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Lecture 18

BIOB50Winter2012 Lecture 18 includes images and the required sections from the text!.docx

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University of Toronto Scarborough
Biological Sciences
Marc Cadotte

BIOB50Winter2012 Lecture 18 Chapter 18 Species Diversity in Communities Recall the Competitive Exclusion Principle two species that use a limiting resource in the same way cannot coexist Joseph Grinnell first used the term niche in 1917 as no two species of birds or mammals will be found to occupy precisely the same niche Paradox of the plankton Paradox so many species diversity despite the limited number of resources available How can so many species co exist using the same set of resourcesGE Hutchinson proposed solutions to the paradox of the plankton They are heterogeneity fluctuationsdisturbances and grazingenemies Community MembershipSpecies richness differs among communities due to variation in regional species pools abiotic conditions and species interactions Glacier National Park Montana There is a patchwork of very distinct communities each with unique set of species compositions and species richness However some instances of species moving between communities ie amphibians but the communities are highly distinct No one process is responsible for the distribution and abundance of species rather dependent on three interacting factors These factors act to both include and exclude species from a given community Figure 184 Regional Species pool is the first cut to the community membership Regions of high species richness tend to have communities of high species richness because the role of dispersal in supplying species to communities Reiteration regions of high species richness tend to have communities of high species richness because dispersal supplies species to communities Figure 184 A Species that can disperse to the community pass through the first filter The regional species pool provides an upper limit on the number and types of species that can be present in a community The importance of dispersal can be seen in cases of nonnative species invasions A nonnative example is one where humans are the vector of dispersal ballast water from ships and zebra mussels invasive nonative species in the great lakes region were carried over by ballast water in ships Ballast water from ships is water inside the ship that they push back out that came from the shipnd Figure 184 B2 filter abiotic conditions Species that can tolerate the abiotic conditions in the community pass through the second filter A species may be able to reach a community but be physiologically unable to tolerate the abiotic conditions of the environment Some abiotic constraints are obvious eg fish on land or more subtle a lake might not support organisms that require fast flowing water Example Ballast water species nonnative species find themselves in coastal waters that may not have the temperature salinity or light regimes they need to survive or growrd Figure 184 C 3 filter species interactions Species restricted by andor dependent on particular species interactions in the community pass through the third filter The final cut requires coexistence with other species For species that depend on other species for growth reproduction or survival those other species must be present Species may be excluded from a community by competition predation parasitism or disease1
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