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Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within lineages. Charles Darwin was the first to describe the role of natural selection in speciation in his 1859 book On the Origin of Species. He also identified sexual selection as a likely mechanism, but found it problematic.
Allopatric speciation – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from each other to an extent that prevents or interferes with gene flow.
Sympatric speciation is the evolution of a new species from a surviving ancestral species while both continue to inhabit the same geographic region. In evolutionary biology and biogeography, sympatric and sympatry are terms referring to organisms whose ranges overlap so that they occur together at least in some places. If these organisms are closely related, such a distribution may be the result of sympatric speciation. Etymologically, sympatry is derived from the Greek roots συν ("together") and πατρίς ("homeland"). The term was coined by Edward Bagnall Poulton in 1904, who explains the derivation.
Haldane's rule is an observation about the early stage of speciation, formulated in 1922 by the British evolutionary biologist J. B. S. Haldane, that states that if — in a species hybrid — only one sex is inviable or sterile, that sex is more likely to be the heterogametic sex. The heterogametic sex is the one with two different sex chromosomes; in therian mammals, for example, this is the male.
Peripatric speciation is a mode of speciation in which a new species is formed from an isolated peripheral population. Since peripatric speciation resembles allopatric speciation, in that populations are isolated and prevented from exchanging genes, it can often be difficult to distinguish between them. Nevertheless, the primary characteristic of peripatric speciation proposes that one of the populations is much smaller than the other. The terms peripatric and peripatry are often used in biogeography, referring to organisms whose ranges are closely adjacent but do not overlap, being separated where these organisms do not occur—for example on an oceanic island compared to the mainland. Such organisms are usually closely related ; their distribution being the result of peripatric speciation.
In biology, two related species or populations are considered sympatric when they exist in the same geographic area and thus frequently encounter one another. An initially interbreeding population that splits into two or more distinct species sharing a common range exemplifies sympatric speciation. Such speciation may be a product of reproductive isolation – which prevents hybrid offspring from being viable or able to reproduce, thereby reducing gene flow – that results in genetic divergence. Sympatric speciation may, but need not, arise through secondary contact, which refers to speciation or divergence in allopatry followed by range expansions leading to an area of sympatry. Sympatric species or taxa in secondary contact may or may not interbreed.
In parapatric speciation, two subpopulations of a species evolve reproductive isolation from one another while continuing to exchange genes. This mode of speciation has three distinguishing characteristics: 1) mating occurs non-randomly, 2) gene flow occurs unequally, and 3) populations exist in either continuous or discontinuous geographic ranges. This distribution pattern may be the result of unequal dispersal, incomplete geographical barriers, or divergent expressions of behavior, among other things. Parapatric speciation predicts that hybrid zones will often exist at the junction between the two populations.
Species richness, or biodiversity, increases from the poles to the tropics for a wide variety of terrestrial and marine organisms, often referred to as the latitudinal diversity gradient. The latitudinal diversity gradient is one of the most widely recognized patterns in ecology. It has been observed to varying degrees in Earth's past. A parallel trend has been found with elevation, though this is less well-studied.
Robert Eric Ricklefs is an American ornithologist and ecologist. He was the Curators' Professor of Biology at the University of Missouri, St. Louis from 1996 until August 2019.
Geographic isolation or other factors that prevent reproduction have resulted in a population of organisms with a change in genetic diversity and ultimately leads to the genetic isolation of species. Genetic isolates form new species through an evolutionary process known as speciation. Today, all the species diversity present on earth is the product of genetic isolate and evolution. The current distribution of genetic differences and isolation within and among populations is also influenced by genetic processes, which can give significant input into evolution's basic principles. The resulting genetic diversity within a species' distribution range is frequently unequally distributed, and large disparities can occur at the series of ranges when population dispersion and isolation are critical for species survival. The interrelationship of genetic drift, gene flow, and natural selection determines the level and dispersion of genetic differences between populations and among species assemblages. Geographic and natural elements may likewise add to these cycles and further impact species' advanced examples of hereditary variety such as genetic differences that cause genetic isolation. Genetic variations are often unequally distributed over a species' geographic distribution, with differences between populations at the geographic center and the range's extremities. In general, significant gene flow occurs in core populations, resulting in genetic uniformity, whereas low gene flow, severe genetic drift, and diverse selection conditions occur in range periphery populations, resulting in enhanced genetic isolation and heterogeneity among populations. Genetic differentiation resulted from genetic isolate occurs as significant alterations in genetic variations, such as fluctuations in allelic frequencies, that are accumulated in the populations over time with geographic regional boundaries. Significant genetic diversity can be detected towards the limits of a species' range, where population fragmentation and isolation are more likely to affect genetic processes. Fragmentation is the division of a large population into smaller, geographically separated habitats, resulting in genetic differences within and across groups is also the product of genetic isolate. Regional splitting is produced by a variety of factors, including environmental processes that regularly change a species' indigenous distribution. Additionally, human-caused environmental changes, such as deforestation, land degradation can result in fast changes in a species' distribution, resulting in population decrease, segmentation, and regional isolation. Consequently, communities became geographically and genetically isolated.
Tropical ecology is the study of the relationships between the biotic and abiotic components of the tropics, or the area of the Earth that lies between the Tropic of Cancer and the Tropic of Capricorn. The tropical climate experiences hot, humid weather and rainfall year-round. While many might associate the region solely with the rainforests, the tropics are home to a wide variety of ecosystems that boast a great wealth of biodiversity, from exotic animal species to seldom-found flora. Tropical ecology began with the work of early English naturalists and eventually saw the establishment of research stations throughout the tropics devoted to exploring and documenting these exotic landscapes. The burgeoning ecological study of the tropics has led to increased conservation education and programs devoted to the climate.
Local adaptation is a mechanism in evolutionary biology whereby a population of organisms evolves to be more well-suited to its local environment than other members of the same species that live elsewhere. Local adaptation requires that different populations of the same species experience different natural selection. For example, if a species lives across a wide range of temperatures, populations from warm areas may have better heat tolerance than populations of the same species that live in the cold part of its geographic range.
A biological rule or biological law is a generalized law, principle, or rule of thumb formulated to describe patterns observed in living organisms. Biological rules and laws are often developed as succinct, broadly applicable ways to explain complex phenomena or salient observations about the ecology and biogeographical distributions of plant and animal species around the world, though they have been proposed for or extended to all types of organisms. Many of these regularities of ecology and biogeography are named after the biologists who first described them.
Reinforcement is a process of speciation where natural selection increases the reproductive isolation between two populations of species. This occurs as a result of selection acting against the production of hybrid individuals of low fitness. The idea was originally developed by Alfred Russel Wallace and is sometimes referred to as the Wallace effect. The modern concept of reinforcement originates from Theodosius Dobzhansky. He envisioned a species separated allopatrically, where during secondary contact the two populations mate, producing hybrids with lower fitness. Natural selection results from the hybrid's inability to produce viable offspring; thus members of one species who do not mate with members of the other have greater reproductive success. This favors the evolution of greater prezygotic isolation. Reinforcement is one of the few cases in which selection can favor an increase in prezygotic isolation, influencing the process of speciation directly. This aspect has been particularly appealing among evolutionary biologists.
The scientific study of speciation — how species evolve to become new species — began around the time of Charles Darwin in the middle of the 19th century. Many naturalists at the time recognized the relationship between biogeography and the evolution of species. The 20th century saw the growth of the field of speciation, with major contributors such as Ernst Mayr researching and documenting species' geographic patterns and relationships. The field grew in prominence with the modern evolutionary synthesis in the early part of that century. Since then, research on speciation has expanded immensely.
Reinforcement is a process within speciation where natural selection increases the reproductive isolation between two populations of species by reducing the production of hybrids. Evidence for speciation by reinforcement has been gathered since the 1990s, and along with data from comparative studies and laboratory experiments, has overcome many of the objections to the theory. Differences in behavior or biology that inhibit formation of hybrid zygotes are termed prezygotic isolation. Reinforcement can be shown to be occurring by measuring the strength of prezygotic isolation in a sympatric population in comparison to an allopatric population of the same species. Comparative studies of this allow for determining large-scale patterns in nature across various taxa. Mating patterns in hybrid zones can also be used to detect reinforcement. Reproductive character displacement is seen as a result of reinforcement, so many of the cases in nature express this pattern in sympatry. Reinforcement's prevalence is unknown, but the patterns of reproductive character displacement are found across numerous taxa, and is considered to be a common occurrence in nature. Studies of reinforcement in nature often prove difficult, as alternative explanations for the detected patterns can be asserted. Nevertheless, empirical evidence exists for reinforcement occurring across various taxa and its role in precipitating speciation is conclusive.
Laboratory experiments of speciation have been conducted for all four modes of speciation: allopatric, peripatric, parapatric, and sympatric; and various other processes involving speciation: hybridization, reinforcement, founder effects, among others. Most of the experiments have been done on flies, in particular Drosophila fruit flies. However, more recent studies have tested yeasts, fungi, and even viruses.
This glossary of evolutionary biology is a list of definitions of terms and concepts used in the study of evolutionary biology, population biology, speciation, and phylogenetics, as well as sub-disciplines and related fields. For additional terms from related glossaries, see Glossary of genetics, Glossary of ecology, and Glossary of biology.
The temperature-size rule denotes the plastic response of organismal body size to environmental temperature variation. Organisms exhibiting a plastic response are capable of allowing their body size to fluctuate with environmental temperature. First coined by David Atkinson in 1996, it is considered to be a unique case of Bergmann's rule that has been observed in plants, animals, birds, and a wide variety of ectotherms. Although exceptions to the temperature-size rule exist, recognition of this widespread "rule" has amassed efforts to understand the physiological mechanisms underlying growth and body size variation in differing environmental temperatures.
Taxon cycles refer to a biogeographical theory of how species evolve through range expansions and contractions over time associated with adaptive shifts in the ecology and morphology of species. The taxon cycle concept was explicitly formulated by biologist E. O. Wilson in 1961 after he surveyed the distributions, habitats, behavior and morphology of ant species in the Melanesian archipelago.
References
- ↑ McDowall, R. M. (March 2008). "Jordan's and other ecogeographical rules, and the vertebral number in fishes". Journal of Biogeography. 35 (3): 501–508. doi: 10.1111/j.1365-2699.2007.01823.x .
- ↑ Jordan, David Starr (1908-02-01). "The Law of Geminate Species". The American Naturalist. 42 (494): 73–80. doi: 10.1086/278905 . ISSN 0003-0147.
- ↑ Fitzpatrick, Benjamin M.; Turelli, Michael (2006). "The Geography of Mammalian Speciation: Mixed Signals from Phylogenies and Range Maps". Evolution. 60 (3): 601–615. doi: 10.1111/j.0014-3820.2006.tb01140.x . ISSN 1558-5646. PMID 16637504. S2CID 32663278.
- ↑ Mayr, Ernst, 1904-2005. (1963). Animal species and evolution. Cambridge: Belknap Press of Harvard University Press. ISBN 0-674-03750-2. OCLC 551391.
{{cite book}}: CS1 maint: multiple names: authors list (link) - ↑ Barraclough, Timothy G. (20 June 2019). The evolutionary biology of species (First ed.). Oxford. ISBN 978-0-19-106665-8. OCLC 1104724041.
- ↑ Jordan, David Starr (February 1908). "The Law of Geminate Species". The American Naturalist. 42 (494): 73–80. doi: 10.1086/278905 . ISSN 0003-0147.
- ↑ Allen, J. A. (October 1907). "Mutations and the Geographic Distribution of Nearly Related Species in Plants and Animals". The American Naturalist. 41 (490): 653–655. doi: 10.1086/278852 . ISSN 0003-0147.
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