Chapter 7 Community Ecology

1. Chapter 7Community Ecology By Anna Kimsey

2. What determines number of species in a community? • Species richness: The number of different species a community contains. • Species richness depends largely on the climate and climate structure of the area. • Also dependent on niche structure: how many ecological niches occur in the area. • Dependent on geographical location. • The most species rich environments are tropical rain forests, coral reefs, the deep sea, and large tropical lakes.

3. How can we classify species according to their roles in a community? • Native, nonnative, indicator, keystone, and foundation species play different ecological roles in communities. • Native: those that normally live and thrive in a particular community. • Nonnative: invasive or alien species; migrate into or are deliberately or accidentally introduced into a community; some helpful. Ex: wild African bees moving northward • Indicator: species that serve as early warnings of damage to a community or ecosystem. Ex: presence/absence of trout • Keystone: Keystone species help determine the types and numbers of other species in a community; eliminating a keystone species may dramatically alter the structure and function of a community. Ex: pollination species • Foundation: create and enhance habitats that can benefit other species in a community. Ex: elephants

4. How do species interact with one another? • Species can interact through competition, predation, parasitism, mutualism, and commensalism. • Competition: instead of fighting for resources, most competition involves the ability of one species to become more efficient in acquiring food or other resources. Ex: two lions • Predation: members of one species feed directly on all or part of a living organism of another species. Ex: lions and zebras • Parasitism: Parasitism occurs when one species feeds on part of another organism, usually by living on or in the host. Ex: ticks on humans • Mutualism: two species or a network of species interact in a way that benefits both. Ex: birds on the backs of buffalo • Commensalism: interaction that benefits one species but has little, if any, effect on the other species. Ex: epiphytes and large trees

5. How do communities respond to changes in environmental conditions? • New environmental conditions allow one group of species in a community to replace other groups. • Ecological succession: the gradual change of species composition of a given area. Two main types of succession: • Primary succession: gradual establishment of various biotic communities in lifeless areas where there is no soil in a terrestrial community or no bottom sediment in an aquatic community. Ex: bare rock exposed by a retreating glacier or severe soil erosion; newly cooled lava • Secondary succession: a series of communities with different species develop in places containing soil or bottom sediment. Ex: abandoned farmland; burned or cut forests • Scientists cannot predict the course of succession or view it as a preordained progress toward a stable climax community that is in balance with its environment.

6. Does high species biodiversity increase the stability and sustainability of a community? • Living systems maintain some degree of stability through constant change in response to changing environmental conditions. • Having many different species appears to increase the sustainability of many communities. • Communities with more species tend to have higher net primary productivity (NPP) and can be more resilient than simpler ones.

7. Extra Vocabulary to know • Species evenness: the abundance of individuals within each species in a community • Resource partitioning: occurs when species competing for similar scarce resources evolve more specialized traits that allow them to use shared resources at different times, in different ways, or in different places.