Difference between revisions of "Adaptive radiation" - New World Encyclopedia

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Four of the 13 finch species found on the Galápagos Archipelago, and thought to have evolved by an adaptive radiation that diversified their beak shapes to adapt them to different food sources.

Adaptive radiation is an evolutionary process whereby a single ancestral form (or species) diversifies (or speciates) into several or many related forms (or species). According to this theory, the different descendant taxa are similar, but each is adapted for a particular environmental niche.

It is held that adaptive radiation led to the pattern of over 250,000 species of beetles, 14 different species of Darwin's finches on the Galápagos Islands, over 25,000 types of teleost fishes, and different marsupials in Australia (Luria et al. 1981).

Causes of adaptive radiation

The vigorous phase of diversification characteristic of adaptive radiation is held to be especially linked to the evolution of a new design and/or the movement of the ancestral form into a new ecological space. Examples would be movement into an unoccupied territory or the origin of a new mode of life, such as the development of flight by insects more than 300 million years ago (Luria et al. 1981).

Opportunity

Isolated ecosystems, such as archipelagos and mountain areas, can be colonized by a species which, upon establishing itself, undergoes rapid divergent evolution. Monotremes and marsupials are considered to be examples of geographic isolation. Monotremes evolved before the evolution of placental mammals, and they are found today only in Australia, which has been isolated from the other continents for 50 million years. Marsupials, which also evolved before the appearance of placental mammals, are also common in Australia. It is held that in Australia, marsupials evolved to fill many ecological niches that placental mammals fill on other continent.

Richard Leakey (1994) wrote, "Biologists who have studied the fossil record know that when a new species evolves with a novel adaptation, there is often a burgeoning of descendent species over the next few million years expressing various themes on that initial adaptation—a burgeoning known as adaptive radiation."

Extinction

Adaptive radiation can also occur after mass extinctions. The best example of this is after the Permian-Triassic extinction event, where the fossil records shows that biodiversity increased massively in the Triassic. The end of the Ediacaran and the beginnings of multicellular life lead to adaptive radiations and the genesis of new phyla in the Cambrian period.

Darwin's finches

Darwin's finches—13 speceis of finches that occupy the two dozen or so islands in the Galápagos Archipelago, are often cited as examples of species arising via adaptive radiation. These finches differ mainly in the size and shape of their beaks, with the beaks adapated to the different food they eat (Wells 2000).

Although commonly cited as instrumental in helping Darwin formulate his theory of evolution, Wells (2000) notes that they actually had almost nothing to do with his theory, not being mentioned in the Origin of Species and meriting only a passing reference in Darwin's diary of the Voyage of the Beagle. Darwin did collect 9 of the 13 species (identifying only six of them as species), but failed to correlate beak shape with diet and made no effort ot separate them by island. They do not have seemed to have made much of a impression on Darwin as evidence of evolution.

Nonetheless, these finches do seem to be a textbook case of natural selection, and Darwin did go back years later and reinterprett them in light of his theory, and thus they are now known as "Darwins' finches." However, according to Sulloway (1982), "Darwin was increasingly given credit after 1947 for finches he never saw and for observations and insights about them he never made."

Various field studies on the finches do provide evidence for natural selection working on the microevolutionary level. However, Wells (2000) finds Darwin's finches not to provide very convincing evidence for speciation or adaptive radiation, finding little direct or genetic evidence and noting that the field studies, which originally showed some directional changes in beak depth, exhibited trends in the opposite direction in subsequent studies. He also noted the suggestion of some merging of the species, rather than further diversification.

References
ISBN links support NWE through referral fees

Leakey, R. 1994. The Origin of Humankind. Orion Publishing. ISBN 0297815032.
Luria, S. A., S. J. Gould, and S. Singer. 1981. A View of Life. Menlo Park, CA: The Benjamin/Cummings Publishing Company. ISBN 0805366482.
Sulloway, F. J. 1982. Darwin and his finches: The evolution of a legend. Journal of the History of Biology 15: 1-53.
Wells, J. 2000. Icons of Evolution. Washington, D.C.: Regnery. ISBN 0895262762.
Wilson, E., T. Eisner, W. Briggs, R. Dickerson, R. Metzenberg, R. O'Brien, M. Susman, and W. Boggs. 1973. Life on Earth. Stamford, CN: Sinauer Associates, Inc.

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@@ Line 2: / Line 2: @@
 [[Image:Darwin's finches.jpeg|thumb|Four of the 13 finch species found on the [[Galápagos Islands|Galápagos Archipelago]], and thought to have evolved by an adaptive radiation that diversified their beak shapes to adapt them to different food sources.]]
-'''Adaptive radiation''' is an [[evolution|evolutionary]] process whereby a single ancestral species or form diversifies or [[speciation|speciates]] into several or many related forms or species. The basic form of the different descendant taxa are similar, but each is adapted for a particular environmental niche.
+'''Adaptive radiation''' is an [[evolution|evolutionary]] process whereby a single ancestral form (or [[species]]) diversifies (or [[speciation|speciates]]) into several or many related forms (or species). According to this theory, the different descendant taxa are similar, but each is adapted for a particular environmental niche.
-The presence of over 250,000 species of beetles, the 14 different species of Darwin's finches on the Galápagos Islands, the over 25,000 types of teleost fishes, and the different marsupials in Australia are considered to be examples of adaptive radiation (Luria et al. 1981).
+It is held that adaptive radiation led to the pattern of over 250,000 species of [[beetle]]s, 14 different species of Darwin's finches on the Galápagos Islands, over 25,000 types of teleost [[fish]]es, and different [[marsupial]]s in [[Australia]] (Luria et al. 1981).
 ==Causes of adaptive radiation==
-The vigorous phase of diversification characteristic of adaptive radiation is linked to a new design, particularly when it is tied to movement in to a new ecological space, such as an unoccupied territory or a new mode of life, such as the development of flight by insects more than 300 million years ago (Luria et al. 1981).
+The vigorous phase of diversification characteristic of adaptive radiation is held to be especially linked to the [[evolution]] of a new design and/or the movement of the ancestral form into a new ecological space. Examples would be movement into an unoccupied territory or the origin of a new mode of life, such as the development of flight by [[insect]]s more than 300 million years ago (Luria et al. 1981).
 ===Opportunity===
-Isolated [[ecosystem]]s, such as [[archipelago]]s and [[mountain]] areas, can be colonized by a species which, upon establishing itself, undergoes rapid [[divergent evolution]].
+Isolated [[ecosystem]]s, such as [[archipelago]]s and [[mountain]] areas, can be colonized by a species which, upon establishing itself, undergoes rapid divergent [[evolution]].
-[[Monotremes]] and [[marsupials]] are examples of geographic isolation. Monotremes evolved before the evolution of placental mammals, and they are found today only in [[Australia]], an island. Marsupials, which also evolved before the appearance of placental mammals are also common in Australia. In Australia, marsupials evolved to fill many ecological niches that placental mammals fill on other [[continents]].
+[[Monotreme]]s and [[marsupial]]s are considered to be examples of geographic isolation. Monotremes evolved before the evolution of placental [[mammal]]s, and they are found today only in [[Australia]], which has been isolated from the other continents for 50 million years. Marsupials, which also evolved before the appearance of placental mammals, are also common in Australia. It is held that in Australia, marsupials evolved to fill many ecological niches that placental mammals fill on other [[continent]].
-isolaed for 50 mililion years
+[[Richard Leakey]] (1994) wrote, "Biologists who have studied the [[fossil]] record know that when a new species evolves with a novel adaptation, there is often a burgeoning of descendent species over the next few million years expressing various themes on that initial adaptation&mdash;a burgeoning known as '''adaptive radiation'''."
-marsupials in Austrail
-other contentines (partial exception of Soputh America), mostly placentals.
-[[Richard Leakey]] (see below) wrote, "Biologists who have studied the fossil record know that when a new species evolves with a novel adaptation, there is often a burgeoning of descendent species over the next few million years expressing various themes on that initial adaptation - a burgeoning known as '''adaptive radiation'''. The Cambridge University anthropologist [[Robert Foley]] has calculated that if the evolutionary history of the bipedal apes followed the usual pattern of adaptive radiation, at least sixteen species should have existed between the group's origin 7 million years ago and today."
 ===Extinction===
-Adaptive radiation can also occur after [[mass extinctions]]. The best example of this is after the [[Permian-Triassic extinction event]], where [[biodiversity]] increased massively in the [[Triassic]]. The end of the [[Ediacaran]] and the beginnings of [[multicellular organisms|multicellular life]] lead to adaptive radiations and the genesis of new phyla in the [[Cambrian]] period.
+Adaptive radiation can also occur after [[mass extinction]]s. The best example of this is after the [[Mass extinction#Permian-Triassic extinction event|Permian-Triassic extinction event]], where the fossil records shows that [[biodiversity]] increased massively in the [[Triassic]]. The end of the [[Ediacaran]] and the beginnings of multicellular life lead to adaptive radiations and the genesis of new phyla in the [[Cambrian]] period.
 ==Darwin's finches==
+Darwin's finches&mdash;13 speceis of finches that occupy the two dozen or so islands in the Galápagos Archipelago, are often cited as examples of species arising via adaptive radiation. These finches differ mainly in the size and shape of their beaks, with the beaks adapated to the different food they eat (Wells 2000).
-Darwin's finches&mdash;13 speceis of finches that occup the two dozen or so volcanic islads in the Galapago, are often cited as examples of adaptive radition. These finches difer mainly int eh size nd shape of their beaks, with the beaks adapated to the different good they eat (Wells 2000). Although commonly cited as instrumental in helping Darwin formulate his theory, Wells (2000) notes that they had almost nothing to do with his theory, not bieng mentioned in the Origin of Species and having only a passing reference in his diary of the voyage of the beagle. He did collect 9 of the 13 speices (identifying only six of them as species), , but failed to correlate beak shape with diet and made no effort ot separate them by island. They do not have seemed to have made much of a impression on Darwin as evidence of evolution. But they do seem to be a textbook case of natural selection, and Dawin did go back years later and reinterprett tehm in the list of this theory, thus are now known as "Darwins' finches." According to Sulloway (1982), "Darwin was increasingly given credit after 1947 for finches he never saw and for observations and insights about them he never made." Wells (2000) does not even find them convincing evidence for speciation (there clearly was natural selection), finding little direct or genetic evidence and field studies, that originally showed some directional changes in beak depth, were reversed in subsequent studies.  and a suggestion of some merging of the species, rather than furhter diversification.
+Although commonly cited as instrumental in helping [[Charles Darwin|Darwin]] formulate his theory of evolution, Wells (2000) notes that they actually had almost nothing to do with his theory, not being mentioned in the ''Origin of Species'' and meriting only a passing reference in Darwin's diary of the Voyage of the Beagle. Darwin did collect 9 of the 13 species (identifying only six of them as [[species]]), but failed to correlate beak shape with diet and made no effort ot separate them by island. They do not have seemed to have made much of a impression on Darwin as evidence of evolution.
+Nonetheless, these finches do seem to be a textbook case of [[natural selection]], and Darwin did go back years later and reinterprett them in light of his theory, and thus they are now known as "Darwins' finches." However, according to Sulloway (1982), "Darwin was increasingly given credit after 1947 for finches he never saw and for observations and insights about them he never made."
+Various field studies on the finches do provide evidence for natural selection working on the [[microevolution]]ary level. However, Wells (2000) finds Darwin's finches not to provide very convincing evidence for [[speciation]] or adaptive radiation, finding little direct or genetic evidence and noting that the field studies, which originally showed some directional changes in beak depth, exhibited trends in the opposite direction in subsequent studies. He also noted the suggestion of some merging of the species, rather than further diversification.
 ==References==
-*Wilson, E. et al.  ''Life on Earth,''  by Wilson,E.; Eisner,T.; Briggs,W.; Dickerson,R.; Metzenberg,R.; O'brien,R.; Susman,M.; Boggs,W.; (Sinauer Associates, Inc., Publishers, Stamford, Connecticut), c 1974. Chapters: ''The Multiplication of Species; Biogeography,'' pp 824-877. 40 Graphs, w species pictures, also Tables, Photos, etc.  Includes [[Galápagos Islands]], [[Hawaii]], and [[Australia (continent)|Australia]] subcontinent, (plus [[St. Helena]] Island, etc.).
+* Leakey, R. 1994. ''The Origin of Humankind''. Orion Publishing. ISBN 0297815032.
+* Luria, S. A., S. J. Gould, and S. Singer. 1981. ''A View of Life''. Menlo Park, CA: The Benjamin/Cummings Publishing Company. ISBN 0805366482.
-*Leakey,Richard. ''The Origin of Humankind'' - on adaptive radiation in biology and human evolution, pp. 28-32, 1994, Orion Publishing.
+* Sulloway, F. J. 1982. Darwin and his finches: The evolution of a legend. ''Journal of the History of Biology'' 15: 1-53.
+* Wells, J. 2000. ''Icons of Evolution''. Washington, D.C.: Regnery. ISBN 0895262762.
-Sulloway, F. J. 1982. Darwin and his finches: The evolution of a legend. ''Journal of the History of Biology'' 15: 1-53).
+* Wilson, E., T. Eisner, W. Briggs, R. Dickerson, R. Metzenberg, R. O'Brien, M. Susman, and W. Boggs. 1973. ''Life on Earth''. Stamford, CN: Sinauer Associates, Inc.