Chapter 6 – Ecological Communities

© 2013 Pearson Education, Inc. 6.1 Competition for Shared Resources Resources are limited Species within ecological community compete for resources –Ecological community Species that interact within a specific community

© 2013 Pearson Education, Inc. 6.1 Competition for Shared Resources Interspecific competition –Two or more species compete for the same resource Trees vs. shrubs for light and nutrients Competitive exclusion principle –Two species that directly compete for resources cannot coexist

© 2013 Pearson Education, Inc. 6.1 Competition for Shared Resources Ecological niche –The role an organism fills within its habitat Fundamental niche –Complete range of areas in which an organism could exist Realized niche –Range in which an organism actually exists due to competition

© 2013 Pearson Education, Inc. 6.1 Competition for Shared Resources Ecological niche –Niche differentiation Division of resources Potential competitors may coexist –Example: Warblers in evergreen forests

© 2013 Pearson Education, Inc. 6.1 Competition for Shared Resources Mechanisms of competition –Exploitation competition Consume resource faster –Interference competition Stop competitor from consuming resource

© 2013 Pearson Education, Inc. 6.2 Herbivory, Predation, and Parasitism Herbivores Adapted to feed on plant material –Specialized digestive systems –Ability to detoxify plant chemicals Coevolution –Tit for tat evolution of a prey and species that consumes it Milkweed–monarch butterfly

© 2013 Pearson Education, Inc. 6.2 Herbivory, Predation, and Parasitism Predators –Hunt, kill, and consume prey –Many predators hunt various species –Prey switching Predators focus on most abundant prey species –Prey respond by adapting defenses Protection Camouflage

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6.2 Herbivory, Predation, and Parasitism Parasites –Depend on living host for nourishment –Usually do not kill host –Internal or external May be spread by vectors –Organism that carry parasite but is not itself affected

© 2013 Pearson Education, Inc. 6.2 Herbivory, Predation, and Parasitism Spread of parasite disease governed by 4 factors –Abundance of hosts –Accessibility of hosts –Transmission rate of parasites –Length of life of an infected host

© 2013 Pearson Education, Inc. 6.3 Mutualism and Commensalism Symbioses –Intimate relationship between 2 species Mutualism –Both species benefit Figs and wasps

© 2013 Pearson Education, Inc. 6.3 Mutualism and Commensalism Symbioses –Commensalism One species benefit, other unaffected –Snails and hermit crab

© 2013 Pearson Education, Inc. 6.4 The Flow of Energy in Ecological Communities Energy must flow through ecological communities –Energy flow Transfer and transformation of energy –Organisms classified by trophic level Based on food source

© 2013 Pearson Education, Inc. 6.4 The Flow of Energy in Ecological Communities Food chains/food webs –Depiction of feeding relationships among organisms Primary producers/1 st trophic level –Transform energy from sun or chemicals Primary consumers/2 nd trophic level –Herbivores

© 2013 Pearson Education, Inc. 6.4 The Flow of Energy in Ecological Communities Secondary consumers/3 rd trophic level –Carnivores Tertiary consumers/4 th trophic level –Top carnivores Decomposers –Feed on nonliving organic matter –Feces/dead organisms

© 2013 Pearson Education, Inc. 6.4 The Flow of Energy in Ecological Communities Biomass energy –Food that can be consumed by higher trophic level Trophic level efficiency –Much energy consumed used by organism –Only ~10% available to next trophic level

© 2013 Pearson Education, Inc. Food energy lost in respiration and heat Food energy lost as waste + O 2

© 2013 Pearson Education, Inc. 6.4 The Flow of Energy in Ecological Communities Food webs Depicts all of the feeding relationships –More detailed than food chains More complex food webs provide greater stability

© 2013 Pearson Education, Inc. 6.4 The Flow of Energy in Ecological Communities Keystone species –Named after wedge-shaped keystone that holds arched structures together –Removal causes collapse Keystone species are important in stability of many food webs –Many plants, but some predators –Trophic cascade Loss of carnivores results in explosion of herbivores that destroy primary producers

© 2013 Pearson Education, Inc. FOCUS ON SCIENCE: Trophic Cascades Across Ecosystems Scientists examined trophic cascades Compared ponds with fish and without fish Fish feed on dragonfly larvae Adult dragonflies feed on pollinators

© 2013 Pearson Education, Inc. 6.5 Disturbance and Community Change Ecological disturbance –Loss of many or all species in community Fires, hurricanes, volcanoes, logging Ecological legacies –Resources remaining after disturbance Soil, debris Succession Pattern of change after disturbance

© 2013 Pearson Education, Inc. 6.5 Disturbance and Community Change Primary succession –Virtually all resources removed –Process can take millennia Typically bare rock –Glacial retreat, volcanic eruption Pattern of primary succession –Pioneer species –Facilitation and migration of new species –Climax community

© 2013 Pearson Education, Inc. 6.5 Disturbance and Community Change Secondary succession –Follows disturbances that leave significant legacy Soil, seed bank, wood debris Process much faster –As quick as 70–100 years Old-field succession –Abandoned farm fields

© 2013 Pearson Education, Inc. 6.5 Disturbance and Community Change Cyclic succession –Succession may increase chances of disturbance –Buildup of understory leads to intense fire Some ecosystems are maintained by cyclical succession

© 2013 Pearson Education, Inc. 6.5 Disturbance and Community Change Importance of place –Surrounding areas affect successional change Proximity to other systems Human influences

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