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Chapter 50—An Introduction to Ecology: Distribution and adaptations of organisms
Ecology: the study of the interactions between organisms and their environment
Environment includes-1)abiotic factors—non-living; like temperature, light, water, nutrients, and 2) biotic
factors—all living things
Levels of organization:
Population: group of individuals of the same species living together in a particular area
Community: all the populations in a given geographic location
Ecosystem: includes the commnunity PLUS all the abiotic factors in the area.
Biomes: major types of ecosystems that are typical of a broad geographic region
Biosphere: the entire portion of the Earth inhabited by living things.
The first four categories above (temp, water, sunlight, and wind) are the major components of CLIMATE.
To see the effect of temperature and precipitation on which biome is present we can consider a climograph:
Y axis- temp x-axis- rainfall
see page 1030 for more
Rain shadow: As air hits the western slope of a mountain range (moving west to east), the air
would rise to go over the mountain. It cools and thus creates rain clouds that dump the moisture.
On the other side the air would sink and become warmer allowing it to hold moisture. This leads to
a rain shadow, place with little rain. The Mojave desert and Gobi desert are couple of examples of
this.
Terrestrial Biomes
Biome
Tropical
Rain forest
Savanna
Desert
Typical
latitude
Within 23.5
degrees
latitude of
the equator
Same as
above
Between 15
and 35
degrees
Temp.
23 degrees
C
Varies from
season to
season (cool
and dry, hot
and dry, wet
and warm)
Usually
warm; cool
nights
Rainfall
Abundant
Clear cut
wet and dry
seasons
Very little
Plant
diversity
Lush,
extremely
diverse, many
vertical layers
Grasses and
small shrubs;
Animal
diversity
Birds, bats,
mammals,
insects, very
diverse
Large
herbivores,
insects, and
burrowing
animals
Soil
composition
Nutrient poor
Cacti and
droughtresisant
shrubs
Ants, birds,
rodents,
reptiles
Nutrient poor
Nutrient
poor;
frequent fires
Chaparral
Coastal areas
between 30
and 40
degrees
Temperate
Grassland
Between 30
and 60
degrees
Between 30
and 60
degrees
Temperate
Deciduous
Forest
Mild, rainy
winters and
long, hot
dry
summers
Cold
winters
Varies with
season
Shrubs,
Deer, birds,
ants, rodents,
and reptiles
Seasonal
droughts
grasses
Cold
winters, hot
summers
Average
High diversity
due to high
nutrients and
light, etc;
Large
deciduous
trees
Large
vertebrate
grazers
Invertebrates,
rodents, deers
Taiga
Near 60
degrees; also
high
elevations
Cold
Varies
Conifers;
spruce, pine,
fir, little
undergrowth
Tundra
Above 60
degrees
Cold
Usually
very litle
Grasses,
mosses,
lichens
Mice,squirrels,
jay, insects,
deer, moose,
elk, snowshoe
hare
Insects with no
wings,
migratory
birds, caribou
Nutrient
poor; short
growing
season,
frequent fires
Very fertile;
frequent fires
Nutrient rich
Thin,
nutrient poor,
and acidic
permafrost
Aquatic Biomes
1) ponds and lakes: standing bodies of water
photic zone: upper layer with light for photosynthesis
aphotic zone: below where there is not enough light for photosynthesis
Thermocline: verticle zone of rapid temperature change.
Lakes can be oligotrohic (nutrient-poor) or eutrophic (nutrient-rich)
2) Streams and rivers
Water is cold and clear at beginning and has lots of sediment near where it drains
Many plankton live attached to rocks
3) Wetlands: an area covered with water that supports aquatic plants
Filter pollutants
4) Estuaries: area where the river meets the ocean
Extremely diverse; many organism spawn here, very important both commercially and ecologically; very
polluted
5) Marine ( about 3% salt)
Intertidal zone: zone where the land meets the water
Oceanic zone: regions past the continental shelf
Pelagic zone: open waters
Benthic zone: bottom of ocean
Abyssal zone: Very deepest bottoms of the ocean
INTERESTING NOTE:
WHY IS WATER SO CLEAR IN THE TROPICS?
Water is most dense at 4 degrees C. When air temp. reaches 4 degrees, the upper layer becomes as dense
as the lower layer thus causing a mixing of the upper and lower layers of water. Because most of the
nutrients have fallen to the lower layer, this allows much needed nutrients to reach the upper layers. The
result is a bloom of growth during the spring and fall when the temp hits 4 degrees C. In the tropics,
however, air temps never reach 4 degrees C, and therefore, the upper layers of water remain nutrient
poor. Thus, little grows their and the water is strikingly clear!
Chapter 51: Behavior
Behavior: what an animal does and how it does it
Behavioral ecology: the study of animal behavior based on the expectation that animal’s increase their
Darwinian fitness by optimal behavior
Innate Behavior:
Fixed Action Patterns (FAP): a highly stereotypical behavior that is innate
 building webs
 retrieving egg that falls from nest
 blinking
- usually triggered by a set stimulus; once stimulus presented, action is carried to completion.
- Examples: 1)three-spined stickleback fish—shows agression in response to any object with a red
underbelly; does not matter what shape it is 2) graylag goose—retrieves any round object outside of nest
in attempt to retrieve eggs that may get loose. Will even continue to “push” imaginary egg if you take
egg away while she is returning to the nest.
- FAP’s are adaptive because they prevent animal from having to develop higher level thought. Thought is
expensive. Although FAP’s may sometimes cause animals to waste energy on non-sensical things, it is
still “cheaper” than the price of developing and maintaining and compelx nervous system. If not, then
animals adapt.
Learning:
- the modification of behavior in response to specific experiences
- habituation: loss of responsiveness to unimportant stimuli that do not provide appropriate feedback
- gray squirrels stop responding to alarm call if not followed by an actual threat
- olfactory fatigue
- put hand in cold water—eventually, it doesn’t feel cold anymore
-
-
imprinting: a type of learned behavior with a significant innate component that occurs during a
relatively short critical period. Animal is not born knowing this information, but they are born with the
ability to learn it
- geese or ducks learning who their mother is
- salmon returning to the place where they were born to spawn.
- Birds learning their songs
- Humans learning a language
classical conditioning: learning to associate an unconditioned stimulus with a conditioned response
- dog salivates in response to bell (Pavlov’s dog)
-
-
operant conditioning: (trial and error learning) learning to associate certain behaviors with a reward or
punishment and then tending to repeat or avoid that behavior.
observational learning: the ability to learn by someone else’s trial and error
play: the mimicking of adult behaviors in young animals without any reason; may be for practice (but the
fact that they don’t get any better contradicts this) or it may be evolutionarily adaptive in that it promotes
exercise and keeps muscle tone and coordination in young.
Insight: the ability to perform a correct or appropriate behavior on the first attempt with no prior
experience in that situation. If a monkey is placed in room with boxes and a banana high in the air, they
will have enough insight to stack the boxes.
Other topics to consider from this chapter:
Social behavior
Migration behavior
Agonisitic behavior
Rituals
Territoriality
Dominance hierarchy
Mating behavior
Courtship
Mating systems
Polygamous, monogamous, polyandry, polygyny
Inclusive fitness
Kin selection
Coefficient of relatedness
Chapter 52: Population biology
Demography: the study of factors that affect population size
1. birth rate (fecundity): number of offspring produced per individual per given amount of time.
2. Death rate
3. Age structure: percentage of population a reproductive age, approaching reproductive age, and past
reproductive age. Population will usually grow the fastest within the next generation if most of the
individuals are approaching reproductive age.
4. Generation time: the faster the generation, the faster the population growth. Imagine how much more
quickly the population would grow if women started having babies when they were 15 instead of 25-30.
5. Sex ratio—usually the number of females in the population is the best predictor of population growth.
Two important factors are density (number of individuals in a given area) and dispersion (the spacing
of organisms within an environment).
1. Density: density is measured in several ways: you can physically count them, you can count the number
per unit area and multiply, or you can use the mark-recapture method.
Mark-recapture method: Day 1—you catch and tag as many individuals in a given area as you can, keeping
track of how many you catch. Day 2—you catch individuals again and count the percentage of which are
marked. Then, you set up a ratio to predict the total number:
Number marked on Day 1
*
Total catch on Day 2
Number of marked recaptures
Example: Day 1—catch and mark 40 grasshoppers
Day 2—catch 40 more grasshoppers; of these, 8 were tagged
Therefore, 40 is equal to 8/40 (or 1/5) of the total population.
40 = 1/5 (X)
X = 200
Your turn:
Day 1—catch and mark 70 grasshoppers
Day 2—catch 80 grasshoppers; of these 15 are marked.
What is the total population?
2. Dispersion: Within an area, organisms may be clumped, uniform, or random
Clumped: sometimes the result of resources distribution (i.e., resources are clumped); sometimes
clumped for mating purposes or defence (schools of fish)
Uniform: Usually the result of competition for resources between individuals. Uniformity allows each
individual to have the maximum amount of resources.
Random: result of a lack of competition; possibly found where there is an overabundance of resources.
Not common in nature.
Demography: the study of factors that affect population size
6. birth rate (fecundity): number of offspring produced per individual per given amount of time.
7. Death rate
8. Age structure: percentage of population a reproductive age, approaching reproductive age, and past
reproductive age. Population will usually grow the fastest within the next generation if most of the
individuals are approaching reproductive age.
9. Generation time: the faster the generation, the faster the population growth. Imagine how much more
quickly the population would grow if women started having babies when they were 15 instead of 25-30.
10. Sex ratio—usually the number of females in the population is the best predictor of population growth.
Strategies for leaving as many offspring as possible:
There are three extremes; each represented by a different survivorship curve. Most organisms however, fall
somewhere in between.
Survivorship curve: A plot of the number of individuals born at the same general time that are still alive at
each age.
Type III: Most offspring die young. The few that survive to some critical age tend to live long lives.
Example: oysters—make tons of offspring which are unprotected and float around and get eaten easily.
Those that manage to live long enough to find a place to live and grow a protective shell, tend to live a long
time. Organisms with Type III survivorship curves usually produce many offspring at a time.
Type II: There is an equal chance of dying any time during the individual’s life. Example: Hydra—these
guys are not particularly vulnerable at any time in their life. When they are born, they are practically the
same as an adult.
Type I: Low death rate for young and middle aged individuals, with most organisms dying at old age.
Example: Humans—Most people die when they are old. Organisms with Type I survivorship curves tend to
have fewer offspring but devote resources to making sure they successfully reach adulthood.
Allocation of Resources:
Organisms do not CHOOSE which life history they want. They don’t choose the type I strategy, they don’t
choose when to start reproducing (humans are a semi-exception), they don’t choose when they will die.
Rather, these things are selected for evolutionarily. If an organism is born with an innate ability to produce
thousands of offspring at once and that is a successful life history pattern for it, then it will leave a
disproportionate number of offspring that are genetically predispositioned to also leave many offspring.
Over many generations, these become the norm of the entire population.
Life history is always a trade off between energy used to survive longer and energy used to make babies.
The ultimate “goal” is to make more babies that survive to make babies of their own. If you were to have ten
children and tried to live off a teacher’s salary, then you may find that only a small percentage survive to
reproduce on their own. You may be better off (assuming your goal is to pass on your genes) just having a
few children, all of which you can afford to feed and keep healthy, etc.
Several different aspects of life history:
A. Number of reproductive episodes
1. semelparity—reproduce one time during lifetime; advantage—don’t have -to waste resources on
surviving; can put almost all energy into making offspring; expected if cost of survival is high
(century plant)
2. Iteroparity—reproduce several times during a lifetimes; advantage—young can be cared for until
they reach maturity; expected if survival cost is low and young are unlikely to survive alone
(humans)
B. Clutch Size:
1.
Large clutch size—more babies, but each receives few resources and therefore, smaller percentage
survive.
2. Small clutch size—fewer babies, but each receives a lot of resources and therefore, higher
percentage survive.
Which works better for a given species depends on its particular circumstances.
C. Age at First Reproduction
1. Starting young—it takes up a lot of energy to reproduce (making eggs, mating rituals, courtship,
nesting, rearing young) and takes away resources from adults ability to survive. Reduces lifespan.
2. Starting later—allows one to be stronger and preserve more resources to prepare for offspring;
however, carries the risk that one will die before it has any offspring making all efforts to survive a
waste (in evolutionary terms, fitness=0)
Mathematical Equations for Population growth:
Exponential population growth:
dN/dT = rmaxN
dN/dT = population growth
rmax = intrinsic rate of growth
(Birth rate-death rate)
N = number of individuals in pop.
Models unlimited population growth.
Logistic Population Growth: models population growth with a limit; population growth slows down as
population reaches it carrying capacity.
dN/dT = rmax (N) (K – N)
K=carrying capacity
K
If N is equal to carrying capacity (K), then population growth is zero (ZPG).
Results in sigmoid curve:
Logistic population growth has been modeled in the laboratory (with Paramecium).
However, in the real world, most populations over shoot K at least once before leveling off. Some fluctuate
around K and never truly level off. Some are cylcical (we’ll discuss this later)
Two life history strategies:
K-selected growth or equilibrium populations: these are species that are good competitors, They are likely
to be found living near maximum density. Example: oak trees
r-selected growth or opportunisic species: these are species that are not good competitors, but can live in
variable environments. Because of this they tend to be “pioneers” who live in deserted environments and are
later out-competed by K-selected species (at which point, they find a new place to pioneer). Example:
lichens
Limiting Factors: anything that limits population size
Two kinds:
Density-dependent: intensify as population gets bigger; lack of food or other resource.
Density-independent: affect the same percentage of individuals despite population size; example—a
hurricane (it will wipe out 90% of the tree whether there are 10 trees or 10,000 trees in its path)
Population Cycles
Predator-prey relationships: predator and prey population sizes tend to be cyclic and predator cycles follow
prey cycles.
One can consider herbivore to be predator of grasses and one can see a similar relationship.
Human population explosion:
There are almost 6 billion people in the world right now. Some estimate that 10 billion is our carrying
capacity although technological advances can change that.
It is expected that we will reach 10 billion in less than 20 years if we continue to grow at our current rate. If
we are like other populations, we will likely overshoot our K and then have a crash. This could be
devastating!
Coevolution—a change in one species acts as a selective force on another species and counteradaptation by
the second species, in turn, is a selective force on individuals in the first species.
 Most common example is coevolution of flowering plants and their pollinators
 Example: Passionflower vines and Heliconius butterfly larvae – passionflower vines developed a toxic
compound to prevent them from being eaten by caterpillars. Then, Heliconius caterpillars developed
resistance to the toxic compound. This allowed them to feed on passionflower vines without competition
from other insects. The butterfly lays bright yellow eggs on passionflower vine leaves, but will not lay
them where another butterfly has already laid its eggs. Thus, passionflower vines developed an
adaptation that made some of the leaves have bright yellow spots that looked like butterfly eggs to
prevent the butterfly from laying her eggs there.
Chapter 53: Community Ecology
Types of Interspecific Interactions
(Interspecific – “between species”; Intraspecific – “within a species”)
1) Predation (+, -) one organism benefits, the other harmed



Can include herbivore and the producer they feed on
Can include parasitism (except parasitism involves organism living within body of living host, while
predation involves actually killing the other organism)
Parasites and their hosts coevolve—because of this, we can never eradicate all parasites
-
Plant defenses against herbivores:
-
- Thorns, hooks, spines, etc.
- Production of toxic or distasteful compounds (cinnamin, cloves, and peppermint!)
- Development of coevolutionary adaptations specific to a particular herbivore
Animal defenses against predators:
- Fleeing
- Alarm calls
- Distration to protect vulnerable young
- Mechanical defenses (spines--porcupines)
- Chemical defenses (toxic chemicals—many frogs)
- Hiding
- Cryptic coloration: camoflage; blending into surroundings
- Deceptive coloration: false eyes or false head
- Mimicry: 1) a harmless species mimics coloration of harmful species; only works if there are
more of the harmful species than of the harmless one. 2) two harmful or unpalatable species
resemble each other—causes predator to “learn” color markings more quickly
- Batesian mimicry- harmless mimicking harmful (monarch/viceroy butterflies)
- Mullerian mimicry- two or more harmful resemble each other (bees)
- Aposomatic coloration- warning colors (frogs)
2. Competition: (-, -) both organisms harmed
Competitive exclusion principle: one species, one niche; no two species can exist in identical niches; if true,
competition should be rare in nature (it is)
-
fundamental niche – set of resources a population is theoretically capable of using under ideal
circumstances.
Realized niche – set of resources a population actually uses
Character displacement: the idea that characteristics of individuals will be more divergent in populations
of two species that live together than in species that are completely separated by geographical boundaries.
This is because competition between individuals for the same set of resources has driven each to specialize.
Galapagos finches.
3. Commensalism: (+, 0) one benefits, one neither harmed nor benefitted
-
Very few examples because most organism do some harm, even if minimal
One good example: hermit crab and mollusks—hermit crab benefits from by living in shell of mollusk
after mollusk has died; makes no difference to mollusk
4. Mutualism: (+, +) both benefit
-
ants and acacia trees—tree provides home for ants; ants protect tree by removing fungal spores, stinging
other animals, and clipping vegetation that grows too close.
Feeding Relationships
Producers (autotrophs, produce own food)
Primary consumers (consume producers)
Secondary consumers (consume primary consumers)
Tertiary consumers (consume secondary consumers)
Decomposers (break down dead organic material)
Food web, food chain, biomass pyramids
Biomass pyramids:
- Each level is a trophic level
- Producers at bottom, consumers on top
- Total biomass decrease approximately tenfold at each level. Most of the energy (food) one eats is not
passed onto the next trophic level. On average, only about 10% of the energy one consumes is used from
growth and reproduction. The other 90% is released as heat or is used to perform daily metabolism
necessary for life.
- Top level consumers, thus, have the least energy (biomass); because they are also usually that largest,
there is usually fewest of them as well.
Exotic species: introduced species; can alter entire community structure
Keystone predators: a predator that maintains a higher species diversity in a community by reducing the
densities of strong competitors; prevents competitive exclusion from occurring.
Example: STARFISH – In intertidal zones, there are two species of mussels. One is the far better competitor
and if these two are left alone together, the poorer competitor will go locally extinct. However, starfish
selectively feed on the better competitor mussel, thus reducing their population size and preventing them
from competing the second species into extinction.
Succession
The gradual and predictable changes that a freshly disturbed community goes through until it reaches its
climax community.
Primary succession: the inhabitation of a barren area by pioneer species (r-selected species), like lichens.
Secondary succession: inhabitation of a slightly disturbed are that still has its soil intact (usually by grasses)
Intermediate disturbance hypothesis: species diversity is greatest where disturbances are moderate in both
frequency and severity, because organisms typical of different successional stages will be present.
- If too many disturbances, only a few organisms have time to take residence before disturbance wipes
them out again; Also, dominated by pioneer species (r-selected)
- If too few disturbances, then competitive exclusion causes less diversity and only a few good competitors
(K-selected species) live in the area.
Island Biogeography
- Immigration and extinction rates determine species diversity on island
- Two factors affect immigration and extinction: island size and distance from mainland
- Island size:
- The larger the island, the higher the immigration rate (because they have a larger space to happen
upon)
- The larger the island, the lower the extinction rate
- Distance from mainland:
- The further the island is from the mainland, the lower the immigration rate (fewer species can get
there)
- The more species on the island, the lower the immigration rate and the higher the extinction rates. Thus, an
island will eventually reach equilibrium and the number of species on the island will remain relatively stable
(until a major disturbance) The equilibrium number of species is predictable if one knows: 1) island size
and 2) distance from the mainland.
Chapter 54: Ecosystems
I. The Global Energy Budget:
1022 joules of energy reaches the Earth every day (from the sun).
Only a fraction of that hits photosynthetic organisms.
Then only 1-2% of the energy that hits plants or algae is converted to chemical energy by photosynthesis.
Primary Productivity: the amount of light energy converted to chemical energy by photosynthesis during a given
amount of time.
Gross primary productivity (GPP): total primary productivity
Net primary productivity (NPP): total primary productivity minus the amount used by producers for respiration; the
amount of excess energy that can be passed on to the next trophic level.
A. Water Cycle:
- driven by solar energy
- mostly cycles between oceans and atmosphere by evaporation and precipitation.
- Evaporation exceed precipitation over oceans
- Precipitation exceed evaporation over land
B. Carbon Cycle:
- Mostly conversion of CO2 to glucose by photosynthesis, and conversion of glucose back to CO2 by
respiration.
- Some carbon is diverted from cycle and taken out of circulation for years at a time
- Accumulation in wood
- Accumulation in fossil fuels
- CO2 level in atmosphere fluctuate. They are highest in the winter (when photosynthesis is low) and lowest in
the summer.
- Burning of fossil fuels puts CO2 that was taken out of circulation millions of years ago back into the
atmosphere, causing a sudden increase in atmospheric CO2.
- Ocean acts as a buffer by taking CO2 out of atmosphere. CO2 reacts with water to produce bicarbonate.
C. Nitrogen Cycle
- Nitrogen makes up 80% of the atmosphere in the form of N2 gas. However, it is not usable by organism in
this form.
- Bacteria are necessary for the movement of nitrogen through the ecosystem.
- Nitrogen fixation: conversion of N2 gas to NH3 (ammonia) by bacteria
- NH3 can be used directly by plants
- Nitrification: conversion of NH4 to NO3 by bacteria
- NO3 can also be used directly by plants
- Denitrification: conversion of nitrate back into N2 gas
- Ammonification: conversion of organic nitrogen (from dead organisms) into ammonia by bacteria
D. Phosphorus Cycle
- no movement through atmosphere
- Phosphorus in rock gets into soil by erosion
- Plants take up phosphorus from soil in form of PO4 (phosphate)
- Consumers get phosphorus by eating plants
- When plants animals die, phosphorus put back into soil by decomposers.
- Some phosphorus leaches from soil into bodies of water where it reacts and precipitates and forms sediment
(eventually rock)
Human impact on biogeochemical cycling
A. Agriculture:
- repeated use of the same land for agriculture depletes soil of necessary nutrients.
- These are replaced by fertilizers which upset nitrogen cycle
- Much nitrogen leaches into waters causing eutrification which causes algal blooms
- When algae dies, decomposers explode in population, and therefore use up all the oxygen. This makes the
lake hypoxic and unsuitable for most organisms (also smelly and gross so not suitable for boating, swimming,
etc.)
B. Biological amplification/ Biomagnification:
- Humans produce chemicals that end up in our water systems (via run off or direct dumping)
- These chemicals are taken up by organisms living there; because many (like DDT and PCB’s) are lipidsoluble, they accumulate in organisms and are never eliminated.
- Thus, the chemicals are passed up the food chain.
- At each trophic level, the concentration of the chemical increases causing more trouble as it reaches higher
level consumers.
- DDT—was accumulating in eagle populations; it interfered with deposition of calcium in eggshells; eggshells
broke from weight of mother; populations decreased
C. Greenhouse Effect/Global Warming
- increase in CO2 concentrations in the atmosphere due to burning of fossil fuels
- traps in heat and predicted to cause global warming
D. Ozone Depletion
- there is a protective layer of ozone in the stratosphere; protects us from UV rays
- chlorofluorocarbons (found in refrigerants and some aerosol cans) react with ozone, reducing it to O2.
- Causing ozone to thin; effects are delayed—although cfc’s are gradually being phased out, ozone will continue
to struggle from old cfc’s still floating around.
E. Acid Rain
- nitrogen oxides and sulfur oxides combine with rain to make acidic rain
- acid precipitation includes snow and fog which are actually more problematic
- coal plants, car emissions are the biggest offenders
- drifts to effect “clear air” habitats
- erodes structures, weakens trees, ponds die