Transcript Chapter Eight: Understanding Populations

CHAPTER EIGHT:
UNDERSTANDING POPULATIONS
Section One: How Populations Change
in Size

What is a population?
 Population:
all the members of a species living in the
same place at the same time
 Population
Density: the number of individuals per unit area
or volume
 Population Dispersion: relative distribution or arrangement
of a population’s individuals within a given amount of space
Section One: How Populations Change
in Size

How does a population grow?
 Growth
rate: a change in a population’s size over a
given period of time
 Growth rate= births – deaths
 When the number of births = number of deaths, the
growth rate is 0
Section One: How Population Change
in Size

How fast can a population grow?
 Reproductive
potential: the maximum number of
offspring that each member of a population can
produce
 Exponential growth: populations grow exponentially, or
faster and faster
 Only
happens when there is plenty of space and food in
nature
Section One: How Populations Change
in Size

What limits population growth?
 Carrying
capacity: the maximum population that an
ecosystem can support indefinitely
 Difficult
to predict because ecosystems are always changing
 Resource
Limits
 Competition within a Population
 Members
of population use the same resources in the same
way and compete for that resource
 Territories may be established
Section One: How Populations Change
in Size

Population Regulation
 Density
dependent
 Populations
are large and there are not enough resources
for everyone
 Density
A
independent
certain amount of individual die regardless of population
size
 Such as weather and natural disasters
Section Two: How Species Interact with
Each Other

An Organism’s Niche
 Niche:
the unique role of a species within a ecosystem
 Includes
their home, environmental factors needed for
survival, and all interactions with other animals
Section Two: How Species Interact with
Each Other

Ways Species Interact
 Competition
 Predation
 Parasitism
 Mutualism
 Commensalism
 Symbiosis
and Coevolution
Section Two: How Species Interact with
Each Other

Competition
 When
different individuals or populations attempt to
use the same limited resource
 Can
occur within and between species
 When different species compete for the same resource it is
called a niche overlap
 Indirect competition: species compete but do not come in
direct contact with one another
 Niche restriction: each species uses less of the niche than it is
capable of using

Adaptations reduce competition
Section Two: How Species Interact with
Each Other

Predation
 When
a predator feeds on a prey
 Some organism have adaptations to avoid or defend
against predation
 Predator-prey populations are usually similar because
the predator depends on prey for food
Section Two: How Species Interact with
Each Other

Parasitism
 When
one organism lives in or on another and feeds on
it
 Examples: ticks, tapeworms, fleas, leaches, mistletoe
 Parasites do not kill their host but often weaken it
Section Two: How Species Interact with
Each Other

Mutualism
A
close relationship between species in which both
receive a benefit from the other
 Examples: gut bacteria
Section Two: How Species Interact with
Each Other

Commensalism
A
relationship in which one species benefits while the
other is not harmed or helped
 Example: epiphytes
Section Two: How Species Interact with
Each Other

Symbiosis and Coevolution
 Symbiosis:
a relationship in which two species live in
close association
 Usually
describes relationships where atleast one species
benefits
 May lead to coevolution