Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Enger & Smith

Environmental ScienceA Study of Interrelationships

Thirteenth Edition

Chapter 7

Populations: Characteristics and Issues

Populations: Characteristics and Issues

7.1 Population Characteristics

A population is a group of individuals of the same species inhabiting the same area.

7.1 Population Characteristics

Effect of birthrate and death rate on population size

7.1 Population Characteristics

Age distribution in human populations

Population Density and Spatial Distribution

Population density is the number of individuals per unit area.• High population density

– injures all individuals within the population

– because they compete for resources

7.2 A Population Growth Curve

Biotic potential is the inherent reproductive capacity of a species • (biological ability to produce offspring).

biotic potential is much above replacement level.• natural tendency for increase

7.2 Biotic Potential

7.2 A Population Growth Curve

Population growth follows a pattern: • 1st lag phase• 2nd exponential growth phase • 3rd deceleration phase• 4th stable equilibrium phase

7.2 A Population Growth Curve

A typical population growth curve

Population growth curve

Lag Phase: first portion of the curve slow population growth

Few births

Exponential Growth Phase (Log Phase): More organisms reproducing causing accelerated growth continues if birth rate exceeds death rate

Population growth curve

7.2 Population Growth Curve

• Deceleration Phase: – The population growth rate slows

– death rate and birthrate equal one another

Stable Equilibrium Phase: The death rate and birth rate become equal the population stops growing

7.2 Population Growth Curve

7.3 Factors That Limit Population Size

Limiting Factors--prevent unlimited population growth

• Extrinsic limiting factors

• Intrinsic limiting factors

• Density-dependent factors

• Density-independent factors

Extrinsic limiting factors

Come from outside the population• Predators• Loss of food source• Lack of sunlight• Accidents of nature

7.3 Factors That Limit Population Size

7.3 Factors That Limit Population Size

Intrinsic limiting factors • factors that originate within the population • exercise control over it

• Behavioral changes amongst the population cause lower birthrates and higher death rates.

Other limiting factors

Density-dependent limiting factors • become more effective as the density of the

population increases.

• Denser population– Predators more effective

Other limiting factors

Density-independent limiting factors• population-controlling influences not related to the

density of the population.

• Accidental

• Extrinsic factors

Density dependent or independent?

Mutualism between two species.

A wolf eating rabbits.

A large fire burns down many of the trees in a forest.

A disease kills all the mice in a local radius and the foxes have nothing to eat.

7.4 Categories of Limiting Factors

For most populations, limiting factors recognized as components of environmental resistance

• Raw material availability• Energy availability• Accumulation of waste products• Interactions among organisms

Discussion

What will we do?

7.5 Carrying Capacity

Carrying capacity is the maximum sustainable population for an area.

It is not an inflexible number; it can be influenced by environmental differences

• Successional changes• Climate variations• Disease epidemics• Forest fires, floods, or natural disasters• Nutrient levels in aquatic ecosystems

7.5 Carrying Capacity

7.5 Carrying Capacity

7.6 Reproductive Strategies and Population Fluctuations

Species divided into two broad categories based on their reproductive strategies:

• K-strategists

• r-strategists

K-strategists: Organisms that typically reach a stable population as the population reaches the carrying capacity.

K-strategist characteristics: Usually occupy relatively stable environments

• Large organisms• Long-lived• Produce few offspring

7.6 Reproductive Strategies

7.6 Reproductive Strategies and Population Fluctuations

K-strategist characteristics:• Provide substantial parental care• Reproductive strategy

– invest a great deal of energy in producing a few offspring that have a good chance of living to reproduce.

K-strategists • controlled by density-dependent limiting factors.

K-strategist

7.6 Reproductive Strategies

r-strategist characteristics include:

• Small, short-lived organisms• Produce many offspring• Little if any parental care• Exploit unstable environments• Usually do not reach carrying capacity (boom-bust

cycles)

r-strategist

Reproductive strategy – produce large numbers of offspring to overcome high

mortality.

r-strategists are controlled by density-independent limiting factors.

r-strategist

Summary

The birthrate (natality) is the number of individuals entering the population by reproduction during a certain period.

The death rate is the number of deaths in a population in a certain period.

A typical population growth curve shows a lag phase followed by an exponential growth phase, a deceleration phase, and a stable equilibrium phase at the carrying capacity.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Enger & Smith

Environmental ScienceA Study of Interrelationships

Thirteenth Edition

Chapter 11

Biodiversity Issues

11.3 Invasive Species

Impact populations (affect population size)

Some introductions of exotic species are purposeful, while others are accidental.

Globalization is responsible for spreading thousands of invasive alien species around the world.

11.3 Invasive species

The IUCN estimates about • 30% of birds and 15% of plants are threatened • because they are unable to successfully compete against invasive

exotic species.

Various insects have had an effect on ecosystem structure.• Asian long horned beetle

Freshwater ecosystems have been greatly affected.• Zebra mussel

• Impact populations (affect population size)

11.3 Threats to Biodiversity

The Asian long horned beetle

Overview

http://www.youtube.com/watch?v=Bu6ouKt9zhs

Homework

4 groups

Each group answers one question

Next week (1-29-14), present answers in 5 to 10 minute presentation