Download Chapter 5 - Gull Lake Community Schools

Chapter 5
Populations and
Communities
5-1: Populations




Why is it important to study populations?
What is the difference between exponential
growth and logistic growth?
What factors affect population size?
How have science and technology affected
human population growth?
Understanding how populations grow and shrink is
critical to managing agricultural pests and
diseases and also for knowing how to
protect ecosystems.
What is a Population?

Population  a group of organisms of the same
species that live in a specific geographical area, at
the same time and are able to interbreed





Small populations
 Herd of zebra
Large populations
 Rabbits in Australia
Steady – fairly unchanging numbers
Increasing – exponentially or logistically
 Rabbits in Australia from 24 to 600 million in 100 years
Decreasing – exponentially or logistically
Population Growth





Birth rate  babies born per time
Death rate  deaths per time
Immigration  movement of individuals into a
population
Emigration  movement of individuals out of
a population
Carrying capacity the largest population
that the environment can support at a given
time
Growth Patterns

Exponential growth 
numbers increase by a
certain factor in each
successive period of
time


Bacteria
rabbits

Logistic growth 
starts with a minimum
number of individuals
and reaches a
maximum depending
on the carrying capacity
of the habitat

Most animals are
contained by competition
for food, shelter, mates
and other resources
Factors Affecting
Population Size


Abiotic – plants limited by amount of sunlight and
soil nutrients like nitrogen
Biotic – populations can be limited by number of
pollinators and predator-prey relationships

Density-Dependent – something like a disease

can impact a population and be worse if there are
more individuals
Density-Independent – something like a tornado
can impact a forest but hits no matter how many
trees there are
Human Population

Historic




Hunter-gatherer societies
Cities (near resources)
Industrial revolution and westward expansion
Science and Technology




Medicine; when ill and/or wounded
Health care; especially preventative like vaccines
Clean water
Enough food
5-2: Interactions in Communities


How do predator-prey interactions influence
both predator and prey?
What are two other types of interactions in a
community?
Interactions between organisms are
the basis of communities and are
shaped by changes in the environment
and the evolution of organisms
Predator - Prey Interactions

Predation  one organism kills another for
food




Lion eats zebra
Shark eats fish
Also at microscopic level (daphnia eat amoebas)
Very few organisms have no predator (killer
whales) and most are both predator and prey
Other relationships

Coevolution  two or more organims have
developed responses to one another due to mutual
influence



Faster zebras will require faster cheetahs…. Genetic basis
occurs over many generations (of a population), evolution
does not occur in the lifetime of an individual
Parasitism  fleas, tick, tapeworms; host provides food
and home; parasite has adaptations like the cuticle (skin)
of tapeworm that keeps it from being digested
Herbivory  defenses like thorns so that a plant isn’t eaten
(grazed). Also includes chemical defenses…..monarch eat
milkweed that is toxic to many herbivores – and then the
monarch also becomes toxic!
Symbioses

Symbiosis is a relationship between two
species in close association with each other.

Mutualism  both species benefit



Cleaner fish get meal and protection while predator is
freed from potential parasites
Pollinators are a great example of this interaction
Commensalism  one species benefits and the
other is neither harmed or helped

Orchids are epiphytes, plants that grow attached to
other plants…helps them get to sun and doesn’t hurt
tree they are on.