Populations Biology

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PopulationsBiology

• Ecology with Mrs. O
• AP Biology

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Population (definition)

• All members of one species, in one location, at
  same time

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Population Growth

• Reproduction Without restraints ?exponential
  growth!

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Limiting FactorsLimits to growth

• Cause population growth to decrease
• like nutrient availability

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Density Dependent Limiting Factors

• depends on population size
• operate only when the population density reaches
  a certain level.
• operate most strongly when a population is large
  and dense.
• do not affect small, scattered populations as
  greatly
• Examples
• competition
• predation
• parasitism
• disease

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Which of the following is most clearly a case of
density-dependent population regulation?

• 1. the occurrence of rainstorms for an
  opportunistic desert annual
• 2. a dangerous new flu strain that is transmitted
  among humans by sneezing
• 3. the summer drying of savanna grass for an
  insect that feeds on grass sap
• 4. the first hard frost of fall for a population
  of annual morning glory vines

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Which of the following is most clearly a case of
density-dependent population regulation?

• 1. the occurrence of rainstorms for an
  opportunistic desert annual
• 2. a dangerous new flu strain that is transmitted
  among humans by sneezing
• 3. the summer drying of savanna grass for an
  insect that feeds on grass sap
• 4. the first hard frost of fall for a population
  of annual morning glory vines

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Density Independent Factors

• affect all populations in similar ways,
  regardless of the population size.
• Examples of density-independent limiting factors
  include
• unusual weather
• natural disasters
• seasonal cycles
• certain human activitiessuch as damming rivers
  and clear-cutting forests

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Which of the following is a density-independent
factor affecting populations?

• 1. predation
• 2. disease
• 3. a destructive hurricane
• 4. parasites

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Which of the following is a density-independent
factor affecting populations?

• 1. predation
• 2. disease
• 3. a destructive hurricane
• 4. parasites

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Limits to growth leads to logistic growth curves
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logistic growth curve shows the carrying capacity!

• Carrying capacity
• the maximum population size of the species that
  the environment can sustain indefinitely
• or
• The environments maximum load
• Births balance deaths

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Exponentials and logistic growth comparison
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N and K. What are they talking about?

• N population size
• K carrying capacity

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Community Ecology
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Communities

• A community is a group of organisms of different
  species that live in a particular area

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Individualistic Hypothesis vs. Interactive
Hypothesis

• Individualistic Hypothesis
• A community is a chance group of species found in
  the same area because they have similar abiotic
  requirements
• Interactive Hypothesis
• A community is a group of closely linked species
  locked together in mandatory biotic interactions
  that cause the community to function as an
  integrated unit

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Interspecific Interactions

• interactions that occur between populations of
  different species living together in a community
• There are 4 major interspecific interactions
• Predation (and parasitism)
• Competition
• Commensalism
• Mutualism

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Predation

• ( / -)
• beneficial to one species and detrimental to the
  other
• Predation
• When a predator eats its prey
• Predator prey relationships keep population
  sizes in check

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Parasitism

• Parasitism
• Predators that live on or in their hosts, usually
  feeding off their body tissues or fluids
• Usually do not kill their hosts
• Examples

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Plant Defenses Against Herbivores

• Plants Fight Back!
• 2 major mechanisms of defense against getting
  eaten
• Mechanical Defenses
• Thorns, hooks, etc.

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Plant Defenses Against Herbivores

• Chemical Defenses
• Produce chemicals that are distasteful or harmful
  to an herbivore
• Morphine (opium poppy)
• Nicotine (tobacco)

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Animal Defenses Against Predators

• passive (hiding) or active (fleeing)
• Cryptic coloration (camouflage) makes prey
  difficult to spot
• Aposematic coloration (warning coloration)warns
  predators not to eat animals that may be toxic or
  may sting.
• (good for animals the LEARN)

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Animal Defenses Against Predation

• Mimicry
• When one species imitates or mimics another
• Batesian mimicry
• When one edible or harmless species mimics an
  bad-tasting (unpalatable) or harmful species
• Example hawkmoth mimics a snake, king snake
  (nonvenomous) mimcs coral snake (venomous)

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Animal Defenses Against Predation

• Mimicry
• Mullerian mimicry
• Two species, both of which are unpalatable (taste
  bad) or harmful, resemble each other
• Example monarch butterfly (unpalatable) and
  queen butterfly (unpalatable) resemble each other

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Symbiosis- close relationship between two
organisms.

• Parasitism (,-)
• Commensalism (,neutral)
• Mutualism (,)

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Commensalism

• One partner benefits, the other is not affected
• Examples
• Cattle and cattle egret (birds)
• Sea anemone and clownfish
• Clownfish gets a place to live, sea anemone is
  not affected

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Mutualism

• () relationship
• Both partners benefit from the relationship
• You scratch my back, Ill scratch yours
• Examples
• Ants acacia tree
• tree provides high protein food in beltian
  bodies habitat for nests inside thorns ant
  protects against predators
• Mycorrhizae-fungal extentions on plant roots
• Plant gets increased water/nutrition, fungi gets
  food
• Hummingbirds flowers
• Hummingbirds get food, flowers can reproduce

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Parasitism

• One organism (the parasite) gets its nourishment
  from another organism (the host), which is harmed
  in the process
• Endoparasites
• Live within host tissues (tapeworms)
• Ectoparasites
• Feed on external surfaces (mosquitoes)

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Interspecific Competition

• Competition between organisms of different
  species
• The Competitive Exclusion Principle
• Two species with similar needs for the same
  limiting resources cannot coexist in the same
  place
• Niches may overlap but they may not be identical.

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Ecological Niches

• An organisms niche is the specific role it plays
  in its environment
• All of its uses of biotic and abiotic resources
  in its environment
• Example oak tree in a deciduous forest
• Provides oxygen to plants, animals, etc.
• Home for squirrels
• Nesting ground for blue jays
• Takes water out of the soil
• Etc., etc.

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Fundamental v. Realized Niche

• Fundamental Niche includes resources an organism
  could theoretically use (if no competition)
• Realized Niche includes resources it actually
  does use given competition from other species.

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Resource Partitioning

• Similar species develop ways to partition/divide
  resources in order to coexist.

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Dominant Keystone Species

• Dominant Species
• Species in a community that have the highest
  abundance or highest biomass
• Sugar maple in eastern North America
• Keystone Species
• Important to a community because of their
  ecological roles (niches), not by numbers
• Examples
• Sea otters control sea urchin population, which
  controls kelp population
• Sea stars are keystone predators in many aquatic
  environments.

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Ecological Succession

• Ecological succession is a change in the species
  that live in a given area over a period of time
• One community replaces another
• Primary succession occurs in places where soil
  is not yet formed (bare bedrock)
• Secondary succession occurs in places where
  there is soil, but where some disturbance has
  eliminated the previous community

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Ecological Succession
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Ecological Succession

• The first organisms to inhabit an area undergoing
  succession are known as pioneer organisms
• These are usually small organisms (bacteria,
  lichens, algae, etc.)
• The ecosystem goes through a number of stages,
  with each new stage usually consisting of larger
  organisms than the last one
• Once a community has become stable and is not
  changing much, it is known as a climax community

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Causes of Ecological Succession

• There are 3 major causes of ecological
  succession
• Human Activities
• - logging, mining, development, etc.
• Natural Disasters/Disturbances
• - fires, volcanic eruptions, etc.
• 3. Natural Competition Among Species
• - Fictitious example
• - turtles and frogs both eat crickets
• - frogs are faster, turtles are slower
• - frogs eat more crickets, turtles starve
• - turtle population dies out, frog population
• gets bigger