1. Biodiversity, Species
Interactions, and Population
Control
Ch. 5
Miller & Spoolman, 16th ed.

2. Your Goal for this lecture
To be able to explain
how interactions
between
organisms help drive
natural selection

3. Big Idea # 1
Species interactions affect the resource
use and sizes of other populations in an
area

4. Species Interactions
There are 3 main types of species
interactions:
Competition
Predation
Symbiosis

5. Importance of Species Interactions
These types of interactions have a significant
impact on each population involved
These interactions are agents of natural
selection - they influence who survives and is
able to reproduce

6. Competition
Competition for
resources
2 types:
Interspecific - 2
different species
compete for the
resource
Intraspecific -
members of the
same species
compete for the
resource

8. Brainstorm
Make a list of
resources that species
might compete for
Morning Buddies

9. Intraspecific - often fighting involved to
“win” the resource
Can be very intense

10. Interspecific - usually no fighting, just
better at getting it
Less intense since species have slightly
different niches

11. Competitive Exclusion Principle
No two species can
occupy exactly the same
niche because
competition for resources
would be too intense
One species will be
better at getting the
resources
The other species must
leave, adapt, or die

12. Solving the Problem

13. Resource Partitioning
Two species evolve
adaptations that
allow them to use
the same resource
in different ways, at
different times, or in
different places in
order to minimize
competition

14. How about humans?
Are humans subject to the Principle of
Competitive Exclusion? Defend your answer
 Yes! Our use of resources directly competes with other
organisms, and forces them to leave the area or go extinct in
that area (adaptation not possible since we change
environment so quickly)
Kicked
out of
class
buddies

15. Predation
All consumers feed on
other organisms
Herbivores feed on live
plants
Carnivores feed on
animals
Omnivores feed on both

16. Predator-Prey Relationships
Changes in 1 population leads to changes in
other populations

17. How do changes in population
size affect ecosystems?
A change in the size of one population
will affect the size of other populations

18. J-curve
Exponential Pattern of Growth

19. Intrinsic Pattern of Growth
S-curve

20. Intrinsic Pattern of Growth

21. • The size of the predator population affects
the prey population and vice versa
• Who is controlling the rises and falls of
these 2 populations? The Hare or the Lynx?

22. What is anWhat is an
adaptation oradaptation or
strategy that wouldstrategy that would
be helpful to abe helpful to a
predator?predator?
What is anWhat is an
adaptation oradaptation or
strategy that wouldstrategy that would
be helpful to a preybe helpful to a prey
organism?organism?
Song
buddies

23. Structural advantages
 Natural Weapons - Fangs, claws
 Flexible bodies
 Larger Size
Predator Strategies

24. Predator Strategies
Ambush-
Stalk a victim • Venom
Gape & Suck (fish)
Keen
eyesight

25. Predator Strategies
SPEED &
CUNNING
• More intelligent
than prey
• Run faster than
prey
•Hunt in
packs

26. Predator Strategies
Camouflage
Sit in plain site

27. Predator Strategies
Chemical warfare
venom

28. Prey Strategies
Defense Techniques
Inflate
Flee
Fight Back
Stab
Poison

29. Prey Strategies
Structural advantages
Hard Body Coverings
Thorns or Spines
Break away body parts
Natural Weapons

30. Chemical Warfare
Blinding ink
Poison
Offensive
Smells and
Tastes
Prey Strategies

31. Camouflage
Color Change
Counter-shading
Disruptive Patterns
Mimicry
Prey Strategies

32. Mimicry
• Mostly a prey technique
 Optical and sonic illusions
 LOOKS like a predator:
• School of fish;
false eyes;
frilled neck and
inflation

33. Batesian mimicry- a harmless animal
mimics a harmful or unpalatable one
Mullerian mimicy-two or more unpalatable
species resemble each other

34. 2 rules about coloration
Small + beautiful = poisonous
Beautiful + easy to catch = deadly

35. Food for thought
Think of a local species
What adaptations does it have
to catch prey or avoid being
eaten?
food buddies

36. Predator Prey relationships
Predator benefits
Prey does not
…or does it?
Predators
strengthen the
population in the
long term by
preying on the
weaker individuals

37. Coevolution
When two species have lived together and
adapted to each other for a long time such that
changes in the gene pool of one species leads
to changes in the gene pool of the other
species

38. Symbiosis
Symbiosis – when different organism
live in close, physical contact with
one another
Parasitism
Mutualism
Commensalism

39. Parasitism
A form of
symbiosis in
which one
organism benefits
and the other is
hurt
Leeches, fleas,
ticks, tapeworms,
etc

40. Parasitism
Simple parasites - fleas,
ticks, leeches
Move from host to host
Or have only one host their
whole life
Complex parasites -
plasmodium (malaria),
toxoplasmosis
Multiple hosts
Multiple life stages

41. Parasitism and Coevolution
Example: malaria
Parasite infects red blood cells
RBCs are swept into the spleen every few
days and destroyed
Parasite evolved to latch onto blood vessel
with a sticky protein
Body recognizes protein as foreign and will
attack it
Parasite evolves to have many different types
of proteins, so body can never catch up

42. We all get parasites

43. Mutualism
A form of
symbiosis in
which both
organisms
benefit

44. Commensalism
A form of symbiosis
in which one
organism benefits and
the other is not
harmed or helped
Example: sharks and
remoras

45. Summarize
Why are population
interactions a driving force
for natural selection?