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Ecology: Population Ecology (2)
NATURAL SELECTION
• This includes describing how organisms
respond to the environment and how
organisms are distributed.
• Events that occur in the framework of
ecological time (minutes, months, years)
translate into effects over the longer scale of
evolutionary time (decades, centuries,
millennia, and longer).
2
NATURAL SELECTION
3
NATURAL PROCESSES
4
FINCH BEAK SIZE OR SHAPE
5
MODES OF SELECTION
6
MODES OF SELECTION
Disruptive- produces a bimodal curve as the extreme
traits are favored
Stabilizing-reduces variance
over time as the traits move
closer to the mean
Directional-favors a
phenotypic trait (selected by
the environment)
SCENARIO
These photographs show the
same location on Captiva
Island following Hurricane
Charley.
What would happen to a
population of birds who
derive their diets from the
tree tops? The population had
a wide range of beak sizes.
What would happen to the
population gene pool over
time if the new environment
favored smaller beaks? Over
time, which beak would be
most represented in the
population of birds? 8
HYDRANGEA FLOWER COLOR
Hydrangea react to the
environment and ultimately display
their phenotype based on the pH
of their soil.
Hydrangea flower color is affected
by light and soil pH. Soil pH exerts
the main influence on which color
a hydrangea plant will display.
9
FISH AND MAINTAINING HOMEOSTASIS
IN VARIOUS WATER CONDITIONS
Fish and other aquatic
animals deal with
changing environments in
part due to nature and in
part due to human
interactions.
Pressure- their bladder
fills with gas to equalize
internal pressure
10
BIOGEOGRAPHIC REALMS
11
INTRODUCED SPECIES
• What’s the big deal?
• These species are free from
predators, parasites and pathogens
that limit their populations in their
native habitats.
• These transplanted species
disrupt their new community by
preying on native organisms or
outcompeting them for
resources.
12
GUAM: BROWN TREE SNAKE
• The brown tree snake was
accidentally introduced to
Guam as a stowaway in military
cargo from other parts of the
South Pacific after World War II.
• Since then, 12 species of birds
and 6 species of lizards the
snakes ate have become extinct.
• Guam had no native snakes.
Dispersal of Brown Tree Snake
13
SOUTHERN U.S.: KUDZU VINE
• The Asian plant Kudzu was introduced by the U.S. Dept. of Agriculture
with good intentions.
• It was introduced from Japanese pavilion in the 1876 Centennial
Exposition in Philadelphia.
• It was to help control erosion but has taken over large areas of the
landscape in the Southern U.S.
14
INTRODUCED SPECIES
15
NEW YORK: EUROPEAN STARLING
• From the New York Times, 1990
The year was 1890 when an eccentric drug
manufacturer named Eugene Schieffelin
entered New York City's Central Park and
released some 60 European starlings he had
imported from England. In 1891 he loosed 40
more. Schieffelin's motives were as romantic
as they were ill fated: he hoped to introduce
into North America every bird mentioned by
Shakespeare.
Skylarks and song thrushes failed to thrive,
but the enormity of his success with starlings
continues to haunt us. This centennial year is
worth observing as an object lesson in how
even noble intentions can lead to disaster
when humanity meddles with nature.
16
NEW YORK: EUROPEAN STARLING
• From the New York Times, 1990 (cont.)
Today the starling is ubiquitous, with its purple
and green iridescent plumage and its rasping,
insistent call. It has distinguished itself as one
of the costliest and most noxious birds on our
continent.
Roosting in hordes of up to a million, starlings
can devour vast stores of seed and fruit,
offsetting whatever benefit they confer by
eating insects. In a single day, a cloud of
omnivorous starlings can gobble up 20 tons of
potatoes.
17
ZEBRA MUSSELS
• The native distribution of the species is in
the Black Sea and Caspian Sea in Eurasia.
• Zebra mussels have become an invasive
species in North America, Great Britain,
Ireland, Italy, Spain, and Sweden.
• They disrupt the ecosystems by
monotypic (one type) colonization, and
damage harbors and waterways, ships and
boats, and water treatment and power
plants.
18
ZEBRA MUSSELS
• Water treatment plants are
most impacted because the
water intakes bring the
microscopic free-swimming
larvae directly into the facilities.
• The Zebra Mussels also cling on
to pipes under the water and
clog them.
• This shopping cart was left in
zebra mussel-infested waters
for a few months. The mussels
have colonized every available
surface on the cart.
(J. Lubner, Wisconsin Sea Grant,
Milwaukee, Wisconsin.)
19
ZEBRA MUSSEL RANGE
20
SNAKEHEAD FISH
• During all life stages, snakeheads
compete with native species for food
and habitat.
• As juveniles, they eat zooplankton,
insect larvae, small crustaceans, and
the young of other fishes.
• As adults, they feed on other fishes,
crustaceans, frogs, small reptiles, and
sometimes birds and small mammals.
• Their predatory behavior could
drastically disrupt food webs and
ecological conditions, thus forever
changing native aquatic systems by
modifying the array of native species.
22
INQUIRY: DOES FEEDING BY SEA URCHINS
LIMIT SEAWEED DISTRIBUTION?
• W. J. Fletcher of the University of Sydney, Australia reasoned that if sea urchins are
a limiting biotic factor in a particular ecosystem, then more seaweeds should
invade an area from which sea urchins have been removed.
23
INQUIRY: DOES FEEDING BY SEA URCHINS
LIMIT SEAWEED DISTRIBUTION?
• Seems reasonable and a tad obvious, but the
area is also occupied by seaweed-eating
mollusc called limpets.
• What to do? Formulate an experimental
design aimed at answering the inquiry
question.
24
PREDATOR REMOVAL
25
PREDATOR REMOVAL
Removing both
limpets and
urchins or
removing only
urchins
increased
seaweed cover
dramatically
26
PREDATOR REMOVAL
Almost no
seaweed grew in
areas where
both urchins and
limpets were
present (red
line) ,
OR
where only
limpets were
removed (blue
line)
27
RELATIONSHIP BETWEEN TEMPERATURE AND PRECIPITATION
28