Chapter 4
Evolution, Biological
Communities, and Species
Interactions
“Of course, long before you mature,
most of you will be eaten.”
“The picture’s
pretty bleak,
gentlemen. The
earth’s climate is
changing, the
mammals are
taking over, and we
all have brains the
size of a walnut.”
“Now this
end is called
the
thagomizer,
after the late
Thag
Simmons.”
“Evolution’s been good to you, Sid.”
Evolution Produces Species Diversity
• Natural Selection Leads to Evolution
• All Species Live Within Limits
• The Ecological Niche is a Species’ Role and
Environment
– Large Grassland Herbivore
• North America: Pronghorn
• Africa: Antelope
• Australia: Large Kangaroos
• Speciation Maintains Species Diversity
Exaptation
There Are No Half-Evolved Organisms
• Every organism is adapted to its environment
all the time
• Change happens when the environment
changes
– Mass Extinctions
– Exotic Species Invasions
– Climate Change
What Good is Half an Eye?
What Does a Bug See?
What Does a Bug See?
What Good is Half a Wing?
• It’s about Terminal Velocity
– Humans: 50m/sec (Really terminal)
– Mice: 5 m/sec (Generally not terminal)
• True Powered Flight
– Birds
– Bats
– Insects
– Flying Reptiles (Maybe)
What Good is Half a Wing?
• Critters that Glide
– Squirrels
– Marsupials
– Lemurs
– Fish
– Squid
– Lizards
– Snakes
– Frogs
What Good is Half a Wing?
• Critters that Glide are all Small
– Low Terminal Velocity
– Falls usually not fatal
– Selection favors duration and control
• Pre-Flight Uses for Wings
– Catching prey
– Mating displays
– Fighting
– Ground maneuverability
The Bumblebee Myth
• Bumblebees, theoretically, can’t fly
– They can’t glide. Neither can an F-16
• Bumblebees can carry more than their own
weight, something no aircraft can do
– C-130 transport: empty weight of 76,780 pounds
and a maximum takeoff weight of 175,000 pounds
– A C-5 Galaxy: empty weight of 238,000 pounds
and a maximum takeoff weight in wartime of
840,000 pounds
Species Interactions Shape Biological
Communities
•
•
•
•
Competition Leads to Resource Allocation
Predation Affects Species Relationships
Some adaptations help avoid predation
Symbiosis involves intimate relations among
species
• Keystone species have disproportionate
influence
Community Properties Affect Species
And Populations
• Productivity is a measure of biological activity
• Abundance and diversity measure the number and
variety of organisms
• Cormnunity structure describes spatial distribution of
organisms
• Complexity and connectedness are important
ecological indicators
• Resilience and stability make communities resistant to
disturbance
• Edges and boundaries are the interfaces between
adjacent communities
Communities Are Dynamic And
Change Over Time
• The nature of communities is debated
• Ecological succession describes a history of
community development
• Appropriate disturbances can benefit
communities
• Introduced species can cause profound
community change