another to obtain the same resources. Sometimes intra-specific competition is direct, for example when two individuals vie for the same food, or indirect, when one individual's action alters and possibly harms the environment of another individual.

Populations of animals interact with each other and their environment in a variety of ways. One of the primary interactions a population has with its environment and other populations is due to feeding behavior. The consumption of plants as a food source is referred to as herbivory and the animals that do this consuming are called herbivores. There are different types of herbivores. Those that feed on grasses are referred to as grazers.

Animals that eat leaves and other portions of woody plants are called browsers, while those that consume fruits, seeds, sap, and pollen are called frugivores. Populations of carnivorous animals that feed on other organisms are called predators. The populations on which predators feed are called prey. Often, predator and prey populations cycle in a complex interaction. When prey resources are abundant, predator numbers increase until the prey resources wane.

When prey numbers drop, predator numbers dwindle as well. If the environment provides adequate refuge and resources for prey, their numbers may again increase and the cycle begins again. The concept of competitive exclusion suggests that two species that require identical resources cannot coexist in the same location.A population is a group of interacting organisms of the same species and includes individuals of all ages or stages: pre-reproductive juveniles and reproductive adults.

Most populations have a mix of young and old individuals. Quantifying the numbers of individuals of each age or stage gives the demographic structure of the population. In addition to demographic structure, populations vary in total number of individuals, called population sizeand how densely packed together those individuals are, called population density.

Population ecologists often first consider the dynamics of population size change over time, of whether the population is growing in size, shrinking, or remaining static over time.

The most basic approach to population growth is to begin with the assumption that every individual produces two offspring in its lifetime, then dies, which would double the population size each generation.

This population doubling at each generation is how an ideal bacterium in unlimited resources would reproduce. When resources are unlimited, populations exhibit exponential growth, resulting in a J-shaped curve. Source: OpenStax Biology.

population biology

Because the births and deaths at each time point do not change over time, the growth rate of the population in this image is constant. Mathematically, the growth rate is the intrinsic rate of natural increasea constant called rfor this population of size N. The exponential growth equation.

As a result, the population explodes in size very quickly. In nature, a population growing at this dramatic rate would quickly consume all available habitat and resources. In contrast to the model predicted by the exponential growth equation, natural populations have size limits created by the environment. Any individuals born into this population would increase the population size unless the number of deaths balanced or outnumbered births.

If the population size remains the same from one generation to the next, then individuals must also be dying at a similar rate. With exponential population growth, the population growth rate r was constant, but with the addition of a carrying capacity imposed by the environment, population growth rate slows as the population size increases, and growth stops when the population reaches carrying capacity.

When resources are limited, populations exhibit logistic growth. In logistic growth, population expansion decreases as resources become scarce, and it levels off when the carrying capacity of the environment is reached, resulting in an S-shaped curve.

Mathematically, we can achieve this by incorporating a density-dependent term into the population growth equation, where K represents carrying capacity:. What happens to population growth when N is small relative to K? When N is near K?

And when is the population adding the most individuals in each generation?Populationin human biology, the whole number of inhabitants occupying an area such as a country or the world and continually being modified by increases births and immigrations and losses deaths and emigrations.

As with any biological population, the size of a human population is limited by the supply of food, the effect of diseases, and other environmental factors. Human populations are further affected by social customs governing reproduction and by the technological developmentsespecially in medicine and public healththat have reduced mortality and extended the life span.

Few aspects of human societies are as fundamental as the size, compositionand rate of change of their populations. Such factors affect economic prosperity, healtheducation, family structure, crime patterns, language, culture—indeed, virtually every aspect of human society is touched upon by population trends. The study of human populations is called demography —a discipline with intellectual origins stretching back to the 18th century, when it was first recognized that human mortality could be examined as a phenomenon with statistical regularities.

Demography casts a multidisciplinary net, drawing insights from economicssociologystatisticsmedicine, biologyanthropologyand history.

Its chronological sweep is lengthy: limited demographic evidence for many centuries into the past, and reliable data for several hundred years are available for many regions.

The present understanding of demography makes it possible to project with caution population changes several decades into the future. At its most basic level, the components of population change are few indeed. A closed population that is, one in which immigration and emigration do not occur can change according to the following simple equation: the population closed at the end of an interval equals the population at the beginning of the interval, plus births during the interval, minus deaths during the interval.

In other words, only addition by births and reduction by deaths can change a closed population. Populations of nations, regions, continents, islands, or cities, however, are rarely closed in the same way.

If the assumption of a closed population is relaxed, in- and out-migration can increase and decrease population size in the same way as do births and deaths; thus, the population open at the end of an interval equals the population at the beginning of the interval, plus births during the interval, minus deaths, plus in-migrants, minus out-migrants.

Hence the study of demographic change requires knowledge of fertility birthsmortality deathsand migration.

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These, in turn, affect not only population size and growth rates but also the composition of the population in terms of such attributes as sexage, ethnic or racial composition, and geographic distribution. Demographers distinguish between fecundity, the underlying biological potential for reproduction, and fertility, the actual level of achieved reproduction.

The difference between biological potential and realized fertility is determined by several intervening factors, including the following: 1 most women do not begin reproducing immediately upon the onset of puberty, which itself does not occur at a fixed age; 2 some women with the potential to reproduce never do so; 3 some women become widowed and do not remarry; 4 various elements of social behaviour restrain fertility; and 5 many human couples choose consciously to restrict their fertility by means of sexual abstinencecontraception, abortion, or sterilization.

The magnitude of the gap between potential and realized fertility can be illustrated by comparing the highest known fertilities with those of typical European and North American women in the late 20th century.

A well-studied high-fertility group is the Hutterites of North Americaa religious sect that views fertility regulation as sinful and high fertility as a blessing. Hutterite women who married between and are known to have averaged 10 children per woman. Meanwhile, women in much of Europe and North America averaged about two children per woman during the s and s—a number 80 percent less than that achieved by the Hutterites.

population biology

Even the highly fertile populations of developing countries in Africa, Asia, and Latin America produce children at rates far below that of the Hutterites. The general message from such evidence is clear enough: in much of the world, human fertility is considerably lower than the biological potential. It is strongly constrained by cultural regulations, especially those concerning marriage and sexuality, and by conscious efforts on the part of married couples to limit their childbearing.

Dependable evidence on historical fertility patterns in Europe is available back to the 18th century, and estimates have been made for several earlier centuries.Enter your mobile number or email address below and we'll send you a link to download the free Kindle App.

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Then you can start reading Kindle books on your smartphone, tablet, or computer - no Kindle device required. To get the free app, enter your mobile phone number. It is both authoritative and pedagogical. It is the text I have been waiting for. The book is well written and should be part of every student's early training in ecology.

Population biology has been investigated quantitatively for many decades, resulting in a rich body of scientific literature. Ecologists often avoid this literature, put off by its apparently formidable mathematics. This textbook provides an introduction to the biology and ecology of populations by emphasizing the roles of simple mathematical models in explaining the growth and behavior of populations.

The author only assumes acquaintance with elementary calculus, and provides tutorial explanations where needed to develop mathematical concepts. Examples, problems, extensive marginal notes and numerous graphs enhance the book's value to students in classes ranging from population biology and population ecology to mathematical biology and mathematical ecology. The book will also be useful as a supplement to introductory courses in ecology. Read more Read less. Kindle Cloud Reader Read instantly in your browser.

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Population ecology

Ships from and sold by Book Depository US. Ships from and sold by Amazon. FREE Shipping. Customers who viewed this item also viewed. Page 1 of 1 Start over Page 1 of 1. Only 1 left in stock - order soon. A Primer of Ecology. Nicholas J.Once production of your article has started, you can track the status of your article via Track Your Accepted Article.

An interdisciplinary journal, Theoretical Population Biology presents articles on theoretical aspects of the biology of populations, particularly in the areas of demography, ecology, epidemiology, evolution, and genetics. Emphasis is on the development of mathematical theory and models that enhance the Emphasis is on the development of mathematical theory and models that enhance the understanding of biological phenomena.

Articles highlight the motivation and significance of the work for advancing progress in biology, relying on a substantial mathematical effort to obtain biological insight.

Population growth rate based on birth and death rates - Ecology - AP Biology - Khan Academy

The journal also presents empirical results and computational and statistical methods directly impinging on theoretical problems in population biology. Further elaboration on the aims and scope of the journal appears in an editorial. Benefits to authors We also provide many author benefits, such as free PDFs, a liberal copyright policy, special discounts on Elsevier publications and much more.

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ISSN: Theoretical Population Biology. Editor in Chief: N. View Editorial Board. CiteScore: 2. CiteScore values are based on citation counts in a range of four years e. Impact Factor: 1. Submit Your Paper. Supports Open Access. View Articles. Track Your Paper Check submitted paper Check the status of your submitted manuscript in the submission system Track accepted paper Once production of your article has started, you can track the status of your article via Track Your Accepted Article.

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