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Chapter 5

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University of Toronto Mississauga
Monika Havelka

Chapter Five • species interactions take many forms • Competition = multiple organisms seek the same limited resources o intraspecific competition (same species) vs. interspecific competition (different species) o competitive exclusion – when interspecific species exclude another species completely o species coexistence – may produce a stable point of equilibrium in which the population size of each remains fairly constant • Ecological niche: o co-existing species that use same resources tend to adjust to their competitors to minimize competition with them – In such cases, individuals are not fulfilling their entire niche or ecological cycle o Niche = an organism’s use of resources and its functional role in a community o The full niche of a species is called fundamental niche: optimal conditions o realized niche: a subset of fundamental niche due to species interactions (only plays part) o Specialists = narrow niches and very specific requirements o Generalists = broad niches that can use a wide array of habitats and resources • resource partitioning: species divide shared resources by specializing in different ways o Effects: Character displacement = characteristics diverge to lessen competition and Disruptive selection o Fig 5.1 (pg 121) • Exploitative interactions o Predation: individuals of one species capture, kill, and consume individuals of another species o Parasite: an organism that lives in or on another organism (its host) and benefits by deriving nutrients at the host's expense. o Parasitism: parasite depends on host for nourishment or other benefits o Herbivore = animals feed on the tissues of plants • Coevolution o Herbivores exploit plant o May not kill the plant, but affects its growth and survival • Defenses: o Chemicals; thorns, spines, or irritating hairs o Other animals: protect the plant • Mutualists help one another o Two or more species benefit from their interactions o Symbiosis = organisms live in close physical contact o Pollination: bees, bats, birds and others transfer pollen • Herbivores exploit plants- May not kill the plant, but affects its grow • Some interactions have no effect on some participants: o Amensalism – relationship when one organism is harmed and the other is unaffected o Commensalism: one species benefits and the other is unaffected • Ecological communities o Community = interacting populations o Community ecology = study of the patterns and processes of species interactions • Energy passes among tropic level o Tropic level – as organisms feed on one another this energy moves through community from one rank in feeding hierarchy or tropic level to another o Producers/ autotrophs – first tropic level (grass)  Capture solar energy: terrestrial green plants, cyanobacteria, algae – use photosynthesis to produce sugars  Chemosynthetic bacteria use the geothermal energy in hot springs or deep-sea vents to produce their food o Consumers/heteptrophs – derive their food energy from other organisms – second tropic level(grasshopper)  Eat producers – primary consumers  Most primary are herbivores – eat plants o Prey on primary consumers – secondary consumers – third trophic level (bird) o Fourth level – tertiary consumers – predators that fee
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