BIO 111 TEST 3 STUDY GUIDE: ECOLOGY
❖ THE BIOSPHERE
• studying the biosphere contributes to the study of ecology. The
distribution of living organisms on Earth is not uniform. WHY?
• Why are organisms distributed in patches? Think of Canada vs Rain
o ABIOTIC factors (for uneven distribution) to consider:
1. The distribution of dry land is not uniform. There is more land in Northern
Hemisphere vs Southern Hemisphere, so we can assume there are more organisms
in the Northern Hemisphere.
2. Seasons are caused by uneven solar radiation, which is caused by the tilt of
Earth’s axis as it rotates around the sun. This means that the intensity of sunlight
is lower at higher latitudes. This accounts for temperature differences between
the equatorial habitats and your more northern or more southern areas. Radiation
from the sun is spread over more surface area at higher latitudes, so its
intensity is lower. The light rays also have to pass through more atmospheric
gases, which lowers the amount of radiation that reaches Earth’s surface.
3. Because of the uneven heating of the atmosphere, we have wind currents,
prevailing winds. There are areas where air rises as it warms up, then sinks as it
cools. This causes movements of air and in addition to the rotation of the earth,
these factors cause prevailing wind currents.
4. Wind currents and ocean currents can have profound effects on climate,
especially movements of water (because water has a high heat capacity). Water
can store and move thermal energy around the world. EX: The Gulf Stream ocean
current. London and North Equatorial are on the same latitude, but the climate is
milder in London because of the ocean currents that surround it. These
movements of water can really affect climate. EX: California current is cold.
5. Interactions of currents and geography influence climate. A prevailing wind
blowing over a mountain range can cause a rain shadow; which is when warm,
wet air coming off the ocean rises up a mountain range and produces lots of cloud
buildup and rain and you get a side with a wet forest, while on the other side, the
air will be dry and you will get a desert.
o Terrestrial Ecosystems’ assemblages of plants and animals: we find that similar
latitudes always have similar biomes (assemblage of plants and animals). (EX:
Canada’s pine forests are on same latitude as Siberia’s pine forests) Species may not
be exactly the same, but the look of the places will be very similar. (EX: Russia’s “step”
vs. US “short grass prairie”)
• There are many biomes in our Hemisphere.
1. Starting from the North Pole South, we have the Tundra. Tundra is a part
of the habitat that has permafrost-the soil never thaws, so there is a
permanent layer of frozen soil. Since water doesn’t drain in the soil, when
snow melts, it just puddles and the ground stays wet, boggy. Therefore, not many trees grow in the Tundra because their trees can’t dig down. There are
mainly sedges, small willows and marshy plants. There are lots of insects
and few animals.
2. Moving South, you encounter - Coniferous Forest.
3. Moving further (east of the Mississippi River), you encounter-Temperate
Deciduous Forest. In the North there are Sugar Maples in these forests
while in the South there are Hickory and Oak trees.
4. (west of the Mississippi River), you encounter-Tall Grass Prairie
5. (further west), you encounter-Short Grass Prairie (Temperate
• The assemblages of plants in these terrestrial ecosystems determine what
types of animals live there. Furthermore, the assemblage of plants is
determined by a combination of temperature and rainfall.
1. The two plants have very similar morphology because they recently evolved from
a common ancestor.
2. They have become adapted to similar habitats by natural selection.
o A combination of amount of rainfall and average temperature is what
determines these biomes and makes them different from each other. (EX: low
temp all year- Tundra. lil warmer, low rainfall-Coniferous Forest. high temp, high
rainfall-Tropical Rain Forest. warm, low rainfall-Warm Desert)
(**stopped this lecture to do Biomes Video**)
❖ NORTH AMERICAN BIOMES
o The largest, easily recognizable subdivisions of the biosphere are called
biomes. Each biome is characterized by a particular general type of
plant and animal community. These communities look much the same
wherever the biome occurs, but the particular species making up the
biome vary from place to place. This suggests the plants and animals
have adapted in similar ways to the environment. A biome is a collection of
similar and related ecosystems.
o 3 ways to look at a biome:
1. A biome is the largest subdivision of the biosphere.
2. It is a type of ecosystem or community shaped by a particular
combination of climate and topography.
3. A biome is a collection of smaller, similar, and related ecosystems.
1. TUNDRA – adjoins the artic regions and North America and Eurasia.
• beautiful, dotted with lakes and streams, mosses, sedges, willows. • cold and frost shape the landscape. under 3 feet, its only permafrost. the
layer of permafrost prevents the penetration of liquid water into plant
root, so the vegetation is sparse.
• as a result, the Tundra appears waterlogged, in spite of relatively light
• Caribu is the dominant herbivore in the Tundra of North America while the
Reindeer fills this role in Eurasia. other animals are the muskox, wolverine,
artic fox, lemming. their activity is geared for short summers and long
winters. many of the animals posses extra fax and fur levels. some change
color in season.
• the food chains of the Tundra are simple and limited because of the low
amount of plants and animals involved. Because animals man rely on one
particular plant or species, population of animals in the Tundra show
extreme oscillation in numbers. Owl (predator) will oscillate with lemming
2. ALPINE TUNDRA – occurs on high mountains in the temperate zone.
• alpine forget-me-nots grow 11,000 ft in Rocky Mountain National Park.
• the marmot is an inhabitant of the Alpine Tundra.
3. NORTHERN CONIFEROUS FOREST – stretches across North America and Eurasia
and is just south of the Tundra.
• occur in mountainous areas like cascades, rockies.
• summers are cruel and winters and cold, and rainfall is moderate.
• dominant plants are evergreen trees, pine, fern. because the forest floor is
shaded year round, the forest floor is usually very bare.
• animals are adapted for life in the cool forest; squirrels, beaver, porcupine
depend directly on trees for food and shelter. black-tail deer, black bear,
bobcat, wolf and moose, dwell in the ecosystem that make up the forest,
• a biome is not just a single homogenous community. it consists of
smaller, related ecosystems. the Northern Coniferous Forest consists of
many types of forest that are often very near to one another. along with
many different types of forests, creeks and rivers may also be a part of this
biome. Ecological succession could turn these lakes into land then into trees
• even though redwood trees are coniferous, they are not a part of the
Northern Coniferous Forest biome.
4. MOIST CONIFEROUS FOREST – stretches from Alaska to Northern California.
• the Pacific Ocean moderates temperatures, cooling in the summer and
warming in the winter. masses of air moving in from ocean deposit
moisture in the form of rain or fog. these forests can get 200 in rain a year.
• unlike the drier, colder Northern Coniferous Forest, the understory
vegetation in this forest is good because light can filter through to the
bottom. • animals of the Moist Coniferous Forest are similar to animals in Northern
Coniferous Forest, but these animals’ adaptations to cold are not as
5. TEMPERATE/ EASTERN DECIDUOUS FOREST – forests of eastern north America
are very different than the forests in the north and west.
• these have trees that lose their leaves every fall.
• Deciduous Forest occurs in areas of abundant, year-round,
precipitation. temperatures are moderate and there are distinct
• one covered a lot of area, but now half of the original 1% remains.
• like other biomes, it is not uniform in species composition.
• animals are gray squirrel, wild turkey, black bear, raccoon, and white tailed
dear, insects in spring.
• the most striking characteristic of the Deciduous Forest is the brilliant
display of color in Autumn when the chlorophyll breaks down.
6. GRASSLANDS – are found on every continent except Antarctica.
• Grasslands usually occupy the interior of continents where rainfall is
relatively light. Grasslands occur in areas too dry to support forest but too
wet to be desert.
• Tall Grass Prairie was one dominant in the EAST. Short Grass Prairie in WEST
are called the plains.
• Trees are limited. Since rainfall is light, so nutrients are not leached from
the soil, thus grassland soils are the most fertile in the world. a lost of
grassland is devoted to agriculture.
• animals are usually runners like the antelope, bison, prairie dog.
7. TROPICAL SAVANNA BIOME – (does not occur in North America) grassland with
• occurs in warm regions with abundant rainfall, but also a prolonged dry
season in which fires occur.
• not many plant species dwell in the Savanna. a few species of grass and
trees are dominant in wide areas.
• although, its animal diversity is unrivaled: wildebeests, zebra, giraffe, lion,
8. CHAPARRAL – occur in temperature areas with winter rains, but hot, dry
• vegetation consists of evergreen shrubs.
• all Chaparral areas look very much alike, even though the animals are
• unrelated species of plants and animals have adapted to the similar
environment. this convergence happens in all biomes. • characteristics like long roots, tree knees, reflective leaf surfaces help any
species in the Chaparrals conserve water.
• fire affects the Chaparral. some plants in the Chaparral germinate with fire. In
a way, fire maintains the Chaparral.
• animals are coyote, gray fox, mule deer. most others are small and
9. DESERT – light rainfall, dry.
• form in rain shadows sometimes (EX: Cascades in Washington)
• climate and topography can shape biomes
• plants and animals have crazy adaptations to store water. catfish store water
in cells, reptiles have dry feces, some never need to drink.
10. TROPICAL RAIN FOREST – seasonal variation in temperature is very very low.
• climate is warm and rainy with one dry season.
• plant growth is dense, dark, and stratified in layers.
• there is little growth on the floor because light cannot penetrate that far.
• its diversity is its biggest characteristic.
• animals are mostly herbivores and some spend their whole life in trees.
• the species making up a biome differ from place to place.
• each biome has a characteristic structure wherever it occurs.
• in each biome, plants and animals have been shaped by a particular type of
environment. this illustrates how organisms adapt to their environments.
(**continuing biosphere lecture**)
o Aquatic Habitats (many types like: rivers and streams, slower moving water,
estuaries where fresh water and sea water mix, oceans, large freshwater lakes, and
large saltwater lakes)
• Salinity & Species Diversity:
o there is a correlation between salinity levels and organisms that can
o Ocean salinity is around 35; many species live in that salinity level.
o Marine salinity; a rapid drop off of species number that can
tolerate this level of salinity. (EX: Great Lakes and Dead Sea)
o Brackish Water (estuary where fresh water and oceanic water
meet; less salty than ocean); big dip in number of species. the
diversity is very low. this phenomenon is called the Brackish
Water Paradox. some say diversity is so low here because the
amount of variability that can happen to the species (like estuaries
having tidal fluctuation in dry years & floods, oxygen levels,
temperature, tidal fluctuations) makes it a harsh environment to live
in. BUT, the Caspian Sea has brackish water and much lower species diversity than the ocean. BUT it doesn’t have tides, fluctuations. Its
like one big freshwater lake without the species diversity it should
have. No one can explain this.
o Fresh Water; lots of species
o take home: most important environmental factor that
determines species diversity in aquatic habitat is how much salt
is dissolved in the water.
aquatic habitat types:
• Freshwater Lakes
➢ Life Zones: light limit of penetrating into water is about 300 ft, so most
animals live in the upper water column. Animals can’t live at the bottom
where there is no light. plants can emerge from the shore with roots in
➢ Seasonal Changes (in lakes in temperate areas) Seasonal Turnover in
water occurs. Winter: ice covers a thin layer of water that is just below
4°. 4° water sits right below that layer because water at 4° is denser.
There is little circulation because no winds affect water under the ice.
Spring: when the ice from winter melts, warms, and sinks down, winds
create currents that produce a turnover of the water temperatures. this
creates a whole mix and brings nutrients up to the top of the lake.
Summer: a barrier between the cold & warm water called a thermocline
that does not allow cold and warm water to mix. Warm is at top and cold
is at bottom. Fall: another Spring-like turnover of water occurs.
• Streams & Rivers
➢ (fast-flowing) - water moves fast, so there is lots of aeration, a lot of
oxygen content. although, the water moving fast washes away nutrients.
➢ (slower-flowing) – water moves slow, so there is lower oxygen. but
there is more nutrients for plant growth.
• Estuaries (EX: Chesapeake Bay)
➢ fresh water rivers mix with seawater
➢ In Louisiana, we have 2 types of estuaries because our state is at latitude
where a transition between salt march estuaries and mangrove estuaries
• Coral Reefs
➢ (EX: The Great Barrier Reef)
➢ Corals under great stress undergo a phenomenon called bleaching.
Healthy corals are brown because of symbiotic algae that are harbored
to tissues of the coral. When the corals are stressed due to pollution, etc;
they expel the symbiotic algae and it leaves the corals a white color.
Coral reefs usually do not recover from this. • The Open Ocean = Aquatic “Desert”
➢ this is the aquatic desert because of the lack of food in this habitat makes
is very hard to live there. the open ocean is clear because there is no food
and nutrients. when there are no plankton, other fish have nothing to eat.
➢ this can be compared to Louisiana’s brown, nutritious water that makes
us the #1 in fishery.
➢ Life Zones: (same as in freshwater) light penetrates about 300 ft and
then photosynthetic activity is low below that. animals on bottom are
benthic and animals that swim around are pelagic.
1. Both coral reefs and tropical rain forests have very high species diversity.
2. In both ecosystems, abiotic conditions have been very stable for a long time.
A (T, T, related)
*Species diversity is related to stability of a habitat.
• Hydrothermal Vents are unique aquatic ecosystems. (cool video bout them)
➢ people used to think all ecosystems on earth were sustained by
photosynthetic activity, but then hydrothermal vents were discovered.
Hydrothermal vents have a lot of variability in organisms even though
they occur at the bottom of the ocean with no sunlight. the ecosystem
is supported by primary producers called chemoautotrophic bacteria
that obtain energy from oxidation of hydrogen sulfide. organisms eat
these bacteria or harbor energy from these bacteria.
➢ In Gulf of Mexico, we have hydrocarbon seeps where methane gas leaks
out of cracks in the seabed and there are communities like above ^ except
bacteria use methane instead of hydrogen sulfide.
o Ocean-Air Interactions
o interactions between prevailing winds and ocean currents can
also cause changes in local climate.
o El Nino year: wind direction south of the equator changes, which
prevents a mixing of water off the west coast of South America. this
means the productivity of the area goes down. fish die in el nino
years. changes in winds affect the amount of moisture carried west
east, which means, this affects rainfall on land masses like the US.
o take home: occasional changes in wind direction can have an
effect on global climate.
❖ OCEAN DESSERT VIDEO
• Sargasso Sea is a paradox. It is calm, and open sea. The open sea is
usually marine desert, because of lack of plankton for nutrients.
Although, the Sargasso Sea has plankton and productivity is very low.
Why do so many animals live in such an unproductive place? Its
stability allows for slow development and no extinction. • The Sargasso Angler fish has a history of adapting to living life among
Sargasso weed. Natural selection has molded the Sargasso Angler
fish. It has camouflage and other protective and hunting mechanisms.
• The Sargasso Sea offers a place to hide. Sargasso weed is a refuge for
poor swimmers. One disadvantage of living on Sargasso Weed is: as
the weed grows larger, they produce less air bubbles to keep them
afloat. Sooner or later they sink.
• The open ocean has many fast-swimming organisms.
• The Flying Fish finds ways to make nests in the Sargasso Sea out of
Sargasso Weeds. After hatching, the tiny fish quickly swim free, on
their own against ocean predators.
• Sargasso Weed is a refuge for swimming organisms too. They also
provide a place for things to grow on. Barnacles and goose barnacles
and worms live side-by-side and share food on the Sargasso Weed.
• Sargasso colonies are also home to tentacle animals. The animals
hide in exoskeletons. When the Sargasso weed dies, the skeletons of
the animals end up on shore. These tentacles animals may live next to
an anemone; its stinging cells catch copepods, which are food for
Sargasso dwellers. Slugs eat anemones.
• “Sinkermyknee” is a Sargasso weed neighbor that stings copepods
• SO Sargasso weed has provided living space for animals at sea. It
has created a community filled with contradictions. It is nutrient
poor, but species rich. A desert full of life.
❖ VOLCANOES OF THE DEEP SEA
• The oldest living fossil in the world - Paleodictyon nodosum
• Bound for the Galapagos Drift, Alvin (sea camera)
• A volcanic process underground was building elaborate structures.
Water descending into fishers in the seafloor was apparently
interacting with hot rocks beneath, to reemerge as a black cocktail of
poisonous chemicals. It was difficult for scientists to understand the
geological processes at work, but the animals were impossible to
comprehend. They were living in water hot enough to melt lead. Life
shouldn’t have been present at all.
• The worm alvinella was among these organisms. They danced in and
out of the poison water.
• Humans didn’t think to look in the dark, boiling water for life. The
discovery of these hypothermal vents was the first step in making a
connection to the fossils of the Paleodictyon found in Spain to the
mysterious life forms on the sea floor.
• Alvin traveled to the bottom of the sea floor, and glimpsed creatures
never seen by human eyes. These soft-body animals will never leave
a fossil trace, but they have probably been around for hundreds of
millions of years – like phantoms of the sea. • Alvin landed on a fantastic landscape – it was a recent volcanic
eruption. (Alvin was between the American and Atlantic Sea plates:
the Mid-Ocean Ridge. It is the largest geological feature on the face
of the earth. The large outer shell of the earth floats on a hot
underlying layer. Where the plates move apart, magna rises to form
the Mid-Ocean Ridge. The volcanic system is the oven of plant earth.
It bakes the earth’s crust, boils sea water, and serves up nutrients to
the animals of the abyss, and occasionally roasts them alive, like what
happened at this eruption.)
• It was like the ruins of an ancient civilization of life burned away.
Although, scientists were puzzled at what Alvin was seeing: Spaghetti
worms covered the rocks, and there were large anemones growing.
Crabs, octopus, even fish, giant tubeworms, and golden mussels.
There were billons of tiny white feather duster that were filtering
nutrients from the hot water emerging from the rocks. Live hadn’t
just returned, but it had come back with larger scale and vigor
than was believable. It was a place of darkness and no seasons and
no time, but it was driven by the inner earth. At the center of the life
was a 40ft high volcanic monument, decorated with 6ft long
tubeworms. The tubeworms prospered in the hottest water
upward and at the bottom, there worms tubes, but no worms. They
were unable to move and had starved to death. With no mouth or
stomach and planted permanently in the rock, the tubeworms
seemed like plants instead of animals. But scientist found
specialized bacteria in the tubeworms’ tissues that were using
chemical energy in hot water to make nutrients. They were, in
effect, turning poison into food and sharing it with their host, the
tubeworm. The red filaments on the top of the worms draw in
hydrogen sulfide from the water to feed the bacteria inside. This
is called chemosynthesis. The tubeworms red color comes from
blood containing hemoglobin. So who are these animals that share
• 5 billion years ago, a giant star blew itself into a supernova. Debris
from that created our sun. It’s believed that the planets that formed,
orbiting around the sun, growing larger and larger, acquiring debris
from space. The Earth cooled and built a solid crust, the oceans
formed, life flourished by harnessing energy from the sun using
photosynthesis. It was once believed that the sun’s radiation was the
only source of energy for all life on earth, but deep in the earth’s
crust, radiation from the old supernova still exists. This energy
gives life to deep-sea animals.
• Alvin found so many products of this radiation, including “The Lost
City.” Enormous limestone structures stand and bacteria lives here.
Ancient methane chemistry allows life. How was life on earth
building complex structures? Paleodictyon is a living fossil. Over hundreds of millions of years, the creatures have learned how to
build hexagonal patterns. They’ve survived mass extinction. What’s it
• Scientists began finding hydrothermal structures everywhere
along the Mid-Ocean Ridge. Life was rich. The structures were so
perfect for the animals living in them that the geology seemed alive.
At the center of the relationship between the animals and the flow of
energy from the crust are hundreds of species of specialized
bacteria growing on the rocks. They use chemical energy from the
hot water to produce nutrients. The shrimp on the rocks use these
bacteria as food. Most shrimp burn off their extremities while trying
to eat these bacteria.
• Mid-Atlantic Ridge held a fantastic vent, the size and shape of a
football stadium. Chemosynthetic bacteria weren’t just on the rocks,
but on the shrimps themselves. They scrape this layer off and eat it.
Scientists probed deeper into the crust itself and made the most
important discovery. In total darkness, in 3000lb of pressure and in
230 F water, the microscopic parasite hyperthermophile. This is the
harshest environment on earth. Yet its molecules of DNA share our
4 base chemicals, the language of DNA. We are related to them in
this sense. This is where life began on earth. We evolved from this.
• With the discovery of microbes living in the vents, scientists
considered that most of the biomass on earth lives beneath the
volcanoes of the deep sea. No one knows why vents shut off and
leave mounds of minerals behind. This is where the scientists
searched for their mysterious hexagonal fossils. In the “Valley of
Paleodictyon,” they looked where there was no life and that ended up
being the animal’s secret. They found thousands of paleodictyons.
They dissected the sections of the sample gathered, and the
hexagonal tunnels were present, but no paleodictyons were
present. Although, scientists now believe that the paleodictyon is
forming bacteria in its tunnels, which enables it to live in the
sparse chemical remnants of the volcanoes in the deep sea. They
have outlived all forms of life on earth.
❖ POPULATION ECOLOGY
• A population is all of the individuals of one species in the same place at
the same time.
• People that study population ecology are interested in:
1. size: how many individuals are in it
2. density: “”
3. distribution: how they’re distributed among the available habitat
4. age structure: how many young organisms vs. how many old organisms, etc • Distribution
o the special distribution of the individuals in a population varies from
species to species and from habitat to habitat.
o there are 3 general ways to distribute
1. clumped – clumped together in separate sections
2. uniform – uniform distribution
3. random – completely random distribution
**effects on population growth under ideal conditions with no limitation on growth
• Population Size & Exponential Growth
o a population just beginning to growl shows exponential growth. (J shape
curve) growth rate = birth rate – death rate
• Influence of death rate on population growth
o with no deaths, population grows very fast
o with deaths, the rate of a population reaching a certain number of
individuals is slowed.
o both are still J-shaped growth curves
• Life history affects population growth
o (EX: populations that reproduce at 4 years old will grow faster than
population that reproduce at 6 years old. )
o this creates a lag in achieving the same size as the faster population
** effects on population growth under non-ideal conditions**
• Limits on growth
o if not enough nesting sites are available, there will be competition
o other competitive factors include: food, space, places to hide. The
combination of all these factors leads to limits on population growth.
o the environmental carrying capacity is where the J-shape curve of
exponential growth levels off. when a population reaches this point,
limiting factors have been reached. the actual size of population that can
be supported by the environment’s available resources is called the
carrying capacity. this causes the growth curve to change from a J shape
to an S shape.
• Limits can be density-dependent or density-independent
1. density dependent factors depend on the number of individuals in the
o EX: in bees, the number of eggs laid each day decreases as population
density increases & as the population density increases, the lifespan
of the bees decreases. (both of these seem to happen because they
don’t want the population to overgrow) 2. density independent factors do not depend on the number of
individuals in a population
o EX: drought where animals die. (it doesn’t matter how many
individuals there are; without water, everything will die)
• boom and bust population pattern
o when favorable growth conditions are occurring, there will be an
increase in population growth (boom) (this will be a J-shape curve
because there are no limits to population growth here) but then you
can reach limit of the resources and exceed the carrying capacity
and when the resources are used up the population falls (bust)
o EX: *lemming population in biome video fluctuating from year to
year depending on plant availability* warm springs with lots of
plants- lemmings boom. harsh winter-lemmings bust
• Survivorship Patterns
o If the data of the US people were plotted as the number of survivors
at each age, the result is a survivorship curve.
o the death rate increases as age increases in humans. the death curve
is steeper for men.
o different species have different survivorship curves (3 types)
1. Type I curve: EX: goats. mortality is highest very late in life
2. Type II curve: EX: lizard. mortality does not vary with age
(ends up showing a linear relationship between survivorship
3. Type III curve: EX: shrub. mortality is highest early in life
(very few survive to be old.)
o Type I & Type III are extremes, while Type II is a middle ground.
The two extremes represent r-selected & K-selected species. These
are Life History Strategies
o r-selected species:
▪ shorter development
▪ reproduce when very young
▪ few breeding episodes with many young per episode
▪ parental investment is small
▪ high mortality rate, shorter life span
▪ EX: lemmings
▪ *better for an unpredictable environment*
o K-selected species:
▪ longer development
▪ reproduce later in life
▪ more breeding episodes with few young per episode
▪ parental investment is large
▪ lower mortality rate, longer life span
▪ EX: humans • Life history traits are subject to evolutionary selection pressure
o EX: Cichlids prefer large guppies & Killifish prefer small guppies
o Data of this study shows that the phenotype of the guppies is
affected by the presence of different predators.
o Killifish (eat small fish) so the guppies tend to be larger.
o Cichlids (eat large fish) so the guppies tend to be smaller.
o The phenotype of the adult guppies is affected by the presence of
different predators’ preferred traits.
o Embryo weight is a measure of how much parental energy is put
into each egg. In streams with Killifish (eat small fish), the females
lay fewer eggs, but the eggs are larger. In streams with Cichlids (eat
large fish), the females lay lots of eggs that are small.
• Global Human Population Growth
o human population grew very slowly until Industrial Evolution
o our population doubles every 50 years
o The Black Death caused a huge dent in population growth
• Changes in US Survivorship Curve
o There used to be a higher mortality rate early in life
o Some factors that have contributed to our survivorship curve
changes are prenatal care, immunizations, vaccines, things to stop
diseases. Some very old diseases are reoccurring, like whooping
• Population Age Structure
o If you divide the population into pre-reproductive age,
reproductive age, and post-reproductive age, and make a pyramid
model; that shows the population age structure.
1. a population age structure shaped like a triangle will grow over
2. a population age structure shaped like a rectangle will stay the
same (as people come into reproductive age, the same amount
leaves it) (this is a concern in European countries)
3. a population age structure shaped like an inverted triangle will
decrease over time.
4. In China, the government wanted to limit population growth and
this changed the population age structure from a rectangle to an
upside down triangle.
o the point is that population studies are not only interesting to
biologists but to government as well, in terms of health care,
where to build schools, etc.
❖ COMMUNITY ECOLOGY
• a community is all of the populations in the same place at the same
time. • community ecology encompasses all of the biotic components of an
ecosystem and how they interact.
• many communities make up a biome (EX: Deciduous Forest
community and river community and stream community make up the
• people that study community ecology are interested in:
➢ Species Richness - how many species there are in a particular area.
o EX: species richness of birds is high near the equator and in the tropics and
low in the artic and in high altitudes. What causes this?
• Patterns in Community Structure
• Species richness is high at the equator and falls off as you near the poles. Why is
biodiversity higher in the tropics (near equator)?
1. Species Area Effect
o area of habitat for species is high in tropic places because there’s
more structure and space for animals. EX: as the area of trees
increases, the number of insects increases. more area; more
2. Primary Productivity
o the green plants photosynthesizing and producing biomass
(growth of trees). the productivity levels are associated with
species richness. EX: in warm areas with year-round tree growth,
there are more species.
1. Salt marshes are highly productive.
2. Salt marshes have high species diversity.
*This is an exception to the productivity hypothesis, which makes these ideas about
community ecology fuzzy.
3. Intermediate Disturbance hypothesis
o relates species richness as a function of disturbances. EX: in a
rainforest, a tree falls and that opens up the sub-canopy level to
more light and more shrubs and trees can grow, which increases
o frequent disturbances results in low species richness
o infrequent disturbances results in low species richness
o Maximum richness occurs at intermediate levels of
o high disturbance leads to r-selected species while low
disturbance leads to K-selected species.
o regular disturbances creates a mix of the two life history
strategies. 4. Diversity-Stability Hypothesis (opposite of last idea)
o relates stability to species richness. EX: an increase in stability
results in an increase in species diversity
**think of Tropics relation to all these hypothesizes. It’s an exception how?**
• Ecological Succession (2 types) – changes in communities over time.
1. Primary Succession - colonization of an abiotic habitat.
o EX: bare rock with no organisms, organic matter comes in from dead
lichens, rock is broken down, soil forms, weed species form, shrubs
form, trees form, then finally, a