{"id":98270,"date":"2008-08-07T08:25:00","date_gmt":"2008-08-07T08:25:00","guid":{"rendered":"http:\/\/weblogs.madrimasd.org\/\/universo\/archive\/2008\/08\/07\/98270.aspx"},"modified":"2010-01-22T03:48:34","modified_gmt":"2010-01-22T02:48:34","slug":"evolucion-de-la-biodiversidad-a-lo-largo-de-la-historia-de-la-tierra","status":"publish","type":"post","link":"https:\/\/www.madrimasd.org\/blogs\/universo\/2008\/08\/07\/98270","title":{"rendered":"Evoluci\u00f3n de la Biodiversidad a lo largo de la Historia de la Tierra"},"content":{"rendered":"

Se ha venido dando por cierto que la biodiversidad ha incrementado desde el origen de La Tierra. En principio, el patr\u00f3n m\u00e1s aceptado por los cient\u00edficos fue denominado<\/SPAN><\/B> Curva de Sepkoski <\/FONT><\/A>El ya fallecido <\/SPAN>J. John Sepkoski, fue Catedr\u00e1tico de Paleontolog\u00eda de la Universidad de Chicago, y recopil\u00f3 los datos que dieron nombre al patr\u00f3n que detect\u00f3. Abajo os mostramos su famosa curva. Sin embargo, como podr\u00e9is observar, recientes investigaciones<\/SPAN><\/B> publicadas en la revista Science<\/SPAN><\/B> y recogidas en dos notas de prensa por Terra Daily en este<\/FONT><\/A> y tambi\u00e9n en este<\/FONT><\/A> enlace ofrecen un cuadro totalmente distinto<\/SPAN><\/B>. Abajo incluimos las dos.  <\/SPAN>Al menos desde hace cientos de millones de a\u00f1os, no parece haber existido incremento de biodiversidad alguno en la faz del planeta<\/SPAN><\/B>, como m\u00ednimo en los oc\u00e9anos. <\/o:p><\/SPAN><\/P>

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Diversidad de los fondos oce\u00e1nicos durante el cret\u00e1cico<\/o:p><\/FONT><\/A><\/SPAN><\/P>Fuente: Sciencedaily<\/FONT><\/A><\/SPAN><\/SPAN>

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No se trata de un descubrimiento intrascendente, ni mucho menos. De ser corroborado nos indicar\u00eda que la capacidad de carga de especies de invertebrados en los oc\u00e9anos de La Tierra parece haberse saturado, o al menos estabilizado, desde antes de finales del Cret\u00e1cico<\/B>.<\/SPAN> Hasta la fecha se supon\u00eda que la variedad de organismos que yacen en la tierra creci\u00f3 lentamente al principio, para adoptar luego un crecimiento exponencial<\/SPAN><\/B>. Por el contrario, los nuevos resultados corroboran los previamente compilados por Spekoski en lo que concierne a que los tr\u00f3picos han sido m\u00e1s ricos en especies de invertebrados marinas desde hace 450 millones de a\u00f1os que las latitudes elevadas<\/SPAN><\/B>.  <\/SPAN>Resumiendo, de haber existido un incremento de diversidad a lo largo del Fanerozoico, este ha sido poco significativo<\/SPAN><\/B>. <\/o:p><\/SPAN><\/P>

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Curva de Sepkoski Fuente Bulletin of American Paleonlology<\/FONT><\/SPAN><\/A><\/SPAN><\/o:p><\/SPAN><\/P>

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Tal hecho no significa que la biodiversidad global no se alterara<\/SPAN><\/B>. Muy por el contrario, la nueva curva detecta m\u00e1s bien una curva ondulante alrededor de un valor medio, con \u00e9pocas de p\u00e9rdidas y ganancias<\/SPAN><\/B>. Nadie duda de que se dieran extinciones masivas seguidas por s\u00fabitos incrementos del n\u00famero de especies (radiaciones)<\/SPAN><\/B>. Todav\u00eda se desconoce si los or\u00edgenes de tales cambios fueron causados por<\/SPAN><\/B> eventos catastr\u00f3ficos (impactos de grandes meteoritos, gigantescas erupciones volc\u00e1nicas, fragmentaci\u00f3n y fusi\u00f3n de los continentes) y\/o cambios clim\u00e1ticos de gran magnitud y\/o por la propia din\u00e1mica interna de la biosfera, como sistema complejo. Eso si, los ensamblajes locales en las comunidades locales se asemejan mucho  <\/SPAN>a lo largo de los \u00faltimos cientos de millones de a\u00f1os<\/SPAN><\/B>. \u00bfOcurri\u00f3 lo mismo en las masas de tierra emergidas?. No lo sabemos a \u201cciencia cierta\u201d.<\/o:p><\/SPAN><\/P>

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Extinciones causadas por cat\u00e1strofes naturales<\/o:p><\/FONT><\/A><\/SPAN><\/P>

Fuente Nacional Science Fundation<\/FONT><\/A><\/SPAN><\/SPAN><\/o:p><\/SPAN><\/P>

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El nuevo estudio parte de mejores bases de datos<\/SPAN><\/B>, potencia computacional, colaboraci\u00f3n de numerosos investigadores de varios pa\u00edses etc. Empero el punto clave son los inventarios m\u00e1s completos<\/SPAN><\/B>. De nuevo vuelve a la palestra la necesidad de inventariar adecuadamente los recursos naturales, una actividad denostada<\/SPAN><\/B>, que se traduce en escaso n\u00famero de publicaciones y el descr\u00e9dito ante sus colegas de cient\u00edficos que se han afanado durante a\u00f1os, casi en silencio, en recopilar evidencias. Como ya argumentamos en otro post, la crisis de la taxonom\u00eda ha generado que<\/FONT><\/A> la masa cr\u00edtica de tax\u00f3nomos y paleont\u00f3logos s\u00ed decreciera exponencialmente<\/SPAN><\/B> (en el sentido amplio del t\u00e9rmino). Tal hecho no se encuentra justificado por criterios l\u00f3gicos<\/SPAN><\/B>. De seguir as\u00ed, a medio plazo pocos descubrimientos m\u00e1s de esta guisa podr\u00e1n salir a la palestra. Nos topamos de nuevo con la irrazonable racionalidad de la ciencia<\/SPAN><\/B>. M\u00e1s valen 100 papers insustanciales que un buen trabajo de investigaci\u00f3n. \u00a1Falso!<\/SPAN><\/B>.     <\/SPAN> <\/SPAN>  <\/SPAN> <\/SPAN> <\/SPAN><\/SPAN><\/o:p><\/SPAN><\/P>

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Huella de un Dinosaurio Jur\u00e1sico<\/FONT><\/A><\/o:p><\/SPAN><\/P>

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Species Have Come And Gone At Different Rates Than Previously Believed<\/FONT><\/A><\/o:p><\/SPAN><\/P>

by Staff Writers; <\/SPAN>Santa Barbara<\/SPAN><\/st1:City> <\/SPAN>CA<\/SPAN><\/st1:State><\/st1:place> (SPX) <\/SPAN>Jul 09, 2008<\/SPAN><\/st1:date><\/o:p><\/SPAN><\/P>


<\/SPAN>Diversity among the ancestors of such marine creatures as clams<\/SPAN><\/B>, sand dollars and lobsters showed only a modest rise beginning 144 million years ago with no clear trend afterwards<\/SPAN><\/B>, according to an international team of researchers.  <\/SPAN>This contradicts previous work showing dramatic increases beginning 248 million years ago and may shed light on future diversity<\/SPAN><\/B>. \u00abSome of the time periods in the past are analogies for what is happening today from global warming,\u00bb says Jocelyn Sessa of <\/SPAN>Penn<\/SPAN><\/SPAN><\/B><\/st1:PlaceName> <\/SPAN><\/B>State<\/SPAN><\/B><\/st1:PlaceType><\/st1:place>. \u00abUnderstanding what happened with diversity in the past can help us provide some prediction on how modern organisms will fare. If we know where we have been, we know something about where it will go.\u00bb <\/o:p><\/SPAN><\/P>

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J. John Sepkoski<\/SPAN><\/o:p><\/SPAN><\/P>

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Using contemporary statistical methods and a paleobiology database, the researchers report in the July 4 issue of Science<\/SPAN><\/B>, a new diversity curve that shows that most of the early spread of invertebrates took place well before the Late Cretaceous<\/SPAN><\/B>, and that the net increase through the period since, is proportionately small relative to the 65 million years that elapsed<\/SPAN><\/B>. The research team was led by John Alroy of the <\/SPAN>University<\/SPAN><\/st1:PlaceType> of <\/SPAN>California<\/SPAN><\/st1:PlaceName><\/st1:place> at <\/SPAN>Santa Barbara<\/SPAN><\/st1:place><\/st1:City>. <\/o:p><\/SPAN><\/P>

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One key to the new curve is the Paleobiology Database, housed at the <\/SPAN><\/B><\/SPAN>National<\/SPAN><\/B><\/st1:PlaceName> <\/SPAN><\/B>Center<\/SPAN><\/B><\/st1:PlaceType><\/st1:place> for Ecological Analysis and Synthesis, <\/SPAN><\/B>University<\/SPAN><\/B><\/st1:PlaceType> of <\/SPAN><\/B>California<\/SPAN><\/B><\/st1:PlaceName><\/st1:place>, <\/SPAN><\/B>Santa Barbara<\/SPAN><\/B><\/st1:place><\/st1:City>. Previous research was based on databases of marine invertebrate fossils that recorded only the first occurrence of an organism and the last occurrence of the organism. There was no information in between for the organism. \u00abOver 30 years ago, researchers looked at the curve they had and considered that perhaps diversity did not increase at all<\/SPAN><\/B>,\u00bb says Mark E. Patzkowsky of <\/SPAN>Penn<\/SPAN><\/st1:PlaceName> <\/SPAN>State<\/SPAN><\/st1:PlaceType><\/st1:place>. \u00abWhat researchers saw was the diversity curve leveled off for quite some time and then took off exponentially<\/SPAN>. However, diversity results are strongly controlled by sampling techniques<\/SPAN><\/B>.\u00bb <\/o:p><\/SPAN><\/P>

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The new database allows researchers to standardize sample size because<\/SPAN><\/B> it includes multiple occurrences of each fossil. Researchers can randomly choose equal samples from equal time spans to create their diversity curve. This new curve uses 11 million-year segments, but the researchers hope to reduce the time intervals to 5 million years to match the interval of the previous <\/SPAN>curve, known as Sepkoski<\/SPAN><\/B>. The data for this study contains 284,816 fossil occurrences of 18,702 genera that equals about 3.4 million specimens from 5384 literature sources. The old curve, developed by J. John Sepkoski Jr., used<\/SPAN><\/B> a database that contained only about 60,000 occurrences. <\/o:p><\/SPAN><\/P>

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The researchers also looked<\/SPAN><\/B> at evenness in diversity<\/SPAN><\/B>. If there are 100 specimens divided into 10 time intervals, they could be divided with 10 individual specimens in each interval, or 91 specimens could be in one interval with one each in the remainder. The more even the distribution, the higher the evenness<\/SPAN><\/B>.<\/o:p><\/SPAN><\/P>

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\u00abEvenness says something about resource distribution,\u00bb says Patzkowsky. \u00abMuch of invertebrate diversity has been attributed to diversity increase in the tropics, but the curve is not driven by that totally. It seems that 450 million years ago was not so different from today because it also contained more diversity in the tropics<\/SPAN><\/B>. \u00abThe major points of the<\/SPAN><\/B> Sepkoski curve<\/SPAN> are still seen in the new curve. Some things that are not seen, such as the decrease in diversity due to the Cretaceous Tertiary (KT) extinction 65 million years ago are not visible because of<\/SPAN><\/B> the scale of the intervals used. The extinction and recovery in the KT took less than 11 million years and so do not show. <\/o:p><\/SPAN><\/P>

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Some things not seen on the Sepkoski curve include a peak in the Permian. <\/SPAN><\/B>Also unexpected is that the diversity in the Jurassic<\/SPAN><\/B> (206 to 144 million years ago) is lower than diversity in the Triassic <\/SPAN><\/B>(248 to 206 million years ago), indicating a dip and rise in the diversity curve.  <\/SPAN>The curve then rises in the Cretaceous and remains more or less flat after that<\/SPAN><\/B>. The previously thought exponential increase in diversity is not there<\/SPAN><\/B>. <\/o:p><\/SPAN><\/P>

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\u00abComparing diversity through time is about how our world works, about the origin of species and how diversity changes with temperature,\u00bb says Sessa. \u00abIf we think that the net increase over time will not get much greater, things are very different from if the diversity increases exponentially<\/SPAN><\/B>.\u00bb <\/o:p><\/SPAN><\/P>

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Species Diversity Less Dramatic Than Believed<\/FONT><\/A><\/o:p><\/SPAN><\/P>

by Misha Kidambi;<\/SPAN>College Station<\/SPAN><\/st1:City> <\/SPAN>TX<\/SPAN><\/st1:State><\/st1:place> (SPX) <\/SPAN>Jul 10, 2008<\/SPAN><\/st1:date>

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The analysis helped the researchers conclude that the increase in species diversity through the Phanerozoic Era was much less dramatic than previously believed<\/SPAN><\/B>.<\/o:p><\/SPAN><\/P>

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A study published in the current issue of Science challenges the long-held belief that diversity of marine species has been increasing continuously since the origin of animals. Dr. Thomas D. Olszewski<\/SPAN><\/B>, a geology and geophysics professor at Texas A and M University<\/SPAN><\/B>, has been a part of the international team that carried out this decade-long study, which concludes that most of the diversification occurred early on<\/SPAN><\/B> – relatively speaking. <\/o:p><\/SPAN><\/P>

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\u00abThe general understanding for many decades has been that since the rise of the modern major groups of animals about 545 million years ago (i.e., since the beginning of the Phanerozoic Era), the diversity of animal life in the seas has undergone a roughly four-fold exponential increase<\/SPAN><\/B>,\u00bb says Olszewski. A steep increase in the diversity was believed to have occurred only between 145 million and 60 million years ago. But many paleontologists were doubtful about the accuracy of this theory<\/SPAN><\/B>, which was derived using older methods.<\/o:p><\/SPAN><\/P>

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Olszewski explains that the older methods did not account for many important occurrences in the history of the Earth, including changes in the geography of Earth due to continental drift and variations in the state of global climate<\/SPAN><\/B>. Collaborative efforts of 35 researchers from the <\/SPAN>U.S.<\/SPAN><\/st1:place><\/st1:country-region>, <\/SPAN>Germany<\/SPAN><\/st1:place><\/st1:country-region>, the <\/SPAN>UK<\/SPAN><\/st1:place><\/st1:country-region>, <\/SPAN>France<\/SPAN><\/st1:place><\/st1:country-region> and <\/SPAN>Slovakia<\/SPAN><\/st1:place><\/st1:country-region> resulted in a more accurate interpretation of the prehistoric data. Olszewski says that the researchers used a \u00abfundamentally new analysis, which differs in several important aspects from the previous [methods used for] <\/SPAN><\/B>understanding of the history of marine diversity.\u00bb<\/o:p><\/SPAN><\/P>

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The analysis helped the researchers conclude that the increase in species diversity<\/SPAN><\/B> through the Phanerozoic Era was much less dramatic than previously believed<\/SPAN><\/B>. \u00abDiversity levels comparable to the present day appear to have been reached after a few tens of millions of years following the first appearance of modern animal groups<\/SPAN><\/B>,\u00bb says Olszewski. The new fossil data also indicate that the current pattern of distribution of life – with low species diversity in the poles and a very high diversity in the tropics – was established some 450 million years ago<\/SPAN><\/B>. With the huge amount of data that was used for the analysis<\/SPAN><\/B>, (fossil occurrences representing nearly 3.5 million specimens) it also became possible to assess the diversity changes in local ecological communities as well as in that of the global total. <\/o:p><\/SPAN><\/P>

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Again, the researchers concluded that local ecological communities have changed relatively little since the establishment of marine animal ecosystems during the Phanerozoic Era<\/SPAN><\/B>. So what bearing do the study conclusions have on the life on Earth today? Maybe a great deal, Olszewski says. \u00abAs global climatic conditions change, either naturally or anthropogenically, (animal) life responds, which in turn can influence human life,\u00bb says Olszewski. \u00abUnderstanding what life was like under different conditions can help us assess and prepare for the consequences of this ongoing change,\u00bb he adds. <\/o:p><\/SPAN><\/P>

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 <\/o:p><\/SPAN>Juan Jos\u00e9 Ib\u00e1\u00f1ez<\/o:p><\/SPAN><\/P><\/p>\n","protected":false},"excerpt":{"rendered":"

Se ha venido dando por cierto que la biodiversidad ha incrementado desde el origen de La Tierra. En principio, el patr\u00f3n m\u00e1s aceptado por los cient\u00edficos fue denominado Curva de Sepkoski El ya fallecido J. John Sepkoski, fue Catedr\u00e1tico de Paleontolog\u00eda de la Universidad de Chicago, y recopil\u00f3 los datos que dieron nombre al patr\u00f3n que detect\u00f3. Abajo os mostramos su famosa curva. Sin embargo, como podr\u00e9is observar, recientes investigaciones publicadas en la revista Science y recogidas en dos notas de prensa por Terra Daily en este y tambi\u00e9n en este enlace ofrecen un cuadro totalmente distinto. Abajo incluimos las\u2026<\/p>\n","protected":false},"author":26,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"ngg_post_thumbnail":0},"categories":[586,607,615,601],"tags":[],"blocksy_meta":{"styles_descriptor":{"styles":{"desktop":"","tablet":"","mobile":""},"google_fonts":[],"version":4}},"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.madrimasd.org\/blogs\/universo\/wp-json\/wp\/v2\/posts\/98270"}],"collection":[{"href":"https:\/\/www.madrimasd.org\/blogs\/universo\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.madrimasd.org\/blogs\/universo\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.madrimasd.org\/blogs\/universo\/wp-json\/wp\/v2\/users\/26"}],"replies":[{"embeddable":true,"href":"https:\/\/www.madrimasd.org\/blogs\/universo\/wp-json\/wp\/v2\/comments?post=98270"}],"version-history":[{"count":2,"href":"https:\/\/www.madrimasd.org\/blogs\/universo\/wp-json\/wp\/v2\/posts\/98270\/revisions"}],"predecessor-version":[{"id":134719,"href":"https:\/\/www.madrimasd.org\/blogs\/universo\/wp-json\/wp\/v2\/posts\/98270\/revisions\/134719"}],"wp:attachment":[{"href":"https:\/\/www.madrimasd.org\/blogs\/universo\/wp-json\/wp\/v2\/media?parent=98270"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.madrimasd.org\/blogs\/universo\/wp-json\/wp\/v2\/categories?post=98270"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.madrimasd.org\/blogs\/universo\/wp-json\/wp\/v2\/tags?post=98270"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}