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Chapter 37 Communities and Ecosystems PowerPoint Lectures for Biology: Concepts & Connections, Sixth Edition Campbell, Reece, Taylor, Simon, and Dickey Lecture by Brian R. Shmaefsky Copyright © 2009 Pearson Education, Inc. COMMUNITY STRUCTURE AND DYNAMICS 37.1 A community includes all the organisms inhabiting a particular area ▪ 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 ▪ 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 ● Competition lowers the carrying capacity of competing populations 37.3 Competition may occur when a shared resource is limited ▪ Ecological niche ● Sum of an organism’s use of biotic and abiotic resources ● Interspecific competition occurs when the niches of two populations overlap ▪ The role of an organism in an ecosystem ▪ Part of a habitat where and organism makes it home 37.4 Mutualism benefits both partners ▪ Mutualism → Symbiosis that is beneficial to both organisms involved 37.5 Predation leads to diverse adaptations in prey species ▪ Predation benefits the predator but kills the prey ▪ Prey adapt using protective strategies ● Camouflage ● Mechanical defenses ● Chemical defenses 37.6 Herbivory leads to diverse adaptations in plants ▪ 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 ▪ Parasitism→ the parasite benefits and the host is negatively affected ▪ 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 ▪ 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 ▪ Trophic structure ● A pattern of feeding relationships consisting of several different levels ▪ Food chain ● Pathway of energy flow in an ecosystem. The arrows represent the flow of energy. ● **Only 10% of the energy from one trophic level is passed to the next trophic level. ▪ Producers ● Support all other trophic levels ● Autotrophs Examples: ● Photosynthetic producers ● Plants on land ● Cyanobacteria in water ▪ Consumers ● Heterotrophs ● Primary consumers (eat producers) ● Secondary consumers (eat primary consumers) ● Tertiary consumers (eat secondary consumers) ● Quaternary consumers (eat tertiary consumers) ▪ Detritivores and decomposers ● Derive energy from dead matter and wastes ● Examples: worms, fungi, bacteria Plant A terrestrial food chain Producers Phytoplankton An aquatic food chain Grasshopper Plant A terrestrial food chain Primary consumers Zooplankton Producers Phytoplankton An aquatic food chain Mouse Secondary consumers Herrin g Grasshopper Primary consumers Zooplankton Producers Phytoplankton Plant A terrestrial food chain An aquatic food chain Snake Tertiary consumers Tuna Mouse Secondary consumers Herrin g Grasshopper Primary consumers Zooplankton Producers Phytoplankton Plant A terrestrial food chain An aquatic food chain Trophic level Hawk Quaternary consumers Killer whale Snake Tertiary consumers Tuna Mouse Secondary consumers Herrin g Grasshopper Primary consumers Zooplankton Producers Phytoplankton Plant A terrestrial food chain An aquatic food chain 37.9 Food chains interconnect, forming food webs ▪ Food web - A network of interconnecting food chains Quaternary, tertiary, and secondary consumers Tertiary and secondary consumers Secondary and primary consumers Primary consumers Producers (plants) 37.10 Species diversity includes relative abundance and species richness ▪ Species diversity defined by two components ● Species richness ● Relative abundance ▪ Plant species diversity in a community affects the animals ▪ Species diversity has consequences for pathogens 37.11 Keystone species have a disproportionate impact on diversity 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 keeps sea urchin population down, which would take over a habitat and eat all the kelp Keystone Keystone absent 37.12 Disturbance is a prominent feature of most communities ▪ 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 ▪ Communities change drastically following a severe disturbance ▪ Ecological succession ● Colonization by a variety of species ● A success of change gradually replaces other species ▪ 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 Annual Perennial plants plants and grasses Shrubs Softwood trees such as pines Time Hardwood trees 37.13 Invasive species can devastate communities ▪ Introduction of rabbits in Australia 600 Km 1980 1900 19 20 Australia 1910 0 9 18 18 80 1870 Key 70 8 1 Frontier of rabbit spread Origin: 1860 1890 00 19 10 19 192 20 0 1910 19 192 0 191 0 1910 1880 ECOSYSTEM STRUCTURE AND DYNAMICS 37.14 Ecosystem ecology emphasizes energy flow and chemical cycling ▪ 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 Chemical cycling Energy flow Chemical energy Light energy Heat energy Chemical elements Bacteria and fungi 37.15 Primary production sets the energy budget for ecosystems ▪ 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 ● Ex: forest debris, crops, waste 37.16 Energy supply limits the length of food chains ▪ A pyramid of production ● Illustrates the cumulative loss of energy transfer in a food chain Tertiary consumers Secondary consumers Primary consumers 10 kcal 100 kcal 1,000 kcal Producers 10,000 kcal 1,000,000 kcal of sunlight ▪ The dynamics of energy flow apply to the human population Trophic level Secondary consumers Primary consumer s Producers Human meat-eaters Human vegetarians Cattle Corn Corn 37.18 Chemicals are cycled between organic matter and abiotic reservoirs ▪ Ecosystems are supplied with a continual influx of energy from → ● 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 Consumers 3 2 Producer s Decomposer s 1 Nutrients available to producers Abiotic reservoir Geologic processes 4 37.19 The carbon cycle depends on photosynthesis and respiration ▪ Carbon is the major ingredient of all organic molecules ▪ The return of CO2 to the atmosphere by respiration closely balances its removal by photosynthesis ▪ The carbon cycle is affected by burning wood and fossil fuels CO2 in atmosphere 5 Burning 3 Cellular respiration Photosynthesis 1 Wood and fossil fuels Decomposition Higher-level consumers Primary consumers Wastes; death Decomposers (soil microbes) Plants, algae, cyanobacteria 4 Detritus 2 Plant litter; death 37.20 The phosphorus cycle depends on the weathering of rock ▪ 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 6 Uplifting of rock 3 Weathering of rock Runoff Phosphates in rock Animals Plants 1 Assimilation 2 Phosphates in solution Detritus Phosphates in soil (inorganic) 5 Rock Precipitated (solid) phosphates Decomposition Decomposers in soil 4 37.21 The nitrogen cycle depends on bacteria ▪ Nitrogen is an essential component of proteins and nucleic acids ▪ Nitrogen has two abiotic reservoirs ● Air ● Soil ▪ Nitrogen fixation converts N2 to nitrogen used by plants ● Carried out by some bacteria and cyanobacteria Nitrogen (N2) in atmosphere 8 Animal Plant 6 Assimilation by plants Organic compounds Nitrogen fixation Death; wastes 5 Denitrifiers Organic compounds 3 Nitrates in soil (NO3–) Nitrogen-fixing bacteria in root nodules Detritus Free-living nitrogen-fixing bacteria and cyanobacteria Decomposers 4 1 Nitrifying bacteria 7 Decomposition Ammonium in soil (NH4+) Nitrogen fixation 2 37.22: Ecosystem alteration can upset chemical cycling ▪ 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 Nitrate concentration in runoff (mg/L) 80.0 60.0 Deforested 40.0 20.0 4.0 3.0 Completion of tree cutting Control 2.0 1.0 0 1965 1966 1967 1968 37.23: David Schindler talks about the effects of nutrients on freshwater ecosystems ▪ Major changes in terrestrial ecosystems disrupt chemical cycling ▪ These changes can increase nutrients in aquatic ecosystems ● Algal and cyanobacteria blooms ● Eutrophication - the enrichment of an ecosystem with chemical nutrients, typically compounds containing nitrogen, phosphorus, or both. ▪ The most serious current threats ● Acid precipitation ● Changes in land use ● Climate warming Producer Herbivore (primary consumer) Energy flow Chemical cycling Decomposer s Carnivore (secondar y consumer) Ecosystems involve the processes of (a) (b) in which in which makes a chemical elements (c) one-way trip from solar energy to chemical energy to heat is are from converted by incorporated by (d) (e) to chemical into energy of components of detritivores return elements to organic molecules which pass through (f)
