Section 5.1How Populations Grow

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.

I Can…

• LS 2.1 I can use quantitative evidence to explain factors that affect population size and carrying capacity within an ecosystem.

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?

Vocabulary

• Population density

• Population distribution

• Age structure

• Immigration

• Emigration

• Exponential growth

• Logistic growth

• Carrying capacity

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?

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.

Geographic Range

• The places a population lives

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

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

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

Density and Distribution most common

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

Population Growth

• Birthrate, death rate, and the rate at which individuals enter or leave a population all affect population growth.

Birthrate and Death Rate

• Population increase = more births than deaths

• Population stable = birthrate equal death rate

• Population decrease= death rate is greater than birthrate

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

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

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.

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!

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?

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

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

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

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

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.

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.

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?

The End ☺