CHAPTER 8COMMUNITY
ECOLOGY
HOW DO ORGANISMS INTERACT? Fighting/ competition Breeding Predator/ prey Symbiosis
INTERSPECIFIC COMPETITION Different species compete for
space or resources Causes animals to shift niches,
adapt, evolve, migrate, or go extinct
REDUCING COMPETITION Animals become more
specialized in what they eat/ where they live, when they are active
Resource partitioning Character displacement
REDUCING COMPETITION Resource partitioning:
Species evolve ways to share limited resources
Different times of day/ yearDifferent usesDifferent places
9-5
Resource Partitioning in 5 species of Warbler
Black skimmerseizes small fishat water surface
Flamingofeeds on minuteorganismsin mud
Scaup and otherdiving ducks feed onmollusks, crustaceans,and aquatic vegetation
Louisiana heron wades intowater to seize small fish
Brown pelican dives for fish,which it locates from the air
Avocet sweeps bill throughmud and surface water in search of small crustaceans,insects, and seeds
Oystercatcher feeds onclams, mussels, and other shellfish into which it pries its narrow beak
Dowitcher probes deeplyinto mud in search ofsnails, marine worms,and small crustaceans
Herring gull is atireless scarialavenger
Ruddy turnstone searchesunder shells and pebblesfor small invertebrates
Knot (a sandpiper)picks up worms andsmall crustaceans leftby receding tide
Piping plover feedson insects and tinycrustaceans on sandy beaches
Resource partitioning via specialized feeding niches:
Reduces competition and allows sharing of limited resources
REDUCING COMPETITION Character displacement:
Organisms change physical characteristics to become specialized
Finches develop different size and shape beaks to reduce competition
PREDATION Predator eats prey species Predators often feed on the old/
sickly/ weak/ least fit This reduces competition among
prey Predators control prey
populations
CONTROL HYPOTHESES Problem: both hypotheses
assume too much.Top-down- that lynx only eat rabbits and rabbits are only eaten by lynx
Bottom-up- that only rabbits eat veggies
TOP-DOWN CONTROL HYPOTHESIS Says that predators control prey
pops Ex: Lynx eat rabbits so rabbits
decrease. Rabbits decrease so there is less food for the lynx so the lynx crash. Less lynx means less predators so rabbits increase which allows the lynx to increase.
BOTTOM-UPCONTROL HYPOTHESIS Food sources influence
population Ex: Rabbits eat too much
vegetation so there isn’t enough food. Rabbits crash. Veggies grow back and then rabbits increase.
PREDATORS Pursuit: Fast runners, ability to
see from above, hunt cooperatively in packs
PREDATORS Ambush: use camouflage to hide in
plain sight and surprise their prey
PREDATORS Chemical warfare: bite and inject
venom into prey
PREY DEFENSE Run, swim, fly fast Highly developed sight/ smell/
hearing Protective shells/ bark/ spines Change colors Mimicry Camouflage Chemical warfare
Mimicry
Behaviors
PLANTS Plants develop many defense
chemicals Pepper, caffeine, cyanide,
cocaine, opium, strychnine, peyote, nicotine, rotenone, mustard, nutmeg, oregano, cinnamon, mint
PARASITISM One organism lives on or in
another organism and lives off of it
PARASITISM Some parasites have a different
host for each life stage
MUTUALISM Two species acting together so
both benefitPollination: bees and flowersNutritional: coral and zooxanthellae
Food + protection: ox pecker birds and rhinos
Gut inhabitation: bacteria in termites/ humans to aid in digestion
COMMENSALISM Two species interact and one
benefits while the other is basically unaffected
NATIVE SPECIES Species that are normally found
in a particular area and they thrive in that environment
NONNATIVE/ INVASIVE/ ALIEN/ INTRODUCED/ EXOTIC SPECIES A species that is not originally
found in that location Some are harmful, others are
benign, others are helpful
NON-NATIVE SPECIES A non-native species that DOES
NOT harm it’s new environment Usually plants Ex: Goldfish
INVASIVE SPECIES Any non-native specie of plants,
animals, etc that:Is harmful to native crittersNegatively affects it’s new
environment Can hurt new environment
economicallyExamples: zebra mussels, brown
anoles, African bees, Kudzu
INVASIVE SPECIES Zebra mussels (Great
Lakes): Released via ship
ballasts (1988) Filter out nearly all
the phytoplankton (and small zooplankton)
Bad and good
INVASIVE SPECIES:ZEBRA MUSSELS DISTRIBUTION
INVASIVE SPECIES:ZEBRA MUSSELS DISTRIBUTION
2004!
INVASIVE SPECIES Asian green mussels in Tampa
Bay
INVASIVE SPECIES
African bees: Introduced into the
wild in South America (1956).
The Africanized bee escaped and began to dominate honey bee.
INVASIVE SPECIES: AFRICANIZED KILLER BEES
INVASIVE SPECIES
Kudzu (from Japan)
INTRODUCED SPECIES Can be on
purpose or on accident
Monitor lizards and Burmese Pythons in South Florida/ Everglades
Pets that are released when they get too big to handle safely
INTRODUCED SPECIES Lionfish in the FL
Keys Accidentally
introduced during Hurricane Andrew
Massive efforts are underway to curb the population
Fishing, “delicacy” at restaurants, cookbooks
INDICATOR SPECIES Species that
serve as an early warning system for damage/ danger/ pollution for a community
INDICATOR SPECIES Birds and butterflies Sensitive to
environmental changes
Both bird and butterfly populations are declining worldwide…
FROGS Great indicator
species Super
vulnerable to environmental disruption at different points in their life cycles
FROGS Eat bugs (pesticides), no shell on
eggs (UV radiation), thin permeable skin that easily absorbs pollutants from the water and air
FROGS Not just one thing Declining in every region of the
world Habitat loss, prolonged drought,
pollution, increase in UV radiation, increased parasitism, & overhunting
WHY DO WE CARE ABOUT THE FROGS?1. Tells us environmental
conditions are degrading2. Amphibians are important parts
of ecosystems3. They might have genetic
secrets humans want for Rx
KEYSTONE SPECIES Have great effect on ecosystems Loss can lead to population
crashes or even extinction of other species
KEYSTONE SPECIES Pollinators- bees, hummingbirds,
butterflies, bats Top predators- wolves, sharks,
bears, alligators Waste management- dung
beetles
FOUNDATION SPECIES Play a major role in shaping the
community or habitat Benefits other species Ex: elephants knock down trees
which allow grasses to grow. Antelopes eat the grass…
WHAT IS A BIOLOGICAL COMMUNITY? Physical appearance/
distribution of species Species diversity (Species
richness and evenness) Niche structure (how many and
similarity)
DIVERSITY What does it mean if you say
there is high species richness but low species evenness?
FACTORS AFFECTING SPECIES DIVERSITY Latitude
Highest near equator Pollution (aquatic systems) Net primary productivity Habitat disturbance Time
THEORY OF ISLAND BIOGEOGRAPHY Species Equilibrium Model Rate at which new species
immigrate and established species go extinct affects the number of different species found on an island
THEORY OF ISLAND BIOGEOGRAPHY Two factors influence the
extinction and immigration rates:Size of the island- smaller island = fewer species therefore it has low immigration and high extinction rates
Distance from nearest mainland- Assuming equal rate of extinction on two islands, one closer to mainland will have higher immigration rates
High
Low
Rat
e of
imm
igra
tion
or e
xtin
ctio
n
Equilibrium number
Immigration and extinction rates
Number of species on island
(a)
High
Low
Rat
e of
imm
igra
tion
or e
xtin
ctio
n
Small island
Effect of island size
Number of species on island
(b)
Large island
Low
Rat
e of
imm
igra
tion
or e
xtin
ctio
n
Far island
Effect of distance from mainland
Number of species on island
(c)
Near island
Immigration(near island)
Immigration(far island)
Extinction
REVIEW What is a niche? What is a fundamental niche? What is a realized niche?
REVIEW What is a generalist species? What is a specialist species?
CHANGING COMMUNITIES Communities change over time
due to disturbances and changing ecological conditions
This gradual change is known as ECOLOGICAL SUCCESSION
Two types: primary and secondary
PRIMARY SUCCESSION Gradual establishment of biotic
communities on nearly lifeless ground
Takes a very long timeNeeds soil!
PRIMARY SUCCESSION STEP ONE Pioneer species- first species
attach to bare rock, soil begins to gather
Lichens, mosses Decompose and breakdown rock
PRIMARY SUCCESSIONSTEP TWO Patches of soil build up Early successional plant species:
Small annuals (live only for 1 year) Small perennial grasses (live for at least 2 years)
Thrive in harsh conditions, grow quickly
Lichens and mosses are eliminated
PRIMARY SUCCESSIONSTEP THREE Hundreds to thousands of years
later… Soil becomes deeper an contains
more nutrients Midsuccessional plant species
Herbs, grasses, low shrubsTrees
PRIMARY SUCCESSIONSTEP FOUR Trees grow up and make lots of
shade Late successional plant species
Mostly treesMust be able to tolerate shade
PRIMARY SUCCESSION Can occur in small ponds
Influx of sediments can allow plants to invade
Turns into a marsh and then dry land
SECONDARY SUCCESSION Natural community has been
disturbed somehow Soil still remains Much faster than primary
succession Abandoned farmlands, cut/
burned forests, polluted streams, land that was dammed or flooded
DISTURBANCE Any change in
environmental conditions that disrupts a community
Fire, drought, flooding, mining, clear-cutting, pesticides, invasion, etc…
Not always bad
SECONDARY SUCCESSION Plants begin to grow back
quicker because of the soil already present
X
ECOLOGICAL SUCCESSION 3 factors that affect the rate of
successionFacilitation- one species makes area habitable for other species
Inhibition- early species hinder growth of later species
Tolerance- late successional species are unaffected by earlier species
CHAPTER 9POPULATION
ECOLOGY
POPULATION DYNAMICS Study of how populations
change in SIZE, DENSITY, and AGE DISTRIBUTION
POPULATION DISTRIBUTION Clumping Most populations live in clumps
CLUMPING Why live in clumps? Resources vary from place to
place Living in a herd/ flock/ school
provides protection from predators
Predators are almost guaranteed a meal
Some form temporary groups for mating purposes
POPULATION DISTRIBUTION Uniform- allows species to
maximize limited resources
POPULATION DISTRIBUTION Random- very few species are
randomly distributed
POPULATION SIZE What four factors determine
change in population size?
Hint: pop change= (? + ?) – (? + ?)
AGE STRUCTURE Pre-reproductive Reproductive Post-reproductive
Remember the population pyramids?
POPULATION GROWTH Intrinsic rate of increase (r)
Rate a population would grow at if it had unlimited resources
Biotic potentialCapacity for growth
BIOTIC POTENTIAL Environmental conditions within
species range of tolerance Generalists Easily adapt to change Resistance to disease and
predators Enough food Ability to migrate and live in
other areas
HIGH RATE OF GROWTH Individuals:
Reproduce earlyReproduce oftenHave a lot of babies each timeHave short generation times
POPULATION GROWTH Populations cannot grow
indefinitely Environmental resistance- all
the factors that act to control population growth
ENVIRONMENTAL RESISTANCE Environmental conditions
outside of range of tolerance Low reproductive rate Specialists Not enough food/ resources Too many predators/ competition Unsuitable habitat Unable to change
CARRYING CAPACITY K Maximum number of individuals
of a given species that can be sustained indefinitely in a given space
Growth slows down as population reaches K
EXPONENTIAL GROWTH Population grows at
a fixed rate Grows slowly at
first then growth explodes
Creates a J-shaped population graph
LOGISTIC GROWTH Rapid exponential population
growth followed by decline until population levels off
K VS GROWTH What happens when growth
exceeds K? Overshoot- happens when
population exceeds K Due to a reproductive time lagBirth rate must fall and death rate must rise
Dieback or crash UNLESS organisms can change to another resource
POPULATION DENSITY CONTROLS Density-
INDEPENDENT population controlsAffect population size regardless of density
Floods, fires, freezes, hurricanes, tornadoes, pollution, habitat destruction, pest control
POPULATION DENSITY CONTROLS Density-DEPENDENT
population controlsGreater effect with higher density
Competition, predation, parasitism, and infectious disease
EX: Black Plague in Europe & Citrus canker
POPULATION FLUCTUATIONS Stable population size
Size fluctuates only slightly above and below carrying capacity
Ex: species found in rain forests
POPULATION FLUCTUATIONS Irruptive
Short period of explosive growth Followed by a crashShort-lived, rapid reproducersEx: seasonal bugs
POPULATION FLUCTUATIONS Cyclic fluctuations
Have periods of up and down over a longer amount of time
Lemmings 3-4 year cyclesLynx and snowshoe hares 10 year cycles
POPULATION FLUCTUATIONS Irregular patterns
No distinct patternNot really understood why
ASEXUAL REPRODUCTION Only 1 organism needed Offspring are exact genetic
clones Usually smaller, simpler, single-
celled organisms Budding, binary fission
SEXUAL REPRODUCTION 97% of organisms Need 2 organisms Sex cells (gametes) combine to
create one new, genetically unique organism with DNA from both parents
SEXUAL REPRODUCTION NEGATIVES Men don’t give birth. Women
must produce 2 kids to replace both parents.
Increased chance of genetic defects during meiosis
Courtship & mating rituals can be time consuming and dangerous
SEXUAL REPRODUCTIONPOSITIVES Genetic diversity is an
advantage when environments change
Males can gather food and protect the women and children
FUNDAMENTAL REPRODUCTIVEPATTERNS 2 types Depends on where you find them
on the S-shaped population curve
Basic characteristics of reproduction
R-SELECTED SPECIES Have capacity for high-rate of
pop increase (r) Reproduce early Make lots of eggs/ have lots of
babies Little to no parental care Produce so many to ensure
some survive
R-SELECTED SPECIES Ex: bugs, algae, bacteria,rodents Tend to be opportunists Able to take over after a
disturbance Can easily crash
K-SELECTED SPECIES Reproduce later in life Few babies that develop inside
mom Live longer Born large, develop slowly Parental care until they reach
reproductive age
K-SELECTED SPECIES Called K-selected because they
do well in competition near their carrying capacity
Typically follow logistic growth Prone to extinction Most mammals, birds of prey,
and large/ long lived plants
LIFE EXPECTANCIES Individuals tend to have different
life expectancies Can show this on a survivorship
curve
SURVIVORSHIP CURVE
Age
Per
cent
age
surv
ivin
g (lo
g sc
ale)
100
10
1
0
0.01
Late Loss
Constant Loss
Early Loss
SURVIVORSHIP CURVE
Age
Per
cent
age
surv
ivin
g (lo
g sc
ale)
100
10
1
0
0.01
Early Loss:Survivorship is low early in life, lots of babies die,
only a few adults age and make it through adulthood
SURVIVORSHIP CURVE
Age
Per
cent
age
surv
ivin
g (lo
g sc
ale)
100
10
1
0
0.01
Constant Loss: constant death rate among all ages
Ex: song birds
SURVIVORSHIP CURVE
Age
Per
cent
age
surv
ivin
g (lo
g sc
ale)
100
10
1
0
0.01
Late Loss:High survivorship to a certain age then very high mortality
POPULATION AND GENETICS Founder effect:
Genetic diversity is limited when a few individuals colonize a new habitat
Geographically isolated from old pop
POPULATION AND GENETICS Demographic bottleneck:
Only a few individuals survive a catastrophic disturbance like a hurricane or human disturbances (hunting, deforestation)
POPULATION AND GENETICS Genetic drift:
Random changes in gene frequencies that allow certain individuals to breed more which makes their genes more dominant
POPULATION AND GENETICS Inbreeding:
Individuals in a very small pop breed with each other
Can increase frequency of defective genes
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