Chapter 14“Populations”

14.1 “Populations and How They Grow”

Objective:

– Describe the different ways that populations may change.

Populations

A group of organisms of a single species that live in a given area.

Changes in Population Size

In nature populations will stay relatively the same in number.

HOWEVER, sometimes those numbers will change dramatically.

Growth Rate A change in population size. (+

or -) Depends on how many

organisms are added and removed (immigration & emigration).

AND interaction between organisms.

Why do Populations Grow?

Ideal conditions (adequate food supply, shelter, protection from predators) = growth.

Birth rates are higher than death rates.

Mexican Population Growth

Baby Boom If ideal conditions continue,

the larger the population gets, the faster it grows.

Exponential Growth = constant growth that takes place under ideal conditions.

Exponential Growth in Bacteria

Growth with Limits

In nature, exponential growth does not continue forever.

Growth slows down because resources are limited.

Growth with Limits

Carrying Capacity

Growth Limits continued... Zero Population Growth

– birth rate and death rate are the same– population stays the same = steady-

state

Carrying Capacity– the largest # of individuals of a

population that a given environment can support

Boom & Bust In nature species increase

in # until they reach their carrying capacity.

Some however reach a “boom” and then crash in size “the bust”.

Boom and Bust

14.2 “Why Populations Stop Growing”

Objective:–Identify the factors that control population growth in nature.

Population Growth

Limited by the size and density of a population.

Population Density = the # of organisms in a given area.

Limiting Factor = a factor that causes a population to decrease.

Density-Dependent Limiting Factors

Depends on population size, affects large & dense pops more.

Include:– Competition– Predation– Parasitism– Disease– Crowding & Stress

Competition

When populations become too crowded, organisms will compete for resources.

Can occur between different species = evolutionary change.

Increases death rates.

Predation

Predator-Prey relationship controls populations.

Defenses for both predator & prey.

Predator Prey Graph

ParasitismRange in size from microscopic

(bacteria) to tapeworms (30+ cm).

Like predators, parasites take nourishment at the expense of their hosts.

Host-specific.

Parasites – tapeworm

Crowding and Stress

Most organisms need a certain amount of space.

Overcrowding causes disturbances among organisms leading to weakening.

Density-Independent Limiting Factors

Affects populations regardless of size.

Some examples include: unusual weather seasonal cycles human activities:

–damming rivers–clear-cutting forests

Clear Cut Forest