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Community Ecology

Community Ecology. Community: A group of populations of different species living close enough to interact. Classifying Community Interactions. Interspecific interactions = interactions w/ other species C ompetition Predation Herbivory Symbiosis F acilitation.

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Community Ecology

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  1. Community Ecology Community: A group of populations of different species living close enough to interact

  2. Classifying Community Interactions • Interspecific interactions = interactions w/ other species • Competition • Predation • Herbivory • Symbiosis • Facilitation

  3. Interspecific Interactions (+ or -) • Competition (-/-)  Can lead to competitive exclusion • Two species can not coexist w/ identical niches (ecological role – how it fits into an ecosystem) • CAN exist if exhibit resource partitioning •  Can lead to character displacement • species characteristics are more divergent in sympatric vs. allopatric populations (EX: Galapagos finches)

  4. Interspecific Interactions (+ or -) What makes a good predator? • Predation (+/-) • Avoiding predation 101 • Hide • Flee • Fight ‘em off • Unite (can be signaled by “alarm calls”) • Cryptic Coloration (AKA camoflage) • Aposematic coloration (suggests poison) • Batesian mimicry (harmless species mimics a harmful one) • Müllerian mimicry (two unpalatable species mimic each other)  can be seen across variety of species EX: black and yellow stripes on yellow jacket and snakes)  becomes a kind of aposematic mimicry

  5. Interspecific Interactions (+ or -) • Herbivory (+/-) • Successful Herbivores: • Chemical sensors for poison • Strong sense of smell • Adapted digestive system • Successful Plants: • Chemical toxins • Harmful features (spines, thorns) “Locoweeds” Venus fly trap

  6. Interspecific Interactions (+ or -) • Symbiosis: 2+ species live in direct and intimate contact with one another (3 types) • Parasitism (+/-): a parasite feeds off a host which is harmed in the process • Can largely affect population density • Endoparasites vs. Ectoparasites • Mutualism (+/+) • Commensalism (+/0) Cattle egrets Vibrio fisheri in Hawaiian bobtail squid

  7. Interspecific Interactions (+ or -) • Facilitation (+/+) or (+/0) • Not in direct, intimate contact with other species • Mainly in plants • Some plants make soil more hospitable for others plants to grow by • Moderating pH • Soaking up excess salt • Replenishing oxygen levels

  8. Characteristics of Successful Biological Communities • Species diversity (2 components) • Species richness • Species abundance • More diverse means • More stability year to year • More productive • Better recovery from environmental stresses • More resistance to invasive species Which forest is more diverse?

  9. Impacts of Trophic Structure on Communities • Structure and dynamics in a community depend on trophic structure of feeding relationships between species • Transfer of food energy between species in a community is called a food chain

  10. Food Chains vs. Food Webs • Food chains are not isolated but linked together in food webs

  11. Why are food chains short? • 2 main hypotheses: • Energetic hypothesis • Believed that only about 10% of energy is passed no to next trophic level • EX: a producer level consisting of 100kg of plant material can support about 10kg of herbivore biomass (the total mass of all individuals in a population) • Dynamic stability hypothesis • Long food chains are less stable than short food chains • Top feeders experience harder impact from environmental shocks

  12. High Impact Species • Dominant species • Have highest biomass • Control abundance of other species • Keystone species • Typically not abundant • Important due to ecological role (niche) • Ecosystem Engineers • EX: Beavers turn forests into wetlands

  13. Bottom-up vs. top-down control How does then number of individuals in a trophic level influence biomass of other trophic levels? Bottom-up model Top-down model NVHP Can be used to help benefit certain populations biomanipulation • NVHP

  14. Disturbance yields diversity! • Equilibrium model vs. non-equilibrium model of a community • Disturbance  non-equilibrium model • Intermediate disturbance hypothesis yields most diversity • high disturbance = eliminate many species • Low disturbance = create competition  dominant species prevail

  15. Disturbance leads to Succession • Ecological Succession – re-colonization by new or returning species • Primary succession – no soil intact • Begins with autotrophic or heterotrophic prokaryotes • Secondary succession – soil still intact What are some disturbances? Abiotic? Biotic?

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