案例一2004年遭遇的第一起被诉案件 .93.ppt

案例一2004年遭遇的第一起被诉案件 .93.ppt

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案例一2004年遭遇的第一起被诉案件 .93

Ecology Lecture 11 Ralph Kirby Niche Constraint Community Structure All organisms can live and reproduce over a specific range of environmental condition These differ from organism to organism These environmental conditions vary in time and space Thus there is overlap in any environmental gradient However, cannot assume there is no interaction between species Problem is that such interactions are many and relatively diffuse Usually the removal of a single species will have very limited effects and this makes analysis of interactions difficult Removal of multiple species can be major Food webs Provide a limited but useful view of interactions Provide information on indirect effects See lynx and white spruce Presence of lynx is good for white spruce due to survival of seedlings Keystone predation Predation can also influence outcome of interactions between prey species The starfish preys on many species of mussels, barnacles, limpets, etc Remove starfish from experimental plots and compare to normal situation Number of prey species in experimental plots was halved Diversity was decreased as better competitors excluded other species Indirect mutualism Two herbivorous Daphnia spp. and their predators, midge larvae and salamander larvae Salamander larvae prey on large Daphnia Midge prey on small Daphnia Salamander and midge can survive together Midge cannot survive alone Salamander can survive alone Thus there are both direct and indirect interactions within a community How do you tell which are important Rivet model System stable until enough species are lost to make whole system collapse Redundancy model Most species are not needed A few key species are important Both models are probably correct and importance of each varies with ecosystem Most systems it is not easy to tell how important each species is Can try to do this by splitting species into functional groups Each group has a similar function and perhaps can replace each other Trophic levels Primary producers

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