AP Environmental Science
Ecosystems: Adaptation and Niches - chapter 4
I. Natural selection/microevolution can be used to explain adaptations to the environment
A. natural selection results when three conditions are met:
1. overproduction of offspring
2. individual variation
3. competition for limited resources
 example - snails
B. selection can be directional, stabilizing, or diversifying
C. microevolution can also occur by random changes known as genetic drift. This
phenomenon usually results from a bottleneck and/or the founder effect.
D. Limits to adaptation – why don’t populations just evolve whatever they need?
II. Ecological niches
A. definition; fundamental vs. realized niches
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co-evolution
B. specialists vs. generalists (fig. 4-15)
C. niches are related to resource use and competition – more on this in chapter 5
and fig. 4-16
III. Speciation | basic overview | more details
A. speciation refers to the production of a new species. This usually happens
when two populations are physically separated and each adapts differently over
time. (fig. 4-12 - foxes in N America)

biodiversity and evolution are of course closely related. We will study
biodiversity in more detail in a later unit, but we should note that
"hotspots" of evolution are also hotspots of biodiversity
B. new species are formed when the two groups become reproductively isolated.
What can cause reproductive isolation?
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sexual selection -- preference for size, color, etc.
o birds of paradise
o the Irish elk -- huge antlers considered an example of "runaway
sexual selection"
parasites (refer to reading in chap. 5)
timing of mating
size/shape changes
hybrid sterility
animation
C. Speciation helps us understand biogeography, as we will see later. Bursts of
speciation in a new geographical area are called adaptive radiation.
D. Examples of Natural Selection
1. Examples that do not involve new species:
a. industrial melanism – moths in England – (check
out why this is a good example)
b. pesticide resistance (more)
c. antibiotic resistance (view animation of this
process and another animation)
d. sickle-cell anemia
e. changes in salmon size as a result of fishing
2. examples involving formation of new species (speciation)
a. Cichlid fish in Lake Victoria
b. shell fish in intertidal zones
c. rainforests – adaptive radiation of insests,
rodents, etc.
d. arctic char in an Iceland lake
e. plants
f. observed examples of speciation
g. directional vs. stabilizing selection
h. species on islands are often larger or smaller than
their mainland counterparts
i. finches in Galapagos