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To start using this template, click “File” -- “Make a Copy”02/15/2018 COURSE ### Principles of Evolution ____________________________________________________________________________ ____ From previous sections-Term/Concept - Motivation, Historical Examples, Composition of Regional Biotas,Ecological Approaches, ____________________________________________________________________________ ____ Chapter 07: Biodiversity and Evolution -Term - Motivation -Term - Patterns of Origin & Extinction -More explanation -Incredible variety of life on the planet. Why? Why is there more diversity at the equator than at the poles? More diversity at the tropical vs dessert? Why do we have more diversity at the bottom of the ocean than at the top? -Ecological vs Evolutionary Measurements: There are two approaches to the biodiversity issue, on ecologic the other evolutionary. They Are related approaches. Ecologist is concerned with what is out there now, and how it changes in contemporary time. Evolutionary biology is concerned with what has happened over the last 3.5 bYA. -Ecological An ecologist goes out to a pound, lake, a forest inventory plot and tallies the different species with a certain group, say insects or fungi, or trees ,or orchids . There are problems with finding everything and the sheer taxonomic challenge is formidable but one can compare the biodiversity of different places and situations. -Evolutionary A student of evolution has to be more indirect. Both the time and spatial coverage are much larger, so one ends up collecting records of taxa that have been found form musea, herbaria, and published reports in several different literatures. The
To start using this template, click “File” -- “Make a Copy”02/15/2018 catalogue is always incomplete and imperfect and there are several different taxonomic styles involved. -Ecological approaches: Let us being with the ecological approach, because that is driven by its own important interests. In a given locality, the species present are a subset of hose available from the surrounding region, the set of potential colonizers. The regional species are determined by the range of ecological opportunity the region as well as by the history of that region. -Influential factors: The factors that can drive a species to local extinction are severe climatic events, rapid changes in the habitat, an overdose of predation, parasitism or disease, competition, loss of food or other resources, on which the organism depends, random demographic loss. -Wallace suggested that climatic evenness would promote species persistence (maximum biomass) , but later studies do not seem to support that view. In fact a modicum of local disturbance is beneficial to biodiversity, because it allows the habitat to support species at different stages of ecological succession. Either total disruption or total stasis seem to lead to reduced biodiversity. -Saturation: The question comes up of how saturated communities may be. Are they at biodiversity equilibrium or not? New species come in one at a time. Some are incorporated but others dropped out. Once extinctions are balanced by new arrivals, a quisi-equilibrium is established, and species richness seems to settle down. Without tracking the community over time, of course, there is really no good way of knowing whether it is now saturated . We can do some computer modeling, but that is never good as assessing actual reality over time. -Species richness: In general local species richness (# different species present) is a subset regional richness. If local richness is determined mostly by autology instead the local richness should generally increase with regional richness If local richness is
To start using this template, click “File” -- “Make a Copy”02/15/2018 determined mostly by synecology then local richness is less depend on regional richness. --Community convergence: one thing that is known is that communities gradually move toward their “full stocking” levels which may different from different regions but there are general patterns that we are likely to see. We find, for example, more lizards in deserts than in wetlands. We generally see more species of birds in habitats with greater variation in the heights of the vegetations. Though that turns out to be the reverse in SA. We do not know what to make of that exception. -Historical factors: There are also historical factors that do not necessarily leap out at one from the local biota. Consider the temperate forests of Europe, NA, Northeastern Asia. THese regions have forested areas in the ratio 1:1.3:1 butt the tree diversity 1:2:6. Those ratios are matched at higher taxonomic levels. (biota of europe is limited, North america is twice that, and NE Asia is quite rich) -The Pleistocene glaciation essentially wiped out the temperate forest in Europe, and shoved that in the North America into the Mexican Gulf, but in Asia it just moved southward. Asia benefited from the previously tropical taxa, then diversifying tinto temperature forms, argumenting the temperate remnants, further north. -The history of Diversity: Since the Cambrian life has increased in diversity, in spite of that fact there had been mass extinctions. -
To start using this template, click “File” -- “Make a Copy”02/15/2018 -More explanation -The number of taxa, N, increases as a function of speciation rate (S) and decreases as a function of extinction rate (E). Where R is the net rate of increase. If R>0 we have increase R<0 we have a decrease. -Organization & Extinction rates: the data we have suggest that the value of R was highest in the Cambrian and Ordovician, decreasing ever since, thought it shows a lot of ups and downs, including five mass extinction events. (end of Ordovician, late Devonian, Permian/Triassic Boundary, end of the Triassic, Mesozoic/Cenozoic boundary) Biodiversity has been steadily accumulating since the Cambrian. -Correlation: What is also interesting is that S and E are (+) correlated. That whenever a extinction happens rapidly so does subsequent speciation. Turnover is a couple phenomenon. There is strong suspicion that the twin process of speciation and extinction are coupled. -a) It seems that highly specialized species are apt to speciate, following the opening up of the divergent ecological opportunity but are also prone to extinction as environment change. -B) Small population are more likely to undergo a genetic revolution, the sort of founder effect that can lead to speciation, but they are also more likely to become extinct from demography sampling or ecological catastrophe.
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Course: PRINC OF EVOLUTION
Professor: P. SMOUSE
Term: Spring 2018
Tags: Biology and evolution
Name: Week 9 notes
Description: These notes cover Biodiversity and Mutational Variation
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