Download Populations

14.3
Populations
• group of organisms that belong to the same species
and live in a particular place at the same time
• measured in terms of size, density, dispersion,
growth rate, age structure, and survivorship
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Population Size
– the number of individuals that the population
contains
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Population Density
– Density is a measure of how crowded the
population is
– The measure of the number of individuals divided
by the area they live in
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Population Dispersion
– describes the distribution of individuals within the
population
– Three types
• Random
• Uniform
• Clumped
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Three Patterns of Population Dispersion
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Population Dynamics
• Age Structure
– indicates the percentage of individuals at each
age
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Patterns of Mortality
– Populations show three patterns of mortality or
survivorship curves:
• Type I (low mortality until late in life)
• Type II (constant mortality throughout life)
• Type III (high mortality early in life followed by
low mortality for the remaining life span).
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Survivorship Curves
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
14.4
Population Growth Rate
• Demographers, scientists who study population
dynamics, define the growth rate of a population as
the amount by which a population’s size changes in a
given time
• Population Size
– Birth rate - death rate = growth rate
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
The Exponential Model
• describes perpetual growth at a steady rate in a
population
• assumes constant birth and death rates and no
immigration or emigration
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
The Logistic Model
• birth rates fall and death rates climb as the population
grows
• When the carrying capacity is reached, the number
of individuals the environment can support is reached
and population growth becomes stable
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Two Population Growth Models
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Population Regulation
• Population-limiting factors, such as competition, are
density-dependent because the effect on each
individual depends on the number of other individuals
present in the same area.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Population Regulation
• Population-limiting factors, such as bad weather and
fires, are density-independent because the effect
on each individual does not depend on the number of
other individuals present in the same area.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Perils of Small Populations
– Small populations have low genetic diversity and
are subject to inbreeding, so they are less likely to
adapt to environmental changes
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
14.5
Community Stability
– Disturbances can alter a community by
eliminating or removing organisms or altering
resource availability
– Species richness may improve a community’s
stability
– Areas of low species richness may be less stable
in the event of an ecological disturbance
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Ecological Succession
• is a change in the species composition of a
community over time
• Primary Succession
– is the assembly of a community on newly created
habitat
– occurs in areas that have been recently exposed
to the elements and lack soil
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Ecological Succession
• Secondary Succession
– is the change in an existing community following a
disturbance
– occurs in areas where the original ecosystem has
been cleared by a disturbance
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
The Complexity of Succession
• The traditional description of succession is that the
community proceeds through a predictable series of
stages until it reaches a stable end point, called the
climax community.
• Primary succession typically proceeds from lichens
and mosses to a climax community.
• Secondary succession typically proceeds from weeds
to a climax community.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Ecological Succession at Glacier Bay
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.