Ecosystem communities: Food webs and Trophic dynamics

Food webs

Main article: Food webs

Early naturalists in the 16th-18th century realized the importance of food and feeding as an agent of transfer for energy and nutrients among species. They also understood that the supply ultimately depended upon plants converting energy from the sun into organic matter that gets eaten by herbivores. The first person to fully elaborate and place the concept of food chains into a scientific framework was Charles Elton in his classical book 'Animal Ecology'.^[35] Elton^[35] defined ecological relations through food-chains, food-cycles, food-size, and described numerical relations among different functional groups and their relative abundance. Elton's term 'food-cycle' was replaced by 'food-web' in a subsequent ecological text^[36] and has been used ever since. Elton's book, however, broke conceptual ground on ecological perspectives and food-web diagrams became more popular as a result.^[37] Today, food-webs are found in every introductory text book on ecology and it is also popular in the mainstream reference to ecology. Food-webs are an effective way to conceptually illustrate the interactive links among species in a community.^[38]

Food-webs summarize the complexity of communities. There are different dimensions that describe a community food-web, including species composition (type of species), richness (number of species), biomass & productivity, and stability. The food-web diagram illustrates species composition and shows how a change in a single species can influence many others. Microcosm studies simplify food-web research into semi-isolated units such as small springs, decaying logs and cowpats. Principals gleaned from food-web microcosm studies are used to extrapolate smaller dynamic concepts to larger systems.^[39]Food-chain length is an important parameter in describing larger food-web dynamics. The food-chain length is defined as:

"The number of transfers of energy or nutrients from the base to the top of a food web..." ^[40]:269

There are different ways of calculating food-chain length depending on what parameters of the food-web dynamic are being considered: connectance, energy, or interaction.^[40] Hence, in a simple example of connectance a deer is one step removed from the plants it eats (chain length = 1) and a wolf that eats the dear is two steps removed (chain length = 2). The relative amount or strength of influence that these parameters have on the food-web are used to address questions about:

• the identity or existence of a few dominant species (called strong interactors or keystone species)
• the total number of species and food-chain length (including many weak interactors) and
• how community structure, function and stability is determined.^[39]

Trophic dynamics

Main article: Trophic dynamics

Links in food-webs relate of primary importance to feeding relations or trophism (The Greek root of the word τροφή, trophē, means food or feeding). Elton^[35] noted how important and influence the feeding relations had on ecosystem structure. He proposed that ecosystems naturally sort into a ‘pyramid of numbers’ when the relative abundance of each functional group is stacked into their respective trophic levels. Functional groups are broadly categorized as autotrophs (e.g., plants), heterotrophs (e.g., deer, wolves), and detrivores (e.g., bacteria, fungi). It is not always entirely clear what creatures belong in what group. Some organisms are omnivores, meaning they eat both plant and animal tissues and don't fit neatly into a category. However, it has been suggested that omnivores have a greater functional ecosystem influence as predators because relative to herbivores they are comparatively inefficient at grazing.^[41] Every species fits into an ecosystem in a particular way that is called its ecological niche. The ecological niche of a species describes their unique habitat requirements and influence or roles within the ecosystem.

Trophic levels stem from the systems view of ecology that groups smaller components of the system to formulate a macroscopic image of the larger functional design. Trophic levels are abstractions of the system, but they explain real phenomena. For example, it is understood that functional trophic groups sort out hierarchically into trophic levels because it requires specialized adaptations to become a photosynthesizer or a predator, but rarely a skillful combination of both. These functional adaptations to trophism (feeding) solidifies emergent ecosystem principals of functional groups.^[41] Moreover, species become so specialized at their respective ecological niche that they competitively exclude other competitor species from living in the same geographic area if they strongly share the same ecological niche. This is called the competitive exclusion principle.^[42]

Functional groups are usually depicted in hierarchical schemes with three or more trophic levels including primary producers (autotrophs) and levels of heterotrophic consumers including the herbivores (primary consumers), predators (secondary consumers), predators that eat predators (tertiary consumers), and ultimately ending at the detrivores in the soil ecosystems.^[22] The pyramidal arrangement of trophic levels is a consistent feature across ecosystems with the primary producers having the larger base and consumer densities and amounts of energy decreasing as species become further removed from the photosynthetic source of production.^[44] The size of each level in the pyramid generally represents biomass, which is often measured as the dry weight of an organism.^[22] Trophic levels and food webs can be used to depict and calculate mathematical and statistical parameters such as those used in other kinds of network analysis, including graph theory.^[45]

Food-web links point to direct trophic relationships among species, but there are also indirect effects that can alter the abundance, distribution, or biomass in the trophic levels. For example, predators eating herbivores indirectly influence the control and regulation of primary production in plants. Although the predators do not eat the plants directly, they regulate the population of herbibores that are directly linked to plant trophism. The net effect of direct and indirect relations is called trophic cascades. Trophic cascades are separated into species-level cascades, where only a subset of the food-web dynamic is impacted by a change in population numbers, and community-level cascades, where a change in population numbers has a dramatic effect on the entire food-web, such as the distribution of plant biomass.^[46] The keystone species concept is closely aligned to species-level cascades, where a single species occupies a particularly strong node in the food-web and its removal results in the collapse of the food-web structure and extinction of other species. Sea otters (Enhydra lutris) are the classical example of a keystone species because they limit the density of urchins that feed on kelp. If sea otters are removed from the system, the urchins graze until the kelp beds disappear and this has a dramatic effect on community structure.^[47] Hunting of sea otters, for example, is thought to have lead to the extinction of the Steller's Sea Cow (Hydrodamalis gigas).^[48] While the keystone species concept has been used extensively as a conservation tool, it has been criticized for being poorly defined. Different ecosystems express different complexities and so it is unclear how applicable and general the keystone species model can be applied. To better understand the keystone species and trophic cascade models, ecologists conduct removal experiments to measure the relative impact, strength and influence of interaction among different species on community dynamics.^[47][46]

Behavioral Ecology

Main article: Behavioral ecology

Adaptation is the central unifying concept in behavioral ecology.[5] Behaviors can be recorded as traits and inherited in much the same way that eye and hair color can. As such, behaviors are subject to the forces of natural selection. Hence, behaviors can be adaptive in nature, meaning that they evolved and serve a functional utility such as enhancing ones opportunity to successfully reproduce and increase fitness.^[49] Fitness is measured in terms of reproductive success. An animal with behaviors that afford it some degree of leverage in the struggle for existence such that it survives to pass on its heritable traits to its offspring is considered fit if the adaptation succeeds and propagates more of its kind in subseqent generations. A measure of fitness is the numerical differential and representation in frequency of a trait over subsequent generations.^[50]

Scope

Ecology is usually considered as a branch of biology, the general science that studies living organisms. It is associated with the highest levels of biological organization, including the individual organism, the population, the ecological community, the ecosystem and the biosphere as a whole. When referring to the study of a single species, a distinction is often made between its "ecology" and its "biology". For example, "polar bear biology" might include the study of the polar bear's physiology,morphology, pathology and ontogeny, whereas "polar bear ecology" would include a study of its prey species, its population andmetapopulation status, distribution, dependence on environmental conditions, etc.

Because of its focus on the interrelations between organisms and their environment, ecology is a multidisciplinary science that draws on many other branches, including geology and geography, meteorology, soil science, genetics, chemistry, physics, mathematics and statistics. Due to its breadth of scope, 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. It has been argued that the mechanistic models which have driven the development of most other sciences are inappropriate for unraveling the complex interactions in most ecosystems, and that progress in ecology is better served by a central paradigm driven by information theory and complexity theory.^[51]

Ecology is also a highly applied science, especially with respect to issues of natural resource management. Efforts related to wildlife conservation, habitat management, mitigation of ecological impacts of environmental pollution, ecosystem restoration, species reintroductions, fisheries, forestry and game management are often the direct domain of applied ecology. Urban development, agricultural and public health issues are also often informed by ecological perspectives and analysis.

Disciplines

Main article: Ecology (disciplines)

Ecology is a broad discipline comprising 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 examines how the physiological functions of organisms influence the way they interact with the environment, both biotic and abiotic.
• Ecomechanics uses physics and engineering principles to examine the interaction of organisms with their environment and with other species.
• Behavioral ecology examines the roles of behavior in enabling an animal to adapt to its environment.
• Population ecology studies the dynamics of populations of a single species.
• 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.
• Systems ecology is an interdisciplinary field focusing on the study, development, and organization of ecological systems from a holistic perspective.
• Landscape ecology examines processes and relationship in a spatially explicit manner, often across multiple ecosystems or very large geographic areas.
• Evolutionary ecology studies ecology in a way that explicitly considers the evolutionary histories of species and their interactions.
• Political ecology connects politics and economy to problems of environmental control and ecological change.

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, marine ecology, etc. The primary technique used for investigation is often used to subdivide the discipline into groups such as chemical ecology, molecular ecology, field ecology, quantitative ecology, theoretical ecology, and so forth.

Subdivisions of ecology are not mutually exclusive; indeed, very few exist in isolation. Many of them overlap, complement and inform each other. For example, the population ecology of an organism is a consequence of its behavioral ecology and intimately tied to its community ecology. Methods from molecular ecology might inform the study of the population, and all kinds of data are modeled and analyzed using quantitative ecology techniques, often motivated by basic results in theoretical ecology.

Levels of organization

See also: Biological organisation

One of the unique and complex aspects to ecology is that there are emergent phenomena operating at different environmental scales of influence, ranging from molecular to galactic spheres. These scaled phenomena require different sets of scientific explanation, which is otherwise captured in the expression 'the sum is greater than the parts'.^[13][21] An understanding of these emergent phenomena operating at different scales requires a conceptual distinction between ecology and the environment. While the environment of an organism includes everything in the universe that is external to it, only some levels are more evidently of direct importance and this is called the effective environment.^[2]

Ecosystems are most commonly studied at the local or effective community scale, such as measurements of primary production in a wetland^[52] or the analysis of predator-prey dynamics affecting amphibian biomass^[53]. Ecological relations also regulate the flux of energy, nutrients, and climate all the way up to the planetary scale. The global sum of ecosystems is known as thebiosphere where ecological theory has been used to explain self emergent regulatory phenomena at the planetary scale. This is known as the Gaia hypothesis^[21]. The Gaia hypothesis is an example of holism in ecology because it tests for principals relating to an evolving and self regulating planetary ecosystem that requires different explanations than those governing ecosystems at a smaller scale, such as a single wetland.

Biosphere

Main articles: Biosphere, Biodiversity, and Unified neutral theory of biodiversity

For modern ecologists, ecology can be studied at several levels, as defined in the biological organisation of life: population level (individuals of the same species in the same or similar environment), 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), thelithosphere (or sphere of soils and rocks), and the atmosphere (or sphere of the air). The biosphere (or sphere of life), 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 that 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. (Recently, though, a competing theory has emerged, that life originated around hydrothermal vents in the deeper ocean. See Origin of life.) 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, protected from UV rays by the ozone layer. Diversification of terrestrial species is thought to be increased by the continents drifting apart, or alternately, colliding. 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, hydrogen, 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.

Although 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 (a simple sugar) and releases free oxygen. Glucose thus becomes the secondary energy source that drives the ecosystem. Some of this glucose is used directly by other organisms for energy. Other sugar molecules can be converted to 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 (like mammals) break the glucose back down into its constituents, waterand 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 that store water, ensure thermal and climatic stability, and facilitate 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 attempted to simulate the biosphere in a small-scale model, called Biosphere 2.

Ecosystem

Main article: Ecosystem

A central principle of ecology is that each living organism has an ongoing and continual relationship with every other element that makes up its environment. The sum total of interacting living organisms (the biocoenosis) and their non-living environment (the biotope) in an area is termed an ecosystem. Studies of ecosystems usually focus on the movement of energy and matter through the system.

Almost all ecosystems run on energy captured from the sun by primary producers viaphotosynthesis. This energy then flows through the food chains to primary consumers(herbivores who eat and digest the plants), and on to secondary and tertiary consumers(either carnivores or omnivores). Energy is lost to living organisms when it is used by the organisms to do work, or is lost as waste heat.

Matter is incorporated into living organisms by the primary producers. Photosynthetic plants fix carbon from carbon dioxide and nitrogen from atmospheric nitrogen or nitrates present in the soil to produce amino acids. Much of the carbon and nitrogen contained in ecosystems is created by such plants, and is then consumed by secondary and tertiary consumers and incorporated into themselves. Nutrients are usually returned to the ecosystem viadecomposition. The entire movement of chemicals in an ecosystem is termed a biogeochemical cycle, and includes the carbonand nitrogen cycle.

Ecosystems of any size can be studied; for example, a rock and the plant life growing on it might be considered an ecosystem. This rock might be within a plain, with many such rocks, small grass, and grazing animals -- also an ecosystem. This plain might be in the tundra, which is also an ecosystem (although once they are of this size, they are generally termed ecozones orbiomes). In fact, the entire terrestrial surface of the earth, all the matter which composes it, the air that is directly above it, and all the living organisms living within it can be considered as one, large ecosystem.

Ecosystems can be roughly divided into terrestrial ecosystems (including forest ecosystems, steppes, savannas, and so on),freshwater ecosystems (lakes, ponds and rivers), and marine ecosystems, depending on the dominant biotope.

Dynamics and stability

Main articles: Biogeochemistry, Homeostasis, and Population dynamics

Ecological factors that 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. Abiotope 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 a 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, microorganisms. Each population is the result ofprocreations between individuals of the 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 (inbreeding) can result in reduced genetic diversity, which can further weaken the biocenose.

Biotic ecological factors also influence biocenose viability; these factors are considered as either intraspecific or interspecific relations.

Intraspecific relations are those that are established between individuals of the same species, forming a population. They are relations of cooperation 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 (for example,mutualism (relation ++) or competition (relation --). 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). A high predator to prey ratio can have a negative influence on both the predator and prey biocenoses in that low availability of food and high death rate prior to sexual maturity can decrease (or prevent the increase of) populations of each, respectively. Selective hunting of species by humans that leads to population decline is one example of a high predator to prey ratio in action. Other interspecific relations include parasitism, infectious disease, and competition for limited resources, which can occur when two species share the sameecological niche.

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 recycling of the elements (in particular carbon, oxygen, and nitrogen) as well as the water are called biogeochemical cycles. They guarantee a durable stability of the biosphere (at least when unchecked human influence and extreme weather or geological phenomena are left aside). This self-regulation, supported by negative feedbackcontrols, 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, called theclimax, which is reached after a succession of events (for example a pond can become a peat bog).

Spatial relationships and subdivisions of land

Main articles: Biome and ecozone

Ecosystems are not isolated from each other, but are interrelated. For example, water may circulate between ecosystems by 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, such as tundra or steppes. The biospherecomprises 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 the physical environment (for example, oceans or mountain ranges) and the climate. Their variation is generally related to the distribution of species according to their ability to tolerate temperature, dryness, or both. For example, one may findphotosynthetic algae only in the photic part of the ocean (where light penetrates), whereas conifers are mostly found in mountains.

Though this is a simplification of a more complicated scheme, latitude and altitude approximate a good representation of the distribution of biodiversity within the biosphere. Very generally, the richness of biodiversity (as well for animal as for plant species) is decreasing most rapidly near the equator and less rapidly as one approach the poles.

The biosphere may also be divided into ecozones, 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.

Ecological crisis

Main article: Ecological crisis

Generally, an ecological crisis occurs with the loss of adaptive capacity when the resilienceof an environment or of a species or a population evolves in a way unfavourable to coping withperturbations that interfere with that ecosystem, landscape or species survival (Note: The concept of resilience is not universally accepted in ecology, and moreso represents a contingent within the field that take a holist view of the environment. There are also many ecologists that take a reductionistic perspective and that believe that the environment, at base, is indeterministic). 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)^{[citation needed]}. It may be that the environment becomes unfavourable for the survival of a species (or a population) due to an increased pressure ofpredation (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 vary in length and severity, occurring within a few months or taking as long as a few million years. They can also be of natural or anthropic origin. They may relate to one unique species or to many species, as in an 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; 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 favoured 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 (see homeorhesy).

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 (see in particular indigenous people), 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(great apes, panda, whales) are also factors influencing the well-being of people.

Due to the increases in technology and a rapidly increasing population, humans have more influence on their own environment than any other ecosystem engineer.

Historical roots of ecology

Main article: History of ecology

Ecology as a scientific discipline is relatively young, reaching prominence mostly in the second half of the 20th century. However, systematic ecological studies can trace roots toancient times, with Aristotle and Theophrastus, for example, making early observations on animal migrations and plant biogeography respectively. Several notable 19th century scientists such as Alexander Humboldt (1769 – 1859), Charles Darwin (1809 – 1882), Alfred Russel Wallace (1823 – 1913) and Karl Möbius (1825 – 1908) made many important contributions, from laying down the foundation of biogeography to identifying an interacting groups of organisms as a functionally connected community (biocoenosis).

The term "ecology" itself (German: Oekologie) was first coined by the German biologist Ernst Haeckel in 1866, who defined it as "the comprehensive science of the relationship of the organism to the environment."^[54] The first significant textbook on the subject (together with the first university course) was written by the Danish botanist, Eugenius Warming. For this early work, Warming is sometimes identified as the founder of ecology.^[55]

See also

Main article: Outline of ecology

• Acoustic ecology
• Agroecology
• Biodiversity
• Biotope
• Climate
• Conservation movement
• Earth science
• Ecohydrology
• Ecological economics
• Ecological Forecasting
• Ecology movement
• Ecology of contexts
• Ecosystem
• Ecosystem model
• Ecological Relationships
• Ecotope
  • ELDIS, a database on ecological aspects of economical development.
• Environment
• Forest farming
• Forest gardening
• Habitat conservation
• Human ecology
• Knowledge ecology
• Landscape ecology
• Landscape limnology
• Natural capital
• Natural resource
• Natural resource management
• Nature
• Sustainability
• Sustainable development

Lists

• Index of biology articles
• Glossary of ecology
• List of ecologists
• List of important publications in biology#Ecology
• Outline of biology

Notes

1. ^ Begon, M.; Townsend, C. R., Harper, J. L. (2006). Ecology: From individuals to ecosystems. (4th ed.). Blackwell. ISBN 1405111178.
2. ^ ^{a b c d e f g h i j k l} Allee, W.; Emerson, A. E., Park, O., Park, T., and Schmidt, K. P. (1949). Principles of Animal Ecology. W. B. Saunders Company. ISBN 0721611206.
3. ^ Smith, R.; Smith, R. M. (2000). Ecology and Field Biology. (6th ed.). Prentice Hall. ISBN 0321042905.
4. ^ Begon, M.; Townsend, C. R., Harper, J. L. (2006). Ecology: From individuals to ecosystems. (4th ed.). Blackwell. ISBN 1405111178.
5. ^ ^{a b c d e f} Kormondy, E. (1995). Concepts of ecology. (4th ed.). Benjamin Cummings. ISBN 0134781163.
6. ^ Proulx, S. R.; Promislow, D. E. L.; Phillips, P. C. (2005), "Network thinking in ecology and evolution", Trends in Ecology & Evolution 20 (6): 345-353
7. ^ Omerod, S.J.; Pienkowski, M.W.; Watkinson, A.R. (1999). "Communicating the value of ecology". Journal of Applied Ecology 36: 847-855.
8. ^ Phillipson, J.; Lowe, P.; Bullock, J.M. (2009). "Navigating the social sciences: interdisciplinarity and ecology". Journal of Applied Ecology 46: 261-264.
9. ^ Steward T. A. Pickett, Mary L. Cadenasso, J. Morgan Grove, Peter M. Groffman, Lawrence E. Band, Christopher G. Boone, William R. Burch Jr., C. Susan B. Grimmond, John Hom, Jennifer C. Jenkins, Neely L. Law, Charles H. Nilon, Richard V. Pouyat, Katalin Szlavecz, Paige S. Warren, Matthew A. Wilson (2008). "Beyond Urban Legends: An Emerging Framework of Urban Ecology, as Illustrated by the Baltimore Ecosystem Study".BioScience 58: 139-150.
10. ^ Aguirre, A.A. (2009). "Biodiversity and Human Health". EcoHealth. doi:10.1007/s10393-009-0242-0.
11. ^ Costanza, R.; d'Arge, R.; de Groot, R.; Farber, S.; Grasso, M.; Hannon, B.; et al. (1997). "[http://www.uvm.edu/giee/publications/Nature_Paper.pdf The value of the world’s ecosystem services and natural capital]". Nature 387: 253-260.
12. ^ Millennium Ecosystem Assessment, 2005. Ecosystems and Human Well-being: Biodiversity Synthesis. World Resources Institute, Washington, DC.
13. ^ ^{a b} Odum, E. P. (1977). "The emergence of ecology as a new integrative discipline". Science 195: 1289-1293.
14. ^ Campbell, Neil A.; Brad Williamson; Robin J. Heyden (2006). Biology: Exploring Life. Boston, Massachusetts: Pearson Prentice Hall. ISBN 0-13-250882-6.
15. ^ ^{a b} Smith, John M.; Szathmary, Eors (1999), The Origins of Life: From the Birth of Life to the Origins of Language, Oxford: Oxford University Press, ISBN 019286209X
16. ^ Miller, Stanley, L. (1953), "A production of amino acids under possible primitive Earth conditions.", Science 117: 528-529
17. ^ Ernst, S. K. Morgan; Enquist, Brian J.; Brown, James H.; Charnov, E. L.; Gillooly, J. F.; Savage, Van M.; et al. (2003), "Thermodynamic and metabolic effects on the scaling of production and population energy use", Ecology Letters 6: 990-995
18. ^ Allègre, Claude J.; Manhès, Gérard; Göpel, Christa (1995), "The age of the Earth", Geochimica et Cosmochimica Acta 59: 1455-1456
19. ^ Wills, C.; Bada, J. (2001), The Spark of Life: Darwin and the Primeval Soup, Cambridge, Massachusetts: Perseus Publishing
20. ^ Catling, D. C.; Claire, M. W. (2005), "How Earth’s atmosphere evolved to an oxic state: A status report", Earth and Planetary Science Letters237: 1-20
21. ^ ^{a b c d} Lovelock, J. (2003). "The living Earth". Nature 426: 769-770.
22. ^ ^{a b c d e f g} Rickleffs, Robert, E. (1996). The Economy of Nature. University of Chicago Press. pp. 678. ISBN 0716738473.
23. ^ Shimeta, J.; Jumars, P. A.; Lessard, E. J. (1995), "Influences of turbulence on suspension feeding by planktonic protozoa; experiments in laminar shear fields", Limnolology and Oceanography 40 (5): 845-859
24. ^ Etemad-Shahidi, A.; Imberger, J. (2001), "Anatomy of turbulence in thermally stratified lakes", Limnolology and Oceanography 46 (5): 1158–1170
25. ^ Grace, J. (2004). "Understanding and managing the global carbon cycle". Journal of Ecology 92: 189–202.
26. ^ Hastings, A. Byers, J. E., Crooks, J. A., Cuddington, K., Jones, C. J., Lambrinos, J. G., Talley, T. S. and Wilson, W. G. (2007). "Ecosystem engineering in space and time". Ecology Letters 10: 153–164.
27. ^ Jones, Clive G.; Lawton, John H.; Shachak, Moshe (1994). "Organisms as ecosystem engineers". Oikos 69: 373-386.
28. ^ Wright, J.P.; Jones, C.G. (2006). "The Concept of Organisms as Ecosystem Engineers Ten Years On: Progress, Limitations, and Challenges".BioScience 56: 203-209.
29. ^ ^{a b} Laland, K. N.; Odling-Smee, F.J.; Feldman, M.W. (1999). "Evolutionary consequences of niche construction and their implications for ecology".PNAS 96: 10242-10247.
30. ^ Gould, S.J.; Lloyd, E.A. (1999). "Individuality and adaptation across levels of selection: How shall we name and generalize the unit of Darwinism?". Proceedings of the National Academy of Science 96 (21): 11904-11909.
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References

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External links

• stanford.edu/entries/ecology/ Ecology (Stanford Encyclopedia of Philosophy)
  • Science Aid: Ecology High School (GCSE, Alevel) Ecology.
  • Ecology Journals List of scientific journals related to Ecology
• Ecology Dictionary - Explanation of Ecological Terms
  • [8] International Society for Behavioral Ecology