Download genetic drift

Islands Introduction
Islands are similar because they are unique
Islands Unit Overview
The Story:
•
This unit is about both biological and geological
evolution.
•
Islands provide interesting, unusual examples of
evolutionary change on a scale that is small and
easy to understand.
•
While the results of island evolution tend to be very
different from evolution on a continental
landmass, the mechanisms are the same.
Islands simply become the context to learn
evolutionary
mechanisms.
Student Outcomes:
 Understand the process of biological evolution on
isolated island systems.
 Observe the results of biological evolution and
describe the specific mechanisms that drive it.
 Connect the unique biological evolution of
organisms on an isolated island system to the
island’s geology.
 Gain an understanding of earth’s geological
processes involved in island formation by
observing evidence of plate tectonics, and rock
samples.
I. What is an Island?
A. Definition: Islands are isolated environments with unique living
organisms (biology) and unique physical characteristics (geology)
II. Why Do We Study Islands?
A. Islands are similar because they are unique
B. Islands are dynamic and often experience change, both biologically
and geologically, more rapidly than continental landmasses
C. Islands are smaller than continents, therefore easier to study.
D. Islands allow us to study two major themes in science: Evolution
(Biological Science) and Plate Tectonics (Earth Science).
III. What Happens to Organisms on Islands Over Time?
A. Migrate, Survive, Reproduce, Adapt, Evolve or Go Extinct
IV. Effects Are Unique on Islands
A. Species on islands are unique.
B. Identify unique adaptations found in the organisms below.
Dodo Bird (extinct) Mauritius
Giant Galapagos Tortoise
- Galapagos
Elephant Bird (extinct) Madagascar
IV. Effects Are Unique on Islands (continued)
A. Species on islands are unique.
B. Identify unique adaptations found in the organisms below.
Giant burrowing
cockroach - Australia
Kiwi Bird - New Zealand
Moa (extinct)
IV. Effects Are Unique on Islands (continued)
A. Species on islands are unique.
B. Identify unique adaptations found in the organisms below.
Pygmy hippopotamus - Madagascar
Rattleless
rattlesnake - Santa
Catalina Island
Tree climbing kangaroo
- New Guinea
IV. Effects Are Unique on Islands (continued)
A. Species on islands are unique.
B. Identify unique adaptations found in the organisms below.
Tasmanian devil - Tasmania
Lesser bird of paradise Indonesia
Komodo dragon Komodo Island
V. Causes Are Similar on Islands
A. The mechanisms that cause islands to be unique are similar:
1. Dispersal Ability - pioneer species are good at migrating to
new locations
2. Size Change - organisms are larger or smaller than normal
3. Loss of Dispersal Ability - species easily lose ability to
emigrate
4. Endemism - species tend to evolve and remain native to that
area only
5. Relictualism - populations are small and have a greater
chance of extinction
6. Loss of Defensive Adaptations - defense capabilities are
reduced in predator-free environments
7. Archipelago Speciation - many species may evolve from one in
the same island group
8. Adaptive Radiation - many species may evolve from one in the
VI. Mechanisms For Evolution are Similar on Islands
A. Natural Selection - “Best Fit” Survive
•
Ex. Camouflage, size, speed, adaptations, sex appeal,
strength, intelligence, predictable human impact etc.
B. Genetic Drift - “Lucky” Survive
A. Ex. Extreme weather, isolation, epidemic diseases, genetic
mutations, unequal gender balance, geologic activity etc.
Mechanisms of Island
Evolution
What Biological Processes Make the Organisms
on Islands So Unique?
Numbers on these slides correspond to your HW.
Presentation available @ www.redwood.org/stewart
Highlight information in blue.
Dispersal
1. Define dispersal:
•
The process of scattering or spreading from a
certain area.
2. Give examples of how plants disperse their seeds.
•
Birds
chance
•
Wind
chance
•
Float
chance
•
Shoots out of fruit
natural
•
Spring open and scatter
natural
3. Analysis: How is dispersal important to evolution on
islands? How life arrives.
Evolution and Natural Selection
Evolution •
The process of modern organisms descending
from ancient organisms; change over time.
Charles Darwin
4. Variation
• Variations will be selected for or against. Organisms
with more adaptive variations are more likely to survive and
pass on their inherited variations.
Fitness Organisms with more successful offspring have a higher
fitness: the combination of physical traits and behaviors that
help an organism survive and reproduce in its environment.
Measured by the number of successful offspring.
Evolution and Natural Selection
5. Survival of the Fittest •
Individuals with characteristics best suited
to their environment survive.
6. Natural Selection •
The process in nature that results in the
most fit (best adapted) organisms
producing offspring. 3 steps:
variation --> selection --> reproduction.
•
The mechanism that drives evolution.
7. Adaptation •
The process that enables organisms and
species to become better suited to their
environments.
Evolution and Natural Selection
Evolution does NOT occur in the following ways:
•
A Desire to Change
•
Use and Disuse
•
Passing on Acquired Traits
Evolutionary Theory Evolves: Genetic Drift
8.
What is genetic drift? Give 2 examples.
•Genetic change in a population, occurring in the absence of
natural selection, due to random, chance events.
•Separation of populations so that they do not interbreed to
produce fertile offspring.
•One of the most common ways in which new species form is
when populations are separated.
•Examples of events leading to genetic drift:
-mutation
-chance dispersal
-extreme weather
-Geographic barriers
Evolution of new
species: Speciation
 Speciation •
Darwin’s Finches
The process of new species evolving from preexisting ones. This may be due to natural selection,
genetic drift, or both.
 Niche •
The combination of an organism’s habitat and it’s
role in that habitat. (address + profession)
Why can no two species occupy the same niche?
•
Competition arises for food and space. The most
efficient species will survive and reproduce.
Evolutionary Theory Evolves: Genetic Drift
Punctuated Equilibrium •
Rapid periods of speciation
(evolution) due to genetic drift and
other random (stochastic) factors
after long periods of gradualism
(deterministic)
•
Rapid speciation may occur when a
small population of a species
becomes isolated from the main part
of the population or due to other
factors.
Evolutionary Theory Evolves: Genetic Drift
9. How are genetic drift and natural selection different?
Evolution by natural selection occurs predictably, slowly
and gradually.
Evolution due to genetic drift is unpredictable and to some
degree random (stochastic)
10. How are genetic drift and natural selection similar?
Both lead to change over time (evolution).
11. Analysis: What is unique to the evolutionary process on
islands and why?
Islands are ISOLATED (distant) and small so genetic drift is
more likely. AND factors influencing natural selection may be
different.