Biodiversity, Species Interactions,
and Population Control
Chapter 5
Biodiversity, Species Interactions,
and Population Control
Chapter 5 Part 1: Species
Interactions
Review!
 What is evolution?
• Change in a species over time (many
generations!)
 What is natural selection?
• Pressures of environment ‘select’ genes
that survive to produce more offspring
 What is an adaptation?
• Trait that improves chances for survival and
reproduction
Coevolution
 The process by which
two species evolve in
response to changes
in each other over
time
• Sometimes organisms
that are closely
connected to one
another by ecological
interactions evolve
together.
Coevolution: A Langohrfledermaus
Bat Hunting a Moth
Species Interact in Five Major Ways
 Interspecific Competition
 Predation
 Parasitism
 Mutualism
 Commensalism
Most Species Compete with One Another
for Certain Resources
 Competition
• When two species compete, their niches overlap
 Competitive exclusion principle – no two
species can occupy exactly the same ecological
niche for very long
• Both species suffer harm
• Migration or predation will ultimately occur
Some Species Evolve Ways to Share
Resources
 Resource
partitioning –
species evolve to
reduce niche overlap
 Use shared resources
at different
• Times
• Places
• Ways
Specialist Species of Honeycreepers
Sharing the Wealth: Resource
Partitioning
Predator or Prey?
 Predation – act of one
organism eating
another organism
• Predator – organism
that does the eating
• Prey – organism that
gets eaten
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Most Consumer Species Feed on Live
Organisms of Other Species
 Predators may capture prey by:
• Walking
• Swimming
• Flying
• Pursuit and ambush
• Camouflage
• Chemical warfare
Most Consumer Species Feed on Live
Organisms of Other Species
 Prey may avoid
capture by
• Camouflage
• Chemical warfare
• Warning coloration
• Mimicry
• Deceptive looks
• Deceptive behavior
Important lesson to remember:
 If an organism is small and beautiful… it is
probably poisonous.
 If it is strikingly beautiful and easy to catch…it is
probably deadly.
Predation: Population Control
 Cyclic fluctuations, boom-and-bust cycles
• Top-down population regulation
• Controlled by predation
• Bottom-up population regulation
• Controlled by scarcity of one or more resources
Your Turn!
 Predator Prey Relationships
Video Clip
 Orca Training Session
• 22:42 to 31:00
Mutualism: Clownfish & sea anemone
 Both organisms
derive mutual benefit
 Intimate and
obligatory
 Neither can survive
for long periods
without the other
Mutualism: Oxpeckers Clean Rhinoceros;
Anemones Protect and Feed Clownfish
Parasitism: Tapeworm and Humans

Parasite lives on or in the host and benefits at
the expense of the host
Parasitism: Tree with Parasitic Mistletoe,
Trout with Blood-Sucking Sea Lampreys
Commensalism: Flatworms and
horseshoe crabs
 Only one member
benefits
• sharing space, defense,
shelter, food
 Flatworms that live on
the gills of horseshoe
crabs obtain food from
the host, but do not
negatively affect the
host
Commensalism: Bromiliad Roots on Tree
Trunk Without Harming Tree
Your Turn!
 http://www.pbs.org/wnet/nature/lessons/symbioti
c-strategies/video-segments/1496/
• Ecological Relationships
•
•
•
•
•
Predation
Competition
Commensalism
Mutualism
Parasitism
Biodiversity, Species Interactions,
and Population Control
Chapter 5 Part 2: Population
Dynamics
Populations Have Certain
Characteristics
 Population dynamics – study of how
characteristics of a population changes in
response to changes in the environmental
conditions
 Populations differ in
• Distribution
• Numbers
• Age structure
Density
 Number of individuals of a population in a given
area
Distribution Patterns
Random
Independent of
other organisms
No habitat
preference
Distribution Patterns
Uniform
Even spacing
Evidence for intraspecific competition
(among other sea
otters)
Distribution Patterns
Clumped
Organisms tend to
be together
Habitat preference
Behavioral
preference such as
herding
Most common!
Why clumping?
 Species tend to
cluster where
resources are
available
 Protects some
animals from
predators
 Packs allow some to
get prey
 Temporary groups for
mating and caring for
Populations Can Grow, Shrink, or
Remain Stable
 Population size governed by
•
•
•
•
Births
Deaths
Immigration
Emigration
 Population change =
(births + immigration) – (deaths + emigration)
Populations Can Grow, Shrink, or
Remain Stable
 Age structure – number of individuals in a given
age class
• Pre-reproductive age
• Reproductive age
• Post-reproductive age
Density Dependent Limiting Factors
 Operates more
strongly when a
population is large
and overcrowded
 Predation – more
prey organisms –
predator numbers will
increase
Density Dependent Limiting Factors
 Parasitism –
crowding helps
parasites travel from
one host to another
 Crowding – higher
levels of stress (direct
influence on immune
system)
Density Dependent Limiting Factors
 Competition
• Intraspecific –
members of the
SAME species
compete
• Interspecific –
competition
between
DIFFERENT
species
Density-Independent Limiting Factors
 Will affect population regardless of its size
 Natural Disasters
Forest fires
Floods
Earthquake
Oil Spill
Genetic Diversity Can Affect the Size
of Small Populations
 Minimum viable population size – number of
individuals endangered species need for longterm survival
•
•
•
•
Founder effect
Demographic bottleneck
Genetic drift
Inbreeding
Case Study: Exploding White-Tailed Deer
Population in the U.S.
 1900: deer habitat destruction and uncontrolled
hunting
 1920s–1930s: laws to protect the deer
 Current population explosion for deer
• Lyme disease
• Deer-vehicle accidents
• Eating garden plants and shrubs
 Ways to control the deer population