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Chapter 5

Chapter 5- Species Interactions and Community Ecology.docx

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Monika Havelka

Chapter 5- Species Interactions and Community Ecology Species Interactions Categories of species interactions: Competition  When multiple organisms seek the same limited resource  Subtle and indirect, involving the consequences of one organism’s ability to match/outdo others in procuring resources  Takes place among:  Members of the same species (intraspecific competition); population level phenomenon  Members of two or more different species (interspecific competition) o Competitive exclusion- one species is very effective competitor and may exclude another species from resource use entirely o Species coexistence- neither competing species fully excludes the other, they may life side by side at a certain ratio of population sizes  Fundamental niche- The full niche of a species (may exploit resources)  Realized niche- The portion of the fundamental niche that is fully realized (used) by a species  Resource Partitioning- The process by which species adapt to competition by evolving to use slightly different resources, or to use their shares resources in different ways, thus minimizing interference with one another o Character displacement- Occurs when competing species evolve physical characteristics that reflect their reliance on the portion of the resource they use  Negative effect on other participants because each takes resources the others could have used Predation  Predation- Process by which individuals of one species (predator) hunt, capture, kill, and consumer individuals of another species (prey)  Causes cycles in population sizes: 1. Increase in population size of prey creates more food for predators, which may survive and reproduce more effectively as a result 2. As predator population rises, additional predation drives down population of prey 3. Fewer prey causes some predators to starve so that predator population declines 4. Prey population rises again, starting cycle again  Has evolutionary ramifications; individual predators that are more adept at capturing prey will likely live longer, healthier lives and be better able to provide for their offspring than will less adept individuals  Positive/negative effect on other participants Parasitism  Parasitism- Relationship in which one organism (parasite) depends on another (the host) for nourishment or some other benefit while doing the host no harm  Does not result in organism’s immediate death but it contributes to host’s eventual death  May reside inside the host (tapeworms) or outside the host (ticks)  Parasitoids- insects parasitize other insects, often killing them in process  Coevolution- parasites and hosts evolve in response to one another Herbivory  Herbivory- Occurs when animals feed on the tissues of plants  Does not kill a plant outright, but may affects its growth and reproduction  To protect themselves, plants may:  Recruit certain animals as allies to assist in their defence  Release volatile chemicals when they are bitten/pierced Mutualism  Mutualism- Relationship in which two or more species benefit from interaction with one another; each partner provides some resource/service that other needs  Symbiosis- occur between organisms that live in close physical contact  Pollination- Interaction of key significance to agriculture and our food supply Unaffected Interactions  Amensalism- Relationship in which one organism is harmed and the other is unaffected  Hard to prove that organism doing the harm is not in fact besting a competitor for a resource  Commensalism- One species benefits and the other is unaffected  Facilitation- Influences the structure and composition of communities and how they change through time Ecological Communities Trophic levels  A rank in the feeing hierarchy of a food chain; organisms at higher trophic levels consume those at lower trophic levels, thus energy passes among trophic levels  Producers- Compose the first trophic level o Capture solar energy and photosynthesis to produce sugars  Consumers- Organisms that derive their food energy from other organisms o Primary consumers- consumers that eat producers and compose of second trophic level (deer, grasshoppers, etc); most are herbivores because they consumer plants o Secondary consumers- prey on primary consumers and compose of third trophic level (wolves, birds, rodents, etc); carnivors because they eat animals o Tertiary consumers- predators that feed at even higher trophic levels (hawks, owls) o Omnivors- Animals that eat both plant and animal food  Detritivores and Decomposers o Detririvores- Organisms that consume nonliving organic matter (millipedes, soil insects, etc) o Decomposers- Break down leaf litter and other nonliving matter further into simpler constituents that can then be taken up and used by plants (fungi, bacteria)  Energy, biomass, and numbers decrease at higher trophic levels  Each trophic level contains just 10% of the energy of the trophic level below it  Trophic pyramid- Diagram showing the trophic levels in a good chain from bottom to top, with autotrophs at the bottom, moving up through the various levels of consumers; biomass, energy and numbers of individuals decrease upward through trophic levels Food Webs  Food webs show feeding relationships and energy flow  Food chain- Linear series of feeding relationship in which primary producers are eaten by primary consumers who are eaten by secondary consumers and so on  Food Wed- Visual representation of feeding interactions within an ecological community that shows an array of relationships between organisms at different trophic levels Organisms Roles in Communities  Keystone Species- A species that has strong/far reaching impact; removal of these species will have ripple effects and will alter large portion of the food web  Examples- Elimination of wolves leads to increase in moose population and impacts on vegetation and on all other animals in the area Communities Responding to Disturbances  Resistance- Community that resists change and remains stable despite disturbance  Resilience- Community changes in response to disturbance but later returns to its original state  Community may be modified by disturbance permanently and may never return to its original state  Succession follows sever disturbance  Succession- Series of changes in the composition and structure of an ecological
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