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BIOLOGY CONCEPTS & CONNECTIONS Fourth Edition Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor CHAPTER 36 Communities and Ecosystems Modules 36.1 – 36.4 From PowerPoint® Lectures for Biology: Concepts & Connections Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 36.1 A community is all the organisms inhabiting a particular area • All the organisms in a particular area make up a community • A number of factors characterize every community – Biodiversity – The prevalent form of vegetation – Response to disturbances – Trophic structure (feeding relationships) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 36.1 • Biodiversity is the variety of different kinds of organisms that make up a community • Biodiversity has two components – Species richness, or the total number of different species in the community – The relative abundance of different species Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings STRUCTURAL FEATURES OF COMMUNITIES 36.2 Competition may occur when a shared resource is limited • Interspecific competition occurs between two populations if they both require the same limited resource • A population's niche is its role in the community – The sum total of its use of the biotic and abiotic resources of its habitat Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The competitive exclusion principle – Populations of two species cannot coexist in a community if their niches are nearly identical High tide Chthamalus Balanus Ocean Low tide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 36.2 • Competition between species with identical niches has two possible outcomes – One of the populations, using resources more efficiently and having a reproductive advantage, will eventually eliminate the other – Natural selection may lead to resource partitioning Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 36.3 Predation leads to diverse adaptations in both predator and prey • Predation is an interaction where one species eats another – The consumer is called the predator and the food species is known as the prey • Parasitism can be considered a form of predation Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 36.4 Predation can maintain diversity in a community • A keystone species exerts strong control on community structure because of its ecological role • A keystone predator may maintain community diversity by reducing the numbers of the strongest competitors in a community – This sea star is a keystone predator Figure 36.4A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Predation by killer whales on sea otters, allowing sea urchins to overgraze on kelp – Sea otters represent the keystone species Figure 36.4B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 36.5 Symbiotic relationships help structure communities • A symbiotic relationship is an interaction between two or more species that live together in direct contact • There are three main types of symbiotic relationships within communities – Parasitism – Commensalism – Mutualism Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Parasitism is a kind of predator-prey relationship – The parasite benefits and the host is harmed in this symbiotic relationship – A parasite obtains food at the expense of its host – Parasites are typically smaller than their hosts Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Commensalism is a symbiotic relationship where one partner benefits and the other is unaffected • Examples of commensalism – Algae that grow on the shells of sea turtles – Barnacles that attach to whales – Birds that feed on insects flushed out of the grass by grazing cattle Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Mutualism is a symbiotic relationship where both partners benefit • Examples of mutualism – Nitrogen-fixing bacteria and legumes – Acacia trees and the ants of the genus Pseudomyrmex Figure 36.5B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 36.6 Disturbance is a prominent feature of most communities • Disturbances include events such as storms, fires, floods, droughts, overgrazing, and human activities – They damage biological communities – They remove organisms from communities – They alter the availability of resources Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 36.6 • Ecological succession is a transition in the species composition of a community following a disturbance – Primary succession is the gradual colonization of barren rocks by living organisms – Secondary succession occurs after a disturbance has removed the vegetation but left the soil intact Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings ECOSYSTEM STRUCTURE AND DYNAMICS 36.8 Energy flow and chemical cycling are the two fundamental processes in ecosystems • A community interacts with abiotic factors, forming an ecosystem • Energy flows from the sun, through plants, animals, and decomposers, and is lost as heat • Chemicals are recycled between air, water, soil, and organisms Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • A terrarium ecosystem Chemical cycling (C, N, etc.) Light energy Chemical energy Heat energy Figure 36.8 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 36.9 Trophic structure is a key factor in ecosystem dynamics • A food chain is the stepwise flow of energy and nutrients – from plants (producers) – to herbivores (primary consumers) – to carnivores (secondary and higher-level consumers) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings TROPHIC LEVEL Quaternary consumers Carnivore Carnivore Tertiary consumers Carnivore Carnivore Secondary consumers Carnivore Carnivore Primary consumers Herbivore Zooplankton Producers Plant Phytoplankton A TERRESTRIAL FOOD CHAIN AN AQUATIC FOOD CHAIN Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 36.9A • Decomposition is the breakdown of organic compounds into inorganic compounds • Decomposition is essential for the continuation of life on Earth • Detritivores decompose waste matter and recycle nutrients – Examples: animal scavengers, fungi, and prokaryotes Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 36.9B 36.10 Food chains interconnect, forming food webs • A food web is a network of interconnecting food chains – It is a more realistic view of the trophic structure of an ecosystem than a food chain Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Wastes and dead organisms Tertiary and secondary consumers Secondary and primary consumers Primary consumers Producers (Plants, algae, phytoplankton) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Detritivores (Prokaryotes, fungi, certain animals) Figure 36.10 36.11 Energy supply limits the length of food chains • Biomass is the amount of living organic material in an ecosystem • Primary production is the rate at which producers convert sunlight to chemical energy – The primary production of the entire biosphere is about 170 billion tons of biomass per year Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • A pyramid of production reveals the flow of energy from producers to primary consumers and to higher trophic levels Tertiary consumers 10 kcal Secondary consumers 100 kcal Primary consumers 1,000 kcal Producers 10,000 kcal 1,000,000 kcal of sunlight Figure 36.11 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Only about 10% of the energy in food is stored at each trophic level and available to the next level – This stepwise energy loss limits most food chains to 3 - 5 levels – There is simply not enough energy at the very top of an ecological pyramid to support another trophic level Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 36.12 Connection: A production pyramid explains why meat is a luxury for humans • The dynamics of energy flow apply to the human population as much as to other organisms – When we eat grain or fruit, we are primary consumers – When we eat beef or other meat from herbivores, we are secondary consumers – When we eat fish like trout or salmon (which eat insects and other small animals), we are tertiary or quaternary consumers Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Because the production pyramid tapers so sharply, a field of corn or other plant crops can support many more vegetarians than meateaters TROPHIC LEVEL Secondary consumers Primary consumers Human meat-eaters Human vegetarians Cattle Corn Corn Producers Figure 36.12 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 36.13 Chemicals are recycled between organic matter and abiotic reservoirs • Ecosystems require daily infusions of energy – The sun supplies the Earth with energy – But there are no extraterrestrial sources of water or other chemical nutrients • Nutrients must be recycled between organisms and abiotic reservoirs – Abiotic reservoirs are parts of the ecosystem where a chemical accumulates Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • There are four main abiotic reservoirs – Water cycle – Carbon cycle – Nitrogen cycle – Phosphorus cycle Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 35.14 Water moves through the biosphere in a global cycle • Heat from the sun drives the global water cycle – Precipitation – Evaporation – Transpiration Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Solar heat Water vapor over the sea Precipitation over the sea (283) Net movement of water vapor by wind (36) Evaporation from the sea (319) Water vapor over the land Evaporation and transpiration (59) Precipitation over the land (95) Oceans Flow of water from land to sea (36) Surface water and groundwater Figure 36.14 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 36.15 The carbon cycle depends on photosynthesis and respiration • Carbon is taken from the atmosphere by photosynthesis – It is used to make organic molecules – It is returned to the atmosphere by cellular respiration Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings CO2 in atmosphere Burning Cellular respiration Plants, algae, cyanobacteria Photosynthesis Higher-level consumers Primary consumers Wood and fossil fuels Decomposition Detritivores (soil microbes and others) Detritus Figure 36.15 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 36.16 The nitrogen cycle relies heavily on bacteria • Nitrogen is plentiful in the atmosphere as N2 – But plants cannot use N2 • Various bacteria in soil (and legume root nodules) convert N2 to nitrogen compounds that plants can use – Ammonium (NH4+) and nitrate (NO3–) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Some bacteria break down organic matter and recycle nitrogen as ammonium or nitrate to plants • Other bacteria return N2 to the atmosphere Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Nitrogen (N2) in atmosphere Assimilation by plants Amino acids and proteins in plants and animals Denitrifying bacteria Nitrogen fixation Detritus Nitrogen-fixing bacteria in root nodules of legumes Nitrates (NO3–) Detritivores Decomposition Nitrifying bacteria Nitrogen-fixing bacteria in soil Nitrogen fixation Ammonium (NH4+) Figure 36.16 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 36.17 The phosphorus cycle depends on the weathering of rock • Phosphates (compounds containing PO43-) and other minerals are added to the soil by the gradual weathering of rock • Consumers obtain phosphorus in organic form from plants • Phosphates are returned to the soil through excretion by animals and the actions of decomposers Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Uplifting of rock Phosphates in organic compounds Weathering of rock Phosphates in rock Animals Plants Runoff Detritus Phosphates in solution Phosphates in soil (inorganic) Decomposition Rock Precipitated (solid) phosphates Detritivores in soil Figure 36.17 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings