Communities and Ecosystems

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Communities and Ecosystems
37.1 Multiple Species Interact in Communities
~Communities are composed of coexisting populations of multiple species ~An ecosystem consists of a biotic community plus its abiotic environment ~Each species in a community has a place where it normally lives and a set of resources necessary for its life activities ~Ecologists describe the diversity of a community by measuring species richness and the relative abundance of each species. * Populations interact in many ways.

* Populations that share a habitat often compete for the limited resources; competition reduces the fitness of both species. * According to the competitive exclusion principle two species cannot indefinitely occupy the exact same niche. * Herbivory is an interaction in which a consumer eats a plant; a predator is an animal that eats another animal. * A Keystone species has a pivotal role in the Community

* A keystone species make up a small proportion of a community’s biomass but had a large influence on the community’s composition. * Closely Interacting species may coevolve
* In coevolution the interaction between the species is so strong that genetic changes in one population select for genetic changes in the other. 37.2 Communities Change over Time
~As species interact with one another and their physical habitats they change the composition of the community which is called succession. ~Primary succession occurs in a preciously unoccupied area beginning with pioneer species that allow soil to develop paving the way for additional organisms to thrive. ~Secondary succession is more rapid than primary succession because soil does not have to build anew. ~Succession may lead toward a stable climax community but true long-term stability is rare. Pockets of local disturbance mean that most communities are a patchwork of successional stages.

37.3 Ecosystems require continuous energy input
* Food webs depict the transfer of...
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