Niche differentiation

The term niche differentiation (synonymous with niche segregation, niche separation and niche partitioning), as it applies to the field of ecology, refers to the process by which competing species use the environment differently in a way that helps them to coexist. Niche differentiation is also defined as the role in which a species plays in the ecosystem, otherwise known as how an organism or species "makes a living."[1] The competitive exclusion principle states that if two species with identical niches (i.e., ecological roles) compete, then one will inevitably drive the other to extinction.[2] This rule also tells us that two species can't have the same exact niche in a habitat and coexist together, at least in a stable manner.[3] When two species differentiate their niches, they tend to compete less strongly, and are thus more likely to coexist. Species can differentiate their niches in many ways, such as by consuming different foods, or using different parts of the environment.

As an example of niche partitioning, several anole lizards in the Caribbean islands share common food needs—mainly insects. They avoid competition by occupying different physical locations. Although these reptiles might occupy different locations, you may also find groups living around the same area, in which can contain up to as many as fifteen different lizards![4] For example, some live on the leaf litter floor while others live on branches. Species who live in different areas compete less for food and other resources, which minimizes competition between species. However, species who live in similar areas compete strongly.[5]

Detection and quantification

The Lotka-Volterra equation states that two competing species can coexist when intra-specific (within species) competition is greater than inter-specific (between species) competition (Armstrong and McGehee 1981). Since niche differentiation concentrates competition within-species, due to a decrease in between-species competition, the Lotka-Volterra model predicts that niche differentiation of any degree will result in coexistence.

In reality, this still leaves the question of how much differentiation is needed for coexistence (Hutchinson 1959). A vague answer to this question is that the more similar two species are, the more finely balanced the suitability of their environment must be in order to allow coexistence. There are limits to the amount of niche differentiation required for coexistence, and this can vary with the type of resource, the nature of the environment, and the amount of variation both within and between the species.

To answer questions about niche differentiation, it is necessary for ecologists to be able to detect, measure, and quantify the niches of different coexisting and competing species. This is often done through a combination of detailed ecological studies, controlled experiments (to determine the strength of competition), and mathematical models (Strong 1982, Leibold 1995). To understand the mechanisms of niche differentiation and competition, much data must be gathered on how the two species interact, how they use their resources, and the type of ecosystem in which they exist, among other factors. In addition, several mathematical models exist to quantify niche breadth, competition, and coexistence (Bastolla et al. 2005). However, regardless of methods used, niches and competition can be distinctly difficult to measure quantitatively, and this makes detection and demonstration of niche differentiation difficult and complex.

Development

Over time, two competing species can either coexist, through niche differentiation or other means, or compete until one species becomes locally extinct. Several theories exist for how niche differentiation arises or evolves given these two possible outcomes.

Current competition (The Ghost of Competition Present)

Niche differentiation can arise from current competition. For instance, species X has a fundamental niche of the entire slope of a hillside, but its realized niche is only the top portion of the slope because species Y, which is a better competitor but cannot survive on the top portion of the slope, has excluded it from the lower portion of the slope. With this scenario, competition will continue indefinitely in the middle of the slope between these two species. Because of this, detection of the presence of niche differentiation (through competition) will be relatively easy. It is also important to remember that there is no evolutionary change of the individual species in this case; rather this is an ecological effect of species Y out-competing species X within the bounds of species Y's fundamental niche.

Via past extinctions (The Ghost of Competition Past)

Another way by which niche differentiation can arise is via the previous elimination of species without realized niches. This asserts that at some point in the past, several species inhabited an area, and all of these species had overlapping fundamental niches. However, through competitive exclusion, the less competitive species were eliminated, leaving only the species that were able to coexist (i.e. the most competitive species whose realized niches did not overlap). Again, this process does not include any evolutionary change of individual species, but it is merely the product of the competitive exclusion principle. Also, because no species is out-competing any other species in the final community, the presence of niche differentiation will be difficult or impossible to detect.

Evolving differences

Finally, niche differentiation can arise as an evolutionary effect of competition. In this case, two competing species will evolve different patterns of resource use so as to avoid competition. Here too, current competition is absent or low, and therefore detection of niche differentiation is difficult or impossible.

Types

Below is a list of ways that species can partition their niche. This list is not exhaustive, but illustrates several classic examples.

Resource partitioning

Resource partitioning is the phenomenon where two or more species divides out resources like food, space, resting sites etc. to coexist. For example, some lizard species appear to coexist because they consume insects of differing sizes.[6] Alternatively, species can coexist on the same resources if each species is limited by different resources, or differently able to capture resources. Different types of phytoplankton can coexist when different species are differently limited by nitrogen, phosphorus, silicon, and light.[7] In the Galapagos Islands, finches with small beaks are more able to consume small seeds, and finches with large beaks are more able to consume large seeds. If a species' density declines, then the food it most depends on will become more abundant (since there are so few individuals to consume it). As a result, the remaining individuals will experience less competition for food.

Although "resource" generally refers to food, species can partition other non-consumable objects, such as parts of the habitat. For example, warblers are thought to coexist because they nest in different parts of trees.[8] Species can also partition habitat in a way that gives them access to different types of resources. As stated in the introduction, anole lizards appear to coexist because each uses different parts of the forests as perch locations.[5] This likely gives them access to different species of insects.

Predator partitioning

Predator partitioning occurs when species are attacked differently by different predators (or natural enemies more generally). For example, trees could differentiate their niche if they are consumed by different species of specialist herbivores, such as herbivorous insects. If a species density declines, so too will the density of its natural enemies, giving it an advantage. Thus, if each species is constrained by different natural enemies, they will be able to coexist.[9] Early work focused on specialist predators;[9] however, more recent studies have shown that predators do not need to be pure specialists, they simply need to affect each prey species differently.[10][11] The Janzen–Connell hypothesis represents a form of predator partitioning.[12]

Conditional differentiation

Conditional differentiation (sometimes called temporal niche partitioning) occurs when species differ in their competitive abilities based on varying environmental conditions. For example, in the Sonoran Desert, some annual plants are more successful during wet years, while others are more successful during dry years.[13] As a result, each species will have an advantage in some years, but not others. When environmental conditions are most favorable, individuals will tend to compete most strongly with member of the same species. For example, in a dry year, dry-adapted plants will tend to be most limited by other dry-adapted plants.[13] This can help them to coexist through a storage effect.

Competition-predation trade-off

Species can differentiate their niche via a competition-predation trade-off if one species is a better competitor when predators are absent, and the other is better when predators are present. Defenses against predators, such as toxic compounds or hard shells, are often metabolically costly. As a result, species that produce such defenses are often poor competitors when predators are absent. Species can coexist through a competition-predation trade-off if predators are more abundant when the less defended species is common, and less abundant if the well-defended species is common.[14] This effect has been criticized as being weak, because theoretical models suggest that only two species within a community can coexist because of this mechanism.[15]

Coexistence without niche differentiation: exceptions to the rule

Some competing species have been shown to coexist on the same resource with no observable evidence of niche differentiation and in “violation” of the competitive exclusion principle. One instance is in a group of hispine beetle species (Strong 1982). These beetle species, which eat the same food and occupy the same habitat, coexist without any evidence of segregation or exclusion. The beetles show no aggression either intra- or inter-specifically. Coexistence may be possible through a combination of non-limiting food and habitat resources and high rates of predation and parasitism, though this has not been demonstrated.

This example illustrates that the evidence for niche differentiation is by no means universal. Niche differentiation is also not the only means by which coexistence is possible between two competing species (see Shmida and Ellner 1984). However, niche differentiation is a critically important ecological idea which explains species coexistence, thus promoting the high biodiversity often seen in many of the world's biomes.

Research using mathematical modelling is indeed demonstrating that predation can indeed stabilize lumps of very similar species. Willow warbler and chiffchaff and other very similar warblers can serve as an example. The idea is that it is also a good strategy to be very similar to a successful species or have enough dissimilarity. Also trees in the rain forest can serve as an example of all high canopy species basically following the same strategy. Other examples of nearly identical species clusters occupying the same niche were water beetles, prairie birds and algae. The basic idea is that there can be clusters of very similar species all applying the same successful strategy and between them open spaces. Here the species cluster takes the place of a single species in the classical ecological models.[16]

See also

References

  1. ^ Jessica Harwood, Douglas Wilkin (August, 2018). "Habitat and Niche". Retrieved from https://www.ck12.org/biology/habitat-and-niche/lesson/Habitat-and-Niche-MS-LS/.
  2. ^ Hardin, Garrett (29 April 1960). "The Competitive Exclusion Principle". Science. 131 (3409): 1292–1297. Bibcode:1960Sci...131.1292H. doi:10.1126/science.131.3409.1292. PMID 14399717.
  3. ^ Khan Academy. "Niches & Competition". https://www.khanacademy.org/science/biology/ecology/community-ecosystem-ecology/a/niches-competition.
  4. ^ Joshua Anderson. "Interspecific Competition, Competitive Exclusion, and Niche Differentiation". Retrieved from https://study.com/academy/lesson/interspecific-competition-competitive-exclusion-niche-differentiation.html.
  5. ^ a b Pacala, Stephen W.; Roughgarden, Jonathan (February 1985). "Population Experiments with the Anolis Lizards of St. Maarten and St. Eustatius". Ecology. 66 (1): 129–141. doi:10.2307/1941313. JSTOR 1941313.
  6. ^ Caldwell, Janalee P; Vitt, Laurie J (1999). "Dietary asymmetry in leaf litter frogs and lizards in a transitional northern Amazonian rain forest". Oikos. 84 (3): 383–397. doi:10.2307/3546419. JSTOR 3546419.
  7. ^ Grover, James P. (1997). Resource competition (1st ed.). London: Chapman & Hall. ISBN 978-0412749308.
  8. ^ MacArthur, Robert H. (October 1958). "Population Ecology of Some Warblers of Northeastern Coniferous Forests". Ecology. 39 (4): 599–619. doi:10.2307/1931600. JSTOR 1931600.
  9. ^ a b Grover, James P (1994). "Assembly Rules for Communities of Nutrient-Limited Plants and Specialist Herbivores". The American Naturalist. 143 (2): 258–82. doi:10.1086/285603. JSTOR 2462643.
  10. ^ Chesson, Peter; Kuang, Jessica J. (13 November 2008). "The interaction between predation and competition". Nature. 456 (7219): 235–238. Bibcode:2008Natur.456..235C. doi:10.1038/nature07248. PMID 19005554.
  11. ^ Sedio, Brian E.; Ostling, Annette M.; Ris Lambers, Janneke Hille (August 2013). "How specialised must natural enemies be to facilitate coexistence among plants?". Ecology Letters. 16 (8): 995–1003. doi:10.1111/ele.12130. PMID 23773378.
  12. ^ Gilbert, Gregory (2005). Burlesem, David; Pinard, Michelle; Hartley, Sue (eds.). Biotic interactions in the tropics: their role in the maintenance of species diversity. Cambridge, UK: Cambridge University Press. pp. 141–164. ISBN 9780521609852.
  13. ^ a b Angert, Amy L.; Huxman, Travis E.; Chesson, Peter; Venable, D. Lawrence (14 July 2009). "Functional tradeoffs determine species coexistence via the storage effect". Proceedings of the National Academy of Sciences. 106 (28): 11641–11645. Bibcode:2009PNAS..10611641A. doi:10.1073/pnas.0904512106. PMC 2710622. PMID 19571002.
  14. ^ Holt, Robert D.; Grover, James; Tilman, David (November 1994). "Simple Rules for Interspecific Dominance in Systems with Exploitative and Apparent Competition". The American Naturalist. 144 (5): 741–771. doi:10.1086/285705.
  15. ^ Chase, Jonathan M.; Abrams, Peter A.; Grover, James P.; Diehl, Sebastian; Chesson, Peter; Holt, Robert D.; Richards, Shane A.; Nisbet, Roger M.; Case, Ted J. (March 2002). "The interaction between predation and competition: a review and synthesis". Ecology Letters. 5 (2): 302–315. CiteSeerX 10.1.1.361.3087. doi:10.1046/j.1461-0248.2002.00315.x.
  16. ^ Scheffer, Marten; van Nes, Egbert H. (2006). "Self-organized similarity, the evolutionary emergence of groups of similar species". Proceedings of the National Academy of Sciences. 103 (16): 6230–5. Bibcode:2006PNAS..103.6230S. doi:10.1073/pnas.0508024103. PMC 1458860. PMID 16585519.

Further reading

External links

Department of Entomology, University of Queensland, Australia.

Accessory pigment

Accessory pigments are light-absorbing compounds, found in photosynthetic organisms, that work in conjunction with chlorophyll a. They include other forms of this pigment, such as chlorophyll b in green algal and higher plant antennae, while other algae may contain chlorophyll c or d. In addition, there are many non-chlorophyll accessory pigments, such as carotenoids or phycobiliproteins, which also absorb light and transfer that light energy to photosystem chlorophyll. Some of these accessory pigments, in particular the carotenoids, also serve to absorb and dissipate excess light energy, or work as antioxidants. The large, physically associated group of chlorophylls and other accessory pigments is sometimes referred to as a pigment bed.The different chlorophyll and non-chlorophyll pigments associated with the photosystems all have different absorption spectra, either because the spectra of the different chlorophyll pigments are modified by their local protein environment or because the accessory pigments have intrinsic structural differences. The result is that, in vivo, a composite absorption spectrum of all these pigments is broadened and flattened such that a wider range of visible and infrared radiation is absorbed by plants and algae. Most photosynthetic organisms do not absorb green light well, thus most remaining light under leaf canopies in forests or under water with abundant plankton is green, a spectral effect called the "green window". Organisms such as some cyanobacteria and red algae contain accessory phycobiliproteins that absorb green light reaching these habitats.In aquatic ecosystems, it is likely that the absorption spectrum of water, along with gilvin and tripton (dissolved and particulate organic matter, respectively), determines phototrophic niche differentiation. The six shoulders in the light absorption of water between wavelengths 400 and 1100 nm correspond to troughs in the collective absorption of at least twenty diverse species of phototrophic bacteria. Another effect is due to the overall trend for water to absorb low frequencies, while gilvin and tripton absorb higher ones. This is why open ocean appears blue and supports yellow species such as Prochlorococcus, which contains divinyl-chlorophyll a and b. Synechococcus, colored red with phycoerythrin, is adapted to coastal bodies, while phycocyanin allows Cyanobacteria to thrive in darker inland waters.

Bacterivore

Bacterivores are free-living, generally heterotrophic organisms, exclusively microscopic, which obtain energy and nutrients primarily or entirely from the consumption of bacteria. Many species of amoeba are bacterivores, as well as other types of protozoans. Commonly, all species of bacteria will be prey, but spores of some species, such as Clostridium perfringens, will never be prey, because of their cellular attributes.

Coexistence theory

Coexistence theory is a framework to understand how competitor traits can maintain species diversity and stave-off competitive exclusion even among similar species living in ecologically similar environments. Coexistence theory explains the stable coexistence of species as an interaction between two opposing forces: fitness differences between species, which should drive the best-adapted species to exclude others within a particular ecological niche, and stabilizing mechanisms, which maintains diversity via niche differentiation. For many species to be stabilized in a community, population growth must be negative density-dependent, i.e. all participating species have a tendency to increase in density as their populations decline. In such communities, any species that becomes rare will experience positive growth, pushing its population to recover and making local extinction unlikely. As the population of one species declines, individuals of that species tend to compete predominantly with individuals of other species. Thus, the tendency of a population to recover as it declines in density reflects reduced interspecific competition (between-species) relative to intraspecific competition (within-species), the signature of niche differentiation (see Lotka-Volterra competition).

Daspletosaurus

Daspletosaurus ( das-PLEET-o-SAWR-əs; meaning "frightful lizard") was a genus of tyrannosaurid dinosaur that lived in western North America between about 77 and 74 million years ago, during the Late Cretaceous Period. The genus Daspletosaurus contains two species. Fossils of the earlier type species, D. torosus, have been found in Alberta, while fossils of the later second species, D. horneri, have been found only in Montana. A possible third species, also from Alberta, awaits formal identification. (Daspletosaurus sp.)

Daspletosaurus is closely related to the much larger and more recent tyrannosaurid Tyrannosaurus rex. Like most tyrannosaurids, Daspletosaurus was a multi-tonne bipedal predator equipped with dozens of large, sharp teeth. Daspletosaurus had the small forelimbs typical of tyrannosaurids, although they were proportionately longer than in other genera.

As an apex predator, Daspletosaurus was at the top of the food chain, probably preying on large dinosaurs like the ceratopsid Centrosaurus and the hadrosaur Hypacrosaurus. In some areas, Daspletosaurus coexisted with another tyrannosaurid, Gorgosaurus, though there is some evidence of niche differentiation between the two. While Daspletosaurus fossils are rarer than other tyrannosaurids', the available specimens allow some analysis of the biology of these animals, including social behavior, diet and life history.

Dominance (ecology)

Ecological dominance is the degree to which a taxon is more numerous than its competitors in an ecological community, or makes up more of the biomass.

Most ecological communities are defined by their dominant species.

In many examples of wet woodland in western Europe, the dominant tree is alder (Alnus glutinosa).

In temperate bogs, the dominant vegetation is usually species of Sphagnum moss.

Tidal swamps in the tropics are usually dominated by species of mangrove (Rhizophoraceae)

Some sea floor communities are dominated by brittle stars.

Exposed rocky shorelines are dominated by sessile organisms such as barnacles and limpets.

Earth-colored mouse

The earth-colored mouse (Mus terricolor) is a species of rodent in the family Muridae.

It is found in India, possibly Indonesia, Nepal, and Pakistan. The earth-colored mouse lives in cultivated fields in raised moist mounds of Earth, where they burrow and locate their nest about 20 cm or 8 inches deep. Living in a raised mound of soil offers them more oxygen flow from air coming through the surrounding sides as well as from above. In contrast, their co-existing sibling species Mus booduga burrow in the flat parts of the field, which allows for niche differentiation.

Feeding frenzy

In ecology, a feeding frenzy occurs when predators are overwhelmed by the amount of prey available. For example, a large school of fish can cause nearby sharks, such as the lemon shark, to enter into a feeding frenzy. This can cause the sharks to go wild, biting anything that moves, including each other or anything else within biting range. Another functional explanation for feeding frenzy is competition amongst predators. This term is most often used when referring to sharks or piranhas. It has also been used as a term within journalism.

Gorgosaurus

Gorgosaurus ( GOR-gə-SOR-əs; meaning "dreadful lizard") is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period (Campanian), between about 76.6 and 75.1 million years ago. Fossil remains have been found in the Canadian province of Alberta and possibly the U.S. state of Montana. Paleontologists recognize only the type species, G. libratus, although other species have been erroneously referred to the genus.

Like most known tyrannosaurids, Gorgosaurus was a bipedal predator weighing more than two metric tons as an adult; dozens of large, sharp teeth lined its jaws, while its two-fingered forelimbs were comparatively small. Gorgosaurus was most closely related to Albertosaurus, and more distantly related to the larger Tyrannosaurus. Gorgosaurus and Albertosaurus are extremely similar, distinguished mainly by subtle differences in the teeth and skull bones. Some experts consider G. libratus to be a species of Albertosaurus; this would make Gorgosaurus a junior synonym of that genus.

Gorgosaurus lived in a lush floodplain environment along the edge of an inland sea. It was an apex predator, preying upon abundant ceratopsids and hadrosaurs. In some areas, Gorgosaurus coexisted with another tyrannosaurid, Daspletosaurus. Although these animals were roughly the same size, there is some evidence of niche differentiation between the two. Gorgosaurus is the best-represented tyrannosaurid in the fossil record, known from dozens of specimens. These plentiful remains have allowed scientists to investigate its ontogeny, life history and other aspects of its biology.

Hutchinson's rule

The observation that the trophic structures (i.e. mouths) of sympatric congeneric species generally vary by a factor of ~1.3. This variation presumably leads to niche differentiation, allowing coexistence of multiple similar species in the same habitat, by partitioning food resources. The rule's legitimacy has been questioned, as other categories of objects also exhibit size ratios of roughly 1.3.

Interspecific competition

Interspecific competition, in ecology, is a form of competition in which individuals of different species compete for the same resources in an ecosystem (e.g. food or living space). This can be contrasted with interspecific cooperation, a type of symbiosis. Competition between members of the same species is called intraspecific competition.

If a tree species in a dense forest grows taller than surrounding tree species, it is able to absorb more of the incoming sunlight. However, less sunlight is then available for the trees that are shaded by the taller tree, thus interspecific competition. Leopards and lions can also be in interspecific competition, since both species feed on the same prey, and can be negatively impacted by the presence of the other because they will have less food.

Competition is only one of many interacting biotic and abiotic factors that affect community structure. Moreover, competition is not always a straightforward, direct, interaction. 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, then lowered fecundity, growth, or survival may result in at least one species. Interspecific competition has the potential to alter populations, communities and the evolution of interacting species. On an individual organism level, competition can occur as interference or exploitative competition.

Direct competition has been observed between individuals, populations and species, but there is little evidence that competition has been the driving force in the evolution of large groups. For example, between amphibians, reptiles and mammals.

Mycotroph

A mycotroph is a plant that gets all or part of its carbon, water, or nutrient supply through symbiotic association with fungi. The term can refer to plants that engage in either of two distinct symbioses with fungi:

Many mycotrophs have a mutualistic association with fungi in any of several forms of mycorrhiza. The majority of plant species are mycotrophic in this sense. Examples include Burmanniaceae.

Some mycotrophs are parasitic upon fungi in an association known as myco-heterotrophy.

Nocturnality

Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite.

Nocturnal creatures generally have highly developed senses of hearing, smell, and specially adapted eyesight. Such traits can help animals such as the Helicoverpa zea moths avoid predators. Some animals, such as cats and ferrets, have eyes that can adapt to both low-level and bright day levels of illumination (see metaturnal). Others, such as bushbabies and (some) bats, can function only at night. Many nocturnal creatures including tarsiers and some owls have large eyes in comparison with their body size to compensate for the lower light levels at night. More specifically, they have been found to have a larger cornea relative to their eye size than diurnal creatures to increase their visual sensitivity: in the low-light conditions. Nocturnality helps wasps, such as Apoica flavissima, avoid hunting in intense sunlight.

Diurnal animals, including squirrels and songbirds, are active during the daytime. Crepuscular species, such as rabbits, skunks, tigers, and hyenas, are often erroneously referred to as nocturnal. Cathemeral species, such as fossas and lions, are active both in the day and at night.

Organotroph

An organotroph is an organism that obtains hydrogen or electrons from organic substrates. This term is used in microbiology to classify and describe organisms based on how they obtain electrons for their respiration processes. Some organotrophs such as animals and many bacteria, are also heterotrophs. Organotrophs can be either anaerobic or aerobic.

Antonym: Lithotroph, Adjective: Organotrophic.

Recruitment (biology)

In biology, especially marine biology, recruitment occurs when a juvenile organism joins a population, whether by birth or immigration, usually at a stage whereby the organisms are settled and able to be detected by an observer.There are two types of recruitment: closed and open.In the study of fisheries, recruitment is "the number of fish surviving to enter the fishery or to some life history stage such as settlement or maturity".

Resource (biology)

In Biology and Ecology, a resource is a substance or object in the environment required by an organism for normal growth, maintenance, and reproduction. Resources can be consumed by one organism and, as a result, become unavailable to another organism. For plants key resources are light, nutrients, water, and place to grow. For animals key resources are food, water, and territory.

Réunion kestrel

The Réunion kestrel (Falco duboisi) is an extinct bird of prey which belongs to the falcon family. It inhabited the Mascarene island of Réunion and was part of the Western Indian Ocean radiation of kestrels.

Known from subfossil bones and the writings of Dubois published in 1674, this bird was larger than its relative F. punctatus on Mauritius, being about the size of a common kestrel, or around 35 cm from head to tail, with males being noticeably smaller than females. This trait, while present in most birds of prey, is most pronounced in the larger, bird-eating species and reduces between-sex competition by niche differentiation. It can be assumed that the bird was of the same generally brownish coloration as its closest relatives, with a lighter underside and darker spots or stipples, the tail, brown or more probably grey, being banded and tipped black. Its feet were yellow and large relative to the bird's overall size. The wingspan was 60–70 cm, its wings being more rounded than those of the common kestrel - just as in the Mauritius bird - for increased maneuvrability when hunting in the forest. It is probable, but not certain, that the only difference between the sexes was their size. The bird fed mainly on birds, but certainly also on insects and the local gecko; Dubois noted that despite their small size they were able to prey on (presumably half-grown) domestic chickens.

Thorius

Thorius, also known as minute salamanders, pigmy salamanders, or Mexican pigmy salamanders, is a genus of salamanders in the family Plethodontidae. They are endemic to Mexico and found in southern Veracruz and Puebla to Guerrero and Oaxaca.Thorius is the most species-rich tropical salamander genus relative to its distribution area (Bolitoglossa and Pseudoeurycea have many more species but also much wider distribution areas). It is not uncommon for two or even three species to occur in the same place. In such cases, species have diverged in terms of body size and dentition, apparently facilitating niche differentiation.The members of this genus are characterized by a small body — some species are less than 2 cm (0.79 in) in snout–vent length (tail roughly doubles the total body length). Their extreme miniaturization is accompanied by determinate growth and skeletal reduction. Their skeleton also shows unique features, such as ossifications of many elements that remain cartilaginous in other salamanders. Consequently, they are easy to distinguish from other salamanders. In contrast, they tend to be similar in appearance, making it difficult to distinguish species. However, molecular genetic methods have greatly facilitated identification of new species.

Zhongjianosaurus

Zhongjianosaurus is a genus of dromaeosaurid belonging to the Microraptoria. Believed to hail from the Yixian Formation, specifically the middle of the Jehol Biota, it is the smallest known microraptorine thus far discovered and one of the smallest non-avian theropod dinosaurs.

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Microorganisms
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