Sustainable Ecology
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Evolution of Biodiversity
Biodiversity Web - Maximised Genetic Variation
Biodiversity is the result of 3.5 Billion years of Evolution. The origin of Life has not been definitely established by science, however some evidence suggests that life may already have been well established only a few hundred million years after the formation of the Earth. Until approximately 600 million years ago, all life consisted of Archaea, Bacteria, Protozoans and simular Single-Celled Organisms.
The history of Biodiversity during the Phanerozoic (the last 540 Million years), starts with rapid growth during the Cambrian Explosion - a period which during nearly every Phylum of Multicellular Organism first appreared. Over the next 400 million years or so. invertebrate diversity showed little overall trend, and vertebrate diversity shows an overall exponential trend. This dramatic rise in diversity was marked by periodic, massive losses of diversity classified as Mass Extinction Events. A significant loss occurred when Rainforests collapsed in the Carboniferous. The worst was the Permo-Triassic Extinction, 251 million years ago. Vertebrates took 30 million years to recover from this event.
The Fossil Record suggests that the last few million years featured the Greatest Biodiversity in History. However not all Scientists support this view, since there is uncertainty as to how strongly the Fossil Record is biased by the greater availability and preservation of recent Geologic Sections. Some Scientists believe that corrected for sampling Artifacts, modern Biodiversity may not be much different from Biodiversity 300 million years ago, whereas others consider the fossil records reasonably reflective of the Diversification of life. Estimates of the present Global Macroscopic Species Diversity vary from 2 Million to 100 Million, with a best estimate of somewhere near 9 Million, the vast majority of Anthropods. Diversity appears to increase continually in the absence of Natural Selection.
Evolutionary Diversification
The Existence of a "Global carrying Capacity", limiting the amount of Life that can live at once, is debated, as is the question of whether such a limit would also cap the number of Species. While records of life in the sea shows a Logistic pattern of Growth, Life on land (Insects, Plants and Tetrapods) show an exponential rise in diversity.
As one author states, "Tetrapods have not yet invaded 64 per cent of Potentially Habitable Modes, and it could be that without Human Influence the Ecological and Taxonomic Diversity of Tetrapods would continue to increase in an exponetial fashion until most or all of the available Ecospace is filled.
Global Carrying Capacity
On the other Hand, changes through the Phanerozoic correlate much better with Hyperbolic Model (widely used in Population Biology, Demography and Macrosociology, as well as Fossil Biodiversity) than with exponential and logistic Models. The latter Models imply that changes in diversity are guided by first-order Positive Feedback (more Ancestors, and more Descendants) and / or a Negative Feedback arising from Resource Limitations. Hyperbolic Model implies a second-order positive feedback. The hyperbolic pattern of the World Population growth arises from a second-order positive feedback between diversity and community structure complexity. The simularity between the curves of Biodiversity and Human Population probably comes from the fact that both are derived from the Interference of the Hyperbolic Trend with Cyclical and Stochastic Dynamics.
Most Biologists agree however that the period since Human emergence is part of a New Mass Extinction, named Holocene Extinction Event, caused primarily by the Impact of Humans are having on the Environment. It has been argued the the present rate of Extinction is sufficient to eliminate most Species on Planet Earth within a 100 Years.