No population can continue growing indefinitely due to limitations on resources and competition among species. Populations can grow, shrink, or stay the same depending on births, deaths, immigration, and emigration. When a population exceeds the carrying capacity of its environment, the population may crash due to lack of resources or disease. Communities and ecosystems change over time in response to environmental conditions through the process of ecological succession as different species colonize and replace one another.

1. 5-25-2
Limits Population GrowthLimits Population Growth

2. Concept to UnderstandConcept to Understand
No population can continue to growNo population can continue to grow
indefinitely because of limitations onindefinitely because of limitations on
resources and because of competitionresources and because of competition
among species for those resources.among species for those resources.

3. Population SizePopulation Size
Populations can grow, shrink, or stay thePopulations can grow, shrink, or stay the
samesame
Population size may vary in cycles based onPopulation size may vary in cycles based on
births, deaths, immigration & emigrationbirths, deaths, immigration & emigration
Population change = (Births + Immigration) – (Deaths + Emigration)Population change = (Births + Immigration) – (Deaths + Emigration)

4. Reproductive patternsReproductive patterns
1. Some species have many offspring, usually1. Some species have many offspring, usually
small and give them little or no parental caresmall and give them little or no parental care
or protection.or protection.

Ex. Algae, frogs, most insectsEx. Algae, frogs, most insects

5. Reproductive patternsReproductive patterns
2. Some species have few offspring, usually2. Some species have few offspring, usually
fairly large and invest parental care andfairly large and invest parental care and
protection.protection.

Ex. People, elephants, whales, birds of preyEx. People, elephants, whales, birds of prey

6. Population LimitsPopulation Limits
• No population can growNo population can grow
indefinitelyindefinitely
• Limiting factors that keepLimiting factors that keep
populations frompopulations from
uncontrolled expansionuncontrolled expansion
calledcalled EnvironmentalEnvironmental
ResistanceResistance
• Examples: water, light,Examples: water, light,
space, nutrients, predators,space, nutrients, predators,
disease, or competitiondisease, or competition

8. Population LimitsPopulation Limits
• Exponential growthExponential growth
– rapid growth in a– rapid growth in a
population.population.
• Carrying capacityCarrying capacity ––
maximum populationmaximum population
size that ansize that an
ecosystem canecosystem can
supportsupport

9. Population CrashPopulation Crash
When a population exceeds its carrying capacity itsWhen a population exceeds its carrying capacity its
population can crash.population can crash.
Caused by little to no environmental resistance.Caused by little to no environmental resistance.

10. Population CrashPopulation Crash
Population crashes are morePopulation crashes are more
likely when organisms cannotlikely when organisms cannot
move easily to newmove easily to new
ecosystems.ecosystems.
Crash caused byCrash caused by::
1. Not enough resources (like1. Not enough resources (like
food and water)food and water)
2. New Diseases2. New Diseases
Ecosystems could beEcosystems could be
destroyed permentantly!!destroyed permentantly!!

11. Humans Not Except fromHumans Not Except from
Population ControlsPopulation Controls
Bubonic plague (14Bubonic plague (14thth
century) 25 million killedcentury) 25 million killed
Famine in Ireland (1845) – 1 million died & 3Famine in Ireland (1845) – 1 million died & 3
million emigrated to USmillion emigrated to US
AIDS – 27 million dies 2 million each yearAIDS – 27 million dies 2 million each year
Technology, social, and cultural changesTechnology, social, and cultural changes
extended earth’s carrying capacity for humansextended earth’s carrying capacity for humans
Expand indefinitely or reach carryingExpand indefinitely or reach carrying
capacity?capacity?

12. 5-3 How Do Communities and Ecosystems5-3 How Do Communities and Ecosystems
Respond to Changing EnvironmentalRespond to Changing Environmental
Conditions?Conditions?
Concept 5-3Concept 5-3 The structure and speciesThe structure and species
composition of communities andcomposition of communities and
ecosystems change in response toecosystems change in response to
changing environmental conditionschanging environmental conditions
through a process called ecologicalthrough a process called ecological
succession.succession.

13. SuccessionSuccession
SuccessionSuccession – the gradual, sequential– the gradual, sequential
re-growth of species in an areare-growth of species in an area
1. Primary succession1. Primary succession – the– the
development of a community in an areadevelopment of a community in an area
that has not supported life previouslythat has not supported life previously

Ex. Bare rock, volcanic island,Ex. Bare rock, volcanic island,
Mosses are usually first life.Mosses are usually first life.

16. Time
Balsam fir,
paper birch,
and white
spruce forest
community
Jack pine,
black spruce,
and aspenHeath mat
Small herbs
and shrubsLichens and
mossesExposed
rocks
Stepped Art
Fig. 5-10, p. 89

17. SuccessionSuccession
2. Secondary succession2. Secondary succession – the sequential– the sequential
replacement of species that followsreplacement of species that follows
disruption of an existing communitydisruption of an existing community

Ex. Abandoned farmland.Ex. Abandoned farmland.

Burned or cut forests.Burned or cut forests.

Heavily polluted streams.Heavily polluted streams.

Flooded land.Flooded land.

18. Annual
weeds
Mature oak and hickory
forestYoung pine forest
with developing
understory of oak
and hickory trees
Time
Shrubs and
small pine
seedlingsPerennial
weeds and
grasses
Stepped Art
Fig. 5-11, p. 90

19. Limits to ChangeLimits to Change
Inertia (persistence)Inertia (persistence) is the ability of a livingis the ability of a living
system, such as a grassland or forest, to survivesystem, such as a grassland or forest, to survive
moderate disturbances.moderate disturbances.
ResilienceResilience is the ability of a living system to beis the ability of a living system to be
restored through secondary succession after arestored through secondary succession after a
more severe disturbance.more severe disturbance.
Ex. Tropical rain forest: inertia – yes resilient – noEx. Tropical rain forest: inertia – yes resilient – no
Ex. Grassland: inertia – no resilient - yesEx. Grassland: inertia – no resilient - yes