Natures Exists in Several Levels Individual, population,
community, ecosystem, biosphere Population is all the same members
of the same species in a given area. This is the unit of evolution
Community is all the populations. Looks at species interactions.
Communities can be grouped together to form biomes Ecosystem looks
ate energy and matter flow, biotic/abiotic Biosphere is all earths
ecosystems (anywhere life occurs)
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Population Characteristics Population size is the total number
of individuals within a defined area at a given time. Population
density is the number of individuals per unit area at a given time.
Used to set hunting/fishing laws, wildlife boundaries, etc Larger
organisms usually have smaller density due to less resources High
density = easy to find mates, but more competition and disease
Population distribution is how individuals are distributed in
respect to one another Random no pattern (solitary animals with
large territories) (least common) Uniform individuals evenly spaced
out (territorial animals, competition) Clumped large groups of
organisms (fish, birds). Enhances feeding opportunities and
protection (most common) Population sex ratio is males vs. females.
Usually close to 50:50. Helps predict future populations Population
age structure is dispersion of how many individuals fall in certain
age groups. Most important is how many individuals fall in
reproduction age
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Factors That Influence Population Size Biotic potential is how
a population would grow if there was unlimited resources
(reproductive characteristics) Density dependent factors influence
an individuals probability of survival and reproduction in a manner
that depends on population size Limiting resources a resource a
population cannot live without and occurs in quantities lower than
the population would require to increase in size (food, water,
shelter, nutrients, competition) Carrying capacity is the max
population an ecosystem can support. It can overshoot, then birth
rates decrease and death rates increase Density independent factors
have the same effect on an individuals probability of survival and
reproduction at any population size Natural disaster, weather,
temp, habitat destruction
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Growth Models Natural population growth rate growth rate =
birth rate death rate Intrinsic growth rate is maximum possible
growth rate Actual population growth rate (Crude birth rate +
immigration rate) (Crude death rate + emigration rate) Exponential
growth model N t = N 0 e rt (j curve) e=natural log, t=time, N t
=future population, N 0 =current population, r=intrinsic growth
rate Population grows very rapidly (lots of food/space and little
comp) Density independent Logistic growth model starts off
exponential, but slows as population approaches carrying capacity
(s curve, density dependent) Variations of the logistic say a
population can overshoot the carrying capacity
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You have just been offered a job that will last one month. You
have 2-salary options. You can either receive $10 a week with a $5
per week raise every week, or you can receive one penny for your
first day on the job, and then double the previous days pay for
each of the remaining days. Calculate which option would be better.
How does this compare to the two different types of population
growth? $70 vs 10,000,000
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You decide to invest $1000 in a savings account. Your
investment will grow at a rate of 10% each year. Assuming that you
reinvest the interest each year, how much money will you have in 30
years?
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Doubling Time and the Rule of 70 The doubling time or Rule of
70 is a useful tool for calculating the time it will take for a
population (or money) to double. The rule of 70 explains the time
periods involved in exponential growth at a constant rate. To find
the approximate doubling time of a quantity growing at a given
annual percentage, such as 10%, divide 70 by the percentage growth
rate. Remember, the Rule of 70 is an approximation, the actual Rule
is 69.3. So the doubling time for the $1000 investment with an
annual percentage rate of 10% is 70/10 = 7 years The actual Rule of
69.3 is 69.3/10 = 6.93 years Here is an example of a similar AP
multiple-choice question that asks student to calculate doubling
time using the Rule of 70. Example: If the population of rabbits in
an ecosystem grows at a rate of approximately 4 percent per year,
the number of years required for the rabbit population to double is
closest to a. 4 years b. 8 years c. 12 years d. 17 years e. 25
years
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Solution: 70/4 = 17.5 years, the closest answer to 17.5 would
be d 17 years.
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Reproductive Strategies and Survivorship Curves K-selected
species population grows slowly until the carrying capacity R
selected species have a high intrinsic growth rate (reproduce early
and often) TraitK-selected speciesR-selected species Life
spanLongShort Time to reproductive maturityLongShort Number of
reproductive eventsFewMany Number of offspringFewMany Size of
offspringLargeSmall Parental carePresentAbsent Population growth
rateSlowFast Population regulationDensity dependentDensity
independent Population dynamicsStable, near carrying capacityHighly
variable
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Population cycles Boom and bust cycle (common in r-strategists)
Rapid increase in a population, then a rapid drop off More
predictable (temp or nutrient changes) Strategy is get it while it
is good Predator prey cycle If the prey reproduces successfully due
to ideal conditions, the predator will soon have success as well
Predators population shortly trails preys population change
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Species Interactions Competition when individuals struggle for
the same limiting resource Members of same species compete of
niches overlap Direct vs. indirect Competitive exclusion principle
two species competing for the same limited resource cannot coexist
(one will be driven out) Reduce competition by hunting at different
times, using different habitats, and evolution of body shape/size
(finches) Predation the use of one species as a resource by another
species. Does not always result in death True predators consume and
kill their pray Herbivores consume plants, but dont usually kill
them Parasites live in or on host, but only consume a small piece
without usually killing host. Pathogens make host sick Parasitoids
lay eggs in host, and they eat their way out killing the host
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Continued Mutualism both species benefit from one another
(birds/pollination, humans/bacteria, coral/algae, lichens)
Commensalism one species benefits, and the other is neither helped
nor harmed (fish/sharks, tree branches as perches for birds)
Commensalism, mutualism, and parasitism are all examples of
symbiotic relationships, ones where two species live in close
association with one another
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Keystone and Indicator Species Most ecosystems can exist
without the presence of one of its species A keystone species is
one that is disproportionately important to the community Typically
occur in small numbers (sea star example) Ecosystem engineers are
create or maintain the habitat for other species (grizzly bear)
Indicator species are used as the standard to evaluate the health
of an ecosystem Typically sensitive to change, so they can give
warning signs (trout and poll) Indigenous species are ones that
naturally live in an area Invasive species are ones that are
introduces to a new ecosystem (zebra musssles)
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Primary Succession Ecological succession is the gradual
replacement of species over time Primary succession occurs on
abandoned or new land masses where there is no soil Rock is covered
by lichens and mosses (dont need soil) They secrete an acid that
breaks down rock to create soil Lichen and mosses die and add
organic matter to soil Soil gets deeper so grasses move in If
climate favors, trees will follow Secondary succession occurs in
areas that have been disturbed, but still have soil and nutrients
Often after natural disasters Grasses/flowers usually arrive within
a year (pioneer species) Seeds come by wind, and trees quickly
follow and compete for sun When everything is in balance, called
climax community
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Aquatic Succession
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Factors That Influence Species Richness Four majors factors 1.
Latitude angular distance north or south of the equator. Further
away from equator, less variety of animals because cold and little
sun 2. Time more time allows for more species to evolve 3. Habitat
size larger habitats typically means more species because
dispersing species land here, can support more species, and a wider
range of environmental conditions 4. Distance from other
communities
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Theory of Island Biogeography Theory of island biogeography-
the theory that explains that both habitat size and distance
determine species richness.