Chapter 45

COMMUNITIES AND ECOSYSTEMS

A. CommunityAll populations of organisms living

in a defined area.Habitat - the physical place where an

organism lives.What is habitat of a koala?

Niche - the role the organism has in the community (producer).What is niche of a koala?

1. Community InteractionsOrganisms in communities interact

through competition, symbiosis or predation.

Interspecific CompetitionIndividuals of different species compete

for same resources (food, shelter, space).

What are possible outcomes of interspecific competition? one individual excludes the other (principle of competitive exclusion) they coexist (resource partitioning)

Principle of competitive exclusionTwo species cannot coexist indefinitely in

the same niche.

When present alone, each has the same fundamental niche (all resources a species is capable of using).

When present together, each has a different realized niche (all resources a species actually uses).

When a new species enters an area, competition may lead to the extinction of a native population or species.

Resource partitioningCompeting species can coexist if they

use the same resource in a slightly different way or at a different time.

SymbiosisOne species living in or on another.mutualism - both species benefit.

commensalism - one species benefits with no apparent effect on the other.

parasitism - one species benefits & the other is harmed.

parasitoidism - one species benefits & the other dies as a result.

PredationOne species (predator)

kills another (prey) for food.

Prey species often have adaptations that help them avoid being eaten.

camouflage

warning coloration

mimicry

2. Ecological SuccessionChange in the species composition

of a community over time. Primary succession

Occurs in an area where no community previously existed.

Caused by volcanoes, road cuts & glaciers.

Pioneer species are lichens & mosses. Takes hundreds of years for a climax

community to develop.

Secondary successionOccurs in an area where a

community is disturbed but not decimated (some soil & life remain).

Caused by fires, hurricanes & agriculture.

Pioneer species are herbs & weeds. Occurs faster than primary succession.

Few communities ever reach true climax conditions.

LupinesLupines are legumes that add

nitrogen to the soilThey are pioneer species in

volcanic soil

B. EcosystemAll the biotic (living organisms) and

abiotic (nonliving environment) components in a defined area.

Ecosystems interact.All ecosystems require a constant

input of energy.Chemicals are cycled within

ecosystems.

1. Energy FlowEnergy flows in one direction

through an ecosystem.Route of energy flow is determined by an

ecosystem’s trophic structure.

photo- or chemoautotrophs

animals that eat producers

animals that eat herbivores

animals that eat carnivores

Food web - several species function at more than one trophic level.

Test Your Cerebrum:What is the niche of (think food

chain) chemoautotrophic bacteria?

Is all of the energy stored by individuals at one trophic level available to the next?No - energy needs of individual, second law of thermodynamics.

On average, ~10% (2-30%) is transferred.

Energy transfer in Cayuga Lake:

algae store 1,500 kcal

aquatic herbivores store 150 kcalsmelt fish store 15 kcalhumans store 1.5 kcal

Food chains rarely extend beyond 4 trophic levels.

Other types of pyramids can be used to describe ecosystems.

pyramid of numbers - shows number of organisms at each trophic level.

pyramid of biomass - shows total weight of organisms at each trophic level.

Consider the food chain: hawk – rabbit – clover.

Clover contains 10 calories of food value, rabbit 500 calories, hawk 1200 calories.

Each species has a different daily caloric requirement:

clover: sunlightrabbit: 100 calories of foodhawk: 300 calories of food

How many clover plants, per day, does it take to support a hawk?

Hawk needs 300 calories from eating rabbits, so needs 3,000 rabbit calories available since only 10% moves up the food chain.

3,000 rabbit calories (where food energy is 500 calories per rabbit) means you need 6 rabbits to feed the hawk.

6 rabbits then need 100 calories of grass each, or 600 grass calories total.

SO they feed on 6,000 calories of grass (since only 10% is available to them).

Each clover plant is 10 calories so 600 clover plants = 6,000 calories.SO it takes 600 clover plants PER DAY to support one hawk!

2. Biogeochemical CyclesThe biological & geological processes

that recycle chemicals vital to life. Water cycle

Carbon cycle

Nitrogen cycle

N Cycle QuizWhat is the original source of

nitrogen on Earth?What fixes N from a gas into a

usable form? (2 things) In what form do plants take in N?How do plants use N?How do humans get N and why do

they need it?How does N return to the

atmosphere?

How do humans interrupt the N Cycle?Fertilizer: producing N fertilizer

started from leftover weaponsRunoff into water from crop fieldsCauses birth defectsWe overload the nitrate pool

Industry: air emissionsDomesticated cattle: farts & burps

(maybe modify with kangaroo fart/intestinal bacteria DNA)

New N Cycle StudyU of CA researchers have found

that forest trees can use N found in sedimentary rock and boost their productivity.

Forests over N-rich rock were 50% more productive than forests over N-poor rock.

N was traced using radio-isotopesAnother factor in the N & C cycles!

Phosphorous cycle

Certain elements or compounds taken up by organisms cannot be metabolized or excreted.

They accumulate in the organism (bioaccumulation) and may reach toxic levels. heavy metals (lead, arsenic, mercury) nonbiodegradable pesticides (DDT)

The effects of bioaccumulated materials are magnified through the food web (biomagnification).

of DDT

What effect does DDT have on top predatory birds?

DDT affects their ability to secrete a firm, calcium-rich eggshell.

DDT ControversyDDT is used to kill female Anopheles mosquitos – most carry a plasmodium parasite that can infect and kill humans. (in 106 nations it is a problem)

In sub-Saharan Africa, about 3,000 children die EACH DAY from malaria.

In WW II, more people died from malaria than combat.

DDT Use Today(read the handout!)

In 2006 the WHO approved DDT indoor use in African countries needing malaria control.

Sanaria in MD is the only company in the world working on a malaria vaccine: 30 scientists in a mini-mall lab. Artesunate is an anti-malarial drug for early treatment.

ALSO counterfeit drug trade is causing 20% of the 1 million malaria deaths each year.

Let’s Review with a ProblemFood chain:

Bamboo (100 K) – needs sunlightbaby panda (2,500 K) – needs 500 Ksnow leopard (6,000 K)–needs 1,500 K

How many bamboo plants, per day, does it take to support a snow leopard?

Note: snow leopards really eat goats & mountain sheep

Solution:You need 6 baby pandas per day

to feed a snow leopard6 baby pandas need 3,000 K total

from bambooThey feed on 30,000 calories of

bamboo (to get the 10% or 3,000)30,000 bamboo K = 300 plants It takes 300 bamboo plants per

day to feed a snow leopard