section 5.1 how populations grow - weebly · 2021. 1. 19. · •because most plants and animals...
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Section 5.1How Populations Grow
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Standard
• BIO1.LS2.1 Analyze mathematical and/or computational representations of population data that support explanations of factors that affect population size and carrying capacities of populations within an ecosystem. Examine a representative ecosystem and, based on interdependent relationships present, predict population size effects due to a given disturbance.
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I Can…
• LS 2.1 I can use quantitative evidence to explain factors that affect population size and carrying capacity within an ecosystem.
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Key Questions
1. How do ecologists study populations?
2. What factors affect population growth?
3. What happens during exponential growth?
4. What happens during logistic growth?
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Vocabulary
• Population density
• Population distribution
• Age structure
• Immigration
• Emigration
• Exponential growth
• Logistic growth
• Carrying capacity
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Introduction
• Southern sea otters are making a comeback after fur hunters nearly wiped them out in the eighteenth century.
• They are still considered endangered because they live only along a short stretch of the California coast.
• Otters are very important for the West Coast’s kelp forests.
• Kelp is increasing where otters are common.
• Why is that?
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Describing Populations
• “How many individuals of this species live here?”
• “Where else do they live?”
• “Are those populations stable, increasing, or decreasing?”
• Ecologists study populations be examining their geographic range, growth rate, density and distribution, and age structure.
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Geographic Range
• The places a population lives
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Growth Rate
• Lionfish are native to the Pacific Ocean, but have been spotted around Florida, throughout the Caribbean, and in the Gulf of Mexico.
• Lionfish in their native habitats- stable
• Lionfish in new areas have very high growth rates- increasing
• Populations can also have negative growth rates- decreasing
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Density and Distribution
• Population density- the number of individuals that can be found per unit area
• Examples-
• Low density- population of ducks in a pond
• High density- algae covering the pond
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Density and Distribution
• Population distribution- the way individuals are spaced out across their range
1. Random- occurs when an individual in a population is independent of other individuals
2. Clumped- can help animals stay safe from predators
3. Uniform- can help each individual find food or take shelter
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Density and Distribution most common
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Age Structure
• Age structure- number of males and females of each age in a population
• Why is this important?• Because most plants and animals
cannot reproduce until they reach a certain age
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Population Growth
• Birthrate, death rate, and the rate at which individuals enter or leave a population all affect population growth.
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Birthrate and Death Rate
• Population increase = more births than deaths
• Population stable = birthrate equal death rate
• Population decrease= death rate is greater than birthrate
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Immigration and Emigration
• Immigration- movement of individuals into an area occupied by an existing population • Squirrels immigrating into an oak grove in a forest in search of acorns
• Emigration- movement of individuals out of an area • Local food shortage or lack of other limiting resource can cause emigration
• Young animals may emigrate to find mates or establish new territories
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Exponential Growth
• Under ideal conditions with unlimited resources, a population will increase exponentially. This means that the larger the population gets, the faster it grows.
• J-curve
1. Organisms that reproduce rapidly
2. Organisms that reproduce slowly
3. Organisms in new environments
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1. Organisms that Reproduce Rapidly
• Some bacteria can reproduce every 20 minutes.
• They can produce huge populations in a matter of days.
• If nothing interferes with this exponential growth, the population will become larger and larger, faster and faster, until it approaches an infinitely large size.
Population is rapidly increasing.
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2. Organisms that Reproduce Slowly
• Many organisms grow and reproduce much more slowly that bacteria.
• Female elephants can produce a single offspring only every 2-4 years.
• If exponential growth continued indefinitely, the result would still be impossible.
• In the unlikely event that all descendants of a single elephant pair survived and reproduced, there would be nearly 20 million elephants after 750 years!
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3. Organisms in New Environments
• Sometimes, when an organism migrates or is moved to a new environment, its population grows exponentially for a time.
• Why do you think this is the case?
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Logistic Growth
• Natural populations do not grow exponentially for long…something stops exponential growth.
• Logistic growth occurs when a population’s growth slows and then stops, following a period of exponential growth.
• S-curve
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Phases of Growth
• Phase 1- Exponential Growth• Resources are unlimited
• Individuals grow and reproduce rapidly
• Few individuals die and many offspring are produced
• Population size and rate of growth increase more and more rapidly
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Phases of Growth
• Phase 2- Growth Slows Down• Rate of population growth
begins to slow down
• Does NOT mean the population size decreases
• The size still increases, but at a slower rate
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Phases of Growth
• Phase 3- Growth Stops• The rate of population
growth drops to 0
• Size of population levels off
• Under some conditions, the population will remain at or near this size indefinitely
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Carrying Capacity
• Carrying capacity- the maximum number of individuals of a particular species that a particular environment can support
• Once a population reaches the carrying capacity of the environment, a variety of biotic and abiotic external factors affect the population in ways that stabilize it at that size.
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Carrying Capacity Example
• Seasonal changes in food and water availability cause seasonal changes in the carrying capacity of certain environments for wildebeests.
• These seasonal changes in carrying capacity drive Africa’s extraordinary migrations.
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Section 5.1 Exit Ticket
1. What characteristics do ecologists study to learn about populations?
2. What factors determine the rate at which a population is increasing or decreasing?
3. What happens to the growth of a population when resources are limited?
4. How does logistic growth occur?
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The End ☺