Due to environmental modifcations by other species

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Unformatted text preview: ivorship, etc. due to environmental modifcations by other species First thing to colonize after storm is grass Myrica Cerifera- facilitated by grass growth (which produces an environment preventing other species growth in the beginning, then as it ages and dies out makes good environment) Red Cedar, cacti also do it Joshua Tree in desert, modifies environment around it; temperatures under it decrease, causing growth of organic matter, and it creates microclimate conducive Nurse Plant syndrome - (Joshua Tree) – nucleation – a plant survives due to the microclimate created by the tree (the preexisting individual) Plant facilitates advancement of other organisms Ex. Crabtree vs. Contrary creeks Surface mining shaft mining and strip mining lead to the decrease in pH which elminates diversity in streams. Contrary creek acid mine drainage, yellow boy, low acidity and low pH water eats gills of fish and kills them Waste seeds form feces in DC spread in Contrary Riparian zone to promote growth In order to compare them you need Index of Biotic Integrity (good=high) Figure 3.42 Index of biological integrity (diversity) Gives an IBI score from 12-60; 60 is good Pgs. 82-85 IBI to assess body of water If you want to look at a community of stream and want to evaluate it you need a reference to compare it to (to indicate diversity and water quality) Healthy aquatic community- is similar to an undisturbed habitat in same region Look at number of native kind of species, look at number of fish, number of macro invertebrates, the higher the different kind indicates the healthier If you have more insectivores you have increased stream health More omnivores indicates decreased stream health Robert Pain- looks at predators Figure 17.16 Keystone Species Defined Apex predators but also abundance, energy flow, and environmental modification Keystone species are those whose influence on the community is disproportionate to their biomass (abundance) Despite low biomass (sometimes Apex Predators) All Keystone species are those that despite low biomass exert strong affects on the structure that they inhabit Sea otters, snails, Pisaster, fish etc. Unlike: Dominant species are ones that have significant influence on community by virtue of high biomass Dominate species - have an influence on the community b/c HIGH BIOMASS Also by abundance, affect on energy flow, and environmental modification Apex predators – have a strong influence on the environment they live in Consumers can exert control on community or food web structure over the environment in which they live (Figure 17.6) Compare to the arctic island food web in Fig. 17.3 Introduced apex predator in the James River American shad- not so many anymore b/c new species Blue catfish- eat American shad (introduced by Department of Game and Fisheries) Relate to Lake Victoria problem Fig 17.17 Over 400 species of fish evolved in that lake (prior to uninvasive species) Nile perch and Nile talapia introduced in 50’s, now only 3 dominant groups of fish in the lake Omena only native still existing Apex predators(top of food chain) in Lake Victoria largest catastrophic thing now; hugely simplified the food web Introduced apex predator in the Chesapeake Bay Fig. 17.17 Sn...
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