BIO 373 1st Edition Lecture20 Outline of Last Lecture I Communities contd a Shannon index b Species composition c Interactions i Direct and indirect ii Trophic cascade vs trophic facilitation iii Competitive networks vs competitive hierarchies iv Dominant vs keystone species d Ecosystem engineers e Context dependence Outline of Current Lecture I Communities contd a Changes in communities i Agents of change 1 Abiotic 2 Biotic ii Succession 1 Primary and secondary succession These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute 2 Early modes of succession 3 Connel and Slatyer s 3 modes of succession a Facilitation model b Tolerance model c Inhibition model Current Lecture Communities Contd Changes in communities o Can be caused by human impacts o Agents of change in communities Abiotic Fire storms earth quakes tsunamis Disturbance abiotic events that injure or kill individuals and create opportunities for other individuals Stress an abiotic factor that reduces growth and reproduction of individuals but does not injure or kill them Biotic Competitive networks and hierarchy Pests and disease Predator prey interaction o Succession Deterministic factors Succession change in usually dominant species composition in communities over time Primary succession low frequency and high intensity of disturbance very few communities Secondary succession intermediate frequency and intensity of disturbance Little succession can be low or high frequency low intensity Trajectory of succession Succession progresses through various stages that include a climax stage o stable end point that changes little If catastrophic pioneer stage formed through primary succession Secondary succession will occur after a disturbance alters a community greatly but does not destroy all life Early modes Space for time substitution Clements believed plan communities are like superorganisms group of species working together towards a deterministic end climax stage Gleason communities are the random product of fluctuating environmental conditions acting on individual species Connell and Slatyer 3 modes of Succession Facilitation model o Clements early species modify environment in ways that benefit later species species facilitations leads to climax community Tolerance model o Assumes earliest species modify environment but in neutral ways Inhibition model o Early species modify environment negatively and inhibit later species
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