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COMMUNITY STRUCTURE AND DYNAMICS Copyright © 2009 Pearson Education, Inc. ◦ 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 – What kind of communities exist at Miramar College? Copyright © 2009 Pearson Education, Inc. ◦ Interspecific interactions – Relationships with other species in the community – Can have positive (+) or negative (-) effects on each species Copyright © 2009 Pearson Education, Inc. 1. Interspecific competition (usually -/-) – Two different species compete for the same limited resource – Squirrels and black bears Copyright © 2009 Pearson Education, Inc. Bear and Squirrel by ~magooey on deviantART ◦ Competition occurs when ecological niche of species overlap – Ecological niche: Sum of an organism’s use of biotic and abiotic resources Copyright © 2009 Pearson Education, Inc. 2. Mutualism: both populations benefit (+/+) ◦ Example: Reef-building corals – Photosynthetic dinoflagellates and heterotrophic cnidarian Copyright © 2009 Pearson Education, Inc. 3. Predation: benefits the predator but kills prey (+/-) However, can lead to evolutionary adaptation Copyright © 2009 Pearson Education, Inc. 4. Herbivory is not usually fatal and leads to adaptation in plants (+/-) – Plants must expend energy to replace the loss Plants have numerous defenses against herbivores – Spines and thorns – Chemical toxins Copyright © 2009 Pearson Education, Inc. 5. A parasite lives on or in a host from which it obtains nourishment (+/-) – Internal parasites include nematodes and tapeworms – External parasites include aphids and mosquitos Copyright © 2009 Pearson Education, Inc. Pathogens are disease-causing parasites (+/-) – Pathogens can be bacteria, viruses, fungi, or protists Copyright © 2009 Pearson Education, Inc. Non-native pathogens can have rapid and dramatic impacts Non-native pathogens can cause a decline of the ecosystem Example: Snakehead fish Copyright © 2009 Pearson Education, Inc. Trophic structure – A pattern of feeding relationships consisting of several different levels Food chain – Sequence of food transfer up the trophic levels Copyright © 2009 Pearson Education, Inc. Producers – Support all other trophic levels – Examples?? Copyright © 2009 Pearson Education, Inc. Producers – Support all other trophic levels – Examples: – Phytoplankton and plants Consumers – Heterotrophs – – – – Primary consumers Secondary consumers Tertiary consumers Quaternary consumers Copyright © 2009 Pearson Education, Inc. Producers – Support all other trophic levels Consumers – Heterotrophs – Primary consumers – Secondary consumers – Tertiary consumers – Quaternary consumers Detritivores and decomposers – Derive energy from dead matter and wastes Copyright © 2009 Pearson Education, Inc. 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 Herring Grasshopper Primary consumers Zooplankton Producers Phytoplankton Plant A terrestrial food chain An aquatic food chain Snake Tertiary consumers Tuna Mouse Secondary consumers Herring 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 Herring Grasshopper Primary consumers Zooplankton Producers Phytoplankton Plant A terrestrial food chain An aquatic food chain Food web – A network of interconnecting food chains Example: Mercury poisoning Quaternary, tertiary, and secondary consumers Tertiary and secondary consumers Secondary and primary consumers Primary consumers Producers (plants) Copyright © 2009 Pearson Education, Inc. Species diversity defined by two components 1. Species richness 2. Relative abundance A B Copyright © 2009 Pearson Education, Inc. Keystone species Keystone – 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 Copyright © 2009 Pearson Education, Inc. Keystone absent 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 Copyright © 2009 Pearson Education, Inc. Invasive species can devastate communities Invasive species: non-native species spreading beyond their point of introduction and causing environmental or economic damage Example: Snakehead fish Copyright © 2009 Pearson Education, Inc. Communities change drastically following a severe disturbance Ecological succession – Colonization by a variety of species – A success of change gradually replaces other species Copyright © 2009 Pearson Education, Inc. 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 plants Perennial plants and grasses Copyright © 2009 Pearson Education, Inc. Shrubs Softwood trees such as pines Time Hardwood trees Introduction of rabbits in Australia 600 Km Australia Key Frontier of rabbit spread Origin: 1860 Copyright © 2009 Pearson Education, Inc. ECOSYSTEM STRUCTURE AND DYNAMICS Copyright © 2009 Pearson Education, Inc. 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 Copyright © 2009 Pearson Education, Inc. A terrarium has the components of an ecosystem Chemical cycling Energy flow Light energy Chemical energy Heat energy Chemical elements Bacteria and fungi Copyright © 2009 Pearson Education, Inc. Primary production – The amount of solar energy converted to chemical energy – Carried out by ________________ – Produces biomass – Amount of living organic material in an ecosystem Copyright © 2009 Pearson Education, Inc. Primary production of different ecosystems Open ocean Estuary Algal beds and coral reefs Desert and semidesert scrub Tundra Temperate grassland Cultivated land Boreal forest (taiga) Savanna Temperate deciduous forest Tropical rain forest 0 500 1,000 1,500 2,000 2,500 Average net primary productivity (g/m2/yr) Copyright © 2009 Pearson Education, Inc. A pyramid of production – Illustrates the cumulative loss of energy transfer in a food chain Tertiary consumers 10 kcal Secondary consumers 100 kcal Primary consumers Producers Copyright © 2009 Pearson Education, Inc. 1,000 kcal 10,000 kcal 1,000,000 kcal of sunlight Trophic level Secondary consumers Human meat-eaters Human Primary consumers vegetarians Producers Corn Cattle Corn Biogeochemical cycles – Cycle chemicals between organisms (biotic) and the Earth (abiotic) Decomposers play a central role in biogeochemical cycles Copyright © 2009 Pearson Education, Inc. Consumers 3 2 Producers Decomposers 1 Nutrients available to producers Abiotic reservoir Geologic processes 4 Biotic: Carbon is basis of organic molecules Abiotic: Carbon is found ___________ The return of CO2 to the atmosphere by respiration closely balances its removal by photosynthesis Copyright © 2009 Pearson Education, Inc. CO2 in atmosphere 5 Burning 3 Cellular respiration Photosynthesis 1 Higher-level consumers Wood and fossil fuels Primary consumers Wastes; death Decomposers (soil microbes) Plants, algae, cyanobacteria 4 Detritus 2 Plant litter; death Biotic: organisms require phosphorus for ___________. Abiotic: No atmospheric component; abiotic resevoir found in rocks, soil Copyright © 2009 Pearson Education, Inc. 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 Biotic: Nitrogen is essential for ________. Abiotic: Nitrogen found in air and soil Nitrogen fixation converts N2 to nitrogen used by plants – Carried out by some bacteria and cyanobacteria Copyright © 2009 Pearson Education, Inc. Nitrogen fixation Leguminous root nodules TEM of rhizobia in root nodule cell Rhizobium in symbiosis Azotobacter Klebsiella some Clostridium 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 (NH4+) in soil Nitrogen fixation 2 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 Copyright © 2009 Pearson Education, Inc. Producer Herbivore (primary consumer) Energy flow Chemical cycling Decomposers Carnivore (secondary consumer)