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© 2011 Pearson Education, Inc. Ecological Communities AP Environmental Science Mr. Grant Lesson 29
© 2011 Pearson Education, Inc. Objectives: Define the term trophic level. Characterize feeding relationships and energy flow, using them to construct trophic levels and food webs. Distinguish characteristics of a keystone species. Characterize succession, community change, and the debate over the nature of communities. Perceive and predict the potential impacts of invasive species in communities. Explain the goals and the methods of restoration ecology.
© 2011 Pearson Education, Inc. Trophic Level: Rank in the feeding hierarchy of a food chain. Organisms at higher trophic levels consume those at lower trophic levels. Define the term trophic level.
© 2011 Pearson Education, Inc. Characterize feeding relationships and energy flow, using them to construct trophic levels and food webs. Energy is transferred in food chains among trophic levels. Lower trophic levels generally contain more energy, biomass, and individuals. Food webs illustrate feeding relationships and energy flow among species in a community.
© 2011 Pearson Education, Inc. Ecological communities Community = an assemblage of populations of organisms living in the same place at the same time -Members interact with each other -Interactions determine the structure, function, and species composition of the community Community ecologists are people interested in how: -Species coexist and relate to one another -Communities change, and why patterns exist
© 2011 Pearson Education, Inc. Energy passes through trophic levels One of the most important species interactions -Who eats whom? Matter and energy move through the community Trophic levels = rank in the feeding hierarchy -Producers (autotrophs) -Consumers -Detritivores and decomposers
© 2011 Pearson Education, Inc. Producers: the first trophic level Producers, or autotrophs (“self-feeders”) = organisms capture solar energy for photosynthesis to produce sugars -Green plants -Cyanobacteria -Algae Chemosynthetic bacteria use the geothermal energy in hot springs or deep-sea vents to produce their food
© 2011 Pearson Education, Inc. Consumers: consume producers Primary consumers = second trophic level -Organisms that consume producers -Herbivores consume plants -Deer, grasshoppers Secondary consumers = third trophic level -Organisms that prey on primary consumers -Carnivores consume meat -Wolves, rodents
© 2011 Pearson Education, Inc. Consumers occur at higher trophic levels Tertiary Consumers = fourth trophic level -Predators at the highest trophic level -Consume secondary consumers -Are also carnivores -Hawks, owls Omnivores = consumers that eat both plants and animals
© 2011 Pearson Education, Inc. Detritivores and decomposers Organisms that consume nonliving organic matter -Enrich soils and/or recycle nutrients found in dead organisms Detritivores = scavenge waste products or dead bodies -Millipedes, soil insects Decomposers = break down leaf litter and other non- living material -Fungi, bacteria -Enhance topsoil and recycle nutrients
© 2011 Pearson Education, Inc. Energy, biomass, and numbers decrease Most energy organisms use is lost as waste heat through cellular respiration -Less and less energy is available in each successive trophic level -Each level contains only 10% of the energy of the trophic level below it There are also far fewer organisms and less biomass (mass of living matter) at the higher trophic levels A human vegetarian’s ecological footprint is smaller than a meat-eater’s footprint
© 2011 Pearson Education, Inc. Pyramids of energy, biomass, and numbers
© 2011 Pearson Education, Inc. Food webs show relationships and energy flow Food chain = a series of feeding relationships Food web = a visual map of feeding relationships and energy flow -Includes many different organisms at all various levels -Greatly simplified; leaves out most species
© 2011 Pearson Education, Inc. Distinguish characteristics of a keystone species. Keystone species have impacts on communities that are far out of proportion to their abundance. Top predators are frequently considered keystone species, but other types of organisms also exert strong effect on communities.
© 2011 Pearson Education, Inc. Some organisms play big roles Community dynamics are complex -Species interactions differ in strength and over time Keystone species = has a strong or wide-reaching impact -Far out of proportion to its abundance Removal of a keystone species has substantial ripple effects -Alters the food chain
© 2011 Pearson Education, Inc. Characterize succession, community change, and the debate over the nature of communities. Succession is a stereotypical pattern of change within a community through time. Primary succession begins with an area devoid of life. Secondary succession begins with an area that has been severely disturbed. Communities may undergo phase shifts involving irreversible change if disturbance is severe enough. Clements held that communities are discrete, cohesive units. His view has largely been replaced by that of Gleason, who held that species may be added to and deleted from communities through time.
© 2011 Pearson Education, Inc. Species can change communities Trophic Cascade = predators at high trophic levels indirectly affect populations at low trophic levels -By keeping species at intermediate trophic levels in check -Extermination of wolves led to increased deer populations, which overgrazed vegetation and changed forest structure Ecosystem engineers = physically modify the environment -Beaver dams, prairie dogs, ants, zebra mussels
© 2011 Pearson Education, Inc. Communities respond to disturbances Communities experience many types of disturbance -Removal of keystone species, spread of invasive species, natural disturbances -Human impacts cause major community changes Resistance = community of organisms resists change and remains stable despite the disturbance Resilience = a community changes in response to a disturbance, but later returns to its original state A disturbed community may never return to its original state
© 2011 Pearson Education, Inc. Primary succession Succession = the predictable series of changes in a community -Following a disturbance Primary succession = disturbance removes all vegetation and/or soil life -Glaciers, drying lakes, volcanic lava Pioneer species = the first species to arrive in a primary succession area (i.e. lichens)
© 2011 Pearson Education, Inc. Secondary succession Secondary succession = a disturbance dramatically alters, but does not destroy, all local organisms -The remaining organisms form “building blocks” which help shape the process of succession -Fires, hurricanes, farming, logging Climax community = remains in place with few changes -Until another disturbance restarts succession
© 2011 Pearson Education, Inc. Communities may undergo shifts The dynamics of community change are more variable and less predictable than thought -Conditions at one stage may promote another stage -Competition may inhibit progression to another stage -Chance factors also affect changes Phase (regime) shift = the overall character of the community fundamentally changes -Some crucial threshold is passed, a keystone species is lost, or an exotic species invades -i.e. overfishing and depletion of fish and turtles has allowed algae to dominate corals
© 2011 Pearson Education, Inc. Community cohesion Frederick Clements = viewed communities as cohesive entities, with integrated parts -Its members remain associated over space and time -The community shared similar limiting factors and evolutionary histories Henry Gleason = maintained that each species responds independently to its own limiting factors -Species join or leave communities without greatly altering the community’s composition -The most widely accepted view of ecologists today
© 2011 Pearson Education, Inc. Perceive and predict the potential impacts of invasive species in communities. Invasive species such as the zebra mussel have altered the composition, structure, and function of communities. Humans are the cause of most modern species invasions, but we can also respond to invasions with prevention and control measures.
© 2011 Pearson Education, Inc. Invasive species threaten stability Invasive species = non-native (exotic) organisms that spread widely and become dominant in a community -Introduced deliberately or accidentally from elsewhere -Growth-limiting factors (predators, disease, competitors, etc.) are removed or absent -They have major ecological effects -Chestnut blight from Asia wiped out American chestnut trees Some species help people (i.e., European honeybees)
© 2011 Pearson Education, Inc. Two invasive mussels
© 2011 Pearson Education, Inc. Controlling invasive species Techniques to control invasive species -Removing them manually -Applying toxic chemicals -Drying them out -Depriving them of oxygen -Stressing them with heat, sound, electricity, carbon dioxide, or ultraviolet light Control and eradication are hard and expensive Prevention, rather than control, is the best policy
© 2011 Pearson Education, Inc. Explain the goals and the methods of restoration ecology. Restoration ecology is the science of restoring communities to a previous, more functional or more “natural” condition, variously defined as before human or before recent industrial impact. Restoration ecology informs the growing practice of ecological restoration.
© 2011 Pearson Education, Inc. Altered communities can be restored Humans have dramatically changed ecological systems -Severely degraded systems cease to function Ecological restoration = efforts to restore communities Restoration is informed by restoration ecology = the science of restoring an area to an earlier condition -To restore the system’s functionality (i.e. filtering of water by a wetland) -It is difficult, time-consuming, and expensive It is best to protect natural systems from degradation in the first place
© 2011 Pearson Education, Inc. Restoration efforts Prairie restoration = replanting native species, controlling invasive species The world’s largest project = Florida Everglades -Flood control and irrigation removed water -Populations of wading birds dropped 90-95% -It will take 30 years and billions of dollars to restore natural water flow
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