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