{"id":136572,"date":"2010-09-21T13:59:19","date_gmt":"2010-09-21T12:59:19","guid":{"rendered":"http:\/\/www.madrimasd.org\/blogs\/universo\/?p=136572"},"modified":"2010-09-21T16:42:17","modified_gmt":"2010-09-21T15:42:17","slug":"el-secreto-de-la-biodiversidad-de-los-bosques-tropicales-la-ecologia-del-suelo","status":"publish","type":"post","link":"https:\/\/www.madrimasd.org\/blogs\/universo\/2010\/09\/21\/136572","title":{"rendered":"El Secreto de la Biodiversidad de los Bosques Tropicales: La Ecolog\u00eda del Suelo"},"content":{"rendered":"

Dos art\u00edculos aparecidos casi simult\u00e1neamente en las Revistas Science y Nature apuntan a que el secreto de la gran biodiversidad de especies arb\u00f3reas tropicales se encuentra escondido en la ecolog\u00eda del suelo<\/span><\/strong>. Y seguir\u00e1n descubriendo m\u00e1s cuando estudien el medio ed\u00e1fico con la atenci\u00f3n que merece. Ambos estudios van m\u00e1s all\u00e1, postulando que la abundancia relativa de las especies tambi\u00e9n obedece a los mismos mecanismos ed\u00e1ficos<\/strong><\/span>. Ser\u00edan pues las comunidades del suelo las que determinan el paisaje a\u00e9reo<\/span><\/strong>.\u00a0Ya vimos en otros post<\/a> como la acci\u00f3n de los ingenieros ed\u00e1ficos (termitas, hormigas, etc.) del suelo da cuenta tambi\u00e9n de su fertilidad. El objetivo planteado en ambos estudios intentaba corroborar o refutar la denominada hip\u00f3tesis de<\/span><\/strong> Janzen-Connell<\/span><\/strong>.<\/p>\n

\u00a0\"bosque-tropical-fuente-argentina-salta\"<\/p>\n

Bosque Tropical. Fuente: Argentina-Salta<\/a><\/p>\n

\u00a0<\/p>\n

\u00bfPor qu\u00e9 en los bosques tropicales cohabitan tantas especies?<\/span><\/strong> \u00bfPorqu\u00e9 la competencia no ha dado lugar a que las \u201cm\u00e1s adaptadas\u201d terminen por reemplazar al resto? Este resulta ser el meollo de la cuesti\u00f3n. Pues bien, las dos publicaciones aludidas dicen haber mostrado que la causa reside en la acci\u00f3n de las comunidades ed\u00e1ficas de estos ecosistemas, y no en la de otras<\/span> epigeas<\/span><\/strong>, es decir que habitan sobre el suelo.<\/p>\n

\u00a0Se sabe desde hace tiempo, que en muchas especies tropicales las semillas y pl\u00e1ntulas crecen mal bajo las canopias de sus progenitores, teniendo m\u00e1s posibilidades de supervivencia si germinan bajo otras especies<\/span><\/strong>. De este modo, <\/span>los tipos de<\/span> \u00e1rboles distintos tienden a entremezclarse<\/span><\/strong> unos entre otros en lugar de api\u00f1arse (distribuci\u00f3n de contagio). Obviamente no todas las especies arb\u00f3reas siguen se comportan igual forma<\/span><\/strong>. De acuerdo a estas \u00faltimas investigaciones, el papel inhibidor de los suelos bajo tipos \u00e1rboles m\u00e1s numerosos es menor que el de los menos abundantes, explic\u00e1ndose as\u00ed la abundancia relativa de los ensamblajes en los ecosistemas tropicales<\/span><\/strong>. Por tanto, <\/span>en los taxones m\u00e1s raros y menos abundantes, la posibilidad de germinaci\u00f3n de una semilla aumenta conforme se dispersa a una mayor distancia<\/span> <\/strong>de su punto de procedencia.<\/p>\n

\u00a0Los investigadores implicados en este estudio se\u00f1alan que los suelos bajo una especie arb\u00f3rea determinada \u201cdeben atesorar m\u00e1s par\u00e1sitos, pat\u00f3genos, antagonistas, etc. de ese tax\u00f3n en cuesti\u00f3n\u201d que de otros, por lo que las semillas tienen mayores posibilidades de prosperar si se desarrollan en suelos bajo el cobijo de otros<\/span><\/strong> \u201cpadres adoptivos\u201d.<\/p>\n

\u00a0\"bosque-tropical-fuente-lyrfutures08s-weblog\"<\/p>\n

Bosque tropical. Fuente: Blog Lyrfutures08\u2032s Weblog<\/a><\/p>\n

Pues bien, personalmente no lo dudo. Ahora bien, se trata de una explicaci\u00f3n fenomenol\u00f3gica muy ambigua<\/span><\/strong>, por cuanto no nos<\/span> informa de cual es el mecanismo exacto, sino de que \u201cparece encontrarse en el suelo\u201d<\/span><\/strong>.<\/span> Todo lo dem\u00e1s son conjeturas que permanecer\u00e1n a la espera de ser corroboradas, siendo posible tambi\u00e9n otras argumentaciones distintas pudieran dar cuenta de los patrones detectados. En cierto sentido, este asunto me recuerda al enigma de los \u201csuelos supresivos<\/a>\u201d del que ya hablamos en un antiguo post. Sin embargo, en el caso que hoy nos ocupa, habr\u00eda un tipo de \u201crespuesta inmune ecosist\u00e9mica\u201d que dar\u00eda cuenta de la estructura arb\u00f3rea del bosque<\/span><\/strong>.<\/p>\n

\u00a0En las notas de prensa que abajo os mostramos, los autores defienden que las especies raras y poco abundantes lo son en funci\u00f3n de este proceso<\/strong>.<\/span> Y aqu\u00ed albergo serias dudas<\/strong><\/span>. Cierto es que la diversidad de especies en los ecosistemas forestales en los tr\u00f3picos h\u00famedos es extraordinaria. Ahora bien, la distribuci\u00f3n de abundancia, sigue los mismos patrones que en la mayor parte de los ecosistemas<\/span><\/strong> de cualquier \u00edndole, es decir la denominada ley o curva de Willis<\/a>. En consecuencia, resulta un tanto especulativo adscribir tales patrones de abundancia al mecanismo que defienden, a no ser que se demostrara que tambi\u00e9n se da comunidades (y no solo terrestres, sino de todo tipo, como las acu\u00e1ticas e incluso las del microbioma humano). No existen tales evidencias<\/span><\/strong>.<\/p>\n

\u00a0En cualquier caso, corroborarse los resultados de ambos estudios, se demostrar\u00eda que cada suelo, bajo una especie vegetal determinada, atesora \u201cde alguna forma\u201d informaci\u00f3n sobre la misma, como una espacie de huella digital que condiciona su estructura y din\u00e1mica<\/span><\/strong>.<\/p>\n

\u00a0Por \u00faltimo, los autores defienden que sus resultados refutan la denominada<\/span><\/strong> Teor\u00eda Neutral de la Biodiversidad<\/a>. No entrar\u00e9 en tales disquisiciones, por cuanto soy de la opini\u00f3n de que en la naturaza no hay nada neutral (se me antoja un vocablo excesivamente antropoc\u00e9ntrico como para aplicarlo a los procesos naturales). Abajo os dejo las noticias as\u00ed como informaci\u00f3n adicional sobre el tema en espa\u00f1ol-castellano. \u00a0<\/p>\n

\u00a0Juan Jos\u00e9 Ib\u00e1\u00f1ez\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0<\/span>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/strong><\/p>\n

\u00a0De acuerdo a \u00a0Pedro Jordano, mi amigo Patricio Garc\u00eda Fayos y otros<\/a>:<\/p>\n

\u00a0Hip\u00f3tesis de Janzen-Connell postula que<\/strong> <\/span>el principal beneficio de la dispersi\u00f3n de semillas es el alejamiento de estas de la planta madre, escapando de la alta mortalidad denso-dependiente debida a pat\u00f3genos, depredadores de semillas y\/o herbivor\u00eda que tiene lugar bajo la copa materna. Predice que el punto de mayor probabilidad de reclutamiento se produce a cierta distancia de la planta materna, donde se maximiza conjuntamente la probabilidad de llegada de la semilla y la probabilidad de supervivencia a depredadores tras la dispersi\u00f3n.<\/p>\n

\u00a0En este art\u00edculo publicado en la revista \u201cEcosistemas<\/a> se describe tambi\u00e9n la mencionada \u201chip\u00f3tesis de Janzen-Connell\u201d.<\/strong> Reproducimos un par vde p\u00e1rrafos:<\/p>\n

\u00a0Los hongos fit\u00f3fagos<\/strong> pueden tener marcados efectos en la germinaci\u00f3n de semillas y el establecimiento de pl\u00e1ntulas (Gilbert 2002; Packer y Clay 2003). La inoculaci\u00f3n experimental de pl\u00e1ntulas con el ascomiceto pat\u00f3geno Botryosphaeria dothidea triplic\u00f3 su tasa de mortalida<\/strong>d (Gilbert y De Steven 1996). No todos los hongos son pat\u00f3genos, pues muchos hongos endo- y ectomicorr\u00edzicos son simbiontes (Allen et al. 2003). La inoculaci\u00f3n de endomicorrizas puede elevar las tasas de crecimiento y la tolerancia a la sequ\u00eda <\/strong>(Bereau et al. 2000; Vijaya y Srivasuki 2001). El impacto de los hongos en las pl\u00e1ntulas puede ser complicado e importante<\/strong>, y requiere m\u00e1s estudios.<\/p>\n

\u00a0Muchos enemigos naturales tienen un hospedador espec\u00edfico a nivel de especie, g\u00e9nero o familia<\/strong> (Coley y Barone 1996; Novotny et al. 2002), y con frecuencia la intensidad de su ataque disminuye con la distancia a los adultos conespec\u00edficos<\/strong> (e.g., Blundell y Peart 1998). Estas observaciones, junto con la dispersi\u00f3n de semillas restringida por la distancia, forman la esencia de la hip\u00f3tesis de Janzen-Connell del mantenimiento de la diversidad de especies en bosques tropicales<\/strong> (Janzen 1970, Connell 1971). Las pruebas de esta hip\u00f3tesis, que predice que las pl\u00e1ntulas reclutan con mejor \u00e9xito separadas por una cierta distancia de lo<\/strong>s adultos relacionados, manteniendo as\u00ed una alta diversidad, han tenido resultados mixtos, pero en conjunto apoyan esta idea <\/strong>(Hammond y Brown 1998). El modelo de Janzen-Connell es un caso especial en que la mortalidad depende de la densidad, lo cual ocurre en muchos bosques<\/strong> (Condit et al. 1994; Webb y Peart 1999; Harms et al. 2000). La mortalidad dependiente de la densidad puede evitar que las especies comunes ocupen todo el espacio disponible, y por consiguiente puede ser importante en el mantenimiento de la diversidad en bosques tropicales<\/strong>.<\/p>\n

\u00a0<\/p>\n

Biodiversity’s Holy Grail Is In The Soil<\/a><\/h2>\n

\u00a0Scott Mangan, post doctoral fellow from the University of Wisconsin-Milwaukee, discovered that underground organisms are key to the maintenance of species diversity and patterns of tree-species relative abundance<\/strong>.<\/em><\/p>\n

\u00a0Terradaily<\/strong><\/span>; by Staff Writers; Ancon, Panama (SPX) Jun 30, 2010<\/p>\n

\u00a0Why are tropical forests so biologically rich?<\/strong> Smithsonian researchers have new evidence that the answer to one of life’s great unsolved mysteries lies underground<\/strong>, according to a study published in the journal, Nature.<\/p>\n

\u00a0\u00abWe’ve known for a long time that tree seedlings do not grow and survive well under their mothers or other adult trees of the same species<\/strong>,\u00bb said Scott Mangan, postdoctoral fellow at the University of Wisconsin-Milwaukee and the Smithsonian Tropical Research Institute in Panama.<\/p>\n

\u00a0\u00abOne explanation for the maintenance of the diversity of tropical trees is that adult trees harbor pests and diseases that harm seedlings of their own species more than they do seedlings of other species<\/strong>.\u00bb<\/p>\n

\u00a0The experiments show that underground organisms are key to the maintenance of species diversity and patterns of tree-species relative abundance<\/strong>. The detrimental effects of soil organisms from adult trees not only explain seedling growth and survival patterns, but moreover that these effects are much more severe for seedlings of rare species than for seedlings of common species<\/strong>.<\/p>\n

\u00a0Mangan planted seedlings of five species under adults of each species in the forest and coupled that experiment with a greenhouse experiment in which he grew seedlings of each species in soil collected around the base of each of the other species<\/strong>.<\/p>\n

\u00a0Consistent across experiments, Mangan and colleagues found that the ability of seedlings of a species to survive when grown in soil from the same species actually predicted how common or rare they are as adults<\/strong>.<\/p>\n

\u00a0Their result closely mirrors results presented in Science magazine this week<\/strong> by Liza Comita and colleagues, based on a survey of survival of 30,000 tree seedlings-part of a major effort to understand forest dynamics worldwide sponsored, in part, by the HSBC Climate Partnership.<\/p>\n

\u00a0\u00abIt’s been more than 30 years since the idea that negative interactions between adults and seedlings of the same species may be driving diversity-the Janzen-Connell Hypothesis<\/strong>-was first proposed, and only now is this story really coming together,\u00bb said co-author Allen Herre, staff scientist at STRI.<\/p>\n

\u00a0\u00abTwo completely different approaches-analysis of long-term forest dynamics observations and direct experiments on Panama’s Barro Colorado Island-are telling us to look for the answer under the ground<\/strong>. Scott’s experiments provide a direct comparison across species of how much their seedlings suffer from a sort of ‘self inhibition’ mediated by these soil organisms<\/strong>.\u00bb<\/p>\n

\u00a0Biologists refer to soil as a \u00abblack box\u00bb because<\/strong> it is notoriously difficult to study a tangle of roots, bacteria, fungi, tiny insects and other creatures without isolating or changing them<\/strong>.<\/p>\n

\u00a0Very similar results in the greenhouse and in the field reveal that plant interactions with soil biota alone-not nutrients<\/strong>, insects, mammals or above-ground diseases-are sufficiently powerful and specific to explain why multiple species co-exist and importantly the strength of those interactions can be measured and plant species that are most abundant are least influenced by the soil biota around their parents<\/strong>.<\/p>\n

\u00a0\u00abWe have dealt yet another blow to the ailing Neutral Theory of Biodiversity<\/strong>, which is premised on the idea that all species are the same,\u00bb said Herre. \u00abThese two publications provide strong evidence that there are stabilizing mechanisms that maintain diversity, and thus that neutral dynamics do not explain plant species diversity and abundance<\/strong>.\u00bb<\/p>\n

Soil-Borne Pathogens Drive Tree Diversity In Forests<\/a><\/h2>\n

\u00a0The research reinforces the conclusion that certain tree species are abundant in forests because they are less susceptible to pathogens in the soil than rarer tree species<\/strong>, says Mangan. <\/em>\u00abStrong negative feedbacks with soil-borne pathogens prevent rare tree species from becoming abundant.<\/strong>\u00ab<\/em><\/p>\n

Terradaily<\/span>;<\/strong> by Staff Writers; Milwaukee WI (SPX) Jun 30, 2010<\/p>\n

What determines plant diversity in a forest? It’s a question even Charles Darwin wanted to unravel. But most research into forest diversity demonstrates only patterns of species survival and abundance rather than the reason for them – until now.<\/p>\n

\u00a0A team of researchers led by biologists at the University of Wisconsin-Milwaukee (UWM) has shown that soil-borne pathogens are one important mechanism that can maintain species diversity and explain patterns of tree abundance in a forest<\/strong>.<\/p>\n

\u00a0The paper, \u00abNegative plant-soil feedbacks predict tree-species relative abundance in a tropical forest<\/strong>,\u00bb is published in the journal Nature<\/strong>. The lead authors are Scott Mangan, a UWM postdoctoral research associate, and Stefan Schnitzer, UWM associate professor of biological sciences. Other authors include Edward A. Herre and Evelyn I. Sanchez of the Smithsonian Tropical Research Institute, Keenan M.L. Mack and James D. Bever of Indiana University, and Mariana C. Valencia of the University of Illinois-Chicago.<\/p>\n

\u00a0In a self-limiting process called \u00abnegative feedback<\/strong>,\u00bb scientists have observed that the farther from the parent tree a seed falls, the better it fares. Negative feedbacks occur when<\/strong> juveniles growing near an adult of the same species are particularly vulnerable to the detrimental effects of enemies that accumulate in the soil near the adult tree.<\/p>\n

\u00a0In both greenhouse and field experiments, the researchers found clues that tree species differ in their susceptibilities to enemies found in the soil, such as viruses, bacteria and fungi<\/strong>.<\/p>\n

\u00a0The research reinforces the conclusion that certain tree species are abundant in forests because they are less susceptible to pathogens in the soil than rarer tree species<\/strong>, says Mangan. \u00abStrong negative feedbacks with soil-borne pathogens prevent rare tree species from becoming abundan<\/strong>t.\u00bb<\/p>\n

\u00a0The study has shown that more abundant tree species exhibit the weakest negative feedbacks – the opposite of what the team expected<\/strong>, says Schnitzer. And when the team scaled up the empirical data using simulation models they<\/strong> created, they found the same relationship between negative feedbacks and abundance<\/strong>.<\/p>\n

\u00a0The next step for the research team is to isolate the exact pathogens that are so powerful against each species. Using a genomics approach, they will examine how soil varies in the plant populations<\/strong>.<\/p>\n

\u00a0Schnitzer emphasizes that the work describes what could be one of many mechanisms that determine species abundance in forests. <\/strong>\u00abWe don’t claim that because we found evidence of one mechanism, that there aren’t others that also could be at work, but we know that this one is probably very important<\/strong>.\u00bb<\/p>\n

\u00a0\u00a0Resumen del art\u00edculo de la Revista Nature<\/span><\/strong><\/p>\n

\u00a0<\/strong>Negative plant\u2013soil feedback predicts tree-species relative abundance in a tropical forest<\/a><\/p>\n

\u00a0Scott A. Mangan et al. Correspondence to: Scott A. Mangan1<\/a>,2<\/a> Email:\u00a0smangan37@gmail.com<\/a><\/p>\n

\u00a0The accumulation of species-specific enemies around adults is hypothesized to maintain plant diversity by limiting the recruitment of conspecific seedlings relative to heterospecific seedlings<\/strong>1, <\/a>2, <\/a>3, <\/a>4, <\/a>5, <\/a>6<\/a>. Although previous studies in forested ecosystems have documented patterns consistent with the process of negative feedback<\/strong>7, <\/a>8, <\/a>9, <\/a>10, <\/a>11, <\/a>12, <\/a>13, <\/a>14, <\/a>15, <\/a>16<\/a>, these studies are unable to address which classes of enemies<\/strong> (for example, pathogens, invertebrates, mammals) exhibit species-specific effects strong enough to generate negative feedback<\/strong>17<\/a>, and whether negative feedback at the level of the individual tree is sufficient to influence community-wide forest composition. Here we use fully reciprocal shade-house and field experiments to test whether the performance of conspecific tree seedlings (relative to heterospecific seedlings) is reduced when grown in the presence of enemies associated with adult trees. Both experiments provide strong evidence for negative plant\u2013soil feedback mediated by soil biota<\/strong>. In contrast, above-ground enemies<\/strong> (mammals, foliar herbivores and foliar pathogens) contributed little to negative feedback observed in the field<\/strong>. In both experiments, we found that tree species that showed stronger negative feedback were less common as adults in the forest community<\/strong>, indicating that susceptibility to soil biota may determine species relative abundance in these tropical forests<\/strong>. Finally, our simulation models confirm that the strength of local negative feedback that we measured is sufficient to produce the observed community-wide patterns in tree-species relative abundance. Our findings indicate that plant\u2013soil feedback is an important mechanism that can maintain species diversity and explain patterns of tree-species relative abundance in tropical forests<\/strong>.<\/p>\n","protected":false},"excerpt":{"rendered":"

Dos art\u00edculos aparecidos casi simult\u00e1neamente en las Revistas Science y Nature apuntan a que el secreto de la gran biodiversidad de especies arb\u00f3reas tropicales se encuentra escondido en la ecolog\u00eda del suelo. Y seguir\u00e1n descubriendo m\u00e1s cuando estudien el medio ed\u00e1fico con la atenci\u00f3n que merece. Ambos estudios van m\u00e1s all\u00e1, postulando que la abundancia relativa de las especies tambi\u00e9n obedece a los mismos mecanismos ed\u00e1ficos. Ser\u00edan pues las comunidades del suelo las que determinan el paisaje a\u00e9reo.\u00a0Ya vimos en otros post como la acci\u00f3n de los ingenieros ed\u00e1ficos (termitas, hormigas, etc.) del suelo da cuenta tambi\u00e9n de su fertilidad.\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":[596,603,586,618,600],"tags":[46726,1992,46833,1993],"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\/136572"}],"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=136572"}],"version-history":[{"count":11,"href":"https:\/\/www.madrimasd.org\/blogs\/universo\/wp-json\/wp\/v2\/posts\/136572\/revisions"}],"predecessor-version":[{"id":137201,"href":"https:\/\/www.madrimasd.org\/blogs\/universo\/wp-json\/wp\/v2\/posts\/136572\/revisions\/137201"}],"wp:attachment":[{"href":"https:\/\/www.madrimasd.org\/blogs\/universo\/wp-json\/wp\/v2\/media?parent=136572"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.madrimasd.org\/blogs\/universo\/wp-json\/wp\/v2\/categories?post=136572"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.madrimasd.org\/blogs\/universo\/wp-json\/wp\/v2\/tags?post=136572"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}