BIO 373 1st Edition Lecture 22 Outline of Last Lecture I Communities contd a Changes in communities contd i Chapin experiment ii Mechanism of succession iii Alternative stable states 1 Fouling communities 2 Stability change hysteresis II Species Diversity a Spatial scales i Global regional landscape local b Filters i Importance in invasive species c Models of coexistence i Resource portioning ii Intermediate disturbance hypothesis iii Lottery model III Energy in ecosystems Outline of Current Lecture 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 I Species Diversity contd a Hutchinson s model i Paradox of the plankton b Processes that promote coexistence i Paine ii Intermediate disturbance hypothesis iii Hacker and Gaines c Lottery model d Consequences of Diversity i Diversity stability theory e Species richness and community function Current Lecture Species Diversity Contd Hutchinson s Model o Paradox of the plankton 30 40 species 4 5 different resources so how can they coexist Explained that there were so many species because frequent minimal disturbances prevented a species from dominating o Time required for one species to exclude another tc o Time it takes for environmental variation to act on population growth of the two species te o If Tc Te coexistence can not occur because species can reach carrying capacity without disturbance happening o In a fluctuating environment to which competitors are adapted to Tc Te and competitive exclusion can occur Effect of disturbance is not high because species is adapted o Coexistence can only occur when Tc Te Processes that promote coexistence o Paine Tested Hutchinson s idea that competitive exclusion is rare in nature by using predation as an environmental factor precluding competitive exclusion o Intermediate disturbance hypothesis Connel stimulated by Paine s research Coexistence defined by disturbance level At low disturbance competitive exclusion decreases diversity At intermediate disturbance there is a balance between disruption of competition and mortality which increases diversity At high disturbance diversity decreases and mortality increases Predation is considered an agent of change not a disturbance but has that effect o Hacker and Gaines positive interaction in intermediate disturbance hypothesis Importance of facilitation in communities At low disturbance competition decreases diversity Lottery Model o Above theories assume underlying competitive hierarchy o In lottery model all species must have equal chances of obtaining resources made available by stress and disturbance o Must have similar interaction strength and growth rates and be able to respond quickly to events Consequences of diversity o Species diversity can control community function like plant productivity soil fertility water quality resistance to disturbance o Diversity Stability Theory Species richness is positively related to community stability Community stability tendency of a community to remain the same structurally and functionally Low diversity low resistance to change high change in biomass and vice versa o Species richness and community function With similar function species richness has a limit Without similar functions species richness has no limit With a dominate species greater impact more difficult to predict the function of a community Energy in Ecosystems Energy o Ecosystem energy views species within communities as entities linked to each other via the transformation of energy and nutrients achieved when they engage in consumer resource interactions