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Keystone Species
○ The case of the california sea otters
■ Kelp Forests
■ Sea urchins eating Kelp
■ Otters eat sea urchins allowing for kelp to grow which allows for
productivity.
■ Kelp forests act as ecosystems for many species and as nurseries for
young fish.
■ Hunting sea otters for fur impacted the kelp forest ecosystems.
○ The wolves of Yellowstone
■ Grey wolves (canis lupus)
■ Wolves hunt elk
■ Elk populations increase
■ Forest cover population decreases.
■ Though wolves are important predators on elk, they are not the only
factors.
■ Disease , drought, fire, and other predators (e.g. grizzly bears) can also
be factors.
Evolution
○ Natural Selection
■ Organisms with traits most favorable to the environment survive and
reproduce, passing on their traits to their offspring. Others die or do not
reproduce.
■ Traits being selected maximize survival to adulthood and reproductive
success.
○ Artificial selection
■ Decisions that are made by people that impact species.
○ Rapid Reproduction
○ Most Die
■ This population Growth potential is kept in check by limiting factors.
○ Variation
■ Variation exists in every population (some fish are bigger than others,
some fish have more stripes, some fish are faster.)
■ Whichever trait helps them survive the best is passed on to the next
generation.
○ Inherited Variation
■ Some variations are inherited. DNA.
■ Big fish have big baby fish.
■ Striped fish have striped baby fish.
■ Fast fish have fast baby fish.
Speciation
○ Anagenesis
■ Speciation in time
■
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Directional selection causes species to change so much their actors
would be considered different species.
● They would no longer recognize their ancestors and breed with
them.
■ No net increase in species number.
○ Cladogenesis
■ Two Species descend from one
■ Usually twow populations get separated and evolve differences.
■ Sometimes one stays the same, or similar, and another changes
especially if a few individuals end up in a different place.
■ Occasionally speciation can happen in an intact population.
○ Allopatric Cladogenesis
■ Speciation by Geographic Isolation
● Two populations separated by a barrier evolve in separate
directions until they can no longer interbreed.
● Two species result.
○ Allopatric Speciation
■ Tree frogs are a single population.
■ The formation of a river may divide the frogs into two populations.
○ The Tempo of Speciation
■ Gradualism
● Slow and steady change in species.
■ Punctuated equilibrium
● Slow evolution punctuated by short events of rapid evolution.
○ Allometry
■ Rate of growth of body parts.
■ Can change due to single mutations.
■ Paedomorphosis
● Sexually mature juvenile.
● Juvenile appearing adults.
○ Homeotic gene mutations
■ Hox gene mutations can change phenotype dramatically.
Distribution of Species
○ Temperature
■ Seasons can affect species distribution
● Tomatoes need a certain number of warm days in order to ripen;
without that number then they wont grow any seeds.
● Apples need cool/cold weather to flower and to ripen. No apples
can grow in the tropics.
○ True for Grapes and Peaches.
● Polar bears can live in California because it is too hot.
■ Single Event limitations; some organisms can't stand extremes of
temperature.
● If a banana plant freezes even once, then it is dead.
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● If a pika gets too hot for just a few hours, it is dead.
○ Fresh Water
■ Major Factor
○ Light
■ As light fades in the fall, leaves start to fall and eventually the leaves fall.
○ Soil Nutrients
■ Certain plants can grow in soils with fewer nutrients or “poor” soils.
● “Weedy” or “pioneer” species.
■ Others are limited to rich soils
● Mostly crop plants
○ Range of Tolerance
■ Can't live if it's too hot.
■ Can't live if it's too cold.
● True of most limiting factors.
○ Movement
■ Also called dispersal.
■ Not very fast
● Remember that animals have to have the right ecosystem, so
move as slow as the trees.
○ Acorn woodpecker, oak tree.
● Trees move 1-45 km per century.
■ Corridors
● Daily/weekly movement.
● Sometimes trees cannot make it past man made structures.
Extinction
○ Background information.
■ Species constantly go extinct
● When populations are small and habitats are disturbed.
● New arrivals displace native endemics.
○ Examples of extinction: Argentine Ants were displaced and
are wreaking havoc by fighting native ant species.
○ Mountain Top Refugia
■ Pika are widespread and will probably not go extinct any time soon.
■ But what if they were only found on top of one or two mountains since the
last ice age ended and ice retreated.
● They compete with each other for colder habitats.
● As the planet keeps warming, their habitat starts to drastically
decrease.
○ Factors
■ Climate change can force species to compete for certain habitats.
● Pika example
■ Invasive species can harm an ecosystem’s natural inhabitants as they
fight for resources.
● Argentine Ants
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Humans caused extinction.
● Overhunting.
○ Extinction One
■ 439 million years ago.
■ Ordovician-Silurian Extinction
■ CLimate Change
● Drop in sea levels then rise in sea levels.
● World wide glaciers form then glaciers melt.
■ 60% of marine species went extinct.
○ Extinction Two
■ 365 Million years ago.
■ Late Devonian Extinction
■ Probably Climate change.
■ 57% of marine species went extinct.
○ Extinction Three
■ 251 million years ago.
■ Permian - Triassic Extinction.
■ Climate change
● Possible asteroid impact.
● Super volcano
■ 95% of all species went extinct.
○ Extinction Four
■ About 200 Million years ago.
■ End Triassic Extinction
○ Extinction Five
■ “When the dinosaurs went extinct”
■ 65 million years ago
■ Cretaceous - Tertiary Extinction.
■ Climate Change
● Asteroid impact or volcanism caused.
■ 47% of marine animals went extinct.
○ Are we causing an extinction?
■ Climate Change
● Greenhouse effect increased by CO2 emissions.
○ Diversity
■ Sometimes after an extinction event, there is massive speciation as there
are lots of niches that need to be filled.
Aquatic Ecosystems
○ Aquatic Ecosystems
■ 75% of earth is covered in water
○ Marine Ecosystems
■ Different parts of the ocean differ in biotic and abiotic factors (salinity,
depth, availability of light, and temperature) found there.
○ Saltwater
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Phytoplankton
● The base of most saltwater food chains.
● Microscopic algae and cyanobacteria.
● Some with calcium based “shells.”
● Need nutrients
○ A lot of nutrients come from decomposition of rock and
sediments that flow in.
○ Productivity tends to be higher in near shore environments
compared to the open ocean.
■ Zooplankton
● Microscopic animals - larva and immature fish and tiny arthropods.
● Microscopic protists such as foraminifera.
■ Where are there the most fish? Why?
● Shelf and light zone.
■ Marine Snow
■ Hydrothermal Vents
● Only productive part of the deep ocean
● Use chemosynthesis and not photosynthesis.
■ Trade wind effect
● Drag out algae across the oceans.
Estuaries
■ Coastal Body of water
● Partially surrounded by land, in which freshwater and saltwater
mix.
● There are some species that are only found in these zones.
○ Often brought from place to place by people.
● Intertidal zone
○ Between the high and low tide lines.
● Abiotic Factors
○ Sometimes wet, sometimes dry.
○ A lot of sunlight
○ Wave action
Freshwater
■ Photic Zone
● Sunlight penetrates
■ Aphotic zone
● No sunlight
■ Phytoplankton
● Microscopic algae and cyanobacteria.
■ Zooplankton
● Microscopic protists and animals.
■ Oxygen and Temperature
■ Marshes
● No trees
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○
○
● Very slow flowing with many plants
■ Swamps
● Like marshes but with trees
■ Bog
● Stagnant water (water that is not flowing)
● Has a lot of vegetation.
● High nutrient, low oxygen.
■ Lake AP test example - Fall Turnover.
● During the summer, the coldest water is going to be at the bottom,
the warm water will be in the middle, and the hot water will be at
the top.
● Towards the end of fall, the cold (near freezing) water is at the top,
the warm water is in the middle, and the bottom of the lake holds
more cold water.
● The density of water increases as the water gets colder.
● Maximum water density occurs at 4 degrees celsius.
○ Not frozen but cold
● Water from the bottom goes up to the top and water at the top
goes down to the bottom.
○ Water at the bottom is nutrient rich as most of the nutrients
are at the bottom.
● Because of Fall Turnover, a significant amount of nutrients are
brought to the top.
Swamps
■ Another way of thinking about swamps are flooded forests
■ Marsh and Swamps are very different
■ Swamp logging is not uncommon.
Mangrove
■ Shrubby, woody vegetation that can tolerate 100% seawater.
■ They inhabit areas that have a decreased salinity.
■ Huge amount of carbon in the mangrove forests is in the soil.
■ If the mangroves were gone, the carbon rich mud would also be gone.
■ Hard to fish in.
■ Mangrove environments typically have high diversity.
■ Home for many baby fish.
■ Ecosystem engineer
● They change the physical structure of the ecosystem.
● They increase the ecosystem’s productivity.
For test
■ Evolution
■ Distribution, extinction rate, habitat corridor.
■ Aquatic ecosystems
■ Coral reefs
■ Mangroves
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Succession
○ Changes over Time
■ The orderly, natural changes and pieces replacements that take place in
the communities of an ecosystem.
■ Occurs in stages, at each stage, different species of plants and animals
may be present.
■ There are two types of succession.
● Primary succession and Secondary Succession
○ Primary Succession
■ The colonization of barren lands by communities of organisms.
● On land where there are no living organisms and no soil.
■ Takes a Long time.
● Thousands of years.
■ Pioneer Species
● The first species to take hold in an area without soil.
● Lichen, a symbiotic association between an algae and a fungus.
○ Fungus provides water and nutrients, algae provides food
from photosynthesis.
○ Which of the three types of symbiosis is this and why?
○ Decaying lichens and bits of sediment in rock crevices
make first soil
○ Makes it possible for small weedy plants, small ferns,
fungi, and insects to become established.
○ As organisms die, more soil builds.
■ Climax Community
● A stable, mature community.
● After some time, the community reaches equilibrium.
○ Secondary Succession
■ Changes that occur after a disruption.
● In areas that previously contained life, and still may contain soil.
■ The species that grow will differ from pioneer species
● Possibly the same type of organisms that were disrupted will
return but often slightly different for a while.
■ Takes less time than Primary succession.
● 100-200 years.
○ WHY?
■ There is already soil and many organisms can grow
back from roots.
■ Seed Bank
● Seeds in the soil all the time waiting for opportunity.
● Can last hundreds or thousands of years waiting.
○ Old Field
■ Stuck in invasive shrub species.
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Can stop succession from occurring by forming a very dense
canopy and can take up all non shaded areas.
○ Autumn Olive.