The trophic level of an organism is the position it occupies in a food chain. A food chain is a succession of organisms that eat other organisms and may, in turn, be eaten themselves; the trophic level of an organism is the number of steps. A food chain starts at trophic level 1 with primary producers such as plants, can move to herbivores at level 2, carnivores at level 3 or higher, finish with apex predators at level 4 or 5; the path along the chain can form either a one-way flow or a food "web". Ecological communities with higher biodiversity form more complex trophic paths; the word trophic derives from the Greek τροφή referring to nourishment. The concept of trophic level was developed by Raymond Lindeman, based on the terminology of August Thienemann: "producers", "consumers" and "reducers"; the three basic ways in which organisms get food are as producers and decomposers. Producers are plants or algae. Plants and algae do not eat other organisms, but pull nutrients from the soil or the ocean and manufacture their own food using photosynthesis.
For this reason, they are called primary producers. In this way, it is energy from the sun that powers the base of the food chain. An exception occurs in deep-sea hydrothermal ecosystems. Here primary producers manufacture food through a process called chemosynthesis. Consumers are species that can not need to consume other organisms. Animals that eat primary producers are called herbivores. Animals that eat other animals are called carnivores, animals that eat both plant and other animals are called omnivores. Decomposers break down dead plant and animal material and wastes and release it again as energy and nutrients into the ecosystem for recycling. Decomposers, such as bacteria and fungi, feed on waste and dead matter, converting it into inorganic chemicals that can be recycled as mineral nutrients for plants to use again. Trophic levels can be represented starting at level 1 with plants. Further trophic levels are numbered subsequently according to how far the organism is along the food chain.
Level 1: Plants and algae make their own food and are called producers. Level 2: Herbivores eat plants and are called primary consumers. Level 3: Carnivores that eat herbivores are called secondary consumers. Level 4: Carnivores that eat other carnivores are called tertiary consumers. Apex predators by definition are at the top of their food chains. In real world ecosystems, there is more than one food chain for most organisms, since most organisms eat more than one kind of food or are eaten by more than one type of predator. A diagram that sets out the intricate network of intersecting and overlapping food chains for an ecosystem is called its food web. Decomposers are left off food webs, but if included, they mark the end of a food chain, thus food chains start with primary producers and end with decay and decomposers. Since decomposers recycle nutrients, leaving them so they can be reused by primary producers, they are sometimes regarded as occupying their own trophic level; the trophic level of a species may vary.
All plants and phytoplankton are purely phototrophic and are at level 1.0. Many worms are at around 2.1. A 2013 study estimates the average trophic level of human beings at 2.21, similar to pigs or anchovies. This is only an average, plainly both modern and ancient human eating habits are complex and vary greatly. For example, a traditional Eskimo living on a diet consisting of seals would have a trophic level of nearly 5. In general, each trophic level relates to the one below it by absorbing some of the energy it consumes, in this way can be regarded as resting on, or supported by, the next lower trophic level. Food chains can be diagrammed to illustrate the amount of energy that moves from one feeding level to the next in a food chain; this is called an energy pyramid. The energy transferred between levels can be thought of as approximating to a transfer in biomass, so energy pyramids can be viewed as biomass pyramids, picturing the amount of biomass that results at higher levels from biomass consumed at lower levels.
However, when primary producers grow and are consumed the biomass at any one moment may be low. The efficiency with which energy or biomass is transferred from one trophic level to the next is called the ecological efficiency. Consumers at each level convert on average only about 10% of the chemical energy in their food to their own organic tissue. For this reason, food chains extend for more than 5 or 6 levels. At the lowest trophic level, plants convert about 1% of the sunlight they receive into chemical energy, it follows from this that the total energy present in the incident sunlight, embodied in a tertiary consumer is about 0.001% Both the number of trophic levels and the complexity of relationships between them evolve as life diversifies through time, the exception being intermittent mass extinction events. Food webs define ecosystems, the trophic levels define the position of organisms within the webs, but these trophic levels are not always simple integers, because organisms feed at more than one trophic level.
For example, some carnivores eat plants, some plants are carnivores. A large carnivore may eat both smaller car
Kelps are large brown algae seaweeds that make up the order Laminariales. There are about 30 different genera. Kelp grows in "underwater forests" in shallow oceans, is thought to have appeared in the Miocene, 23 to 5 million years ago; the organisms require nutrient-rich water with temperatures between 6 and 14 °C. They are known for their high growth rate—the genera Macrocystis and Nereocystis can grow as fast as half a metre a day reaching 30 to 80 metres. Through the 19th century, the word "kelp" was associated with seaweeds that could be burned to obtain soda ash; the seaweeds used included species from both the orders Fucales. The word "kelp" was used directly to refer to these processed ashes. In most kelp, the thallus consists of leaf-like structures known as blades. Blades originate from the stipes; the holdfast, a root-like structure, anchors the kelp to the substrate of the ocean. Gas-filled bladders form at the base of blades of American species, such as Nereocystis lueteana, to hold the kelp blades close to the surface.
Growth occurs at the base of the meristem. Growth may be limited by grazing. Sea urchins, for example, can reduce entire areas to urchin barrens; the kelp life cycle involves a diploid haploid gametophyte stage. The haploid phase begins when the mature organism releases many spores, which germinate to become male or female gametophytes. Sexual reproduction results in the beginning of the diploid sporophyte stage, which will develop into a mature individual; the parenchymatous thalli are covered with a mucilage layer, rather than cuticle. Kelp may develop dense forests with high production and ecological function. Along the Norwegian coast these forests cover 5800 km2, they support large numbers of animals. Numerous sessile animals are found on kelp stipes and mobile invertebrate fauna are found in high densities on epiphytic algae on the kelp stipes and on kelp holdfasts. More than 100,000 mobile invertebrates per square meter are found on kelp stipes and holdfasts in well-developed kelp forests.
While larger invertebrates and in particular sea urchins Strongylocentrotus droebachiensis are important secondary consumers controlling large barren ground areas on the Norwegian coast, they are scarce inside dense kelp forests. Giant kelp can be harvested easily because of its surface canopy and growth habit of staying in deeper water. Kelp ash is rich in alkali. In great amount, kelp ash can be used in glass production; until the Leblanc process was commercialized in the early 19th century, burning of kelp in Scotland was one of the principal industrial sources of soda ash. Alginate, a kelp-derived carbohydrate, is used to thicken products such as ice cream, salad dressing, toothpaste, as well as an ingredient in exotic dog food and in manufactured goods. Alginate powder is used in general dentistry and orthodontics for making impressions of the upper and lower arches. Kombu, several Pacific species of kelp, is a important ingredient in Chinese and Korean cuisines. Kombu is used to flavor broths and stews, as a savory garnish for rice and other dishes, as a vegetable, a primary ingredient in popular snacks.
Transparent sheets of kelp are used as an edible decorative wrapping for rice and other foods. Kombu can be used to soften beans during cooking, to help convert indigestible sugars and thus reduce flatulence; because of its high concentration of iodine, brown kelp has been used to treat goiter, an enlargement of the thyroid gland caused by a lack of iodine, since medieval times. In 2010, researchers found that alginate, the soluble fibre substance in sea kelp, was better at preventing fat absorption than most over-the-counter slimming treatments in laboratory trials; as a food additive, it may be used to reduce fat absorption and thus obesity. Kelp in its natural form has not yet been demonstrated to have such effects. Commercial production of kelp harvested from its natural habitat has taken place in Japan for over a century. Many countries today consume laminaria products. Laminaria japonica, the important commercial seaweed, was first introduced into China in the late 1920s from Hokkaido, Japan.
Yet mariculture of this alga on a large commercial scale was realized in China only in the 1950s. Between the 1950s and the 1980s, kelp production in China increased from about 60 to over 250,000 dry weight metric tons annually. Kelp has a high rate of growth and its decay is quite efficient in yielding methane, as well as sugars that can be converted to ethanol, it has been proposed. Unlike some biofuels such as corn ethanol, kelp energy avoids "food vs fuel" issues and does not require freshwater irrigation; some of the earliest evidence for human use of marine resources, coming from Middle Stone Age sites in South Africa, includes the harvesting of foods such as abalones and mussels associated with kelp forest habitats. In 2007, Erlandson et al. suggested that kelp forests around the Pacific Rim may have facilitated the dispersal of anatomically modern humans following a coastal route from Northeast Asia to the Americas. This "kelp highway hypothesis" suggested that productive kelp forests supported rich and dive
A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals. Coral belongs to the class Anthozoa in the animal phylum Cnidaria, which includes sea anemones and jellyfish. Unlike sea anemones, corals secrete hard carbonate exoskeletons that protect the coral. Most reefs grow best in warm, clear and agitated water. Called "rainforests of the sea", shallow coral reefs form some of Earth's most diverse ecosystems, they occupy less than 0.1% of the world's ocean area, about half the area of France, yet they provide a home for at least 25% of all marine species, including fish, worms, echinoderms, sponges and other cnidarians. Coral reefs flourish in ocean waters, they are most found at shallow depths in tropical waters, but deep water and cold water coral reefs exist on smaller scales in other areas. Coral reefs deliver ecosystem services for tourism and shoreline protection.
The annual global economic value of coral reefs is estimated between US$30–375 billion and 9.9 trillion USD. Coral reefs are fragile because they are sensitive to water conditions, they are under threat from excess nutrients, rising temperatures, oceanic acidification, sunscreen use, harmful land-use practices, including runoff and seeps. Most coral reefs were formed after the last glacial period when melting ice caused sea level to rise and flood continental shelves. Most coral reefs are less than 10,000 years old; as communities established themselves, the reefs grew pacing rising sea levels. Reefs that rose too could become drowned, without sufficient light. Coral reefs are found in the deep sea away from continental shelves, around oceanic islands and atolls; the majority of these islands are volcanic in origin. Others have tectonic origins. In The Structure and Distribution of Coral Reefs, Charles Darwin set out his theory of the formation of atoll reefs, an idea he conceived during the voyage of the Beagle.
He theorized that subsidence of the Earth's crust under the oceans formed the atolls. Darwin set out a sequence of three stages in atoll formation. A fringing reef forms around an extinct volcanic island as the ocean floor subsides; as the subsidence continues, the fringing reef becomes a barrier reef and an atoll reef. Darwin predicted that underneath each lagoon would be a bedrock base, the remains of the original volcano. Subsequent research supported this hypothesis. Darwin's theory followed from his understanding that coral polyps thrive in the tropics where the water is agitated, but can only live within a limited depth range, starting just below low tide. Where the level of the underlying earth allows, the corals grow around the coast to form fringing reefs, can grow to become a barrier reef. Where the bottom is rising, fringing reefs can grow around the coast, but coral raised above sea level dies. If the land subsides the fringing reefs keep pace by growing upwards on a base of older, dead coral, forming a barrier reef enclosing a lagoon between the reef and the land.
A barrier reef can encircle an island, once the island sinks below sea level a circular atoll of growing coral continues to keep up with the sea level, forming a central lagoon. Barrier reefs and atolls do not form complete circles, but are broken in places by storms. Like sea level rise, a subsiding bottom can overwhelm coral growth, killing the coral and the reef, due to what is called coral drowning. Corals that rely on zooxanthellae can die when the water becomes too deep for their symbionts to adequately photosynthesize, due to decreased light exposure; the two main variables determining the geomorphology, or shape, of coral reefs are the nature of the substrate on which they rest, the history of the change in sea level relative to that substrate. The 20,000-year-old Great Barrier Reef offers an example of how coral reefs formed on continental shelves. Sea level was 120 m lower than in the 21st century; as sea level rose, the water and the corals encroached on what had been hills of the Australian coastal plain.
By 13,000 years ago, sea level had risen to 60 m lower than at present, many hills of the coastal plains had become continental islands. As sea level rise continued, water topped most of the continental islands; the corals could overgrow the hills, forming cays and reefs. Sea level on the Great Barrier Reef has not changed in the last 6,000 years; the age of living reef structure is estimated to be between 8,000 years. Although the Great Barrier Reef formed along a continental shelf, not around a volcanic island, Darwin's principles apply. Development stopped at the barrier reef stage, it formed 300 -- 1,000 m from shore, stretching for 2,000 km. Healthy tropical coral reefs grow horizontally from 1 to 3 cm per year, grow vertically anywhere from 1 to 25 cm per year; as the name implies, coral reefs are made up of coral skeletons from intact coral colonies. As other chemical elements present in corals become incorporated into the calcium carbonate deposits, aragonite is formed. However
Restoration ecology is the scientific study supporting the practice of ecological restoration, the practice of renewing and restoring degraded, damaged, or destroyed ecosystems and habitats in the environment by active human intervention and action. Natural ecosystems provide ecosystem services in the form of resources such as food and timber; these ecosystem processes have been estimated to be worth trillions of dollars annually. There is consensus in the scientific community that the current environmental degradation and destruction of many of the Earth's biota is taking place on a "catastrophically short timescale". Scientists estimate that the current species extinction rate, or the rate of the Holocene extinction, is 1,000 to 10,000 times higher than the normal, background rate. Habitat loss is the leading cause of both species extinctions and ecosystem service decline. Two methods have been identified to slow the rate of species extinction and ecosystem service decline, they are the conservation of viable habitat, the restoration of degraded habitat.
The commercial applications of ecological restoration have increased exponentially in recent years. Restoration ecology is the academic study of the process, whereas ecological restoration is the actual project or process by restoration practitioners; the Society for Ecological Restoration defines "ecological restoration" as an "intentional activity that initiates or accelerates the recovery of an ecosystem with respect to its health and sustainability". Ecological restoration includes a wide scope of projects including erosion control, removal of non-native species and weeds, revegetation of disturbed areas, daylighting streams, reintroduction of native species, habitat and range improvement for targeted species. E. O. Wilson, a biologist, states, "Here is the means to end the great extinction spasm; the next century will, I believe, be the era of restoration in ecology." Restoration ecology emerged as a separate field in ecology in the late twentieth century. The term was coined by John Aber and William Jordan III when they were at the University of Wisconsin–Madison.
However, indigenous peoples, land managers and laypeople have been practicing ecological restoration or ecological management for thousands of years. Considered the birthplace of modern ecological restoration, the first tallgrass prairie restoration was the 1936 Curtis Prairie at the University of Wisconsin–Madison Arboretum. Civilian Conservation Corps workers replanted nearby prairie species onto a former horse pasture, overseen by university faculty including renowned ecologist Aldo Leopold, botanist Theodore Sperry, mycologist Henry C. Greene, plant ecologist John T. Curtis. Curtis and his graduate students surveyed the whole of Wisconsin, documenting native species communities and creating the first species lists for tallgrass restorations. Existing prairie remnants, such as locations within pioneer cemeteries and railroad rights-of-way, were located and inventoried by Curtis and his team; the UW Arboretum was the center of tallgrass prairie research through the first half of the 20th century, with the development of the nearby Greene Prairie, Aldo Leopold Shack and Farm, pioneering techniques like prescribed burning.
The latter-half of the 20th century saw the growth of ecological restoration beyond Wisconsin borders. The 285-hectare Green Oaks Biological Field Station at Knox College began in 1955 under the guidance of zoologist Paul Shepard, it was followed by the 40-hectare Schulenberg Prairie at the Morton Arboretum, started in 1962 by Ray Schulenberg and Bob Betz. Betz worked with The Nature Conservancy to establish the 260-hectare Fermi National Laboratory tallgrass prairie in 1974; these major tallgrass restoration projects marked the growth of ecological restoration from isolated studies to widespread practice. Australia has been the site of significant ecological restoration projects. In 1935 Ambrose Crawford commenced restoring a degraded four acres patch of the Big Scrub at Lumley Park reserve, Alstonville, in northern New South Wales. Clearing of weeds and planting of suitable indigenous flora species were his main restoration techniques; the restored rainforest reserve still exists today and is home to threatened plant and animal species.
In 1936 Albert Morris and his restoration colleagues initiated the Broken Hill regeneration area project, which involved the natural regeneration of indigenous flora on a degraded site of hundreds of hectares in arid western New South Wales. Completed in 1958, the successful project still maintains ecological function today as the Broken Hill Regeneration Area. Restoration ecology draws on a wide range of ecological concepts. Disturbance is a change in environmental conditions. Disturbance can occur at a variety of spatial and temporal scales, is a natural component of many communities. For example, many forest and grassland restorations implement fire as a natural disturbance regime; however the severity and scope of anthropogenic impact has grown in the last few centuries. Differentiating between human-caused and occurring disturbances is important if we are to understand how to restore natural processes and minimize anthropogenic impacts on the ecosystems. Ecological succession is the process by which a community changes over time following a disturbance.
In many instances, an ecosystem will change from a simple level of organization with a few dominant pioneer sp
Parrotfishes are a group of marine species found in shallow tropical and subtropical oceans around the world. With about 95 species, this group displays its largest species richness in the Indo-Pacific, they are found in coral reefs, rocky coasts, seagrass beds, can play a significant role in bioerosion. Parrotfish are named for their dentition, distinct from other fish, including other labrids, their numerous teeth are arranged in a packed mosaic on the external surface of their jaw bones, forming a parrot-like beak with which they rasp algae from coral and other rocky substrates. Maximum sizes vary with the majority of species reaching 30 -- 50 cm in length. However, a few species reach lengths in excess of 1 m, the green humphead parrotfish can reach up to 1.3 m. The smallest species is the bluelip parrotfish; some parrotfish species, including the queen parrotfish, secrete a mucus cocoon at night. Prior to going to sleep, some species extrude mucus from their mouths, forming a protective cocoon that envelops the fish hiding its scent from potential predators.
This mucus envelope may act as an early warning system, allowing the parrotfish to flee when it detects predators such as moray eels disturbing the membrane. The skin itself is covered in another mucous substance which may have antioxidant properties helpful in repairing bodily damage, or repelling parasites, in addition to providing protection from UV light. Most parrotfish species are herbivores, feeding on epilithic algae. A wide range of other small organisms are sometimes eaten, including invertebrates and detritus. A few larger species such as the green humphead parrotfish feed extensively on living coral. None of these are exclusive corallivores, but polyps can make up as much as half their diet or more in the green humphead parrotfish. Overall it has been estimated that less than one percent of parrotfish bites involve live corals and all except the green humphead parrotfish prefer algae-covered surfaces over live corals; when they do eat coral polyps, localized coral death can occur.
Their feeding activity is important for the production and distribution of coral sands in the reef biome, can prevent algal overgrowth of the reef structure. The teeth grow continuously. Whether they feed on coral, rock or seagrasses, the substrate is ground up between the pharyngeal teeth. After they digest the edible portions from the rock, they excrete it as sand, helping create small islands and the sandy beaches; the humphead parrotfish can produce 90 kg of sand each year. Or, on average 250 g per parrotfish per day. While feeding, parrotfish must be cognizant of predation by one of their main predators, the lemon shark. On Caribbean coral reefs, parrotfish are important consumers of sponges. An indirect effect of parrotfish grazing on sponges is the protection of reef-building corals that would otherwise be overgrown by fast-growing sponge species. Analysis of parrotfish feeding biology describes three functional groups: excavators and browsers. Excavators have larger, stronger jaws that can gouge the substrate, leaving visible scars on the surface.
Scrapers have less powerful jaws that can but infrequently do leave visible scraping scars on the substrate. Some of these may feed on sand instead of hard surfaces. Browsers feed on seagrasses and their epiphytes. Mature excavating species include Bolbometopon muricatum, Cetoscarus and Sparisoma viride; these excavating species all feed as scrapers in early juvenile stages, but Hipposcarus and Scarus, which feed as scrapers in early juvenile stages, retain the scraping feeding mode as adults. Browsing species are found in the genera Calotomus, Leptoscarus and Sparisoma. Feeding modes reflect habitat preferences, with browsers chiefly living in grassy seabed, excavators and scrapers on coral reefs; the development of parrotfishes is complex and accompanied by a series of changes in colour. Most species are sequential hermaphrodites, starting as females and changing to males. In many species, for example the stoplight parrotfish, a number of individuals develop directly to males; these directly developing males most resemble the initial phase, display a different mating strategy than the terminal phase males of the same species.
A few species such as the Mediterranean parrotfish are secondary gonochorists. This means that some females do not change sex, the ones that do change from female to male do it while still immature and there are no males with female-like colors; the marbled parrotfish is the only species of parrotfish known not to change sex. In most species, the initial phase is dull red, brown, or grey, while the terminal phase is vividly green or blue with bright pink, orange or yellow patches. In a smaller number of species the phases are similar, in the Mediterranean parrotfish the adult female is brightly colored, while the adult male is gray. In most species, juveniles have a different color pattern from adults. Juveniles of some tropical species ca
Plankton are the diverse collection of organisms that live in large bodies of water and are unable to swim against a current. The individual organisms constituting plankton are called plankters, they provide a crucial source of food to many large aquatic organisms, such as fish and whales. These organisms include bacteria, algae and drifting or floating animals that inhabit—for example—the pelagic zone of oceans, seas, or bodies of fresh water. Plankton are defined by their ecological niche rather than any phylogenetic or taxonomic classification. Though many planktonic species are microscopic in size, plankton includes organisms over a wide range of sizes, including large organisms such as jellyfish. Technically the term does not include organisms on the surface of the water, which are called pleuston—or those that swim in the water, which are called nekton; the name plankton is derived from the Greek adjective πλαγκτός, meaning errant, by extension, wanderer or drifter, was coined by Victor Hensen in 1887.
While some forms are capable of independent movement and can swim hundreds of meters vertically in a single day, their horizontal position is determined by the surrounding water movement, plankton flow with ocean currents. This is in contrast to nekton organisms, such as fish and marine mammals, which can swim against the ambient flow and control their position in the environment. Within the plankton, holoplankton spend their entire life cycle as plankton. By contrast, meroplankton are only planktic for part of their lives, graduate to either a nektic or benthic existence. Examples of meroplankton include the larvae of sea urchins, crustaceans, marine worms, most fish; the amount and distribution of plankton depends on available nutrients, the state of water and a large amount of other plankton. The study of plankton is termed planktology and a planktonic individual is referred to as a plankter; the adjective planktonic is used in both the scientific and popular literature, is a accepted term.
However, from the standpoint of prescriptive grammar, the less-commonly used planktic is more the correct adjective. When deriving English words from their Greek or Latin roots, the gender-specific ending is dropped, using only the root of the word in the derivation. Plankton are divided into broad functional groups: Phytoplankton, autotrophic prokaryotic or eukaryotic algae that live near the water surface where there is sufficient light to support photosynthesis. Among the more important groups are the diatoms, cyanobacteria and coccolithophores. Zooplankton, small protozoans or metazoans that feed on other plankton; some of the eggs and larvae of larger nektonic animals, such as fish and annelids, are included here. Bacterioplankton and archaea, which play an important role in remineralising organic material down the water column. Mycoplankton and fungus-like organisms, like bacterioplankton, are significant in remineralisation and nutrient cycling; this scheme divides the plankton community into broad producer and recycler groups.
However, determining the trophic level of many plankton is not always straightforward. For example, although most dinoflagellates are either photosynthetic producers or heterotrophic consumers, many species perform both roles. In this mixed trophic strategy — known as mixotrophy — organisms act as both producers and consumers, either at the same time or switching between modes of nutrition in response to ambient conditions. For instance, relying on photosynthesis for growth when nutrients and light are abundant, but switching to predation when growing conditions are poor. Recognition of the importance of mixotrophy as an ecological strategy is increasing, as well as the wider role this may play in marine biogeochemistry. Plankton are often described in terms of size; the following divisions are used: However, some of these terms may be used with different boundaries on the larger end. The existence and importance of nano- and smaller plankton was only discovered during the 1980s, but they are thought to make up the largest proportion of all plankton in number and diversity.
The microplankton and smaller groups are microorganisms and operate at low Reynolds numbers, where the viscosity of water is much more important than its mass or inertia. Plankton inhabit oceans, lakes, ponds. Local abundance varies horizontally and seasonally; the primary cause of this variability is the availability of light. All plankton ecosystems are driven by the input of solar energy, confining primary production to surface waters, to geographical regions and seasons having abundant light. A secondary variable is nutrient availability. Although large areas of the tropical and sub-tropical oceans have abundant light, they experience low primary production because they offer limited nutrients such as nitrate and silicate; this results from large-scale ocean water column stratification. In such regions, primary production occurs at greater depth, although at a reduced level. Despite significant macronutrient concentrations, some ocean regions are unproductive; the micronutrient iron is deficient in these reg
Niche construction is the process by which an organism alters its own local environment. These alterations can be a physical change to the organism’s environment or encompass when an organism moves from one habitat to another to experience a different environment. Examples of niche construction include the building of nests and burrows by animals, the creation of shade, influencing of wind speed, alternation of nutrient cycling by plants. Although these alterations are beneficial to the constructor they are not always. For niche construction to affect evolution it must satisfy three criteria: 1) the organism must modify environmental conditions, 2) these modifications must influence one or more selection pressures on a recipient organism, 3) there must be an evolutionary response in at least one recipient population caused by the environmental modification; the first two criteria alone provide evidence of niche construction. Some biologists have argued that niche construction is an evolutionary process that works in conjunction with natural selection.
Evolution entails networks of feedbacks in which selected organisms drive environmental changes, organism-modified environments subsequently select for changes in organisms. The complementary match between an organism and its environment results from the two processes of natural selection and niche construction; the effect of niche construction is pronounced in situations where environmental alterations persist for several generations, introducing the evolutionary role of ecological inheritance. This theory emphasizes that organisms inherit two legacies from their ancestors: genes and a modified environment. A niche constructing organism may not be considered an ecosystem engineer. Ecosystem engineering is a related but non-evolutionary concept referring to structural changes brought about in the environment by organisms; the following are some examples of niche construction: Earthworms physically and chemically modify the soil in which they live. Only by changing the soil can these aquatic organisms live on land.
Earthworm soil processing benefits plant species and other biota present in the soil, as pointed out by Darwin in his book The Formation of Vegetable Mould through the Action of Worms. Lemon ants employ a specialized method of suppression, they live in the trunks of Duroia hirsuta trees found in the Amazonian rain forest of Peru. Lemon ants use formic acid as a herbicide. By eliminating trees unsuitable for lemon ant colonies, these ants produce distinctive habitats known as Devil's gardens. Beavers thereby create lakes that drastically shape and alter riparian ecosystems; these activities modify nutrient cycling and decomposition dynamics, influence the water and materials transported downstream, influence plant and community composition and diversity. Benthic diatoms living in estuarine sediments in the Bay of Fundy, secrete carbohydrate exudates that bind the sand and stabilize the environment; this changes the physical state of the sand. Chaparrals and pines increase the frequency of forest fire through the dispersal of needles, cones and oils littering the forest floor.
The benefit of this activity is facilitated by an adaptation for fire resistance which benefits them relative to their competitors. Saccharomyces cerevisiae yeast creates a novel environment out of fermenting fruit; this fermentation process in turn attracts fruit flies that it is associated with and utilizes for transportation. Cyanobacteria provide an example on a planetary scale through the production of oxygen as a waste product of photosynthesis; this changed the composition of the Earth’s atmosphere and oceans, with vast macroevolutionary and ecological consequences. As creatures construct new niches, they can have a significant effect on the world around them. An important consequence of niche construction is that it can affect the natural selection experienced by the species doing the constructing; the common cuckoo illustrates such a consequence. It parasitizes other birds by laying its eggs in their nests; this had led to several adaptations among the cuckoos, including a short incubation time for their eggs.
The eggs need to hatch first so that the chick can push the host's eggs out of the nest, ensuring it has no competition for the parents' attention. Another adaptation it has acquired is that the chick mimics the calls of multiple young chicks, so that the parents are bringing in food not just for one offspring, but a whole brood. Niche construction can generate co-evolutionary interactions, as illustrated by the above earthworm and yeast examples; the development of many organisms, the recurrence of traits across generations, has been found to depend critically on the construction of developmental environments such as nests by ancestral organisms. Ecological inheritance refers to the inherited resources and conditions, associated modified selection pressures, that ancestral organisms bequeath to their descendants as a direct result of their niche construction. Niche construction has important implications for understanding and conserving ecosystems. Niche construction theory has been anticipated by diverse people in the past, including by the physicist Erwin Schrödinger in his What Is Life? and Mind and Matter essays.
An early advocate of the niche construction perspective in biol