copyright © 2009 pearson education, inc. community structure and dynamics

Copyright © 2009 Pearson Education, Inc.

COMMUNITY STRUCTURE AND DYNAMICS


◦Biological community– An assemblage of populations living close

enough together for potential interaction– Described by its species composition

◦Boundaries of the community vary with research questions

– What kind of communities exist at Miramar College?


◦Interspecific interactions– Relationships with other species in the

community– Can have positive (+) or negative (-) effects on

each species


1. Interspecific competition (usually -/-)– Two different species compete for the same

limited resource– Squirrels and black bears

Bear and Squirrel by ~magooey on deviantART


◦ Competition occurs when ecological niche of species overlap

– Ecological niche: Sum of an organism’s use of biotic and abiotic resources


2. Mutualism: both populations benefit (+/+)

◦ Example: Reef-building corals– Photosynthetic dinoflagellates and heterotrophic

cnidarian


3. Predation: benefits the predator but kills prey (+/-)

However, can lead to evolutionary adaptation


4. Herbivory is not usually fatal and leads to adaptation in plants (+/-)

– Plants must expend energy to replace the loss

Plants have numerous defenses against herbivores

– Spines and thorns– Chemical toxins


5. A parasite lives on or in a host from which it obtains nourishment (+/-)

– Internal parasites include nematodes and tapeworms

– External parasites include aphids and mosquitos


Pathogens are disease-causing parasites (+/-)– Pathogens can be bacteria, viruses, fungi, or

protists


Non-native pathogens can have rapid and dramatic impacts

Non-native pathogens can cause a decline of the ecosystem

Example: Snakehead fish


Trophic structure– A pattern of feeding relationships consisting of

several different levels

Food chain– Sequence of food transfer up the trophic levels


Producers– Support all other trophic levels– Examples??


Producers– Support all other trophic levels– Examples:

– Phytoplankton and plants

Consumers– Heterotrophs

– Primary consumers– Secondary consumers– Tertiary consumers– Quaternary consumers


Producers– Support all other trophic levels

Consumers– Heterotrophs

– Primary consumers– Secondary consumers– Tertiary consumers– Quaternary consumers

Detritivores and decomposers– Derive energy from dead matter and wastes

Plant

A terrestrial food chain

Producers Phytoplankton

An aquatic food chain

Plant




Primaryconsumers

Grasshopper Zooplankton

Plant




Primaryconsumers


Secondaryconsumers

Mouse Herring

Plant




Primaryconsumers


Secondaryconsumers

Mouse Herring

Snake TunaTertiaryconsumers

Plant




Primaryconsumers


Secondaryconsumers

Mouse Herring

Snake TunaTertiaryconsumers

Hawk Killer whale

Quaternaryconsumers

Trophic level


Food web– A network of

interconnecting food chains

Example:Mercury poisoning

Producers(plants)

Primaryconsumers

Secondaryandprimaryconsumers

Tertiaryandsecondaryconsumers

Quaternary,tertiary,and secondaryconsumers


Species diversity defined by two components1. Species richness2. Relative abundance

A

B


Keystone species– A species whose

impact on its community is larger than its biomass or abundance indicates

– Occupies a niche that holds the rest of its community in place

Keystone

Keystoneabsent


Disturbances

– Events that damage biological communities

– Storms, fire, floods, droughts, overgrazing, or human activity

– The types, frequency, and severity of disturbances vary from community to community


Invasive species: non-native species spreading beyond their point of introduction and causing environmental or economic damage

Example: Snakehead fish

Invasive species can devastate Invasive species can devastate communitiescommunities


Communities change drastically following a severe disturbance

Ecological succession– Colonization by a variety of species– A success of change gradually replaces other

species


Primary succession– Begins in a virtually lifeless area with no soil

Secondary succession– When a disturbance destroyed an existing

community but left the soil intact

Time

ShrubsAnnualplants

Perennialplants and

grasses

Softwood treessuch as pines

Hardwoodtrees


Introduction of rabbits in Australia

KeyFrontier of rabbit spreadOrigin: 1860

600 Km

Australia

1910 1980

1910

1910

191

0

1910 1920 1920

192

0 1920

1890

189

0 1880

1880

1870

1870

190

0

1900


ECOSYSTEM STRUCTURE AND DYNAMICS


Ecosystem– All the organisms in a community as well as the

abiotic environment

Components of ecosystems– Energy flow

– Passage of energy through the ecosystem

– Chemical cycling– Transfer of materials within the ecosystem


A terrarium has the components of an ecosystem

Energyflow

Lightenergy

Chemical energy

Chemicalelements

Heatenergy

Bacteriaand fungi

Chemical cycling


Primary production– The amount of solar energy converted to chemical

energy

– Carried out by ________________

– Produces biomass– Amount of living organic material in an ecosystem


Primary production of different ecosystems

Open ocean

Estuary

Algal beds and coral reefs

Desert and semidesert scrub

Tundra

Temperate grassland

Cultivated land

Boreal forest (taiga)

Savanna

Temperate deciduous forest

Tropical rain forest

0 500Average net primary productivity (g/m2/yr)

1,000 1,500 2,5002,000


A pyramid of production– Illustrates the cumulative loss of energy transfer in

a food chain

1,000,000 kcal of sunlight

10 kcal

100 kcal

1,000 kcal

10,000 kcalProducers

Primaryconsumers

Secondaryconsumers

Tertiaryconsumers

Producers

Primaryconsumers

Secondaryconsumers

Humanmeat-eaters

Cattle

CornCorn

Humanvegetarians

Trophic level


Biogeochemical cycles

– Cycle chemicals between organisms (biotic) and the Earth (abiotic)

Decomposers play a central role in biogeochemical cycles

Consumers

Geologic processes

Producers

Decomposers

Nutrientsavailableto producers

Abioticreservoir

4

1

23


Biotic: Carbon is basis of organic molecules

Abiotic: Carbon is found ___________

The return of CO2 to the atmosphere by respiration closely balances its removal by photosynthesis

Photosynthesis

Decomposers(soil microbes)

Cellular respiration

Detritus4

1

2

35

Plants, algae,cyanobacteria

Primaryconsumers

Higher-levelconsumers

Burning

CO2 in atmosphere

Plant litter;death

Wastes; death

Dec

om

po

siti

onWood

and fossilfuels


Biotic: organisms require phosphorus for ___________.

Abiotic: No atmospheric component; abiotic resevoir found in rocks, soil

Animals

1Plants

Detritus

Decomposersin soil

Decomposition

Phosphatesin rock

Weatheringof rock

Runoff

Assimilation

Phosphatesin solution

Phosphatesin soil

(inorganic)

Precipitated(solid) phosphatesRock

Upliftingof rock

6

3

2

4

5


Biotic: Nitrogen is essential for ________.

Abiotic: Nitrogen found in air and soil

Nitrogen fixation converts N2 to nitrogen used by plants

– Carried out by some bacteria and cyanobacteria

Rhizobium in symbiosis

AzotobacterKlebsiella

some Clostridium

Leguminous root nodules TEM of rhizobia in root nodule cell

Nitrogen Nitrogen fixationfixation

Nitrogen (N2) in atmosphere

8 Plant Animal

Assimilationby plants

Organiccompounds

Organiccompounds

Death; wastes

Denitrifiers

Nitratesin soil(NO3

–)

Detritus

Decomposers

DecompositionNitrifyingbacteria

Ammonium (NH4+)

in soil

Nitrogen fixation

Nitrogenfixation

Nitrogen-fixingbacteria in

root nodules

Free-livingnitrogen-fixingbacteria and

cyanobacteria

6

1

2

74

3

5


Chemical cycling in an ecosystem depends on– The web of feeding– Relationships between plants, animals, and

detritivores– Geologic processes

Altering an environment can cause severe losses in chemical cycling

– Erosion– Acid rain

Decomposers

Producer

Energy flow

Chemical cycling

Herbivore(primary

consumer)

Carnivore(secondaryconsumer)

copyright © 2009 pearson education, inc. community structure and dynamics

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