Section 1 How Populations Change
in Size
How many elephants could a single
pair theoretically produce in 750 years?
19 million
Why is this number actually limited?
By their environment
What is a Population?
What is a population?
All the members of a species living
in the same place at the same time
Why is a population also considered a
reproductive group?
Because organisms usually breed with
members of their own population
What two things does population
refer to?
The group in general and to the size
of the population
Properties of Populations
What three ways can populations be
described?
Size, density and dispersion
What is population density?
Number of individuals per unit of
area or volume
What is dispersion and what are the
types of dispersion?
Relative distribution of its
individuals within a given amount of space – even, clumped, random
How Does a Population Grow?
How do populations gain or lose
individuals?
With births or deaths
What is growth rate?
A change in the size of the
population over a given period of time
What is the equation for the growth
rate?
Growth rate = births - deaths
What things can growth rates be
(explain)?
Positive, negative, or zero.
Zero is equal number of births and
deaths
Positive more births than deaths
Negative more deaths than births
How Fast Can a Population Grow?
Why do populations usually stay the
same year to year?
Various factors kill many individuals
before than can reproduce
What do the various factors control
or determine for populations?
How the population evolves
Reproductive Potential
What is biotic potential?
The fastest rate at which its
population can grow
What is reproductive potential?
The maximum number of offspring that
each member of the population can produce
How does reproductive potential
increase and what has the greatest effect?
Individuals produce more offspring at
a time, reproduce more often, and reproduce earlier in life – reproducing
earlier in life
What is generation time?
The average time it takes a member of
the population to reach the age when it reproduces
As a general rule, how do organisms
with small generation times compare to larger organisms?
Smaller organisms have shorter
generation times
Exponential Growth
What is exponential growth?
When populations grow faster and
faster – a larger number of individuals is added in each succeeding time period
When does exponential growth occur in
nature?
When populations have plenty of food
and space and have no competition or predators
What Limits Population Growth?
What things limit growth?
Resources are used up or the
environment changes and deaths increase and births decrease
Carrying Capacity
What is carrying capacity?
The maximum population that the
ecosystem can support indefinitely
Why is carrying capacity hard to
predict?
Because ecosystems change
How is carrying capacity estimated?
Looking at average population size or
by observing a population crash after a certain size has been exeeded
Resource Limits
When does a species reach its
carrying capacity and what is this called?
When it consumes a particular natural
resource at the same rate at which the ecosystem produces the resource –
limiting resource
What determines the carrying capacity
of an environment?
The supply of the most severely
limited resource
Competition Within a Population
Why do members of a population
compete?
Use the same resources in the same
ways
What may individuals compete for
indirectly?
Social dominance or territory
What is territory and why is it
important?
An area defended by one or more
individuals against other individuals – space, food, shelter, breeding sites
What is competition part of the
pressure for?
Natural selelection
What things do organisms spend a
large amount of time and energy competing for?
Mates, food, or homes
Two Types of Population
Regulation
What are the two causes of death in
populations?
Density dependent or density
independent
What is density-dependent regulation
and explain how it occurs with examples?
Deaths occur more quickly in a
crowded population than in a sparse population – limited resources, predation
and disease result in higher rates of deaths in dense populations
What is density-independent
regulation and explain how it occurs with examples?
When a certain proportion of the
population may die regardless of the population density – affects all
populations in a uniform way. Severe
weather and natural disasters
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