Download Chapter 48: Populations and Communities

Chapter 48: Populations and Communities
Section 2: Factors That Control Population Growth
Factors That Control Population Growth

The growth of individuals can be controlled by ___________________________
________________________

Both plant and animal populations can be controlled by several factors
o No single species has ever threatened to __________________________
the entire planet
Density-Dependent Limiting Factor

When factors that control population size operate more strongly on
____________________________________________ than on small ones, they
are called _________________________________________________________
o Usually operate only when a population is _________________________
_____________________________
o Do not affect small, widely scattered populations much

Density-dependent
limiting
factors
include
_______________________________, _____________________,
_____________________________, and ____________________
Competition

When populations become crowded, both plants and animals compete, or
struggle, with one another for _________________, __________________,
_____________________, ___________________________, and other essentials
of life

Competition between members of different yet similar species is a major force
behind ________________________________________________
o No two organisms can occupy the same ____________________ in the
same place at the same time
o When two species compete, both find themselves under pressure from
natural selection to change in ways that decrease their competition

______________________________________________________
Predation

Just about every species serves as __________________ for some other species

Predators and prey _________________________ over long periods of time
o Have become accustomed to each other’s __________________________
_______________________________________

Prey have evolved ___________________________ against predators
o Poisonous chemicals, shells, camouflage

Predators have evolved _____________________________________________
o Stronger teeth and jaws, powerful digestive enzymes, extra keen eyesight

Typically, at some point the prey population grows so large that prey are
numerous and easy to find

With such a large and available food supply to feast upon, there may soon be
almost as many __________________________________________
o This situation cannot last because each predator needs many prey to
satisfy its energy needs

Predator-prey relationships are important in ______________________________
natural populations
Parasitism

Parasites live off their _________________, weakening them and causing disease

Like predators, parasites work most effectively if hosts are present in
_______________________________________

Parasitism works as a density-dependent limiting factor on population growth
Crowding and Stress

Most animals have a built-in behavioral need for a certain amount of
___________________
o ________________________________
o ________________________________
o ________________________________

The number of suitable territories regulates population size in a density-dependent
manner

Certain species fight among themselves if they are overcrowded
o ______________________________________
Density-Independent Limiting Factors

Many species show ________________________________ growth curves
o Populations grow _________________________________ for some time
and then suddenly ______________________

Insects that feed on plant buds and leaves can be washed out by a
____________________________

They may also be harmed by long hot periods of dry weather

Frosts, too, can cause sudden drops in insect populations

For these species, storms, cold weather, dry weather, or
other natural occurrences can nearly wipe out the
population
o Happen regardless of how large or small the
population is
o __________________________________________
__________________________________________
Human Population Growth

Human populations tend to ___________________________________ with time

For a long period of time the human population grew _______________________

Then, ___________________________________________, the world’s human
population grew _________________________________

Today, population growth in the _________ and __________________________
_______________________ has slowed down

Most of the world’s people do not live in these countries
o Instead, they live in _________________, __________________, and part
of ________________________________________________________ –
places where populations are still growing _________________________