Evolución de las Redes Ecológicas y Cadenas Tróficas desde el Cámbrico hasta la Actualidad

Se suponía que la complejidad de las redes ecológicas en general (por ejemplo, las cadenas tróficas) había aumentado conforme avanzaba la evolución desde el origen de la vida. La doctrina estándar sostenía que tal hecho, como también que tal proceso había  sido acompañado por un incremento de la biodiversidad. En muy pocas semanas parece ser que todo este entramado teórico se ha venido abajo. Desde hace más de 500 millones de años, tanto la topología de les mencionadas redes de interacción como el número de especies no parecen haber sufrido modificaciones relevantes. El trabajo sobre la topología de las redes tróficas del Cámbrico ha sido recientemente publicado por PloS Bioloy en acceso abierto, por lo que os podéis bajar el material pinchando el siguiente enlace (al final del post os incluimos el resumen).

 

 

 

Redes ecológicas del presente y pasado

Fuente: Dune et al. (2008) Plos One. Enlace en el texto

 

El estudio fue realizado haciendo uso del material paleontológico preservado en dos yacimientos excepcionales y de modelos de computación. No entraré en detalles, por cuanto lo que interesa a los jóvenes es tal regularidad, mientras que los profesionales disponen del artículo, así como de los dos resúmenes que incluyo al final de este post.

 

 

Propiedades de las Redes ecológicas del presente y pasado

Fuente: Dunne et al. (2008) Plos One. Enlace en el texto.

Leyenda al final de la última figura

 

 Ya hemos venido hablando en varios post de que las redes de los sistemas complejos (ya sean biológicas, sociales o mentales) y artefactos tecnológicos, se encuentran sujetos a una serie de leyes que condicionan su estructura y dinámica. Lo que pudiera sorprender a primera vista deviene de que tales estructuras se alcanzaran relativamente pronto a lo largo de la historia de la vida (al menos desde la aparición de los animales marinos, hace aproximadamente 500 millones de años). Sin embargo, tal descubrimiento no nos debería deparar asombro alguno. Hemos venido mostrando y demostrando que tales arquitecturas emergen espontáneamente en los más disparatados ámbitos, por ser consecuencia de la autoorganización de los elementos de los sistemas abiertos a los flujos de energía, materia e información. Si las redes sociales en Internet se han autoorganizado en pocos años, no resulta insólito que en los ecosistemas naturales se alcanzaran las mismas regularidades en millones de años.

 

 

 Propiedades de las Redes ecológicas del presente y pasado

Fuente: Dunne et al. (2008) Plos One. Enlace en el texto.

Leyenda al final de la última figura

 

Uno debe tener cuidado al generalizar las repercusiones de tales hallazgos por cuanto los patrones detectados no refutan que la vida haya ido ganando en complejidad, como lo demuestra la emergencia de animales cada vez más complejos y sofisticados. La lección e extraer resultaría ser que la estructura invariante de las redes complejas emerge rápidamente debido a las leyes de la física de los sistemas complejos.  ¿Porqué hemos tardado tanto tiempo en percatarnos? De los textos incluidos más abajo se infiere rápidamente que la razón estriba en la carencia de las bases de datos adecuadas. No nos cansaremos de repetir que obtener buenos inventarios es una de las bases fundamentales para extraer conclusiones acertadas en casi todos los ámbitos de las ciencias de la tierra y de la Vida. Sin embargo, en la ciencia moderna se desprecia tal actividad en aras de investigaciones más sofisticadas. ¡Error de bulto!. Por mucha instrumentación y modelización que apliquemos, todo el edificio se viene abajo si no se dispone de buenas bases de datos (trabajo muy arduo, ingrato y despreciado). Los pilares del conocimiento deben hundir sus raíces en los inventarios. Una vez disponiendo de buenos productos todo lo demás viene por añadidura. 

 

 

 

Propiedades de las Redes ecológicas del presente y pasado

Fuente: Dunne et al. (2008) Plos One. Enlace en el texto.

Leyenda al final de la última figura

 

En cualquier caso, nuestro conocimiento del pasado es muy limitado quedando mucho por estudiar. Lo que lo que hoy nos ofrece la ciencia bien pudiera ser refutado en poco tiempo.       

 

Juan José Ibáñez

 

Otros post Previos Relacionados con el Tema

Redes Complejas: Redes Sociales y Redes Ecológicas (Los Mundos Pequeños)

Conectividad, Redes Sociales y Redes Ecológicas

Especies Clave y Nodos Clave: Redes Ecológicas, Redes Sociales

Evolución de la Biodiversidad a lo largo de la Historia de la Tierra

 

 

Continuará…………

 

Juan José Ibáñez

 

 

Find «terradaily «food webs»» on Tribe.net

by Staff Writers; Washington DC (SPX) May 01, 2008


Similarities between half-billion-year-old and recent food webs point to deep principles underpinning the structure of ecological relationships, as shown by researchers from the Santa Fe Institute, Microsoft Research Cambridge and elsewhere It was an Anomalocaris-eat-trilobite world, filled with species like nothing on today’s Earth. But the ecology of Cambrian communities was remarkably modern, say researchers behind the first study to reconstruct detailed food webs for ancient ecosystems.  Their paper, published this week in the open-access journal PLoS Biology, suggests that networks of feeding relationships among marine species that lived hundreds of millions of years ago are remarkably similar to those of today.


Food webs depict the feeding interactions among species within habitats–like food chains, only more complex and realistic. The discovery of strong and enduring regularities in how such webs are organized will help us understand the history and evolution of life, and could provide insights for modern ecology–such as how ecosystems will respond to biological extinctions and invasions.


A multidisciplinary group of scientists led by ecologist Jennifer Dunne of the Santa Fe Institute in Santa Fe, New Mexico and the Pacific Ecoinformatics and Computational Ecology Lab in Berkeley, California, studied the food webs of sea creatures preserved in rocks from the Cambrian, when there was an explosion of diversity of multicellular organisms–including early precursors to today’s species as well as many strange animals that were evolutionary dead ends.

Report co-author Richard Williams of Microsoft Research in Cambridge, UK, developed the cutting edge «Network3D» software that was used for analysis and visualization of the food webs. The researchers compiled data from the 505 million-year-old Burgess Shale in British Columbia, Canada and the even earlier Chengjiang Shale of eastern Yunnan Province, China, dating from 520 million years ago. Both fossil-rich assemblages are unusual because they have exquisitely preserved soft-body parts for a wide range of species. They determined who was eating whom by piecing together a variety of clues.


There was the occasional smoking gun, such as fossilized gut contents in the carnivorous, cannibalistic priapulid worm Ottoia prolifica. However, in most cases, feeding interactions were inferred from where species lived and what body parts they had. For example, grasping claws, swimming lobes, big eyes, and toothy mouthparts suggest that Anomalocaris canadensis, a large, unusual organism with no modern descendents, was a formidable predator of trilobites and other arthropods, consistent with bite marks found on some fossils.


To compare the organization of Cambrian and recent ecosystems, the team used methods for studying network structure, including new approaches for analyzing uncertainty in the fossil data. «Paleontologists have long known that food webs were important but we have lacked a rigorous method for studying them in deep time,» comments co-author and paleontologist Doug Erwin of the Santa Fe Institute and the Smithsonian Institution.

«We have shown that we can reconstruct ancient food webs and compare them to modern webs, opening up new avenues of paleoecology. We were surprised to see that most aspects of the basic structure of food webs seem to have become established during the initial explosion of animal lifeThe Cambrian food webs share many similarities with modern webs, such as how many species are expected to be omnivores or cannibals, and the distribution of how many types of prey each species has. Such regularities, and any differences, become apparent only when variation in the number of species and links among webs is accounted for.


«There are a few intriguing differences with modern webs, particularly in the earlier Chengjiang Shale web. However, in general, it doesn’t seem to matter what species, or environment, or evolutionary history you’ve got, you see many of the same sorts of food-web patterns,» explains Dunne. «What we don’t know,» Dunne adds, «is why food webs from different habitats and across deep time share so many regularities. It could be that species-level evolution leads to stable community-level patterns, for example by limiting the number of species with many predators through selective pressures that result in extinctions or development of predator defences. Or, patterns may reflect dynamically persistent configurations of many interacting species, or fundamental physical constraints on how resources flow through ecological networks


Answering such questions will break new ground at the intersection of ecology, evolution and physics. And it may provide valuable insights into present-day ecology. As Williams points out, «This research is an excellent example of how computational methods can be used as part of an inter-disciplinary study to help produce novel results. By getting a better idea of how ecosystems behaved in the past, we may better comprehend and mitigate what is happening to ecosystems today and in the future.»

www.terradaily.com/reports/

 

  

Compilation and Network Analyses of Cambrian Food Webs

Jennifer A. Dunne1,3*, Richard J. Williams2,3, Neo D. Martinez3,4, Rachel A. Wood5,6, Douglas H. Erwin1,7

1 Santa Fe Institute, Santa Fe, New Mexico, United States of America, 2 Microsoft Research Limited, Cambridge, United Kingdom, 3 Pacific Ecoinformatics and Computational Ecology Lab, Berkeley, California, United States of America, 4 National Center for Ecological Analysis and Synthesis, Santa Barbara, California, United States of America, 5 Grant Institute, School of GeoSciences, University of Edinburgh, Edinburgh, United Kingdom, 6 Edinburgh Collaborative of Subsurface Science and Engineering, University of Edinburgh, Edinburgh, United Kingdom, 7 Department of Paleobiology, National Museum of Natural History, Washington, D.C., United States of America

 

A rich body of empirically grounded theory has developed about food webs—the networks of feeding relationships among species within habitats. However, detailed food-web data and analyses are lacking for ancient ecosystems, largely because of the low resolution of taxa coupled with uncertain and incomplete information about feeding interactions. These impediments appear insurmountable for most fossil assemblages; however, a few assemblages with excellent soft-body preservation across trophic levels are candidates for food-web data compilation and topological analysis. Here we present plausible, detailed food webs for the Chengjiang and Burgess Shale assemblages from the Cambrian Period. Analyses of degree distributions and other structural network properties, including sensitivity analyses of the effects of uncertainty associated with Cambrian diet designations, suggest that these early Paleozoic communities share remarkably similar topology with modern food webs. Observed regularities reflect a systematic dependence of structure on the numbers of taxa and links in a web. Most aspects of Cambrian food-web structure are well-characterized by a simple “niche model,” which was developed for modern food webs and takes into account this scale dependence. However, a few aspects of topology differ between the ancient and recent webs: longer path lengths between species and more species in feeding loops in the earlier Chengjiang web, and higher variability in the number of links per species for both Cambrian webs. Our results are relatively insensitive to the exclusion of low-certainty or random links. The many similarities between Cambrian and recent food webs point toward surprisingly strong and enduring constraints on the organization of complex feeding interactions among metazoan species. The few differences could reflect a transition to more strongly integrated and constrained trophic organization within ecosystems following the rapid diversification of species, body plans, and trophic roles during the Cambrian radiation. More research is needed to explore the generality of food-web structure through deep time and across habitats, especially to investigate potential mechanisms that could give rise to similar structure, as well as any differences.

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