ecology - Scope, History of ecology, Fundamental principles of ecology

The study of the interaction of living organisms with their physical, biological, and chemical environment. Because of the complexity of ecosystems, ecological studies of individual ecosystems or parts of ecosystems are often made, from which links between different systems can be established. In this way, ecologists attempt to explain the workings of larger ecosystems. Important ecological concepts have had considerable influence in conservation; an example is carrying capacity, which relates the available resources of an area to the number of users that can be sustained by these resources. Some ecologists question the role of people in the environment: is humanity dependent on, or independent of, nature? The ecological movement of the 1960s onwards has argued that people must live within the limitations of the Earth's finite supply of resources, and that humanity is very much dependent on its environment. Ecology is therefore seen as a social as well as a scientific subject, providing a link between physical and human environments.

For the journal, see Ecology (journal).

Ecology Portal

Ecology, or ecological science, is the scientific study of the distribution and abundance of living organisms and how the distribution and abundance are affected by interactions between the organisms and their environment.

The word "ecology" is often used in common parlance as a synonym for the natural environment or environmentalism.

Scope

Ecology is usually considered a branch of biology, the general science that studies living organisms. Organisms can be studied at many different levels, from proteins and nucleic acids (in biochemistry and molecular biology), to cells (in cellular biology), to individuals (in botany, zoology, and other similar disciplines), and finally at the level of populations, communities, and ecosystems, to the biosphere as a whole; Because of its focus on the higher levels of the organization of life on earth and on the interrelations between organisms and their environment, ecology draws heavily on many other branches of science, especially geology and geography, meteorology, pedology, chemistry, and physics.

Agriculture, fisheries, forestry, medicine and urban development are among human activities that would fall within Krebs' (1972: 4) explanation of his definition of ecology: "where organisms are found, how many occur there, and why".

As a scientific discipline, ecology does not dictate what is "right" or "wrong".

Consider the ways an ecologist might approach studying the life of honeybees:

The behavioral relationship between individuals of a species is behavorial ecology — for example, the study of the queen bee, and how she relates to the worker bees and the drones. The organized activity of a species is community ecology; The relationship between the environment and a species is environmental ecology — for example, the consequences of environmental change on bee activity.

Disciplines of ecology

Ecology is a broad discipline comprised of many sub-disciplines. A common, broad classification, moving from lowest to highest complexity, where complexity is defined as the number of entities and processes in the system under study, is:

Ecophysiology and Behavioral ecology examine adaptations of the individual to its environment. Community ecology (or synecology) focuses on the interactions between species within an ecological community. Ecosystem ecology studies the flows of energy and matter through the biotic and abiotic components of ecosystems. Landscape ecology examines processes and relationship across multiple ecosystems or very large geographic areas.

Ecology can also be sub-divided according to the species of interest into fields such as animal ecology, plant ecology, insect ecology, and so on. Another frequent method of subdivision is by biome studied, e.g., Arctic ecology (or polar ecology), tropical ecology, desert ecology, etc. The primary technique used for investigation is often used to subdivide the discipline into groups such as chemical ecology, genetic ecology, field ecology, statistical ecology, theoretical ecology, and so forth.

History of ecology

Fundamental principles of ecology

Biosphere

For modern ecologists, ecology can be studied at several levels: population level (individuals of the same species), biocoenosis level (or community of species), ecosystem level, and biosphere level.

The outer layer of the planet Earth can be divided into several compartments: the hydrosphere (or sphere of water), the lithosphere (or sphere of soils and rocks), and the atmosphere (or sphere of the air).

It is thought that life first developed in the hydrosphere, at shallow depths, in the photic zone. Biodiversity is expressed at the ecological level (ecosystem), population level (intraspecific diversity), species level (specific diversity), and genetic level.

The biosphere contains great quantities of elements such as carbon, nitrogen and oxygen. At the ecosystem and biosphere levels, there is a continual recycling of all these elements, which alternate between the mineral and organic states.

While there is a slight input of geothermal energy, the bulk of the functioning of the ecosystem is based on the input of solar energy. Glucose thus becomes the secondary energy source which drives the ecosystem.

Cellular respiration is the process by which organisms (like mammals) break the glucose back down into its constituents, water and carbon dioxide, thus regaining the stored energy the sun originally gave to the plants.

Water is also exchanged between the hydrosphere, lithosphere, atmosphere and biosphere in regular cycles.

For a better understanding of how the biosphere works, and various dysfunctions related to human activity, American scientists simulated the biosphere in a small-scale model, called Biosphere II.

The ecosystem concept

The first principle of ecology is that each living organism has an ongoing and continual relationship with every other element that makes up its environment. An ecosystem can be defined as any situation where there is interaction between organisms and their environment.

The ecosystem is composed of two entities, the entirety of life, the biocoenosis and the medium that life exists in, the biotope. Within the ecosystem, species are connected by food chains or food webs.

The concept of an ecosystem can apply to units of variable size, such as a pond, a field, or a piece of deadwood. For example, an ecosystem can be a stone and all the life under it.

The main questions when studying an ecosystem are:

Whether the colonization of a barren area could be carried out Investigation the ecosystem's dynamics and changes The methods of which an ecosystem interacts at local, regional and global scale Whether the current state is stable Investigating the value of an ecosystem and the ways and means that interaction of ecological systems provide benefit to humans, especially in the provision of healthy water.

Ecosystems are often classified by reference to the biotopes concerned. The following ecosystems may be defined:

As continental ecosystems, such as forest ecosystems, meadow ecosystems such as steppes or savannas), or agro-ecosystems As ecosystems of inland waters, such as lentic ecosystems such as lakes or ponds; or lotic ecosystems such as rivers As oceanic ecosystems.

Another classification can be done by reference to its communities, such as in the case of an human ecosystem.

Dynamics and stability

Ecological factors which can affect dynamic change in a population or species in a given ecology or environment are usually divided into two groups: abiotic and biotic.

Abiotic factors are geological, geographical, hydrological and climatological parameters. Specific abiotic factors include:

Water, which is at the same time an essential element to life and a milieu Air, which provides oxygen, nitrogen, and carbon dioxide to living species and allows the dissemination of pollen and spores Soil, at the same time source of nutriment and physical support Soil pH, salinity, nitrogen and phosphorus content, ability to retain water, and density are all influential Temperature, which should not exceed certain extremes, even if tolerance to heat is significant for some species Light, which provides energy to the ecosystem through photosynthesis Natural disasters can also be considered abiotic

Biocenose, or community, is a group of populations of plants, animals, micro-organisms. Each population is the result of procreations between individuals of same species and cohabitation in a given place and for a given time. the extinction of a species can approach when all biocenoses composed of individuals of the species are in decline.

Biotic ecological factors also influence biocenose viability; The most significant relation is the relation of predation (to eat or to be eaten), which leads to the essential concepts in ecology of food chains (for example, the grass is consumed by the herbivore, itself consumed by a carnivore, itself consumed by a carnivore of larger size).

The existing interactions between the various living beings go along with a permanent mixing of mineral and organic substances, absorbed by organisms for their growth, their maintenance and their reproduction, to be finally rejected as waste. This self-regulation, supported by negative feedback controls, ensures the perenniality of the ecosystems. The ecosystem also tends to evolve to a state of ideal balance, reached after a succession of events, the climax (for example a pond can become a peat bog).

Spatial relationships and subdivisions of land

Ecosystems are not isolated from each other, but are interrelated. For example, water may circulate between ecosystems by the means of a river or ocean current. Water itself, as a liquid medium, even defines ecosystems. These relationships between the ecosystems lead to the concept of a biome.

A biome is a homogeneous ecological formation that exists over a large region as tundra or steppes.

Biomes correspond rather well to subdivisions distributed along the latitudes, from the equator towards the poles, with differences based on to the physical environment (for example, oceans or mountain ranges) and to the climate.

Though this is a simplification of more complicated scheme, latitude and altitude approximate a good representation of the distribution of biodiversity within the biosphere.

The biosphere may also be divided into ecozone, which are very well defined today and primarily follow the continental borders.

Ecosystem productivity

In an ecosystem, the connections between species are generally related to food and their role in the food chain.

These relations form sequences, in which each individual consumes the preceding one and is consumed by the one following, in what are called food chains or food network.

These concepts lead to the idea of biomass (the total living matter in a given place), of primary productivity (the increase in the mass of plants during a given time) and of secondary productivity (the living matter produced by consumers and the decomposers in a given time).

These two last ideas are key, since they make it possible to evaluate the load capacity -- the number of organisms which can be supported by a given ecosystem.

The productivity of ecosystems is sometimes estimated by comparing three types of land-based ecosystems and the total of aquatic ecosystems:

The forests (1/3 of the Earth's land area) contain dense biomasses and are very productive. These ecosystems represent the major part of what humans depend on for food. Extreme ecosystems in the areas with more extreme climates -- deserts and semi-deserts, tundra, alpine meadows, and steppes -- (1/3 of the Earth's land area) have very sparse biomasses and low productivity Finally, the marine and fresh water ecosystems (3/4 of Earth's surface) contain very sparse biomasses (apart from the coastal zones).

Humanity's actions over the last few centuries have seriously reduced the amount of the Earth covered by forests (deforestation), and have increased agro-ecosystems (agriculture). In recent decades, an increase in the areas occupied by extreme ecosystems has occurred (desertification).

Ecological crisis

Generally, an ecological crisis occurs with the loss of adaptive capacity when the resilience of an environment or of a species or a population evolves in a way unfavourable to coping with perturbations that interfere with that ecosystem, landscape or species survival.

It may be that the environment quality degrades compared to the species needs, after a change in an abiotic ecological factor (for example, an increase of temperature, less significant rainfalls).
It may be that the environment becomes unfavourable for the survival of a species (or a population) due to an increased pressure of predation (for example overfishing).
Lastly, it may be that the situation becomes unfavourable to the quality of life of the species (or the population) due to a rise in the number of individuals (overpopulation).

Ecological crises may be more or less brutal (occurring within a few months or taking as long as a few million years). They may relate to one unique species or to many species (see the article on Extinction event).

Lastly, an ecological crisis may be local (as an oil spill) or global (a rise in the sea level due to global warming).

According to its degree of endemism, a local crisis will have more or less significant consequences, from the death of many individuals to the total extinction of a species. Whatever its origin, disappearance of one or several species often will involve a rupture in the food chain, further impacting the survival of other species.

In the case of a global crisis, the consequences can be much more significant;

Sometimes, an ecological crisis can be a specific and reversible phenomenon at the ecosystem scale.

Lastly, if an ecological crisis can cause extinction, it can also more simply reduce the quality of life of the remaining individuals.

During the past decades, this increasing responsibility of humanity in some ecological crises has been clearly observed. Due to the increases in technology and a rapidly increasing population, humans have more influence on their own environment than any other ecosystem engineer.

Some usually quoted examples as ecological crises are:

Permian-Triassic extinction event 250 million of years ago Cretaceous-Tertiary extinction event 65 million years ago Global warming related to the Greenhouse effect.