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Chapter 37 Communities and Ecosystems Introduction: Hungry Hippos A.) All communities and ecosystems have certain features in common B.) Each type of ecosystem has its own unique structure and dynamics C.) Human activities can disrupt the balance of ecosystems COMMUNITY STRUCTURE AND DYNAMICS 37.1 A community includes all the organisms inhabiting a particular area A.) B.) Biological community – An assemblage of populations living close enough together for potential interaction – Described by its species composition Boundaries of the community vary with research questions – Can be a pond – Can be the intestinal microbes of a pond organism 37.2 Interspecific interactions are fundamental to community structure A.) B.) Interspecific interactions – Relationships with other species in the community Interspecific competition – Two different species compete for the same limited resource – – Squirrels and black bears Compete for acorns 37.3 Competition may occur when a shared resource is limited A.) Ecological niche – Sum of an organism’s use of biotic and abiotic resources – Interspecific competition occurs when the niches of two populations overlap B.) Competition lowers the carrying capacity of competing populations C.) Interspecific competition between orange-crowned warbler and Virginia’s warbler 37.4 Mutualism benefits both partners A.) Reef-building corals require mutualism – Photosynthetic dinoflagellates – Live in the cells of each coral polyp – Produce sugars used by the polyps – Provide at least half of the energy used by the coral animals 37.5 EVOLUTION CONNECTION: Predation leads to diverse adaptations in prey species A.) Predation benefits the predator but kills the prey B.) Prey adapt using protective strategies – Camouflage – Mechanical defenses – Chemical defenses 37.6 EVOLUTION CONNECTION: Herbivory leads to diverse adaptations in plants A.) B.) C.) Herbivory is not usually fatal – Plants must expend energy to replace the loss Plants have numerous defenses against herbivores – Spines and thorns – Chemical toxins Herbivores and plants undergo coevolution – A change in one species acts as a new selective force on another – Poison-resistant caterpillars seem to be a strong selective force for Passiflora plants 37.7 Parasites and pathogens can affect community composition A.) A parasite lives on or in a host from which it obtains nourishment – Internal parasites include nematodes and tapeworms – External parasites include mosquitoes and ticks B.) C.) D.) Pathogens are disease-causing parasites – Pathogens can be bacteria, viruses, fungi, or protists Non-native pathogens can have rapid and dramatic impacts – American chestnut devastated by chestnut blight protist – A fungus-like pathogen currently causing sudden oak death on the West Coast Non-native pathogens can cause a decline of the ecosystem 37.8 Trophic structure is a key factor in community dynamics A.) B.) C.) Trophic structure – A pattern of feeding relationships consisting of several different levels Food chain – Sequence of food transfer up the trophic levels Producers – Support all other trophic levels – Autotrophs – D.) Consumers – Heterotrophs – – – – E.) Photosynthetic producers – Plants on land – Cyanobacteria in water Primary consumers Secondary consumers Tertiary consumers Quaternary consumers Detritivores and decomposers – Derive energy from dead matter and wastes 37.9 Food chains interconnect, forming food webs A.) Food web – A network of interconnecting food chains 37.10 Species diversity includes relative abundance and species richness A.) Species diversity defined by two components – Species richness – Relative abundance B.) Plant species diversity in a community affects the animals C.) Species diversity has consequences for pathogens 37.11 Keystone species have a disproportionate impact on diversity A.) Keystone species – A species whose impact on its community is larger than its biomass or abundance indicates – Occupies a niche that holds the rest of its community in place 37.12 Disturbance is a prominent feature of most communities A.) Disturbances – Events that damage biological communities – Storms, fire, floods, droughts, overgrazing, or human activity – The types, frequency, and severity of disturbances vary from community to community B.) Communities change drastically following a severe disturbance C.) Ecological succession – Colonization by a variety of species – A success of change gradually replaces other species D.) E.) Primary succession – Begins in a virtually lifeless area with no soil Secondary succession – When a disturbance destroyed an existing community but left the soil intact 37.13 CONNECTION: Invasive species can devastate communities A.) Introduction of rabbits in Australia ECOSYSTEM STRUCTURE AND DYNAMICS 37.14 Ecosystem ecology emphasizes energy flow and chemical cycling A.) B.) Ecosystem – All the organisms in a community as well as the abiotic environment Components of ecosystems – Energy flow – Passage of energy through the ecosystem – Chemical cycling – Transfer of materials within the ecosystem C.) A terrarium has the components of an ecosystem 37.15 Primary production sets the energy budget for ecosystems A.) Primary production – The amount of solar energy converted to chemical energy – Carried out by producers – Produces biomass – Amount of living organic material in an ecosystem B.) Primary production of different ecosystems 37.16 Energy supply limits the length of food chains A.) A pyramid of production – Illustrates the cumulative loss of energy transfer in a food chain 37.17 CONNECTION: A production pyramid explains why meat is a luxury for humans A.) The dynamics of energy flow apply to the human population 37.18 Chemicals are cycled between organic matter and abiotic reservoirs A.) B.) C.) D.) Ecosystems are supplied with a continual influx of energy – Sun – Earth’s interior Life also depends on the recycling of chemicals – Organisms acquire chemicals as nutrients and lose chemicals as waste products Biogeochemical cycles – Cycle chemicals between organisms and the Earth – Can be local or global Decomposers play a central role in biogeochemical cycles 37.19 The carbon cycle depends on photosynthesis and respiration A.) Carbon is the major ingredient of all organic molecules B.) The return of CO2 to the atmosphere by respiration closely balances its removal by photosynthesis C.) The carbon cycle is affected by burning wood and fossil fuels 37.20 The phosphorus cycle depends on the weathering of rock A.) Organisms require phosphorus for nucleic acids, phospholipids, and ATP – Plants absorb phosphate ions in the soil and build them into organic compounds – Phosphates are returned to the soil by decomposers – Phosphate levels in aquatic ecosystems are typically low enough to be a limiting factor 37.21 The nitrogen cycle depends on bacteria A.) Nitrogen is an essential component of proteins and nucleic acids B.) C.) Nitrogen has two abiotic reservoirs – Air – Soil Nitrogen fixation converts N2 to nitrogen used by plants – Carried out by some bacteria and cyanobacteria 37.22 CONNECTION: Ecosystem alteration can upset chemical cycling A.) B.) Chemical cycling in an ecosystem depends on – The web of feeding – Relationships between plants, animals, and detritivores – Geologic processes Altering an environment can cause severe losses in chemical cycling – Erosion – Acid rain 37.23 TALKING ABOUT SCIENCE: David Schindler talks about the effects of nutrients on freshwater ecosystems A.) Major changes in terrestrial ecosystems disrupt chemical cycling B.) These changes can increase nutrients in aquatic ecosystems – Algal and cyanobacteria blooms – Eutrophication C.) The most serious current threats – Acid precipitation – Changes in land use – Climate warming You should now be able to § Describe the characteristics of a community § Explain how interspecific interactions affect the dynamics of populations § Describe the trophic structure of a community § Explain how species diversity is measured § Describe the role of environmental disturbance on ecological succession § Explain energy and nutrient cycling in ecosystems