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Ecology and Evolution
Exam 4 and Assignment 4 – December 7th
Biomes
• Major landscape associations of organisms
(plants, animals)
• Have a characteristic ‘appearance’
• Defined by regional variations in climate
Tropical Forest – equatorial, rainfall 150 - 450 cm/yr
Figure 19.34a
Savanna – equatorial / mid latitude, rain 75 – 125 cm/year
Figure 19.34b
Desert – mid latitudes, < 25 cm/year rainfall
Figure 19.34c
Chaparral – mid latitudes, coastal,
Figure 19.34d
Grassland – mid latitudes
Figure 19.34e
Temperate Deciduous Forest – mid to high latitudes
Figure 19.31f
Coniferous (Evergreen) Forest – high latitudes
Figure 19.34g
Tundra – arctic (very high) latitudes
Figure 19.34h
What factors are responsible for
creating these different biomes?
How Climate Affects Biome Distribution
• Because of its curvature, Earth receives an
uneven distribution of solar energy
Low angle of incoming sunlight
Sunlight directly overhead
Low angle of incoming
sunlight
Atmosphere
Figure 19.30
Where are certain types of Biomes found?
While the relationship varies slightly, in general:
1000 feet of altitude = 100 miles of latitude = 3.5°F temperature drop
What factors directly affect the
population size of Phoenix?
•
•
•
•
•
Births
Deaths
Immigration
Emigration
Change in population size = B – D + I – E.
A farmer has a pond on his property in
which a fast growing water weed has just
appeared. He calculates that area the
weed covers on his pond doubles each
day, so that after 30 days the pond will
be fully covered. On which day will the
weed cover half of the pond?
Exponential Growth
Growth of Plant on Pond
% of pond covered
100
80
60
40
20
0
0
5
10
15
days
20
25
30
Exponential Growth
• When a population is growing at its
maximum rate.
• Often occurs when a population first
invades an area.
• There is plenty of food and space.
• All species are capable of growing
exponentially, but species differ in their
growth rates.
• In exponential growth, births >> deaths.
Exponential growth
High r
Population size (N)
500
400
300
‘r’ is how fast the
population is growing,
its growth rate
200
Moderate r
Low r
100
Very
low r
0
time
Logistic Growth
• Sometimes populations increase in size to certain
level and then stabilize.
• This type of growth (logistic) yields an S-shaped
curve.
• The population size at which the growth stabilizes
is called the carrying capacity.
• Carrying capacity: maximum population size the
environment can support indefinitely.
• At carrying capacity, births = deaths.
Population size
Carrying capacity
Time
Comparison of Exponential and
Logistic Growth
What factors maintain a population
near its carrying capacity?
• Density-dependent factors: mortality rate
(% of population that dies) depends on
population size.
• disease
• lack of food
• lack of space
• build up of wastes
• predation
What would happen if a densitydependent factor were removed?
• If the population was
already at its carrying
capacity, it would
increase, overshooting
its carrying capacity.
• Population overshoot
• Deer lower carrying
capacity by
overgrazing.
Population Overshoot in Reindeer
What factors affect populations
regardless of their size?
• Density-independent factors: mortality rate (% of
population that dies) independent of population size.
• They are usually natural disasters.
What factors affect populations
regardless of their size?
• Density-independent factors: mortality rate (% of
population that dies) independent of population size.
• They are usually natural disasters.
• Ex. frost, flood, hurricane, hot spell, drought,
volcano.
Factors that affect human population
growth
• Culture and Attitude
• Poorest nations have the highest growth
rates.
• Why? Poorly educated women.
• Rich people have fewer children than
poorer people.
• This trend extends between countries, or
within the US despite ethnic differences.
• Certain religions advocate large families.
Human Population Growth
Ecology: Explaining the distribution
and abundance of organisms
• Interactions between populations
– Predation
– Competition
– Symbioses
KEY PROPERTIES OF COMMUNITIES
• A community
– Is an assemblage of populations of different species
living close enough together for potential interaction
Predation: when one organism
consumes another.
Competition
• When two organisms are competing for the
same resource.
• Interspecific competition: between
members of different species.
• Intraspecific competition: between
members of the same species
• Why type of competition is most intense?
• Intraspecific, because they share the same
niche.
They even share the same interest in
mates!
How to demonstrate competition is
occurring in nature (what kind is this?).
• Remove one species and record effects on other
species.
Symbiosis
• Two different species living in close
association with each other.
• At least one species always benefits.
• Mutualism
• Commensalism
• Parasitism
Mutualism: both benefit
Commensalism: one benefits,
one unaffected
Cattle egrets, again
Parasitism: one benefits, one hurt
What relationship is this?
What relationship is this?
What relationship is this?
What relationship is this?
Explaining the Abundance of
Organisms: Data from the Hudson
Bay Trading Company
• Bought animal furs from
traders.
• Distributed them to Eastern
seaboard and Europe.
• Kept records of pelts bought
each year.
• One fur they bought was the
snowshoe hare.
• Let’s see how the number of
furs varied…
Why the fluctuation in abundance?
• Hypothesis 1: Hare
populations fluctuate with
their food supply.
• Prediction 1: Their food
supply should increase
and decrease along with
hare densities.
• We cannot test prediction
1, because we have no
index of past food
supplies.
• Hypothesis 2: Hare
populations are kept down
by their predators.
• Prediction 2: Their
predator, the lynx, should
increase as the hare
increases, and decrease
following the decline of
the hare.
• Lynx populations rise and
fall in a way that suggests
that hare may be
controlled lynx predation
Conclusion?
• Lynx may indeed
control hare
populations.
• But, what if the
hare population is
controlling the
lynx population?
What would this graph look like if hare were not
controlled by lynx, but instead were controlled
only by food availability?
How do materials travel in
ecosystems?
• If a Sacred Datura takes in
7 units of phosphorus
during the summer, but
loses 3 units, how much
does it have left?
• How did figure that out?
• You used the First Law
of Thermodynamics,
which states: Energy and
Matter cannot be created
or destroyed.
Energy flow in ecosystems
• Consider a cheetah that ingests
10,000 Calories of antelope in a
week, and loses 3,000 from
activities (hunting, mating, etc.)
as well as the energy left in its
urine, feces, hair, nails, etc.
• If the cheetah gets larger by 500
Calories, where did the rest go?
• It’s lost as heat!
Second Law of Thermodynamics
• No energy transformation is 100% efficient,
as energy is always lost as heat.
• Remember your car. Why does it get
warm?
• The energy that’s making it warm could be
used to propel it. It’s not 100% efficient in
coverting gas combustion into motion.
• The same thing happens with the cheetah. It
loses energy as heat.
Implications of Second Law of
Thermodynamics
• Consider a simple
ecosystem.
• 100 units of energy
produced by grass/month.
• How much turns up as
Thomson’s gazelle?
• Only 10 units!
• How much of the gazelle
turns up as cheetah
biomass?
• Only 1 unit!
Why are big fierce animals, which are predators
at top of the food chain, rare?
• Very little energy from primary producers (plants) makes it all
the way to the top of the food chain.
• Called the 10% rule, as only about 10% makes it to the next
trophic (i.e., feeding) level. Other reasons?
Efficiency of Energy Transfer in a Food Chain
Tertiary
consumers
10 kcal
Secondary
consumers
100 kcal
Primary
consumers
Producers
1,000 kcal
10,000 kcal
Figure 19.26
A few terms to know
• Food chain (ex. Grass  antelope  lion)
• Food web (more realistic/complex than food chain; many chains
make up the web)
• Producers (mostly plants: convert sunlight energy to chemical
bond energy (sugars) by photosynthesis)
• Consumers (can’t photosynthesize, must eat other organisms).
These include 2 categories:
- Herbivores (plant eaters)
- Carnivores (animal eaters)
• Decomposers (break down dead organisms, return elements (C,
N, P, etc.) to the soil, where they are recycled.
Quaternary
consumers
Carnivore
Carnivore
Tertiary
consumers
Carnivore
Carnivore
Secondary
consumers
Carnivore
Carnivore
Primary
consumers
Zooplankton
Herbivore
Producers
Plant
Phytoplankton
A terrestrial
food chain
A marine
food chain
Quaternary,
An ecosystem
Food Web
(more realistic)
Is made up of
many food
chains
tertiary,
and
secondary
consumers
Tertiary
and
secondary
consumers
Secondary
and
primary
consumers
Primary
consumers
Producers
(plants)
What do food chains/webs and the Second
Law of Thermodynamics imply about world
hunger?
• Which diet is most energy efficient?
– A beef diet, because it has similar elements to our
own body?
– A milk diet, because then we don’t kill the cow but
still get a high protein meal?
– A vegetarian diet, because the smallest amount of
energy is lost as heat.
• Energetically, a vegetarian diet could feed how
many more people than a totally meat diet?
Efficiency of Energy Transfer in a Food Chain
for which WE are the top consumer
• Eating producers (plants) instead of consumers (animals)
requires less photosynthetic productivity and reduces the
impact on the environment
Human
meat-eaters
Secondary
consumers
Primary
consumers
Human
vegetarians
Corn
Producers
(a)
Cattle
Corn
(b)
Figure 19.27
Why should we care about food webs
and trophic relationships in
ecosystems?
- Energy efficiency and ecosystem impacts of
herbivorous vs. carnivorous diets:
- human carnivory (meat-eating) adds another link to the food
chain in food production, compared to vegetarianism
- this additional link (cows, pigs, chickens, etc.) places greatlyincreased demands on habitat for “feed” production for these
animals. Animals also produce extra wastes.
- Biological magnification of fat-soluble toxins (like
mercury, pesticides, PCB’s) in food webs.
• Biological
magnification
– A process in which fatsoluble toxins become
more concentrated in
successive trophic
levels of a food web.
(Fat-soluble means that
the toxins dissolve, and
are stored, in lipids.)
DDT concentration
increase of 10
million times
DDT in
fish-eating
birds
25 ppm
DDT in large fish
2 ppm
DDT in
small
fish
0.5 ppm
DDT in
zooplankton
0.04 ppm
DDT in water
0.000003 ppm
Figure 20.7
Producer, herbivore, carnivore, or
decomposer?
Producer, herbivore, carnivore, or
decomposer?
Producer, herbivore, carnivore, or
decomposer?
The role of
decomposers
• Most people don’t like to
think of scavengers and
decomposers, but they
serve a vital role.
• What would the world be
like without these
organisms?
• Dead stuff would not
decompose.
• Nutrients would not be
recycled.
Sphagnum moss
• Releases acid as part of its
physiology.
• Acid prevents
decomposing bacteria
from thriving in bogs
• Thus, nutrients aren’t
recycled, because the dead
matter doesn’t decompose.
• Peat moss is harvested,
revealing all kinds of dead
preserved organisms in
bogs.
An example of what was found in a
Danish bog
• The
nitrogen
cycle
Nitrogen (N2)
in
atmosphere
Detritus
Amino
acids and
proteins in
plants and
animals
Denitrifying
bacteria
Detritivores
Assimilation
by plants
Decomposition
Nitrates
(NO3– )
Nitrogenfixing bacteria
in root
nodules of
legumes
Nitrogen
fixation
Nitrifying
bacteria
(b) The nitrogen cycle
Ammonium
(NH4+ )
Nitrogenfixing
bacteria
in soil
Figure 19.29b
• The phosphorous
cycle
Uplifting
of rock
Phosphates
in rock
Weathering
of rock
Phosphates
in organic
compounds
Consumers
Producers
Phosphates
in soil
(inorganic)
Rock
Precipitated
(solid)
phosphates
(c) The phosphorus cycle
Phosphates
in solution
Detritus
Detritivores
in soil
Figure 19.29c
• The carbon
cycle
CO2 in
atmosphere
Photosynthesis
Burning
Producers
Wood and
fossil fuels
Cellular respiration
Higher-level
consumers
Primary
consumers
Decomposition
Detritivores
Detritus
(a) The carbon cycle
Figure 19.29a
How can we explain the diversity
of life on this planet?
Charles Darwin
• Started medical
school.
• Traveled on H.M.S.
Beagle for 5 years,
collecting specimens
from 1831 to 1836.
• Didn't formulate the
idea of evolution until
1837, due to mounting
evidence.
Darwin’s Voyage on the Beagle
Evidence Darwin found
Geographic variation of species
• Galapagos Islands: The resemblance of the
different finches (a variety of bird) on the
individual islands caused him to question
the “fixed” nature of species.
• On Continents: Observed differences
between “fixed” species when they were
separated by long distances on the mainland
Adaptive radiation
• Occurs whenever there are open niches.
• Some individuals of a species expand into
unfilled niches (roles) in the environment.
• Thus, over LONG time periods through
selective reproduction and genetic variation,
the population may evolve slightly and
better fit that role.
Adaptive radiation
Darwin to pigeon and plant breeders
about artificial selection
• By selective breeding,
you can change
appearance of birds,
dogs, cattle
Theory of Evolution by Natural Selection
• 1) There are inheritable differences within a
population.
• 2) Reproduction exceeds carrying capacity.
• 3) Competition for resources.
• 4) Survival of the fittest: most fit survive and
pass down genes to next generation.
Natural Selection affects the
reproductive success of individuals,
and so through time populations
evolve.
• Individuals cannot evolve.
• Individuals either live or die, depending in part on
their adaptations (luck also matters somewhat).
• Populations evolve through changes in the proportion
of certain alleles (genes) in the population.
We call the features that organisms have
that enable them to survive well in their
environment adaptations.
• These adaptations do not happen because animals
and plants "want" them to happen (it's not goaloriented).
• Natural selection can only work with the available
material (the genetic variation) already present in
the population.
• Because of this, many adaptations aren't designed
the 'best' or most logical way.
Mechanisms of Speciation
• A key event in the potential origin of
species occurs when a population is
somehow separated from other populations
of the parent species
• The two modes of
speciation are
– Allopatric
speciation
– Sympatric
speciation
(a) Allopatric speciation
(b)Sympatric speciation
Figure 14.8
Allopatric Speciation
• Geological processes
– Can fragment a population into two or more isolated
populations
– Can contribute to allopatric speciation
Figure 14.9
• Speciation occurs only with the evolution
of reproductive barriers between the
isolated population and its parent population
Homologous and Analogous
structures
• Homologous: similarity in structure and/or
position due to common ancestry
A Homologous structure:
Forelimb bones in mammals
Homologous Structures
• Must be derived from
the same basic body
parts.
• Can be used for a
similar purpose or for
a different purpose.
• Ex. Human forearm,
chimp forearm, and
bird wing.
• They are all derived
from the same parts
but may have different
uses.
Homologous or Analogous
structures
• Homologous: similarity in structure and/or
position due to common ancestry
• Analogous: similarity in function but
different evolutionary origin- no (recent)
common ancestry
Analogous Structures
Homologous or Analogous?
• Turtle shell and Clam shell.
– Analogous: similar function (protection) but
different origins.
• A Dog’s fur and a Mouse’s fur.
– Homologous: Both dogs and mice shared a
common mammalian ancestor, which had fur.
Homologous or Analogous?
• A Bird wing and a Bat wing.
– Both! Homologous as forelimbs
(ancestral reptile had front limbs).
Analogous as wings, each group
developed wings independently (no
common ancestor with wings).
Molecular evidence
• If species share a
common ancestor,
then their DNA, and
the molecules
constructed from that
DNA, should be
similar.
• This has shown to be
true for virtually every
molecular example.
• Example: All organisms
require molecules that
break down sugar to
acquire energy.
• Thus, we could compare
very different creatures
because they all share
that type of molecule…
Molecular evidence: Differences in
Cytochrome C molecule
Cytochrome C: a protein essential in the production of a cell’s energy
Organism
•
•
•
•
•
•
•
•
•
Chimpanzee
Rhesus monkey
Rabbit
Cow
Pigeon
Bullfrog
Fruit fly
Wheat germ
Yeast
Number of Amino Acid
Differences from Humans
0
1
9
10
12
20
24
37
42
More Misunderstandings about
Natural Selection
Natural selection tries to help
individuals become adapted.
Natural selection has no goal. It is
not teleological (goal-oriented).
Natural selection depends upon
random chance. Chance should lead to
randomness, not adaptation.
• Natural selection depends
on mutations to provide
variation, and it is true
that these mutations are
random.
• But natural selection
determines which variants
(genes) get passed on.
• Favorable traits are much
more likely to be passed
on than unfavorable traits,
since the organisms
possessing favorable traits
have a much better chance
of surviving and
reproducing.
Natural selection is the survival of the
fittest and so leads to the evolution of traits
that promote the survival of
individuals.
• Survival is important but
what's really important is
how many fertile offspring
you produce.
• (Ex. Old gorilla never
mates, but young one mates
and dies young. Young one
has been genetically
successful, but not the older
one.)
The Greenhouse Effect:
a) in a greenhouse
b) on the planet as a whole.
a)
b)
Gases which trap the
re-radiating heat:
-CO2 (carbon dioxide)
-CH4 (methane)
-N2O (nitrous oxide)
-Chlorofluorocarbons
(A/C, spray cans)
But, is the Greenhouse Effect from
human activities really changing our
biosphere?
• The best way to answer this question is to
study the earth’s historical climate
Global Temperatures are increasing
Robert A. Rohde
Meehl, G.A., W.M. Washington, C.A. Ammann, J.M. Arblaster, T.M.L. Wigleym and C. Tebaldi (2004). "Combinations of
Natural and Anthropogenic Forcings in Twentieth-Century Climate". Journal of Climate 17: 3721-3727.
Robert A. Rohde
Robert A. Rohde
Is global warming caused by
humans?
• Fact: global temperatures are rising
• Fact: global CO2 levels are rising
• Fact: CO2 levels have risen with the
industrial revolution
• Strong correlation between greenhouse
gasses and temperature.
– this alone does not prove global warming as
human caused
Global Warming controversy
• Use of proxy data vs. use of direct
measurements
• Possibility of taking a global temperature
• Question of normal vs. human caused
change
• Extreme complexity
• Exaggerated claims and politics
Is global warming caused by
humans?
• Very likely human caused to a certain
degree
• Pollution in any amount is harmful
• Even too much of a good thing is harmful
• My opinion: Even if global warming is not
caused by anthropogenic pollution,
pollution is bad…