Evolution: Videos for Students: Evolving Ideas - PBS
Local species richness–productivity. The species-pool hypothesis was inherently contained in Grime’s original explanation of low species richness. Latitude, productivity and species richness Len N. Gillman1, Shane D. Wright2. Competitive exclusion hypothesis, energy–richness hypothesis, forests, A Weld experiment testing the more individuals hypothesis for richness–productivity relationships. lates that productivity increases species richness by increas-
23/02/2014 · Videos for Students: Evolving Ideas
AB - PÄRTEL (Ecology 83: 2361-2366, 2002) and EWALD (Folia Geobot. 38: 357-366, 2003) suggest that the relationship between local species density and soil pH is determined by regional species pool size, which in turn reflects the relative abundance of soil types during the evolutionary history of the flora. Ewald observed that calcareous sites in Central Europe have higher species density and larger species pools than acidic sites, and argues that this is the consequence of a Pleistocene bottleneck for acidophiles. The flora of the southern Blue Ridge Mountains USA has always been associated with primarily acidic soils. We used vegetation and soil data from 3328 100 m2 southern Blue Ridge forest plots to examine the generality of the Pärtel-Ewald hypothesis. The Blue Ridge flora with less than 20% of species confined to sites above pH 4.7 contrasts dramatically with that of Europe. However, regional species pool size increases with pH. Genus- and family-level pools increase with pH, suggesting an ancient origin for this pattern. Mean species density is also strongly positively correlated with soil pH. Thus, both regional species pool size and plot species density of southern Blue Ridge forests fail to conform to predictions derived from the work of Pärtel and Ewald. The increase in species pool with increase in pH exhibited by southern Blue Ridge forests appears to reflect broad species distributions and tolerance for high pH conditions among species that grow predominantly under acid conditions. We conclude that richness on higher pH sites is a consequence of generally more favorable conditions for plant growth and/or establishment. Ewald may be correct in asserting that the abundance of high pH specialists in Central Europe is an historical artifact, but our data contradict the assertion of Pärtel and Ewald that evolution of a flora in a primarily low pH environment will necessarily translate into a negative correlation between pH and species density in local vegetation.
The recent trend toward multidisciplinary syntheses has been generally making hypotheses more complex and difficult to test, although and ever-increasing and more precise data makes the task more feasible than ever, at least situations in which are not interfering. consist of body plans, which scientists have used to classify all life forms, and all significant animal phyla had appeared by the Cambrian Period’s end. The Cambrian Explosion has been difficult to explain and there is still great controversy and many unanswered questions, and it has also been difficult to explain why significant change stopped the explosion. Once the basic body plans appeared and biomes were filled, new plans never appeared again. Why did all fundamental change stop? The emerging view is the same for why complex life with and never changed since then. Not only could innovation confer great benefits, but , further travel along the developmental path made it continually less feasible to backtrack, start over, and take another path, or choose a fundamentally different path. The history of life’s choices was reflected in organisms in several ways, and the source of that inertia began to be understood when biology and chemistry at the cellular and subcellular levels were investigated, particularly after DNA was sequenced and studied. The fact that have not significantly changed in several hundred million years points to the issue. Hox genes have not changed because they control key developmental steps in embryonic development. Not only do Hox genes work, there are no practical ways to significantly change them, as they lay the animal’s structural foundation. Hox genes are called regulatory genes, and the nature of seems to be why animals have not fundamentally changed since the Cambrian Explosion. Imagine a family having a custom home built and, after it was built, they decided that they wanted a basement, four extra stories, central gas heating rather than baseboard electric heating, and a swimming pool on the third floor. It would not be feasible to renovate the home to give it those new features, especially if the family was already living in it. They would need to build a new house from scratch, with a new foundation, and they would have to find a temporary home during the construction period. But an animal has to live in its body all the time. There is no way to redesign and rebuild an animal’s foundation while it lives in its body, and the biological superstructure built on the foundation was designed for foundation. A new superstructure would also have to be designed and built on the new foundation. A six-chambered heart, for instance, could not just be invented and put into a human chest and work, or a second brain, or a third arm. The kinds of changes that feasible have to adhere to the basic structural and biochemical foundations that the phyla represent.Once animals arrived on the evolutionary scene and filled most possible niches, new biological foundations could not be built, with superstructures built atop them, and hope to compete for resources that were already being consumed in the food chains. Developing the original animal body plans took millions of years. There were many other possible body plans that have been developed in the early days of animals, which might have worked wonderfully, but those chosen ones worked well enough for survival and reproduction, and once chosen, there was no going back.