Figure 5.10: Primary ecological succession. Over almost a thousand years, plant communities developed, starting on bare rock exposed by a retreating glacier on Isle Royal, Michigan (USA) in northern Lake Superior. The details of this process vary from one site to another. Question: What are two ways in which lichens, mosses, and plants might get started growing on bare rock?
Active Figure 5.11: Natural ecological restoration of disturbed land. Secondary ecological succession of plant communities on an abandoned farm field in the U.S. state of North Carolina. It took 150–200 years after the farmland was abandoned for the area to become covered with a mature oak and hickory forest. A new disturbance such as deforestation or fire would create conditions favoring pioneer species such as annual weeds. In the absence of new disturbances, secondary succession would recur over time, but not necessarily in the same sequence shown here. Questions: Do you think the annual weeds (left) would continue to thrive in the mature forest (right)? Why or why not? See an animation based on this figure at CengageNOW.
5 2 population growth
5-25-2Limits Population GrowthLimits Population Growth
Concept to UnderstandConcept to UnderstandNo population can continue to growNo population can continue to growindefinitely because of limitations onindefinitely because of limitations onresources and because of competitionresources and because of competitionamong species for those resources.among species for those resources.
Population SizePopulation SizePopulations can grow, shrink, or stay thePopulations can grow, shrink, or stay thesamesamePopulation size may vary in cycles based onPopulation size may vary in cycles based onbirths, deaths, immigration & emigrationbirths, deaths, immigration & emigrationPopulation change = (Births + Immigration) – (Deaths + Emigration)Population change = (Births + Immigration) – (Deaths + Emigration)
Reproductive patternsReproductive patterns1. Some species have many offspring, usually1. Some species have many offspring, usuallysmall and give them little or no parental caresmall and give them little or no parental careor protection.or protection.Ex. Algae, frogs, most insectsEx. Algae, frogs, most insects
Reproductive patternsReproductive patterns2. Some species have few offspring, usually2. Some species have few offspring, usuallyfairly large and invest parental care andfairly large and invest parental care andprotection.protection.Ex. People, elephants, whales, birds of preyEx. People, elephants, whales, birds of prey
Population LimitsPopulation Limits• No population can growNo population can growindefinitelyindefinitely• Limiting factors that keepLimiting factors that keeppopulations frompopulations fromuncontrolled expansionuncontrolled expansioncalledcalled EnvironmentalEnvironmentalResistanceResistance• Examples: water, light,Examples: water, light,space, nutrients, predators,space, nutrients, predators,disease, or competitiondisease, or competition
Population LimitsPopulation Limits• Exponential growthExponential growth– rapid growth in a– rapid growth in apopulation.population.• Carrying capacityCarrying capacity ––maximum populationmaximum populationsize that ansize that anecosystem canecosystem cansupportsupport
Population CrashPopulation CrashWhen a population exceeds its carrying capacity itsWhen a population exceeds its carrying capacity itspopulation can crash.population can crash.Caused by little to no environmental resistance.Caused by little to no environmental resistance.
Population CrashPopulation CrashPopulation crashes are morePopulation crashes are morelikely when organisms cannotlikely when organisms cannotmove easily to newmove easily to newecosystems.ecosystems.Crash caused byCrash caused by::1. Not enough resources (like1. Not enough resources (likefood and water)food and water)2. New Diseases2. New DiseasesEcosystems could beEcosystems could bedestroyed permentantly!!destroyed permentantly!!
Humans Not Except fromHumans Not Except fromPopulation ControlsPopulation ControlsBubonic plague (14Bubonic plague (14ththcentury) 25 million killedcentury) 25 million killedFamine in Ireland (1845) – 1 million died & 3Famine in Ireland (1845) – 1 million died & 3million emigrated to USmillion emigrated to USAIDS – 27 million dies 2 million each yearAIDS – 27 million dies 2 million each yearTechnology, social, and cultural changesTechnology, social, and cultural changesextended earth’s carrying capacity for humansextended earth’s carrying capacity for humansExpand indefinitely or reach carryingExpand indefinitely or reach carryingcapacity?capacity?
5-3 How Do Communities and Ecosystems5-3 How Do Communities and EcosystemsRespond to Changing EnvironmentalRespond to Changing EnvironmentalConditions?Conditions?Concept 5-3Concept 5-3 The structure and speciesThe structure and speciescomposition of communities andcomposition of communities andecosystems change in response toecosystems change in response tochanging environmental conditionschanging environmental conditionsthrough a process called ecologicalthrough a process called ecologicalsuccession.succession.
SuccessionSuccessionSuccessionSuccession – the gradual, sequential– the gradual, sequentialre-growth of species in an areare-growth of species in an area1. Primary succession1. Primary succession – the– thedevelopment of a community in an areadevelopment of a community in an areathat has not supported life previouslythat has not supported life previouslyEx. Bare rock, volcanic island,Ex. Bare rock, volcanic island,Mosses are usually first life.Mosses are usually first life.
SuccessionSuccession2. Secondary succession2. Secondary succession – the sequential– the sequentialreplacement of species that followsreplacement of species that followsdisruption of an existing communitydisruption of an existing communityEx. Abandoned farmland.Ex. Abandoned farmland.Burned or cut forests.Burned or cut forests.Heavily polluted streams.Heavily polluted streams.Flooded land.Flooded land.
AnnualweedsMature oak and hickoryforestYoung pine forestwith developingunderstory of oakand hickory treesTimeShrubs andsmall pineseedlingsPerennialweeds andgrassesStepped ArtFig. 5-11, p. 90
Limits to ChangeLimits to ChangeInertia (persistence)Inertia (persistence) is the ability of a livingis the ability of a livingsystem, such as a grassland or forest, to survivesystem, such as a grassland or forest, to survivemoderate disturbances.moderate disturbances.ResilienceResilience is the ability of a living system to beis the ability of a living system to berestored through secondary succession after arestored through secondary succession after amore severe disturbance.more severe disturbance.Ex. Tropical rain forest: inertia – yes resilient – noEx. Tropical rain forest: inertia – yes resilient – noEx. Grassland: inertia – no resilient - yesEx. Grassland: inertia – no resilient - yes