BIO 373 1st Edition Lecture19 Outline of Last Lecture I human microbiomes a communities i subset of species ii structure iii diversity iv Shannon index v Commonness and rareness Outline of Current 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 Current Lecture Human Microbiomes Communities o Shannon index 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 Looking at proportions of abundance o Species composition What type of species are found in a community Want to understand and know variation of species present and species diversity between communities o Interactions Direct interaction two species interact with each other Indirect interaction two species share a species that they interact with A interacts with B A and C do not interact but A interacts with B and C interacts with B Interactions may be positive or negative Indirect interactions may involve both positive and negative o Can also have direct negative interactions resulting in indirect positive interactions Trophic cascade occurs when predators suppress abundance of prey which helps protect a species in a lower trophic level from predation Trophic facilitation consumer is facilitated by a species facilitating its prey indirect Ex a plant species helps another plant species grow better which helps the consumer of the plant o Competitive networks vs hierarchies Networks indirect species interactions buffer strong direct competition so that no one species dominates the interaction no none wins Hierarchy a species always dominates the interaction o Dominant vs keystone species Keystone large effects on community because of interactions rather than abundance Dominant species dominates a community because of abundance o Ecosystem engineers Species change characteristics of environment Can be a dominant or keystone species o Context dependence Interactions of species in community can change depending on the environment Ex drought or flooding allows or prevents interactions and changes in interactions
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