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chapter notes

Environmental Science
Course Code
Carl Mitchell

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Chapter 9
Species diversity: the number and the variety of species in the world or in a particular region
Species richness: the number of species
Evenness/relative abundance: numbers of individuals of different species are equal or skewed
Taxonomists: scientists who classify species (use physical appearance and genetic makeup to determine)
- Subspecies
Genetic diversity: varieties in DNA present among individuals within species and populations
- what enables a species to adapt to ecological change
inbreeding depression when genetically similar parents mate and produce weak or defective offspring
ecosystem diversity: number/variety of ecosystems diversity of biotic community within specific area
- species are not evenly distributed
- some groups rise in species through adaptive radiation
- or diversified because of a tendency to be separated by barriers that promote allopatric speciation
- or accumulated species through time because of low rates of extinction
- 1.7 million to 2.0 million species of plants, animals, and microorganisms
- total number: 3 million to 100 million
- many are overlooked (i) unexplored areas, (ii) tiny, (iii) difficult to identify
Latitude gradient: species richness generally increases as one approaches the equator
- productivity and climate stability higher amounts of solar energy, heat, and humidity
Æ relatively stable climates similar temperatures and rainfall
- species diversity tends to increase with diversity of habitats
extinction: the last member f a species dies and the species ceases to exist
extirpation: disappearance of a particular population from a given area, but not globally
endangered: a species that is in imminent danger of becoming extirpated or extinct
threatened: likely to become endangered in the near future
- background rate of extinction 1 out of 1000 species every 1000 to 10 000 years
- mass extinction five major episodes
1. Ordovician over 20% of families
2. Devonian over 20% of families
3. Permo-Triassic possibly vocanism, over 50% of families, 80-95% species
4. End-Triassic 20% of families, 50% of genera
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