Ecosystem ecology is the integrated study of living and non-living components of ecosystems and their interactions within an ecosystem framework. This science examines how ecosystems work and relates this to their components such as chemicals, soil and animals. Ecosystem ecology examines physical and biological structures and examines how these ecosystem characteristics interact with each other; this helps us understand how to maintain high quality water and economically viable commodity production. A major focus of ecosystem ecology is on functional processes, ecological mechanisms that maintain the structure and services produced by ecosystems; these include primary productivity and trophic interactions. Studies of ecosystem function have improved human understanding of sustainable production of forage, fiber and provision of water. Functional processes are mediated by regional-to-local level climate and management, thus ecosystem ecology provides a powerful framework for identifying ecological mechanisms that interact with global environmental problems global warming and degradation of surface water.
This example demonstrates several important aspects of ecosystems: Ecosystem boundaries are nebulous and may fluctuate in time Organisms within ecosystems are dependent on ecosystem level biological and physical processes Adjacent ecosystems interact and are interdependent for maintenance of community structure and functional processes that maintain productivity and biodiversityThese characteristics introduce practical problems into natural resource management. Who will manage which ecosystem? Will timber cutting in the forest degrade recreational fishing in the stream? These questions are difficult for land managers to address while the boundary between ecosystems remains unclear. We need better understanding of the interactions and interdependencies of these ecosystems and the processes that maintain them before we can begin to address these questions. Ecosystem ecology is an inherently interdisciplinary field of study. An individual ecosystem is composed of populations of organisms, interacting within communities, contributing to the cycling of nutrients and the flow of energy.
The ecosystem is the principal unit of study in ecosystem ecology. Population and physiological ecology provide many of the underlying biological mechanisms influencing ecosystems and the processes they maintain. Flowing of energy and cycling of matter at the ecosystem level are examined in ecosystem ecology, but, as a whole, this science is defined more by subject matter than by scale. Ecosystem ecology approaches organisms and abiotic pools of energy and nutrients as an integrated system which distinguishes it from associated sciences such as biogeochemistry. Biogeochemistry and hydrology focus on several fundamental ecosystem processes such as biologically mediated chemical cycling of nutrients and physical-biological cycling of water. Ecosystem ecology forms the mechanistic basis for regional or global processes encompassed by landscape-to-regional hydrology, global biogeochemistry, earth system science. Ecosystem ecology is philosophically and rooted in terrestrial ecology; the ecosystem concept has evolved during the last 100 years with important ideas developed by Frederic Clements, a botanist who argued for specific definitions of ecosystems and that physiological processes were responsible for their development and persistence.
Although most of Clements ecosystem definitions have been revised by Henry Gleason and Arthur Tansley, by contemporary ecologists, the idea that physiological processes are fundamental to ecosystem structure and function remains central to ecology. Work by Eugene Odum and Howard T. Odum quantified flows of energy and matter at the ecosystem level, thus documenting the general ideas proposed by Clements and his contemporary Charles Elton. In this model, energy flows through the whole system were dependent on biotic and abiotic interactions of each individual component. Work demonstrated that these interactions and flows applied to nutrient cycles, changed over the course of succession, held powerful controls over ecosystem productivity. Transfers of energy and nutrients are innate to ecological systems regardless of whether they are aquatic or terrestrial. Thus, ecosystem ecology has emerged from important biological studies of plants, terrestrial and marine ecosystems. Ecosystem services are ecologically mediated functional processes essential to sustaining healthy human societies.
Water provision and filtration, production of biomass in forestry and fisheries, removal of greenhouse gases such as carbon dioxide from the atmosphere are examples of ecosystem services essential to public health and economic opportunity. Nutrient cycling is a process fundamental to forest production. However, like most ecosystem processes, nutrient cycling is not an ecosystem characteristic which can be “dialed” to the most desirable level. Maximizing production in degraded systems is an overly simplistic solution to the complex problems of hunger and economic security. For instance, intensive fertilizer use in the midwestern United States has resulted in degraded fisheries in the Gulf of Mexico. Regrettably, a “Green Revolution” of intensive chemical fertilization has been recommended for agriculture in developed and developing countries; these strategies risk alteration of ecosystem processes that may be difficult to restore when applied at broad scales without adequate assessme
Behavioral ecology spelled behavioural ecology, is the study of the evolutionary basis for animal behavior due to ecological pressures. Behavioral ecology emerged from ethology after Niko Tinbergen outlined four questions to address when studying animal behaviors that are the proximate causes, survival value, phylogeny of behavior. If an organism has a trait that provides a selective advantage in its environment natural selection favors it. Adaptive significance refers to the expression of a trait that affects fitness, measured by an individual's reproductive success. Adaptive traits are those. Maladaptive traits are those. For example, if a bird that can call more loudly attracts more mates a loud call is an adaptive trait for that species because a louder bird mates more than less loud birds—thus sending more loud-calling genes into future generations. Individuals are always in competition with others for limited resources, including food and mates. Conflict occurs between predators and prey, between rivals for mates, between siblings and between parents and offspring.
The value of a social behavior depends in part on the social behavior of an animal's neighbors. For example, the more a rival male is to back down from a threat, the more value a male gets out of making the threat; the more however, that a rival will attack if threatened, the less useful it is to threaten other males. When a population exhibits a number of interacting social behaviors such as this, it can evolve a stable pattern of behaviors known as an evolutionarily stable strategy; this term, derived from economic game theory, became prominent after John Maynard Smith recognized the possible application of the concept of a Nash equilibrium to model the evolution of behavioral strategies. In short, evolutionary game theory asserts that only strategies that, when common in the population, cannot be "invaded" by any alternative strategy is an ESS, thus maintained in the population. In other words, at equilibrium every player should play the best strategic response to each other; when the game is two player and symmetric, each player should play the strategy that provides the response best for it.
Therefore, the ESS is considered the evolutionary end point subsequent to the interactions. As the fitness conveyed by a strategy is influenced by what other individuals are doing, behavior can be governed not only by optimality but the frequencies of strategies adopted by others and are therefore frequency dependent. Behavioral evolution is therefore influenced by both the physical environment and interactions between other individuals. An example of how changes in geography can make a strategy susceptible to alternative strategies is the parasitization of the African honey bee, A. m. scutellata. The term economic defendability was first introduced by Jerram Brown in 1964. Economic defendability states that defense of a resource have costs, such as energy expenditure or risk of injury, as well as benefits of priority access to the resource. Territorial behavior arises. Studies of the golden-winged sunbird have validated the concept of economic defendability. Comparing the energetic costs a sunbird expends in a day to the extra nectar gained by defending a territory, researchers showed that birds only became territorial when they were making a net energetic profit.
When resources are at low density, the gains from excluding others may not be sufficient to pay for the cost of territorial defense. In contrast, when resource availability is high, there may be so many intruders that the defender would have no time to make use of the resources made available by defense. Sometimes the economics of resource competition favors shared defense. An example is the feeding territories of the white wagtail; the white wagtails feed on insects washed up by the river onto the bank, which acts as a renewing food supply. If any intruders harvested their territory the prey would become depleted, but sometimes territory owners tolerate a second bird, known as a satellite; the two sharers would move out of phase with one another, resulting in decreased feeding rate but increased defense, illustrating advantages of group living. One of the major models used to predict the distribution of competing individuals amongst resource patches is the ideal free distribution model. Within this model, resource patches can be of variable quality, there is no limit to the number of individuals that can occupy and extract resources from a particular patch.
Competition within a particular patch means that the benefit each individual receives from exploiting a patch decreases logarithmically with increasing number of competitors sharing that resource patch. The model predicts that individuals will flock to higher-quality patches until the costs of crowding bring the benefits of exploiting them in line with the benefits of being the only individual on the lesser-quality resource patch. After this point has been reached, individuals will alternate between exploiting the higher-quality patches and the lower-quality patches in such a way that the average benefit for all individuals in both patches is the same; this model is ideal in that individuals have complete information about the quality of a resource patch and the number of individuals exploiting it, free in that individuals are able to choose which resource patch to exploit. An experiment by Manfred Malinski in 1979 demonstrated that feeding behavior in three-spined sticklebacks follows an ideal free dist
Competition is an interaction between organisms or species in which both the organisms or species are harmed. Limited supply of at least one resource used by both can be a factor. Competition both within and between species is an important topic in ecology community ecology. Competition is one of abiotic factors that affect community structure. Competition among members of the same species is known as intraspecific competition, while competition between individuals of different species is known as interspecific competition. Competition is not always straightforward, can occur in both a direct and indirect fashion. According to the competitive exclusion principle, species less suited to compete for resources should either adapt or die out, although competitive exclusion is found in natural ecosystems. According to evolutionary theory, this competition within and between species for resources is important in natural selection. However, competition may play less of a role than expansion among larger clades.
Competition occurs by various mechanisms, which can be divided into direct and indirect. These apply to intraspecific and interspecific competition. Biologists recognize two types of competition: interference and exploitative competition. During interference competition, organisms interact directly by fighting for scarce resources. For example, large aphids defend feeding sites on cottonwood leaves by ejecting smaller aphids from better sites. In contrast, during exploitative competition, organisms interact indirectly by consuming scarce resources. For example, plants consume nitrogen by absorbing it into their roots, making nitrogen unavailable to nearby plants. Plants that produce many roots reduce soil nitrogen to low levels killing neighboring plants. Interference competition occurs directly between individuals via aggression etc. when the individuals interfere with foraging, reproduction of others, or by directly preventing their physical establishment in a portion of the habitat. An example of this can be seen between the ant Novomessor cockerelli and red harvester ants, where the former interferes with the ability of the latter to forage by plugging the entrances to their colonies with small rocks.
Exploitation competition occurs indirectly through a common limiting resource which acts as an intermediate. For example, use of resources depletes the amount available to others. Apparent competition occurs indirectly between two species which are both preyed upon by the same predator. For example, species A and species B are both prey of predator C; the increase of species A may cause the decrease of species B, because the increase of As may aid in the survival of predator Cs, which will increase the number of predator Cs, which in turn will hunt more of species B. Competition varies from complete symmetric to size symmetric to size-asymmetric; the degree of size asymmetry has major effects on the structure and diversity of ecological communities, e.g. in plant communities size-asymmetric competition for light has stronger effects on diversity compared with competition for soil resources. Competition can occur between individuals of the same species, called intraspecific competition, or between different species, called interspecific competition.
Studies show. This occurs. Since individuals within a population require the same resources, crowding causes resources to become more limited; some individuals do not acquire enough resources and die or do not reproduce. This slows population growth. Species interact with other species that require the same resources. Interspecific competition can alter the sizes of many species' populations at the same time. Experiments demonstrate that when species compete for a limited resource, one species drives the populations of other species extinct; these experiments suggest that competing species cannot coexist because the best competitor will exclude all other competing species. Intraspecific competition occurs when members of the same species compete for the same resources in an ecosystem. Interspecific competition may occur when individuals of two separate species share a limiting resource in the same area. If the resource cannot support both populations lowered fecundity, growth, or survival may result in at least one species.
Interspecific competition has the potential to alter populations and the evolution of interacting species. An example among animals could be the case of lions. In fact, lions sometimes steal. Potential competitors can kill each other, in so-called'intraguild predation'. For example, in southern California coyotes kill and eat gray foxes and bobcats, all three carnivores sharing the same stable prey. An example among protozoa involves Paramecium caudatum. Russian ecologist, Georgy Gause, studied the competition between the
A carnivore, meaning "meat eater", is an organism that derives its energy and nutrient requirements from a diet consisting or of animal tissue, whether through predation or scavenging. Animals that depend on animal flesh for their nutrient requirements are called obligate carnivores while those that consume non-animal food are called facultative carnivores. Omnivores consume both animal and non-animal food, apart from the more general definition, there is no defined ratio of plant to animal material that would distinguish a facultative carnivore from an omnivore. A carnivore at the top of the food chain, not preyed upon by other animals, is termed an apex predator. "Carnivore" may refer to the mammalian order Carnivora, but this is somewhat misleading: many, but not all, Carnivora are meat eaters, fewer are true obligate carnivores. For example, while the Arctic polar bear eats meat most species of bears are omnivorous, the giant panda is herbivorous. There are many carnivorous species that are not members of Carnivora.
Outside the animal kingdom, there are several genera containing carnivorous plants and several phyla containing carnivorous fungi. Carnivores are sometimes characterized by their type of prey. For example, animals that eat insects and similar invertebrates are called insectivores, while those that eat fish are called piscivores; the first tetrapods, or land-dwelling vertebrates, were piscivorous amphibians known as labyrinthodonts. They gave rise to insectivorous vertebrates and to predators of other tetrapods. Carnivores may alternatively be classified according to the percentage of meat in their diet; the diet of a hypercarnivore consists of more than 70% meat, that of a mesocarnivore 30–70%, that of a hypocarnivore less than 30%, with the balance consisting of non-animal foods such as fruits, other plant material, or fungi. Obligate or "true" carnivores are those. While obligate carnivores might be able to ingest small amounts of plant matter, they lack the necessary physiology required to digest it.
In fact, some obligate carnivorous mammals will only ingest vegetation for the sole purpose of its use as an emetic, to self-induce vomiting of the vegetation along with the other food it had ingested that upset its stomach. Obligate carnivores include the axolotl, which consumes worms and larvae in its environment, but if necessary will consume algae, as well as all felids which require a diet of animal flesh and organs. Cats have high protein requirements and their metabolisms appear unable to synthesize essential nutrients such as retinol, arginine and arachidonic acid. Characteristics associated with carnivores include strength and keen senses for hunting, as well as teeth and claws for capturing and tearing prey. However, some carnivores do not hunt and are scavengers, lacking the physical characteristics to bring down prey. Carnivores have comparatively short digestive systems, as they are not required to break down the tough cellulose found in plants. Many hunting animals have evolved eyes facing forward.
This is universal among mammalian predators, while most reptile and amphibian predators have eyes facing sideways. Predation predates the rise of recognized carnivores by hundreds of millions of years; the earliest predators were microbial organisms, which grazed on others. Because the fossil record is poor, these first predators could date back anywhere between 1 and over 2.7 Gya. The rise of eukaryotic cells at around 2.7 Gya, the rise of multicellular organisms at about 2 Gya, the rise of mobile predators have all been attributed to early predatory behavior, many early remains show evidence of boreholes or other markings attributed to small predator species. Among more familiar species, the first vertebrate carnivores were fish, amphibians that moved on to land. Early tetrapods were large amphibious piscivores; some scientists assert that Dimetrodon "was the first terrestrial vertebrate to develop the curved, serrated teeth that enable a predator to eat prey much larger than itself." While amphibians continued to feed on fish and insects, reptiles began exploring two new food types: tetrapods and plants.
Carnivory was a natural transition from insectivory for medium and large tetrapods, requiring minimal adaptation. In the Mesozoic, some theropod dinosaurs such as Tyrannosaurus rex were obligate carnivores. Though the theropods were the larger carnivores, several carnivorous mammal groups were present. Most notable are the gobiconodontids, the triconodontid Jugulator, the deltatheroideans and Cimolestes. Many of these, such as Repenomamus and Cimolestes, were among the largest mammals in their faunal assemblages, capable of attacking dinosaurs. In the early-to-mid-Cenozoic, the dominant predator forms were mammals: hyaenodonts, entelodonts, ptolemaiidans and mesonychians, representing a great diversity of eutherian carnivores
An apex predator known as an alpha predator or top predator, is a predator at the top of a food chain, with no natural predators. Apex predators are defined in terms of trophic dynamics, meaning that they occupy the highest trophic levels. Food chains are far shorter on land limited to being secondary consumers – for example, wolves prey upon large herbivores, which eat plants; the apex predator concept is applied in wildlife management and ecotourism. Apex predators have a long evolutionary history, dating at least to the Cambrian period when animals such as Anomalocaris dominated the seas. Humans have for many centuries interacted with apex predators including the wolf, birds of prey and cormorants to hunt game animals and fish respectively. More ecotourism such as with the tiger shark has become popular, rewilding with predators such as the lynx has been proposed. Apex predators affect prey species' population dynamics and populations of other predators, both in aquatic and in terrestrial ecosystems.
Non-native predatory fish, for instance, have sometimes devastated dominant predators. A lake manipulation study found that when the non-native smallmouth bass was removed, lake trout, the suppressed native apex predator, diversified its prey selection and increased its trophic level; as a terrestrial example, the badger, an apex predator, predates on and competes with the hedgehog, a mesopredator, for food such as insects, small mammals, reptiles and ground-nesting bird's eggs. Removal of badgers caused hedgehog densities to more than double. Predators that exert a top-down control on organisms in their community are considered keystone species. Humans are not considered apex predators because their diets are diverse, although human trophic levels increase with consumption of meat. Apex predators can have profound effects on ecosystems, as the consequences of both controlling prey density and restricting smaller predators, may be capable of self-regulation, they are central to the functioning of ecosystems, the regulation of disease, the maintenance of biodiversity.
When introduced to subarctic islands, for example, Arctic foxes' predation of seabirds has been shown to turn grassland into tundra. Such wide-ranging effects on lower levels of an ecosystem are termed trophic cascades; the removal of top-level predators through human agency, can cause or disrupt trophic cascades. For example, reduction in the population of sperm whales, apex predators with a fractional trophic level of 4.7, by hunting has caused an increase in the population of large squid, trophic level over 4. This effect, called mesopredator release, occurs in marine ecosystems; because apex predators have powerful effects on other predators, on herbivores, on plants, they can be important in nature conservation. Humans have hunted many apex predators close to extinction, but in some parts of the world these predators are now returning, they are threatened by climate change. For example, the polar bear requires extensive areas of sea ice to hunt its prey seals, but climate change is shrinking the sea ice of the Arctic, forcing polar bears to fast on land for long periods.
Dramatic changes in the Greater Yellowstone Ecosystem were recorded after the gray wolf, both an apex predator and a keystone species, was reintroduced to Yellowstone National Park in 1995 as a conservation measure. Elk, the wolves' primary prey, became less abundant and changed their behavior, freeing riparian zones from constant grazing and allowing willows and cottonwoods to flourish, creating habitats for beaver and scores of other species. In addition to their effect on prey species, the wolves' presence affected one of the park's vulnerable species, the grizzly bear: emerging from hibernation, having fasted for months, the bears chose to scavenge wolf kills during the autumn as they prepared to hibernate once again; the grizzly bear gives birth during hibernation, so the increased food supply is expected to produce an increase in the numbers of cubs observed. Dozens of other species, including eagles, magpies and black bears have been documented as scavenging from wolf kills within the park.
Ecologists have debated. Sylvain Bonhommeau and colleagues argued in 2013 that across the global food web, a fractional human trophic level can be calculated as the mean trophic level of every species in the human diet, weighted by the proportion which that species forms in the diet; this analysis gives an average HTL of 2.21, varying between 2.04 and 2.57. These values are comparable to those of non-apex predators like pig. Peter D. Roopnarine criticised Bonhommeau's approach, arguing that humans are apex predators, that the HTL was based on terrestrial farming where indeed humans have a low trophic level eating producers or primary consumers, which as expected places humans at a level above 2. Roopnarine instead calculated the position of humans in two marine ecosystems, a Caribbean coral reef and the Benguela system near South Africa. In these systems, humans eat predatory fish and have a fractional trophic level of 4.65 and 4.5 which in Roopnarine's view makes those h
An ecoregion is an ecologically and geographically defined area, smaller than a bioregion, which in turn is smaller than an ecozone. All three of these are either greater than an ecosystem. Ecoregions cover large areas of land or water, contain characteristic, geographically distinct assemblages of natural communities and species; the biodiversity of flora and ecosystems that characterise an ecoregion tends to be distinct from that of other ecoregions. In theory, biodiversity or conservation ecoregions are large areas of land or water where the probability of encountering different species and communities at any given point remains constant, within an acceptable range of variation. Three caveats are appropriate for all bio-geographic mapping approaches. Firstly, no single bio-geographic framework is optimal for all taxa. Ecoregions reflect the best compromise for as many taxa as possible. Secondly, ecoregion boundaries form abrupt edges. Thirdly, most ecoregions contain habitats. Biogeographic provinces may originate due to various barriers.
Some physical, some climatic and some ocean chemical related. The history of the term is somewhat vague, it had been used in many contexts: forest classifications, biome classifications, biogeographic classifications, etc; the concept of ecoregion of Bailey gives more importance to ecological criteria, while the WWF concept gives more importance to biogeography, that is, distribution of distinct biotas. An ecoregion is a "recurring pattern of ecosystems associated with characteristic combinations of soil and landform that characterise that region". Omernik elaborates on this by defining ecoregions as: "areas within which there is spatial coincidence in characteristics of geographical phenomena associated with differences in the quality and integrity of ecosystems". "Characteristics of geographical phenomena" may include geology, vegetation, hydrology and aquatic fauna, soils, may or may not include the impacts of human activity. There is significant, but not absolute, spatial correlation among these characteristics, making the delineation of ecoregions an imperfect science.
Another complication is that environmental conditions across an ecoregion boundary may change gradually, e.g. the prairie-forest transition in the midwestern United States, making it difficult to identify an exact dividing boundary. Such transition zones are called ecotones. Ecoregions can be categorized using an algorithmic approach or a holistic, "weight-of-evidence" approach where the importance of various factors may vary. An example of the algorithmic approach is Robert Bailey's work for the U. S. Forest Service, which uses a hierarchical classification that first divides land areas into large regions based on climatic factors, subdivides these regions, based first on dominant potential vegetation, by geomorphology and soil characteristics; the weight-of-evidence approach is exemplified by James Omernik's work for the United States Environmental Protection Agency, subsequently adopted for North America by the Commission for Environmental Cooperation. The intended purpose of ecoregion delineation may affect the method used.
For example, the WWF ecoregions were developed to aid in biodiversity conservation planning, place a greater emphasis than the Omernik or Bailey systems on floral and faunal differences between regions. The WWF classification defines an ecoregion as: A large area of land or water that contains a geographically distinct assemblage of natural communities that: Share a large majority of their species and ecological dynamics. According to WWF, the boundaries of an ecoregion approximate the original extent of the natural communities prior to any major recent disruptions or changes. WWF has identified 867 terrestrial ecoregions, 450 freshwater ecoregions across the Earth; the use of the term ecoregion is an outgrowth of a surge of interest in ecosystems and their functioning. In particular, there is awareness of issues relating to spatial scale in the study and management of landscapes, it is recognized that interlinked ecosystems combine to form a whole, "greater than the sum of its parts". There are many attempts to respond to ecosystems in an integrated way to achieve "multi-functional" landscapes, various interest groups from agricultural researchers to conservationists are using the "ecoregion" as a unit of analysis.
The "Global 200" is the list of ecoregions identified by WWF as priorities for conservation. Ecologically based movements like bioregionalism maintain that ecoregions, rather than arbitrarily defined political boundaries, provide a better foundation for the formation and governance of human communities, have proposed ecoregions and watersheds as the basis for bioregional democracy initiatives. Terrestrial ecoregions are land ecoregions, as distinct from marine ecoregions. In this context, terrestrial is used to mean "of land", rather than the more general sense "of Earth". WWF ecologists divide the land surface of the Earth into 8 major ecozones containing 867 smaller terrestrial ecoregions; the WWF effort is a synthesis of
A lake is an area filled with water, localized in a basin, surrounded by land, apart from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, therefore are distinct from lagoons, are larger and deeper than ponds, though there are no official or scientific definitions. Lakes can be contrasted with rivers or streams, which are flowing. Most lakes streams. Natural lakes are found in mountainous areas, rift zones, areas with ongoing glaciation. Other lakes are found along the courses of mature rivers. In some parts of the world there are many lakes because of chaotic drainage patterns left over from the last Ice Age. All lakes are temporary over geologic time scales, as they will fill in with sediments or spill out of the basin containing them. Many lakes are artificial and are constructed for industrial or agricultural use, for hydro-electric power generation or domestic water supply, or for aesthetic, recreational purposes, or other activities.
The word lake comes from Middle English lake, from Old English lacu, from Proto-Germanic *lakō, from the Proto-Indo-European root *leǵ-. Cognates include Dutch laak, Middle Low German lāke as in: de:Wolfslake, de:Butterlake, German Lache, Icelandic lækur. Related are the English words leak and leach. There is considerable uncertainty about defining the difference between lakes and ponds, no current internationally accepted definition of either term across scientific disciplines or political boundaries exists. For example, limnologists have defined lakes as water bodies which are a larger version of a pond, which can have wave action on the shoreline or where wind-induced turbulence plays a major role in mixing the water column. None of these definitions excludes ponds and all are difficult to measure. For this reason, simple size-based definitions are used to separate ponds and lakes. Definitions for lake range in minimum sizes for a body of water from 2 hectares to 8 hectares. Charles Elton, one of the founders of ecology, regarded lakes as waterbodies of 40 hectares or more.
The term lake is used to describe a feature such as Lake Eyre, a dry basin most of the time but may become filled under seasonal conditions of heavy rainfall. In common usage, many lakes bear names ending with the word pond, a lesser number of names ending with lake are in quasi-technical fact, ponds. One textbook illustrates this point with the following: "In Newfoundland, for example every lake is called a pond, whereas in Wisconsin every pond is called a lake."One hydrology book proposes to define the term "lake" as a body of water with the following five characteristics: it or fills one or several basins connected by straits has the same water level in all parts it does not have regular intrusion of seawater a considerable portion of the sediment suspended in the water is captured by the basins the area measured at the mean water level exceeds an arbitrarily chosen threshold With the exception of the seawater intrusion criterion, the others have been accepted or elaborated upon by other hydrology publications.
The majority of lakes on Earth are freshwater, most lie in the Northern Hemisphere at higher latitudes. Canada, with a deranged drainage system has an estimated 31,752 lakes larger than 3 square kilometres and an unknown total number of lakes, but is estimated to be at least 2 million. Finland has larger, of which 56,000 are large. Most lakes have at least one natural outflow in the form of a river or stream, which maintain a lake's average level by allowing the drainage of excess water; some lakes do not have a natural outflow and lose water by evaporation or underground seepage or both. They are termed endorheic lakes. Many lakes are artificial and are constructed for hydro-electric power generation, aesthetic purposes, recreational purposes, industrial use, agricultural use or domestic water supply. Evidence of extraterrestrial lakes exists. Globally, lakes are outnumbered by ponds: of an estimated 304 million standing water bodies worldwide, 91% are 1 hectare or less in area. Small lakes are much more numerous than large lakes: in terms of area, one-third of the world's standing water is represented by lakes and ponds of 10 hectares or less.
However, large lakes account for much of the area of standing water with 122 large lakes of 1,000 square kilometres or more representing about 29% of the total global area of standing inland water. Hutchinson in 1957 published a monograph, regarded as a landmark discussion and classification of all major lake types, their origin, morphometric characteristics, distribution; as summarized and discussed by these researchers, Hutchinson presented in it a comprehensive analysis of the origin of lakes and proposed what is a accepted classification of lakes according to their origin. This