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BIOL 121
Carol Pollock

Biol 121 225 Freeman 1217-20, 1222-30 Jan. 18, 10 Species richness -is a simple count of how many species are present in a given community Species diversity -is a weighted measure that incorporates a species’ relative abundance as well as its presence or absence -hard to do on relatively small study plots Why are some communities more -larger patches of habitat contain more species than do smaller patches – large species rich than others? areas contain more types of niches and therefore support higher number of species Immigration and Extinction rates -immigration rates should decline as the number of species in an area increases – and the theory of island individuals that arrive are more likely to represent a species already present biogeography -extinction rates should increase as species richness increases – niche overlap and competition becomes more intense -the result is an equilibrium – balance between arrival of new species and extinction of existing ones -immigration rates should be higher on large islands close to mainland because immigrants are more likely to find large islands that are close to shore than small ones that are far away -extinction rates should be highest on small islands far from shore, because fewer resources are available to support large populations and because fewer individuals arrive to keep the population going -therefore, species richness should be higher on larger islands than smaller islands and on near shore islands versus remote islands Why is this theory important? (3) -relevant to wide variety of island-like habitats like alpine meadows, lakes, ponds, caves -made specific predictions that could be tested -help inform decisions about design of natural preserves -in general, most-species rich reserves should be ones that are relatively large, and located close to other relatively large habitat areas Why does a strong latitudinal -first, consider two fundamental principles to solve problem: gradient in species diversity exist? (higher species richness near 1) Causal mechanism must be abiotic because latitude is a physical phenomenon equator, and decreasing numbers produced by Earth’s shape going South or North) 2) Species diversity of a particular area is the sum of four processes: speciation, extinction, immigration, emigration (dispersal) -thus, latitudinal gradient must be caused by abiotic factor that affects the rates of these four things -over 30 hypotheses have been proposed to explain latitudinal gradient: e.g. 1) High productivity in tropics promotes high diversity by increasing speciation rates and decreasing extinction rates (productivity is the total amount of P/S per unit area per year) -idea is that increased biomass production supports more herbivores and thus more Biol 121 225 Freeman 1217-20, 1222-30 Jan. 18, 10 predators/parasites/scavengers -speciation rates should increase also when niche differentiation occurs w/n pop. of herbivores, predators, parasites, scavengers -however, there is some evidence that increased productivity can be coupled with decrease in diversity 2) Energy hypothesis – high temperatures increase species diversity by increasing productivity and the likelihood that organisms can tolerate the physical conditions in a region 3) Tropical regions have had more time for speciation to occur than have other regions – tropical regions did not have ‘ice age’ 4) Intermediate disturbance hypothesis: Species diversity is much higher in mid- successional communities than in pioneer or mature communities -regions with moderate type, fq, and severity of disturbance should have high species richness/diversity – with intermediate disturbance levels, communities will contain pioneering as well as late-successional species Definition of ecosystem -an ecosystem consists of the organisms that live in an area together with their physical, or abiotic, environment Primary producer/autotroph -a primary producer is an autotroph (“self-feeder”), an organism that can synthesize its own food from inorganic sources -in most ecosystems, they use solar energy to get food via P/S -but in some such as deep-sea hydrothermal vents, bacteria use chemical energy contained in inorganic compounds like hydrogen gas, methane, H S to2make food -primary producers form basis of ecosystem because they transform energy in sunlight or inorganic compounds into chemical energy stored in sugars -they use the chemical energy in two ways: most supports maintenance/respiration; some makes growth and reproduction possible Net primary productivity -abbreviated NPP, it is the energy invested in new tissue -it represents the amount of energy available to 2 and 3 components of an ecosystem: consumers and decomposers Consumer -eats living organisms -herbivores are consumers that eat plants; carnivores are consumers that eat animals -decomposers and detritivores obtain energy by feeding on the dead remains of other organisms or waste products Decomposer vs. detritivore -both types of consumers obtain energy by feeding on dead organic material (remains, waste) -the decomposer such as certain fungi secrete enzymes that decompose organic material, allowing them to then feed on the material -the detritivore such as earthworms ingest detritus (decomposing organic matter)
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