The data from Cambrian fit this relationship fairly well

The data from Cambrian fit this relationship fairly well -...

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The data from Cambrian fit this relationship fairly well. Diversity during the Paleozoic fit a Logistic growth curve quite well (logistic curve has a feedback where number if individuals [taxa] levels off with increasing density; sigmoid curves in figure below) One can extend this analogy even further and treat Sepkoski's three evolutionary faunas as one might treat competing species . The patterns fit models of species competition. But : the observation is a pattern in the fossil record and we do not know whether the process of competition existed between the two major faunas. This pattern can be seen on a lower taxonomic level also: rodents increase in diversity as the multituberculates (rodent-like mammals) decrease to extinction. Shortly after the brachiopods (clam-like marine invertebrates) bite the
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Unformatted text preview: dust, the bivalves (e.g., clams) diversify extensively. The patterns look like what one might expect from competitive exclusion , and is referred to as ecological replacement since one group with a similar set of key innovations replaces another group (see figure below). Re analysis of the brachiopod/bivalve replacement has suggested that there has been no interaction between the "competing" forms and that they are best though of as "ships that pass in the night". This does not mean that all ecological replacements in the fossil record do not involve competition, just that it is hard to say. A nice way to compare the possibility of interaction, or the lack of it, is illustrated in figure 21.12, pg. 603....
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