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Announcements September 6, 2006 Steve “crocodile hunter” Irwin died Monday morning after being attacked by a stingray while shooting a TV program off Australia's north coast. Evolution and Ecological Interactions Lecture Objectives: 1. Learn basic concepts of Evolution

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September 6, 2006


Steve “crocodile hunter” Irwin died Monday morning after being attacked by a stingray while shooting a TV program off Australia's north coast.


Evolution and Ecological Interactions

Lecture Objectives:

1. Learn basic concepts of Evolution

2. Learn 5 major categories of interactions

  • 3. Understand 2 ways humans alter interactions

Often, there are not enough resources for all individuals in the population

Many individuals die before reproducing

Some individuals are better at surviving and reproducing than others


What is Evolution?

The process of change in the traits of populations over time.

Process by which species' characteristics change over generations.

Traits must have genetic basis.

Evolution does not occur within an individual.

Evolution does not occur within a generation.


What is Evolution?

Evolution occurs primarily through natural selection

Natural Selectionis the process that determines which individuals within a species will reproduce and pass their genes to the next generation.

Proposed by Charles Darwin in his book “On the Origin of Species” published in 1859


Genes— Distinct pieces of DNA that determine an individual’s characteristics.

Population—All organisms of the same kind found within a specific geographic region. (have the potential to interact)

Species— Those organisms potentially capable of reproducing naturally among themselves, and producing viable offspring.


Natural selection can occur when:

* Individuals within a species show genetically determined variation in traits

-this variation makes some individuals better at surviving and reproducing than others

  • * More offspring are produced than survive to reproduce

*Offspring with a particular trait survive better than do those without that trait

*Over several generations, the frequency of that trait increases in the population


Evolution in action

Pepper Moths in England

two forms: light and dark

Prior to 1845, most moths light colored

  • Light colored ones could blend in with lichens on trees

Evolution in action

Pepper Moths in England

Increasing pollution led to soot-covered trees without lichens

  • Light colored moths easy for birds to see on soot-covered tree, dark colored moths harder to see

By 1950, most moths black


Before 1845


Environment changes, now more black moths and fewer white moths survive to adulthood

Several more generations later

Several generations later

Several more generations later



Evolution in action

Resistance to herbicides


Evolution in action

Resistance to antibiotics


Evolution does not just happen on long time scales

  • Evolution is important for real-word issues: agricultural, conservation, health

* Disease dynamics

* Invasive species issues

* Antibiotic and pesticide/herbicide resistance


Red Queen Hypothesis

Lewis Carroll's Through the Looking Glass: “in this place it takes all the running you can do, to keep in the same place."


When two or more species interact closely they can influence each other’s evolutionary direction.

In tightly coevolved interactions, evolutionary change in one species will lead to evolutionary change in other or the second species may go extinct.

Example: host / parasite coevolution


Abiotic – Non-living factors

Biotic – living portion of the environment

What are some biotic factors that contribute to this differential survival and reproduction?

Interactions among organisms

1. Predation

2. Competition

3. Parasitism

4. Commensalism

5. Mutualism


Interactions among organisms

1. Predation(positive for consumer, negative for prey)

One animal consumes another


Types of predators

Active predators: chase & overpower prey

Sit-and-wait predators: motionless until prey close enough to strike


Many prey items have traits that reduce predation

Cryptic Coloration: blend in with environment


Many prey items have traits that reduce predation

Warning Coloration: conspicuous to convey threat


Batesian Mimicry: defenseless species (mimic) is protected from predation by its resemblance to a species that is dangerous

fly (bee mimic)

bumble bee


Interactions among organisms

1. Predation

  • Predator benefits (+) from food
  • Prey is harmed (-) by being eaten

Predation is a (+ / - ) relationship


Interactions among organisms

2. Competition

Competition: organisms compete for the same limited resource

Ex. light, food, mates, habitat, etc.

Competition is a (- / - ) relationship


Interspecific competition:

  • Members of different species competing for resources
  • May lead to competitive exclusion

Photos: Alex Wild


Interactions among organisms

3. Parasitism

1 organism (parasite) living in or on another organism (host), from which it derives nourishment

Ex. Tapeworm

Parasitism is a (+ / - ) relationship


3. Parasitism (+,-)

  • Ectoparasites—Live on host’s surface
    • (e.g., Fleas, lice, some molds)

3. Parasitism (+,-)

  • Endoparasites—Live inside host.
    • (e.g., worms, protozoa, bacteria, fungi)

Ex. Heartworm


Nest Parasitism

Adult cowbirds don’t build nests


Common Yellow-throat


Vectors: animals that carry parasite from one host to another

Examples: Malaria, Lyme Disease, West Nile Virus, Bubonic Plague

Malaria carrying mosquito


Interactions among organisms

4. Commensalism —One organism benefits, while the other is unaffected.

Remora and shark

Commensalism is a ( + / 0 ) relationship


Interactions among organisms

5. Mutualism- Both species benefit.

Acacia and ants

*Tree provides sugar solution that the ants eats

*Ants defends tree against grazers

summary of 5 major interactions
Summary of 5 major Interactions

Individual 1 Individual 2

Predation + -

Competition - -

Parasitism + -

Commensalism + Neutral

Mutualism + +

how have people change these interactions
How have people change these interactions?

1) Introduced species

2) Habitat destruction

Introduction of novel predators and parasites can devastate natural communities.


Over 2,000 species of birds have gone extinct on islands as a result of habitat loss and the introduction of predators and parasites.


Habitat loss, malaria, rats and mongoose


Points to know:

Know what evolution is and how is operates. Understand coevolution.

Know the 5 main types of species interactions.

Understand who benefits from each type of interaction (one or both participants)

Understand how humans may influence these interactions.