Population ecology in the context of "Demographic"

Demography (from Ancient Greek δῆμος (dêmos) 'people, society' and -γραφία (-graphía) 'writing, drawing, description') is the statistical study of human populations: their size, composition (e.g., ethnic group, age), and how they change through the interplay of fertility (births), mortality (deaths), and migration.

Demographic analysis examines and measures the dimensions and dynamics of populations; it can cover whole societies or groups defined by criteria such as education, nationality, religion, and ethnicity. Educational institutions usually treat demography as a field of sociology, though there are a number of independent demography departments. These methods have primarily been developed to study human populations, but are extended to a variety of areas where researchers want to know how populations of social actors can change across time through processes of birth, death, and migration. In the context of human biological populations, demographic analysis uses administrative records to develop an independent estimate of the population. Demographic analysis estimates are often considered a reliable standard for judging the accuracy of the census information gathered at any time. In the labor force, demographic analysis is used to estimate sizes and flows of populations of workers; in population ecology the focus is on the birth, death, migration and immigration of individuals in a population of living organisms, alternatively, in social human sciences could involve movement of firms and institutional forms. Demographic analysis is used in a wide variety of contexts. For example, it is often used in business plans, to describe the population connected to the geographic location of the business. Demographic analysis is usually abbreviated as DA. For the 2010 U.S. Census, The U.S. Census Bureau has expanded its DA categories. Also as part of the 2010 U.S. Census, DA now also includes comparative analysis between independent housing estimates, and census address lists at different key time points.

In ecology, a community is a group or association of populations of two or more different species occupying the same geographical area at the same time, also known as a biocoenosis, biotic community, biological community, ecological community, or life assemblage. The term community has a variety of uses. In its simplest form it refers to groups of organisms in a specific place or time, for example, "the fish community of Lake Ontario before industrialization".

Community ecology or synecology is the study of the interactions between species in communities on many spatial and temporal scales, including the distribution, structure, abundance, demography, and interactions of coexisting populations. The primary focus of community ecology is on the interactions between populations as determined by specific genotypic and phenotypic characteristics. It is important to understand the origin, maintenance, and consequences of species diversity when evaluating community ecology.

The carrying capacity of an ecosystem is the maximum population size of a biological species that can be sustained by that specific environment, given the food, habitat, water, and other resources available. The carrying capacity is defined as the environment's maximal load, which in population ecology corresponds to the population equilibrium, when the number of deaths in a population equals the number of births (as well as immigration and emigration). Carrying capacity of the environment implies that the resources extraction is not above the rate of regeneration of the resources and the wastes generated are within the assimilating capacity of the environment. The effect of carrying capacity on population dynamics is modelled with a logistic function. Carrying capacity is applied to the maximum population an environment can support in ecology, agriculture and fisheries. The term carrying capacity had been applied to a few different processes in the past before finally being applied to human population limits in the 1950s. The notion of carrying capacity for humans is covered by the notion of sustainable population.

An early detailed examination of global limits on human population was published in the 1972 book Limits to Growth, which has prompted follow-up commentary and analysis, including much criticism. A 2012 review in the journal Nature by 22 international researchers expressed concerns that the Earth may be "approaching a state shift" in which the biosphere may become less hospitable to human life, and in which the human carrying capacity may diminish. This concern that humanity may be passing beyond "tipping points" for safe use of the biosphere has increased in subsequent years. Although the global population has now passed 8 billion, recent estimates of Earth's carrying capacity run from two to four billion people, depending on how optimistic researchers are about the prospects for international cooperation to solve problems requiring collective action.

The Journal of Ecology is a bimonthly peer-reviewed scientific journal covering all aspects of the ecology of plants. It was established in 1913 and is published by Wiley-Blackwell on behalf of the British Ecological Society.

The journal publishes papers on plant ecology (including algae) in both terrestrial and aquatic ecosystems. In addition to population and community ecology, articles on biogeochemistry, ecosystems, microbial ecology, physiological plant ecology, climate change, molecular genetics, mycorrhizal ecology, and the interactions between plants and organisms such as animals or bacteria, are published regularly. Besides primary research articles, it publishes "Essay Reviews" and "Forum" articles. In 2008, the first papers in a new series called "Future Directions" were published. These short papers are intended to stimulate debate as to where a field within plant ecology is going, or needs to go.

In population ecology and demography, the net reproduction rate, R₀, is the average number of offspring (often specifically daughters) that would be born to a female if she passed through her lifetime conforming to the age-specific fertility and mortality rates of a given year. This rate is similar to the gross reproduction rate but takes into account that some females will die before completing their childbearing years. An R₀ of one means that each generation of mothers is having exactly enough daughters to replace themselves in the population. If the R₀ is less than one, the reproductive performance of the population is below replacement level.

The R₀ is particularly relevant where sex ratios at birth are significantly affected by the use of reproductive technologies, or where life expectancy is low.