Transcript Unit I: Ecology Lecture 3: Community Interactions

Unit 1.2:
Community
Interactions and
Population Dynamics
Vocabulary
• Symbiosis: “sym-” = with, “bio-” = life; unlike organisms that
live together
• Mimicry: the characteristic of resembling something
poisonous or otherwise dangerous
• Aposematic coloring: bright coloration that warns predators
that a particular prey is dangerous.
• Mutualism: symbiotic relationship in which both organisms
benefit
• Commensalism: symbiotic relationship in which one
organism benefits and the other is unaffected
• Carrying capacity: the largest number of individuals an
environment can support.
• Limiting factor: factor that causes population growth to
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decrease
I. Community Interactions
A. Five types of interactions between species:
1. Predation
a. Predator : has evolved structures and behaviors
to help it find, capture, consume prey
•
Ex: keen eyesight, camouflage, tooth structure
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b. Prey : has evolved structures and
behaviors to help it avoid, escape,
ward off predators
•
Ex: camouflage, bad-taste, quills
1) Aposematic coloring: poisonous species is
brightly colored as a warning to predators
• Wasp, monarch butterfly, coral snake
2) Mimicry: harmless species resembles poisonous
one
• Bumblebee, viceroy butterfly, king snake
3) Plants: (can be considered prey)
• physical defenses: thorns, spikes
• chemical defenses: poisons (poison oak)
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2. Competition:
Two species compete for
limited resources within a “habitat”.
a. A “habitat” is the community where an organism lives:
1) Many species live in the same habitat (like Grass Valley)
b. A “niche” is the “role” it plays in its habitat:
1) A niche includes the foods that organism eats, how it gets this
food; where it reproduces; and abiotic factors (such as
temperature range); where it thrives. (like Bitney)
2) Different species occupy different niches within the same
habitat
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c. Competitive Exclusion Principle: two species
cannot occupy the same niche at the same time
1) Whichever of the two species
is more efficient at using
resources (water, nutrients,
light, food, or space) outcompetes the other species,
survives
2) Like two students trying to sit
in the same seat at the same
time.
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• 3 types of symbiosis
3. Parasitism:
a. Parasite benefits
, host is harmed
1) Ectoparasite : “ecto-” = external
•
ex: ticks, leeches, mosquitoes
2) Endoparasite : “endo-” = internal
•
•
ex: bacteria, tapeworms
Cordyceps fungus
3) Host is not usually killed, b/c then
parasite must find new host
4) Parasites help to keep host population
balanced, prevents overpopulation
b. Host defenses:
1) Physical: skin
2) Chemical: tears, saliva, mucus
•
•
pH of tears, saliva can inhibit bacterial
growth
Mucus: causes clumping of bacteria to
allow body to remove it
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4. Mutualism:
a. Benefits both species
b. ex: pollination: flowers provide
food to animals, animals carry
pollen to other flowers
• “Let me tell you ‘bout the birds and
the bees, and the flowers and the
trees…”
5. Commensalism:
a. One benefits , other
affected
is not
• Clownfish/anemone: clownfish is
protected but anemone gains nothing
• Pitcher plant, red crab spider: spider
gets food, but pitcher plant does too,
so plant is unaffected.
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II. Properties of Populations
A. 3 characteristics that “D-”scribe populations (3 D’s)
1. Distribution: area inhabited by a population
a. Can be small: apple being broken down by bacteria
b. Or large: the ocean travelled by migrating whales
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2. Density: number of individuals per unit of
area or volume
a. Grass Valley has low
population density in
terms of people but
high population density
in terms of pine trees.
b. Los Angeles has high
population density in
terms of people but
low population density
in terms of pine trees.
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3. Dispersion: how organisms are spaced
a. Clumped: clustered groups
1) Because resources (food, living space) are
clumped
2) Social behaviors like herds/flocks/packs are
considered “clumped”
b. Even: consistent distance between
individuals
1) Planned space like a planted orchard
2) Also occurs when plants release chemicals
into soil that prevent other plants from
growing nearby
c. Random: independent locations
1) ex: seed dispersal by wind
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III. Population Growth
A. Growth rate: change in population
size over time, dependent on:
1. Birthrate: # of births in a period of time
(↑ growth rate)
2. Death rate (mortality rate): # of deaths in
a period of time (↓ growth rate)
3. Immigration: individuals moving into a
population. (↑ growth rate)
a. b/c more resources are available
4. Emigration: individuals moving out of a
population. (↓ growth rate)
a. b/c resources are scarce
Growth rate = birth rate – death rate
(assumes no migration)
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B. Exponential Growth: J-shaped curve
1. Unlimited population
growth occurs when:
a. Resources are unlimited:
food, water, space, mates
b. No predation or disease
c. Ex: bacteria divide/double
their population every 20
minutes in optimal
conditions. At this rate, in
one week, a single bacteria
would divide enough to
cover entire planet!
Exponential
2. Plots shows a steep slope
with no leveling at the top
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C. Logistic Growth: S-shaped curve
1. Limiting resources causes the growth of a population to
slow or stop b/c:
a. Decrease in birthrate or immigration
b. Increase in death rate or emigration
2. Plot shows steep slope that levels off at the top
a. Lag phase: population is small, so growth is slow
b. Exponential phase: population grows quickly
c. Deceleration phase: population growth slows as carrying
capacity is reached
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D. Carrying Capacity:
1. Maximum number of individuals an environment can
support
2. Environment cannot support any more so growth rate
levels off
3. Flat portion at top of logistic growth curve
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IV. Limits to Growth
A. Limiting factor: factor that
causes population growth to
decrease
1. limited amounts of food/food
sources
•
pandas only eat bamboo,
bamboo forests have been
cleared, reducing food
availability
2. limited nesting space
3. limited numbers of mates
4. limited amounts of water!
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B. Density-dependent factors: depend on population density
1.
2.
Competition: if more organisms, then more competition for resources;
if fewer organisms, then less competition
Predation: predator-prey relationships keep populations in check
a. If more prey, can support more predators, but when predator population
becomes overpopulated, then will drop b/c not enough prey to support
all the predators
3.
Parasitism and Disease: if more organisms, then greater chance of
infection by parasites.
a. ex: ant population and Cordyceps fungus in jungles
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C. Density-independent factors: affect
all populations in similar ways
regardless of population size
1. Natural disasters: droughts, floods,
fires
2. Seasonal cycles: deciduous trees drop
leaves = less food for some
populations
3. Human disturbances: damming rivers,
clear-cutting forests
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