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 o

f im

mig

rati

on

or

exti

nct

ion

Equilibrium number

Immigration and extinction rates

Number of species on island

(a)

High

Low

Rat

e o

f im

mig

rati

on

or

exti

nct

ion

Small island

Effect of island size

Number of species on island

(b)

Large island

Low

Rat

e o

f im

mig

rati

on

or

exti

nct

ion

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