Encyclopedia
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 environment of an organism includes both physical properties, which can be described as the sum of local abiotic factors such as
solar insolation,
climate and
geology, as well as the other organisms that share its habitat. The term
oekologie was coined in 1866 by the German biologist
Ernst Haeckel, although it seems that
Henry David Thoreau had already invented it in 1852 ; the word is derived from the Greek ????? and ????? ; therefore "ecology" means the "study of the household [of nature]".
The word "ecology" is often used in common parlance as a synonym for the
natural environment or environmentalism. Likewise "ecologic" or "ecological" is often taken in the sense of environmentally friendly.
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 , to cells , to individuals , and finally at the level of
populations, communities, and ecosystems, to the
biosphere as a whole; these latter strata are the primary subjects of ecological inquiries. Ecology is a multi-disciplinary science. 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. Thus, ecology is considered by some to be a holistic science, one that over-arches older disciplines such as biology which in this view become sub-disciplines contributing to ecological knowledge.
Agriculture, fisheries, forestry, medicine and urban development are among human activities that would fall within Krebs' 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". However, ecological knowledge such as the quantification of
biodiversity and population dynamics have provided a scientific basis for expressing the aims of environmentalism and evaluating its goals and policies. Additionally, a holistic view of nature is stressed in both ecology and environmentalism.
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; for example, the activity of bees assures the pollination of flowering plants. Bee hives additionally produce honey which is consumed by still other species, such as bears.
- The relationship between the environment and a species is environmental ecology — for example, the consequences of environmental change on bee activity. Bees may die out due to environmental changes . The environment simultaneously affects and is a consequence of this activity and is thus intertwined with the survival of the species.
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:
- Physiological Ecology and Behavioral ecology examine adaptations of the individual to its environment.
- Population ecology studies the dynamics of populations of a single species.
- Community ecology 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 , 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. Note that these different systems are unrelated and often applied at the same time; one could be a theoretical plant community ecologist, or a polar ecologist interested in animal genetics.
History of ecology
Fundamental principles of ecology
Biosphere
For modern ecologists, ecology can be studied at several levels:
population level , biocoenosis level , ecosystem level, and
biosphere level.
The outer layer of the planet Earth can be divided into several compartments: the
hydrosphere , the
lithosphere , and the
atmosphere . The
biosphere , sometimes described as "the fourth envelope", is all living matter on the planet or that portion of the planet occupied by life. It reaches well into the other three spheres, although there are no permanent inhabitants of the atmosphere. Relative to the volume of the Earth, the biosphere is only the very thin surface layer which extends from 11,000 meters below sea level to 15,000 meters above.
It is thought that life first developed in the hydrosphere, at shallow depths, in the photic zone. Multicellular organisms then appeared and colonized benthic zones. Photosynthetic organisms gradually produced the chemically unstable oxygen-rich atmosphere that characterizes our planet. Terrestrial life developed later, after the
ozone layer protecting living beings from
UV rays formed. Diversification of terrestrial species is thought to be increased by the continents drifting apart, or alternately, colliding. Biodiversity is expressed at the ecological level , population level , species level , and genetic level. Recently technology has allowed the discovery of the deep ocean vent communities. This remarkable ecological system is not dependent on sunlight but bacteria, utilising the chemistry of the hot volcanic vents, are at the base of its food chain.
The biosphere contains great quantities of elements such as
carbon,
nitrogen and
oxygen. Other elements, such as
phosphorus, calcium, and
potassium, are also essential to life, yet are present in smaller amounts. 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. Plants and photosynthetic microorganisms convert
light into chemical energy by the process of
photosynthesis, which creates
glucose and releases free
oxygen. Glucose thus becomes the secondary energy source which drives the ecosystem. Some of this glucose is used directly by other organisms for energy. Other sugar molecules can be converted to other molecules such as
amino acids. Plants use some of this sugar, concentrated in nectar to entice pollinators to aid them in reproduction.
Cellular respiration is the process by which organisms break the glucose back down into its constituents,
water and
carbon dioxide, thus regaining the stored energy the sun originally gave to the plants. The proportion of photosynthetic activity of plants and other photosynthesizers to the respiration of other organisms determines the specific composition of the Earth's atmosphere, particularly its oxygen level.
Global air currents mix the atmosphere and maintain nearly the same balance of elements in areas of intense biological activity and areas of slight biological activity.
Water is also exchanged between the hydrosphere, lithosphere, atmosphere and biosphere in regular
cycles. The oceans are large tanks, which store water, ensure thermal and climatic stability, as well as the transport of chemical elements thanks to large
oceanic currents.
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.
Energy from the sun, captured by primary producers via
photosynthesis, flows upward through the chain to primary consumers , and then to secondary and tertiary consumers , before ultimately being lost to the system as waste heat. In the process, matter is incorporated into living organisms, which return their nutrients to the system via
decomposition, forming
biogeochemical cycles such as the
carbon and
nitrogen cycles.
The concept of an ecosystem can apply to units of variable size, such as a
pond, a field, or a piece of deadwood. A unit of smaller size is called a
microecosystem. For example, an ecosystem can be a stone and all the life under it. A
mesoecosystem could be a
forest, and a
macroecosystem a whole ecoregion, with its
drainage basin.
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. A
biotope is an environmentally uniform region characterized by a particular set of abiotic ecological factors. 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. When a population consists of an insufficient number of individuals, that population is threatened with extinction; the extinction of a species can approach when all biocenoses composed of individuals of the species are in decline. In small populations, consanguinity can result in reduced genetic diversity that can further weaken the biocenose.
Biotic ecological factors also influence biocenose viability; these factors are considered as either intraspecific and interspecific relations.
- Intraspecific relations are those which are established between individuals of the same species, forming a population. They are relations of co-operation or competition, with division of the territory, and sometimes organization in hierarchical societies.
- Interspecific relations—interactions between different species—are numerous, and usually described according to their beneficial, detrimental or neutral effect
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. These permanent recyclings of the elements as well as the
water are called
biogeochemical cycles. They guarantee a durable stability of the biosphere . This self-regulation, supported by negative feedback controls, ensures the perenniality of the ecosystems. It is shown by the very stable concentrations of most elements of each compartment. This is referred to as
homeostasis. The ecosystem also tends to evolve to a state of ideal balance, reached after a
succession of events, the climax .
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. Some species, such as
salmon or freshwater
eels move between marine systems and fresh-water systems. 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. The
biosphere comprises all of the Earth's biomes -- the entirety of places where life is possible -- from the highest mountains to the depths of the oceans.
Biomes correspond rather well to subdivisions distributed along the latitudes, from the
equator towards the poles, with differences based on to the physical environment and to the
climate. Their variation is generally related to the distribution of species according to their ability to tolerate temperature and/or dryness. For example, one may find
photosynthetic algae only in the
photic part of the ocean , while
conifers are mostly found in mountains.
Though this is a simplification of more complicated scheme,
latitude and altitude approximate a good representation of the distribution of
biodiversity within the biosphere. Very generally, the richness of biodiversity is decreasing most rapidly near the
equator and less rapidly as one approaches the poles.
The biosphere may also be divided into
ecozone, which are very well defined today and primarily follow the continental borders. The ecozones are themselves divided into ecoregions, though there is not agreement on their limits.
Ecosystem productivity
In an ecosystem, the connections between species are generally related to
food and their role in the
food chain. There are three categories of organisms:
- Producers -- usually plants which are capable of photosynthesis but could be other organisms such as bacteria around ocean vents that are capable of chemosynthesis.
- Consumers -- animals, which can be primary consumers , or secondary or tertiary consumers .
- Decomposers -- bacteria, mushrooms which degrade organic matter of all categories, and restore minerals to the environment.
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. In a food network, there will be fewer organisms at each level as one follows the links of the network up the chain.
These concepts lead to the idea of
biomass , of
primary productivity and of secondary productivity .
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. In any food network, the energy contained in the level of the producers is not completely transferred to the consumers. And the higher one goes up the chain, the more energy and resources is lost and consumed. Thus, from an energy—and environmental—point of view, it is more efficient for humans to be primary consumers than as secondary consumers and still more so than as a tertiary consumer . An ecosystem is unstable when the load capacity is overrun and is especially unstable when a population doesn't have an ecological niche and overconsumers.
The productivity of ecosystems is sometimes estimated by comparing three types of land-based ecosystems and the total of aquatic ecosystems:
- The forests contain dense biomasses and are very productive. The total production of the world's forests corresponds to half of the primary production.
- Savannas, meadows, and marshes contain less dense biomasses, but are 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 -- have very sparse biomasses and low productivity
- Finally, the marine and fresh water ecosystems contain very sparse biomasses .
Humanity's actions over the last few centuries have seriously reduced the amount of the Earth covered by forests , and have increased agro-ecosystems . In recent decades, an increase in the areas occupied by extreme ecosystems has occurred .
Ecological crisis
Generally, an ecological crisis occurs when the
environment of a species or a population evolves in a way unfavourable to that species survival.
It may be that the environment quality degrades compared to the species needs, after a change in an abiotic
ecological factor .
It may be that the environment becomes unfavourable for the survival of a species due to an increased pressure of
predation .
Lastly, it may be that the situation becomes unfavourable to the quality of life of the species due to a rise in the number of individuals .
Ecological crises may be more or less brutal . They can also be of natural or anthropic origin. They may relate to one unique species or to many species .
Lastly, an ecological crisis may be local or global .
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; some extinction events showed the disappearance of more than 90% of existing species at that time. However, it should be noted that the disappearance of certain species, such as the dinosaurs, by freeing an ecological niche, allowed the development and the diversification of the mammals. An ecological crisis thus paradoxically favored biodiversity.
Sometimes, an ecological crisis can be a specific and reversible phenomenon at the ecosystem scale. But more generally, the crises impact will last. Indeed, it rather is a connected series of events, that occur till a final point. From this stage, no return to the previous stable state is possible, and a new stable state will be set up gradually .
Lastly, if an ecological crisis can cause extinction, it can also more simply reduce the quality of life of the remaining individuals. Thus, even if the diversity of the human population is sometimes considered threatened , few people envision human disappearance at short span. However, epidemic diseases,
famines, impact on health of reduction of
air quality, food crises, reduction of living space, accumulation of toxic or non degradable wastes, threats on keystone species are also factors influencing the well-being of people.
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:
Footnotes
See also
- Ecological Economics
- ELDIS, a database on ecological aspects of economical development.
- Ecology movement
- Deep Ecology
- Human ecology
- Social ecology
- List of ecologists
- List of ecology topics
- List of biology topics
- Important publications in ecology
