1. Types of
Interactions

2. Look at the seaweed forest below. How
many fish do you see? How many
seaweed plants do you count? Why do
you think there are more members of
the seaweed population than members
of the fish population?

3. Interactions with the Environment
• Most living things produce
more living things than will
survive
• A female frog may lay
hundreds of eggs, but the
population of frogs in a
pond will stay about the
same as it was the year
before—Why?
• An organism interacts with
biotic and abiotic factors
that control the size of its

4. Limiting Factors
• Populations cannot
grow without stopping,
because the
environment contains a
limited amount of food,
water, living space, and
other resources
• A resource that is so
scarce that it limits the
size of a population is
called a limiting factor
• Any single resource can
be a limiting factor to a
population’s size

5. Carrying Capacity
• Carrying capacity: largest population that
an environment can support
• When a population is larger than its carrying
capacity, limiting factors cause individuals
to die off or leave
• As individuals die or leave, the population
decreases
• The population will return to a size that the
environment can support

7. Interactions Between Organisms
• Four main ways that species and
individuals affect each other:
Competition
Predators and prey
Symbiotic relationships
coevolution

8. Competition• When 2 or more
individuals or
populations try to use
the same resource,
such as water, shelter,
space, or light, it is
called competition
• Can happen in
populations or between
populations
• Some trees grow tall to
reach light, which
reduces amt. available
to short trees

9. Predators and Prey
• Predator Adaptations
– To survive, predators
have to be able to
catch prey, using
wide variety of
methods and abilities
– Goldenrod spider
ambushes its prey by
blending in with flower
and waiting for its
insect meal to arrive

10. • Prey Adaptations
– Prey have to keep from
being eaten
– Are able to run away, stay
in groups, or camouflage
themselves
– Some are poisonous
– May advertise poison with
bright colors
– Many small fishes swim in
groups called schools
– Other animals stay in
herds, increasing the
likelihood of spotting a
potential predator

11. Camouflage
• One way to avoid being eaten is by
being hard to see
• Blend in with the background
• May mimic twigs, leaves, stones, bark

12. Defensive Chemicals
• Skunk and bombardier
beetle both spray predators
with irritating chemicals
• Bees, ants, and wasps
inject a powerful acid into
their attackers
Bird called the hooded pitohui
contains a deadly toxin—
any predator that eats, or
tries to eat, one of these
animals will likely die

13. Warning Coloration
• Predators will avoid any
animal that has the
colors and patterns
they associate with
pain, illness, or
unpleasant experiences
• Most common warning
colors are
bright shades of red,
yellow,
orange, black, and
white

14. Symbiosis
• Symbiosis: a close, long term
association between two or more
species
• Individuals in a symbiotic
relationship can benefit from, be
unaffected by, or be harmed by the
relationship
• Classified into 3 groups: mutualism,
commensalism, and parasitism

15. Mutualism
• Mutualism both
organisms benefit
• Example: corals
and algae. Coral
provide home for
algae, algae
produce food for
the coral by
photosynthesis

16. Commensalism
• One organism benefits and the other is
unaffected
• Example: relationship between sharks and
smaller fish called remoras. Remoras “hitch a
ride” on sharks and feed on scraps of food left by
sharks. The remoras benefit and sharks are
unaffected.

17. Parasitism• One organism benefits
while the other is
harmed
• Organism that benefits
is called the parasite,
organism that is
harmed is called the
host
• Female wasp lays eggs
on a tomato hornworm;
eggs hatch, young
burrow into caterpillar
body, and actually eat
the caterpillar alive!
Then adult wasps fly
away

18. Coevolution
• When a long term
change takes place
in two species
because of their
close interactions
with one another, this
change is called
coevolution
• Ant and acacia tree
ant protects tree and
tree has special
structures that make
food for ants

19. Coevolution and Flowers
• Flowers have changed over millions of
years to attract pollinators
• Pollinators are attracted to color,
odor, or nectar
• Flowers pollinated by hummingbirds
make nectar with the right amount of
sugar for the bird

20. • Some bats
changed over time
to have long, thin
tongues and noses
to help them
reach the nectar
in flowers
• They help
pollinate as they
travel from flower
to flower