Difference between revisions of "Ecology"

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'''Ecology''' (from [[Greek language|Greek]]: οίκος, ''oikos'', "household"; and λόγος, ''[[logos]]'', "knowledge") is the scientific study of the distribution and abundance of [[life|living organisms]] and the [[interaction]]s among organisms and between 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 [[insolation]] (sunlight), [[climate]], and [[geology]], and biotic factors, which are other organisms that share its [[habitat (ecology)|habitat]].
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'''Ecology''' is a field of [[biology]] that studies "the distribution and abundance of [[organism|organisms]] and the interactions that determine distribution and abundance."<ref>Begon, M., Harper, J. L., &amp; Townsend, C. R. (2006). Introduction: Ecology and its Domain. In Ecology: From Individuals to Ecosystems (4th ed., pp. xi-xii). introduction, Blackwell.</ref> These interactions include both biotic (occurring between living individuals) and abiotic interactions (occurring between and individual and its environment). There are several subdisciplines of ecology that focus on different [[Ecology#Organizational Complexity|levels of organization]] and different types of interactions, such behavioral, disease, sensory, and functional ecology.
  
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The word "ecology" is often used more loosely in such terms as [[social ecology]] and [[deep ecology]] and 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]].
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Ecology is often confused with [[environmentalism]]. While familiarity of the term "ecology" emerged with the growing environmental concerns of the [[The Sixties|1960s]] and [[The Seventies|'70s]], the two have separate meanings and goals. Ecology seeks to understand natural phenomena in the environment whereas environmentalism is a social and political movement.<ref>Institute of Food and Agricultural Sciences. (n.d.) Confusing Ecology with Environmentalism. Fort Lauderdale. University of Florida Extension.</ref> Even though they are separate, the two are closely related, as environmentalism relies on data and evidence from ecologists to support their [[Environmental Issues|goals]] and ecologists apply their findings to [[conservation]] efforts and management strategies.
  
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The term ecology or ''oekologie'' was coined by the [[Germany|German]] biologist [[Ernst Haeckel]] in 1866, when he defined it as "the comprehensive science of the relationship of the organism to the environment."<ref>
 
  
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{{cite book |last=Frodin |first=D.G. |authorlink= |coauthors= |title=Guide to Standard Floras of the World |url=http://books.google.com/books?id=aMjXCF4rmDUC&printsec=frontcover&dq=qjIyUKx2VnKAYDw2zTZA9n6hkuk#PPA72,M1 |year=2001 |publisher=Cambridge University Press |location=Cambridge |isbn=0-521-79077-8 |pages=72 |quote=[ecology is] a term first introduced by Haeckel in 1866 as Ökologie and which came into English in 1873}}</ref>  Haeckel did not elaborate on the concept, and the first significant textbook on the subject (together with the first university course) was written by the [[Denmark|Danish]] [[botany|botanist]], [[Eugenius Warming]].  For this early work, Warming is often identified as the founder of ecology<ref>Goodland, R.J. (1975) The tropical origin of ecology: Eugen Warming’s jubilee. ''Oikos'' '''26''', 240-245.</ref>.
 
  
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== Scope ==
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==Organizational Complexity==
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Ecology is usually considered a branch of [[biology]], the general science that studies living [[organism]]s. Organisms can be studied at many different levels, from [[proteins]] and [[nucleic acid]]s (in [[biochemistry]] and [[molecular biology]]), to [[cell (biology)|cells]] (in [[cellular biology]]), to individuals (in [[botany]], [[zoology]], and other similar disciplines), and finally at the level of [[population]]s, communities, and [[ecosystem]]s, to the [[biosphere]] as a whole; these latter strata are the primary subjects of ecological inquiry.  Ecology is a [[Interdisciplinary|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 [[Natural environment|environment]], ecology draws heavily on many other branches of science, especially [[geology]] and [[geography]], [[meteorology]], [[pedology (soil study)|pedology]], [[genetics]], [[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.  In support of viewing ecology as a subject in its own right as opposed to a sub-discipline of biology, [[Robert Ulanowicz]] stated that "''The emerging picture of ecosystem behavior does not resemble the worldview imparted by an extrapolation of conceptual trends established in other sciences.''"<ref>R. Ulanowicz, ''Ecology: The Ascendent Perspective'', Columbia (1997)</ref>
 
  
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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''.
 
  
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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 [[holism|holistic view]] of nature is stressed in both ecology and environmentalism.
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The discipline of ecology is split up into several subfields, ranging in order of organizational complexity. The smallest field of ecology, is organismal ecology, focusing on the the [[adaptation|adaptations]] and [[physiology]] of an individual. [[Population]] ecology is focused on the interactions that individuals of the same [[species]] have, affecting their population dynamics. [[Community]] ecology investigates how populations of different species interact and affect community composition. [[Ecosystem]] ecology incorporates the abiotic factors that influence individuals, populations, and communities. The largest scale of ecology studies the entire [[biosphere]], specifically the processes that occur in it, how changes in climate and organismal abundance affect it, and reconstruct previous climates and ecosystems on [[Earth]].
  
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Consider the ways an ecologist might approach studying the life of honeybees: 
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Though [[evolution|evolutionary biology]] is a separate field of biology, the two are tightly linked, each not fully explaining phenomena without the other. G. E. Hutchinson combined the two topics through the metaphor of an "evolutionary play in an ecological theater,"<ref>Hutchinson, G. E. (1973). The Ecological Theater and the evolutionary play. Yale Univ. Press.</ref> and as T. G. Dobzhansky states, "nothing in evolution makes sense except in the light of evolution."<ref>Dobzhansky, T. (1973). Nothing in biology makes sense except in the light of Evolution. The American Biology Teacher, 35(3), 125–129. https://doi.org/10.2307/4444260.</ref> While evolution is still heavilly debated and studied, it is important to take it into account when studying each of the levels of organization and to make sense of adaptations, distributions, and life histories.
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* The behavioral relationship between individuals of a [[species]] is behavioral ecology &mdash; for example, the study of the [[queen bee]], and how she relates to the worker [[bee]]s and the [[drone (bee)|drones]].
 
  
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* The organized activity of a species is community ecology; for example, the activity of bees assures the [[pollination]] of [[flowering plant]]s. Bee hives additionally produce [[honey]] which is consumed by still other species, such as [[bear]]s.
 
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* The relationship between the environment and a species is environmental ecology &mdash; for example, the consequences of environmental change on bee activity. Bees may die out due to environmental changes (see [[pollinator decline]]). The environment simultaneously affects and is a consequence of this activity and is thus intertwined with the survival of the species.
 
  
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=== Disciplines of ecology ===
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==Population Ecology==
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{{main|Ecology (disciplines)}}
 
  
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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:
 
  
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* [[Ecophysiology]] and [[Behavioral ecology]] examine adaptations of the individual to its environment.
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Population ecology is concerned with the interactions between members of a single species. A population is defined as a group of potentially interacting individuals of the same species that occupy the same area and can interbreed, for [[Reproduction|sexually reproducing]] species.<ref>Encyclopædia Britannica, inc. (n.d.). Population ecology. Encyclopædia Britannica. Retrieved March 9, 2022, from https://www.britannica.com/science/population-ecology </ref> The geographic area that defines a population can be distinct, such as an isolated lake or mountain peak, or it can be subjective, based upon the goal of the scientist studying the population.<ref>Begon, M., &amp; Harper, J. L. (2006). Life, Death and Life Histories. In C. R. Townsend (Ed.), Ecology: From Individuals to Ecosystems (4th ed., pp. 89–131). chapter, Blackwell.</ref>
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* [[Population ecology]] studies the dynamics of populations of a single species.
 
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* [[Community ecology]] (or '''synecology''') focuses on the interactions between species within an ecological community.
 
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* [[Ecosystem ecology]] studies the flows of energy and matter through the biotic and abiotic components of [[ecosystem]]s.
 
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* [[Systems ecology]] is an interdisciplinary field focusing on the study, development, and organization of ecological systems from a [[holistic]] perspective.
 
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*[[Landscape ecology]] examines processes and relationship across multiple ecosystems or very large geographic areas.
 
  
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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. These fields are not mutually exclusive; one could be a theoretical plant community ecologist, or a polar ecologist interested in animal genetics.
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Interactions that occur in populations are said to be interspecific. The most prominent of these interactions is competition for resources, such as water, food, shelter, and mates. Competition can be strong, where individuals control large territories to secure resources, or it can be less strong, such as in eusocial species like [[humans]] and [[wolves]].  
  
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== History of ecology ==
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=====Modeling=====
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{{main|History of ecology }}
 
  
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== Fundamental principles of ecology ==
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Population dynamics is an important aspect of population ecology that studies how populations change in size and density. Two important growth models are the exponential and logistic growth curves. The exponential growth equation is as follows: ''N<sub>t</sub> = N<sub>0</sub>e<sup>rt</sup>'', where ''N'' is the population size at time ''t'', ''e'' is Euler's number, and ''r'' is the intrinsic growth rate. This model predicts a population continually growing faster and faster without bound. Exponential growth is rare in nature, but examples include [[bacteria]] and [[humans]].
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===Biosphere===
 
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{{main|Biosphere|Biodiversity|Unified neutral theory of biodiversity}}
 
  
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For modern ecologists, ecology can be studied at several levels:  [[population]] level (individuals of the same species in the same or similar environment), [[biocoenosis]] level (or community of species), [[ecosystem]] level, and [[biosphere]] level.
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Most populations in nature do not grow exponentially, they reach a certain density threshold that limits growth, called the carrying capacity. [[Thomas Malthus]] described how at some point in time an expanding population must exceed supply of prerequisite [[natural resources]], i.e., population increases exponentially resulting in increasing competition for means of subsistence, food, shelter, etc. This concept has been termed the "Struggle for Existence". Resources may be plentiful at small population sizes, so initially a population will appear to grow exponentially, however, as resources become less available due to competition, the population growth rate slows down. This is described the by the logistic growth model as follows: ''dN/dt = rN[(K - N) / K]'', where ''K'' is the carrying capacity. Once a population has reached its carrying capacity, it will often remain at that population size, with stochastic fluctuations. Most populations follow this model.
  
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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 [[earth's atmosphere|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 which extends from 11,000 meters below sea level to 15,000 meters above. 
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=====Metapopulations=====
  
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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 [[benthos|benthic zones]]. [[Cyanobacteria|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 [[Ultraviolet|UV]] rays formed. Diversification of terrestrial species is thought to be increased by the continents [[continental drift|drifting apart]], or alternately, colliding. Biodiversity is expressed at the ecological level (ecosystem), population level (intraspecific diversity), species level (specific diversity), 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.  
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Modern approaches to population ecology have incorporated the concept of metapopulations. Inspired by the work of E. O. Wilson and R. H. Macarthur's work on island biogeography, metapopulations are important for discussing smaller populations that are connected to other nearby populations through colonization, [[emigration]], and [[extinction]]. Certain populations can act as sources for the metapopulations whereas others act as sinks and cannot sustain their own populations. Metapopulations have important conservation concerns, as increased habitat fragmentation increases the liklihood of local extinction of a species. Prioritizing which "islands" in a metapopulation should be protected can help to preserve and maintain healthy populations of charismatic species, such as butterflies and birds.
  
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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.
 
  
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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]] (a simple sugar) 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 acid]]s. Plants use some of this sugar, concentrated in [[nectar (plant)|nectar]] to entice pollinators to aid them in reproduction.
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==Community Ecology==
  
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[[Cellular respiration]] is the process by which organisms (like [[mammal]]s) 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. [[airstream|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.
 
  
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Water is also exchanged between the hydrosphere, lithosphere, atmosphere and biosphere in regular [[Water cycle|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 current]]s.
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Community ecology incorporates all the populations of species that occur in the same area and interact.<ref>Krohne, D. T. (2018). The Structure of Communities. In Ecology: Evolution, application, integration (pp. 276–297). essay, Oxford University Press. </ref> The main research questions of community ecologists focus on interactions, niches, strucutre, composition, and assembly.
  
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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]].
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Similar to populations, communities may be difficult to define the boundaries for. Two models for community definition are proposed. F.E. Clements proposed that communities are distinct from eachother, with a set of species unique to each, while H. A. Gleason proposed that communities are not discrete, but continuous, with species prevalence melding communities together through an ecotone.<ref>Dunbar. (1970, January 1). Clements &amp; Gleason - two contrasting views of vegetation associations. UNM Grad Ecology. Retrieved March 11, 2022, from http://unmecology.blogspot.com/2015/08/clements-gleason-two-contrasting-views.html </ref><ref>https://www.britannica.com/science/ecotone</ref> Even though both explanations are in opposition to each other, both are seen in nature. Discrete communities can occur where forests abruptly turn to agricultural land, whereas continuous communities can occur where a grassland gradually turns to a mature forest. The distinction between which model to use depends on the characterisitcs of the ecotone, ranging from abrupt (Clementonian) to gradual (Gleasonian).<ref>Bowersox, M. A., &amp; Brown, D. G. (2001). Measuring the abruptness of patchy ecotones. Plant Ecology, 156(1), 89–103. https://doi.org/https://www.jstor.org/stable/20051137</ref>
  
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=== The ecosystem concept ===
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=====Ecological Niche=====
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{{main|Ecosystem}}
 
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{{Prose|date=August 2007}}
 
  
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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.
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Each species has an ecological niche that determines where it can live and a population can have a positive growth rate. The Hutchinsonian definition of the niche is an "n-dimensional hypervolume" that is defined by all the environmental variables in the ecosystem that species live in. While there are many factors influencing the shape of a species' niche, there are usually a few key variables that are most influential. For wide-scale biogeographical investigations, the hypervolume can be reduced to temperature and rainfall as the most key axes, but at smaller scales, light availability, tide, etc. may be important dimensions to consider for the species in question.
  
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The ecosystem is 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 chain]]s or [[food web]]s. [[Energy]] from the sun, captured by [[primary producers]] via [[photosynthesis]], flows upward through the chain to [[primary consumers]] ([[herbivores]]), and then to [[secondary consumers|secondary]] and [[tertiary consumers]] ([[carnivores]] and [[omnivores]]), 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 cycle|carbon]] and [[nitrogen cycle]]s.  
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As stated, populations can only have positive growth if they lie within their niche. Outside this niche, there is either zero or negative growth. Bringing in metapopulations, this can help to describe source-sink dynamics. While a metapopulation is a conglomerate of disjoint populations, some habitats may be unfavorable to support a species. These are sinks. Other areas may be supportive of the species, and they can disperse to other metapopulations, acting as a source. Conservation efforts should this work on identifying sources versus sinks so that the supportive source habitats can be protected and connections can be made and maintained to other locations.
  
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The concept of an ecosystem can apply to units of variable size, such as a [[pond]], a field, or a piece of dead wood. An ecosystem within another ecosystem is called a [[micro ecosystem]]''.  For example, an ecosystem can be a stone and all the life under it.  A ''meso ecosystem'' could be a [[forest]], and a ''macro ecosystem'' a whole [[eco region]], with its [[drainage basin]].
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=====Interspecific Interactions=====
  
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The main questions when studying an ecosystem are:
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======Positive Interactions======
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* Whether the colonization of a barren area could be carried out
 
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* Investigation the ecosystem's dynamics and changes
 
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* The methods of which an ecosystem interacts at local, regional and global scale
 
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* Whether the current state is stable 
 
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* Investigating the value of an ecosystem and the ways and means that interaction of ecological systems provides benefits to humans, especially in the provision of healthy water.
 
  
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Ecosystems are often classified by reference to the biotopes concerned.  The following ecosystems may be defined:
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======Negative Interactions======
  
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* As [[continental ecosystem]]s, such as [[forest ecosystem]]s, [[meadow ecosystem]]s such as [[steppe]]s or [[savanna]]s, or  [[Agroecology|agro-ecosystem]]s
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=====Community Structure and Composition=====
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* As ecosystems of inland waters, such as [[lentic ecosystem]]s such as [[lake]]s or [[pond]]s; or [[lotic ecosystem]]s such as [[river]]s
 
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* As [[oceanic ecosystem]]s.
 
  
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Another classification can be done by reference to its communities, such as in the case of an [[human ecosystem]].
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=====Community Assembly=====
  
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=== Dynamics and stability ===
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==References==
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{{main|biogeochemistry|Homeostasis|Population dynamics}}
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<references/>
  
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'''Ecological factors''' which affect dynamic change in a [[population]] or [[species]] in a given ecology or [[natural environment|environment]] are usually divided into two groups: abiotic and biotic.
 
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'''Abiotic factors''' are geological, geographical, [[ecohydrology|hydrological]] and climatological parameters.  A '''biotope''' is an environmentally uniform region characterized by a particular set of abiotic ecological factors.  Specific abiotic factors include:
 
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* [[Water]], which is at the same time an essential element to life and a [[natural environment|milieu]]
 
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* [[Earth's atmosphere|Air]], which provides oxygen, nitrogen,  and carbon dioxide to living species and allows the dissemination of [[pollen]] and [[spore]]s
 
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* [[Soil]], at the same time source of nutriment and physical support
 
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** Soil [[pH]], [[Salinity in Australia|salinity]], nitrogen and phosphorus content, ability to retain water, and density are all influential
 
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* [[Temperature]], which should not exceed certain extremes, even if tolerance to heat is significant for some species
 
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* [[Light]], which provides energy to the ecosystem through [[photosynthesis]]
 
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* [[Natural disaster]]s can also be considered abiotic
 
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'''Biocenose''', or community, is a group of populations of plants, animals, micro-organisms.  Each population is the result of [[procreation]]s 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, [[inbreeding|consanguinity (inbreeding)]] can result in reduced [[genetic diversity]] that can further weaken the biocenose.
 
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'''Biotic ecological factors''' also influence biocenose viability; these factors are considered as either intraspecific and interspecific relations.
 
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: '''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.
 
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: '''Interspecific relations'''&mdash;[[biological interaction|interactions]] between different species&mdash;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 [[predator|predation]] (to eat or to be eaten), which leads to the essential concepts in ecology of [[food chain]]s (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 which 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 limiting resources, which can occur when two species share the same [[ecological niche]].
 
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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 (in particular [[carbon]], [[oxygen]] and [[nitrogen]]) as well as the [[water]] are called [[biogeochemical cycle]]s.  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 [[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 [[ecological succession|succession]] of events, the [[climax (biology)|climax]] (for example a pond can become a [[peat bog]]).
 
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=== Spatial relationships and subdivisions of land ===
 
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{{main|Biome|ecozone}}
 
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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 [[eel]]s move between marine systems and fresh-water systems.  These relationships between the ecosystems lead to the concept of a ''biome''.
 
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A [[biome]] is a homogeneous ecological formation that exists over a large region as [[tundra]] or [[steppe]]s. 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.
 
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Biomes correspond rather well to subdivisions distributed along the latitudes, from the [[equator]] towards the [[geographical pole|pole]]s, with differences based on to the physical environment (for example, oceans or mountain ranges) 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 [[photosynthesis|photosynthetic]] [[algae]] only in the ''photic'' part of the ocean (where light penetrates), while [[conifer]]s are mostly found in mountains.
 
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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 (as well for animal than plant species) is decreasing most rapidly near the [[equator]] and less rapidly as one approaches the poles.
 
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The biosphere may also be divided into [[ecozone]]s, 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.
 
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=== Ecosystem productivity ===
 
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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: 
 
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* [[autotroph|''Producers'']] -- usually plants which are capable of [[photosynthesis]] but could be other organisms such as bacteria around ocean vents that are capable of [[chemosynthesis]].
 
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* [[heterotroph|''Consumers'']] -- animals, which can be primary consumers ([[herbivorous]]), or secondary or tertiary consumers ([[carnivorous]] and [[omnivores]]). 
 
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* [[saprotroph|''Decomposers'']] -- [[bacterium|bacteria]], [[mushrooms]] which degrade organic matter of all categories, and restore minerals to the environment. And decomposers can also decompose decaying animals
 
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These relations form sequences, in which each individual consumes the preceding one and is consumed by the one following, in what are called [[food chain]]s or food network. In a food network, there will be fewer organisms at each level<!-- [[chains tropic]] --> as one follows the links of the network up the chain.
 
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These concepts lead to the idea of [[biomass (ecology)|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).
 
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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 (to subsist from vegetables, grains, legumes, fruit, etc.) than as secondary consumers (from eating herbivores, omnivores, or their products, such as milk, chickens, cattle, sheep, etc.) and still more so than as a tertiary consumer (from consuming carnivores, omnivores, or their products, such as fur, pigs, snakes, alligators, etc.). An ecosystem(s) is unstable when the load capacity is overrun and is especially unstable when a population doesn't have an ecological niche and overconsumers.
 
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The productivity of ecosystems is sometimes estimated by comparing three types of land-based ecosystems and the total of aquatic ecosystems:
 
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* The forests (1/3 of the Earth's land area) contain dense biomasses and are very productive.  The total production of the world's forests corresponds to half of the primary production. 
 
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* Savannas, meadows, and marshes (1/3 of the Earth's land area) contain less dense biomasses, but are productive.  These ecosystems represent the major part of what humans depend on for food.
 
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* 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
 
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* Finally, the marine and fresh water ecosystems (3/4 of Earth's surface) contain very sparse biomasses (apart from the coastal zones).
 
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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]]).
 
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=== Ecological Crisis ===<!-- This section is linked from [[Extinction]] -->
 
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Generally, an [[ecological crisis]] occurs with the loss of [[adaptive capacity]] when the [[resilience]] of an [[Natural environment|environment]] or of a species or a population evolves in a way unfavourable to coping with [[Perturbation (biology)|perturbation]]s 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]]).
 
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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]]).
 
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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.
 
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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.
 
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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]]).
 
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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 disease]]s, [[famine]]s, 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.
 
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Due to the increases in technology and a rapidly increasing population, humans have more influence on their own environment than any other [[ecosystem engineer]].
 
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Some common examples of ecological crises are:
 
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* The [[Exxon Valdez oil spill]] off the coast of [[Alaska]] in 1989
 
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* [[Permian-Triassic extinction event]] 250 million of years ago
 
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* [[Cretaceous–Tertiary extinction event]] 65 million years ago
 
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* [[Global warming]] related to the [[Greenhouse effect]]. Warming could involve flooding of the Asian deltas (see also [[eco refugee]]s), multiplication of [[extreme weather]] phenomena and changes in the  nature and quantity of the food resources (see [[Global warming and agriculture]]). See also international [[Kyoto Protocol]].
 
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* [[Ozone layer]] hole issue
 
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* [[Deforestation]] and [[desertification]], with disappearance of many species.
 
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* Volcanic eruptions such as [[1980 eruption of Mount St. Helens|Mount St. Helens]] and the [[Tunguska event|Tunguska]] and other [[impact events]]
 
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* The [[nuclear meltdown]] at [[Chernobyl]] in 1986 caused the death of many people and animals from [[cancer]], and caused mutations in a large number of animals and people. The area around the plant is now abandoned by humans because of the large amount of radiation generated by the meltdown. Twenty years after the accident, the [http://news.bbc.co.uk/2/hi/europe/4923342.stm animals have returned].
 
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==Bibliography==
 
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* Warming, E. (1909) [[Eugenius Warming#'Plantesamfund' or 'Oecology of Plants'|Oecology of Plants]] - an introduction to the study of plant-communities. Clarendon Press, Oxford.
 
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* Haeckel, E. (1866) ''General Morphology of Organisms; General Outlines of the Science of Organic Forms based on Mechanical Principles through the Theory of Descent as reformed by Charles Darwin.'' Berlin. 
 
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== References ==
 
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{{reflist}}
 
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=== Lists ===
 
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* [[List of basic biology topics]]
 
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* [[List of biology topics]]
 
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* [[List of basic ecology topics]]
 
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* [[List of ecology topics]]
 
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* [[List of ecologists]]
 
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* [[List of publications in biology#Ecology|Important publications in ecology]]
 
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=== Related topics ===
 
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* [[Acoustic ecology]]
 
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* [[Deep Ecology]]
 
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* [[Ecological economics]]
 
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* [[Ecology movement]]
 
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* [[Ecosystem]]
 
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* [[Ecosystem model]]
 
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* [[Ecohydrology]]
 
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* [[ELDIS]], a database on ecological aspects of economical development.
 
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* [[Environmental art]]
 
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* [[Environmental science]]
 
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* [[Environmental technology]]
 
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* [[Environmental communication]]
 
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* [[Environmental Psychology]]
 
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* [[Forest farming]]
 
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* [[Human ecology]]
 
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* [[Knowledge ecology]]
 
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* [[Social ecology]]
 
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* [[Systems ecology]]
 
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== External links ==
 
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* [http://www.barrameda.com.ar/ecology What is Ecology?]
 
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* http://www.rgbproject.com DebugLandscapes piece of art about ecology
 
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* [http://www.econguru.com/fundamentals_of_ecology/ Fundamentals of Ecology] Textbook-style investigation to the economy of nature, breaks down in 4 chapters from Population to Ecosystem.
 
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* [http://plato.stanford.edu/entries/ecology/ Ecology (Stanford Encyclopedia of Philosophy)]
 
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[[Category:Ecology]]
 
 
[[Category:Biology]]
 
[[Category:Biology]]

Latest revision as of 06:30, September 29, 2022

Ecology is a field of biology that studies "the distribution and abundance of organisms and the interactions that determine distribution and abundance."[1] These interactions include both biotic (occurring between living individuals) and abiotic interactions (occurring between and individual and its environment). There are several subdisciplines of ecology that focus on different levels of organization and different types of interactions, such behavioral, disease, sensory, and functional ecology.

Ecology is often confused with environmentalism. While familiarity of the term "ecology" emerged with the growing environmental concerns of the 1960s and '70s, the two have separate meanings and goals. Ecology seeks to understand natural phenomena in the environment whereas environmentalism is a social and political movement.[2] Even though they are separate, the two are closely related, as environmentalism relies on data and evidence from ecologists to support their goals and ecologists apply their findings to conservation efforts and management strategies.


Organizational Complexity

The discipline of ecology is split up into several subfields, ranging in order of organizational complexity. The smallest field of ecology, is organismal ecology, focusing on the the adaptations and physiology of an individual. Population ecology is focused on the interactions that individuals of the same species have, affecting their population dynamics. Community ecology investigates how populations of different species interact and affect community composition. Ecosystem ecology incorporates the abiotic factors that influence individuals, populations, and communities. The largest scale of ecology studies the entire biosphere, specifically the processes that occur in it, how changes in climate and organismal abundance affect it, and reconstruct previous climates and ecosystems on Earth.

Though evolutionary biology is a separate field of biology, the two are tightly linked, each not fully explaining phenomena without the other. G. E. Hutchinson combined the two topics through the metaphor of an "evolutionary play in an ecological theater,"[3] and as T. G. Dobzhansky states, "nothing in evolution makes sense except in the light of evolution."[4] While evolution is still heavilly debated and studied, it is important to take it into account when studying each of the levels of organization and to make sense of adaptations, distributions, and life histories.


Population Ecology

Population ecology is concerned with the interactions between members of a single species. A population is defined as a group of potentially interacting individuals of the same species that occupy the same area and can interbreed, for sexually reproducing species.[5] The geographic area that defines a population can be distinct, such as an isolated lake or mountain peak, or it can be subjective, based upon the goal of the scientist studying the population.[6]

Interactions that occur in populations are said to be interspecific. The most prominent of these interactions is competition for resources, such as water, food, shelter, and mates. Competition can be strong, where individuals control large territories to secure resources, or it can be less strong, such as in eusocial species like humans and wolves.

Modeling

Population dynamics is an important aspect of population ecology that studies how populations change in size and density. Two important growth models are the exponential and logistic growth curves. The exponential growth equation is as follows: Nt = N0ert, where N is the population size at time t, e is Euler's number, and r is the intrinsic growth rate. This model predicts a population continually growing faster and faster without bound. Exponential growth is rare in nature, but examples include bacteria and humans.

Most populations in nature do not grow exponentially, they reach a certain density threshold that limits growth, called the carrying capacity. Thomas Malthus described how at some point in time an expanding population must exceed supply of prerequisite natural resources, i.e., population increases exponentially resulting in increasing competition for means of subsistence, food, shelter, etc. This concept has been termed the "Struggle for Existence". Resources may be plentiful at small population sizes, so initially a population will appear to grow exponentially, however, as resources become less available due to competition, the population growth rate slows down. This is described the by the logistic growth model as follows: dN/dt = rN[(K - N) / K], where K is the carrying capacity. Once a population has reached its carrying capacity, it will often remain at that population size, with stochastic fluctuations. Most populations follow this model.

Metapopulations

Modern approaches to population ecology have incorporated the concept of metapopulations. Inspired by the work of E. O. Wilson and R. H. Macarthur's work on island biogeography, metapopulations are important for discussing smaller populations that are connected to other nearby populations through colonization, emigration, and extinction. Certain populations can act as sources for the metapopulations whereas others act as sinks and cannot sustain their own populations. Metapopulations have important conservation concerns, as increased habitat fragmentation increases the liklihood of local extinction of a species. Prioritizing which "islands" in a metapopulation should be protected can help to preserve and maintain healthy populations of charismatic species, such as butterflies and birds.


Community Ecology

Community ecology incorporates all the populations of species that occur in the same area and interact.[7] The main research questions of community ecologists focus on interactions, niches, strucutre, composition, and assembly.

Similar to populations, communities may be difficult to define the boundaries for. Two models for community definition are proposed. F.E. Clements proposed that communities are distinct from eachother, with a set of species unique to each, while H. A. Gleason proposed that communities are not discrete, but continuous, with species prevalence melding communities together through an ecotone.[8][9] Even though both explanations are in opposition to each other, both are seen in nature. Discrete communities can occur where forests abruptly turn to agricultural land, whereas continuous communities can occur where a grassland gradually turns to a mature forest. The distinction between which model to use depends on the characterisitcs of the ecotone, ranging from abrupt (Clementonian) to gradual (Gleasonian).[10]

Ecological Niche

Each species has an ecological niche that determines where it can live and a population can have a positive growth rate. The Hutchinsonian definition of the niche is an "n-dimensional hypervolume" that is defined by all the environmental variables in the ecosystem that species live in. While there are many factors influencing the shape of a species' niche, there are usually a few key variables that are most influential. For wide-scale biogeographical investigations, the hypervolume can be reduced to temperature and rainfall as the most key axes, but at smaller scales, light availability, tide, etc. may be important dimensions to consider for the species in question.

As stated, populations can only have positive growth if they lie within their niche. Outside this niche, there is either zero or negative growth. Bringing in metapopulations, this can help to describe source-sink dynamics. While a metapopulation is a conglomerate of disjoint populations, some habitats may be unfavorable to support a species. These are sinks. Other areas may be supportive of the species, and they can disperse to other metapopulations, acting as a source. Conservation efforts should this work on identifying sources versus sinks so that the supportive source habitats can be protected and connections can be made and maintained to other locations.

Interspecific Interactions
Positive Interactions
Negative Interactions
Community Structure and Composition
Community Assembly

References

  1. ↑ Begon, M., Harper, J. L., & Townsend, C. R. (2006). Introduction: Ecology and its Domain. In Ecology: From Individuals to Ecosystems (4th ed., pp. xi-xii). introduction, Blackwell.
  2. ↑ Institute of Food and Agricultural Sciences. (n.d.) Confusing Ecology with Environmentalism. Fort Lauderdale. University of Florida Extension.
  3. ↑ Hutchinson, G. E. (1973). The Ecological Theater and the evolutionary play. Yale Univ. Press.
  4. ↑ Dobzhansky, T. (1973). Nothing in biology makes sense except in the light of Evolution. The American Biology Teacher, 35(3), 125–129. https://doi.org/10.2307/4444260.
  5. ↑ Encyclopædia Britannica, inc. (n.d.). Population ecology. Encyclopædia Britannica. Retrieved March 9, 2022, from https://www.britannica.com/science/population-ecology
  6. ↑ Begon, M., & Harper, J. L. (2006). Life, Death and Life Histories. In C. R. Townsend (Ed.), Ecology: From Individuals to Ecosystems (4th ed., pp. 89–131). chapter, Blackwell.
  7. ↑ Krohne, D. T. (2018). The Structure of Communities. In Ecology: Evolution, application, integration (pp. 276–297). essay, Oxford University Press.
  8. ↑ Dunbar. (1970, January 1). Clements & Gleason - two contrasting views of vegetation associations. UNM Grad Ecology. Retrieved March 11, 2022, from http://unmecology.blogspot.com/2015/08/clements-gleason-two-contrasting-views.html
  9. ↑ https://www.britannica.com/science/ecotone
  10. ↑ Bowersox, M. A., & Brown, D. G. (2001). Measuring the abruptness of patchy ecotones. Plant Ecology, 156(1), 89–103. https://doi.org/https://www.jstor.org/stable/20051137
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