COMMUNITY ECOLOGY:

STRUCTURE, SPECIES

INTERACTIONS, SUCCESSION,

AND SUSTAINABILITY

The Walker School

Environmental Science

Community Ecology Issues

What factors are most significant in structuring a

community?

What factors are the most significant in determining

its species composition?

What happens to a community when a species is

lost?

What happens to a community when a species is

introduced by humans?

Individualistic Hypothesis

Chance assemblage of different species in a particular area because of similar abioticrequirements

Emphasizes studying single species as the essential units for the interrelationships and distributions of organisms

Predicts that communities should lack discrete geographic boundaries

Indonesian reefs have the greatest species richness

with over 1650 known species.

Interactive Hypothesis

Closely linked species, locked into association by mandatory biotic interactions

Views communities as superorganism.

Predicts that species should be clustered into discrete communities with noticeable boundaries

Presence or absence is governed by other species in group

Pando (or The Trembling Giant) is a clonal colony

of a single male Quaking Aspen (Populus

tremuloides) tree located in the U.S. state of Utah,

all determined to be part of a single living organism

by identical genetic markers and one massive

underground root system. he root system of Pando

is claimed by some to be among the oldest known

living organisms in existence at 80,000 years of age

Community Organization – Bottom-Up Model

*Changes in this community are done by adding or removing minerals

Minerals control community

organization

Nutrients control plant types and number, act as limiting factors

Plants control herbivores, which

in turn control predators

Trophic Cascade Model (top down model)

Plants uptake minerals and make them available to consumers, also recycle them.

Herbivores regulate undergrowth and

other plants

Predators control herbivores, apex

predators

WHAT IS A COMMUNITY?

Typical Community

What abiotic and biotic

components are involved in

this community?

Community Variables

Physical Appearance

Types of Species

Number of Species

Ecological Niches

mft

10

50

20

30

100

Tropicalrain forest

Coniferousforest

Deciduousforest

Thornforest

Tall-grassprairie

Short-grassprairie

Desertscrub

Thornscrub

Plant Species

Stratification

•Relative Size of Populations

•Stratification of Populations

•Distribution of Populations

•Communities are patchy

•Communities do not have defined boundaries

•Increased edges make species more vulnerable to stresses

Types of Species

Species Richness (number of different species)

Species Evenness (population size)

Niche Structure (number of niches)

Niches

Fundamental

Niche

Determined by

abiotic factors

Realized Niche

Determined by

species

competition

WHERE IS MOST OF THE

WORLD’S BIODIVERSITY FOUND?

Rich Environments Have Low Species Evenness

Tropical Rain Forests

Coral Reefs

The Deep Sea

Large Tropical Lakes

Richness Variables

Latitude

Pollution

Habitat Diversity

Net Primary Productivity (NPP)

Habitat Disturbance

Time

Changes in Species Diversity by Latitude

Sp

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Sp

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1,000

100

10

Latitude

80ºN 60 40 20 0

200

100

0

90ºN 60 30 0 30ºS 60

Latitude

What do these graphs say about an organisms “range of tolerance”?

WHAT DIFFERENT ROLES DO

VARIOUS SPECIES PLAY IN

ECOSYSTEMS?

Species Classification

Native (indigenous)

Nonnative (invasive)

Indicator

Keystone

Foundation

Pioneer

Animals Native to Georgiahttp://georgiawildlife.dnr.state.ga.us/

WHAT ARE INVASIVE

SPECIES?

US Invasive Specieshttp://www.invasive.org/

U.S. Invasive Species

African Bees

Cane Toads

Zebra Mussels

Sea Lamprey

European Starling

Bull Frog

Flat Head Catfish

Ragweed

Japanese Maple

Kudzu

Invasive Species in Georgiahttp://www.gainvasives.org/

WHAT DETERMINES THE NUMBER

OF SPECIES ON ISLANDS?

Factors that Influence Island Communities

Degree of isolation (distance to nearest neighbor, and mainland)

Length of isolation (time)

Size of island (larger area usually facilitates greater diversity)

Climate (tropical versus arctic, humid versus arid, etc.)

Location relative to ocean currents (influences nutrient, fish, bird, and seed flow patterns)

Initial plant and animal composition if previously attached to a larger land mass (e.g., marsupials, primates, etc.)

The species composition of earliest arrivals (if always isolated)

Serendipity (the impacts of chance arrivals)

Human activity

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1 10 100 1,000 10,000 100,000

Area (square miles)

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HOW ARE NATIONAL

PARKS LIKE ISLANDS?

Map of US National Parkshttp://www.nps.gov

How are national

parks like islands;

how are they

different?

Yellowstone National Park Example

What role does geology play

in biological isolation?

Parks Dilemma

Reserves and national parks form islands inside

human-altered landscapes (habitat fragmentation).

Reserves could lose species as they 'relaxed

towards equilibrium' (that is they would lose species

as they achieved their new equilibrium number,

known as ecosystem decay).

This is particularly true when conserving larger

species which tend to have larger ranges.

National Parks by Area

Allopatric vs. Sympatric Speciation

Allopatric Speciation is where new gene pools arise

out of natural selection in isolated gene pools

(multiregional hypothesis)

Sympatric Speciation, the idea of different species

arising from one ancestral species in the same area.

(single-origin hypothesis)

Interbreeding between the two differently adapted

species would prevent speciation.

WHAT ARE INDICATOR

SPECIES?

Indicator Species of the World

Trout need clean water with high dissolved oxygen

Birds and butterflies are susceptible to habitat fragmentation and chemical pesticides

Plants can be genetically engineered to detect high level of soil nitrates used in explosives

Frogs are an indicator species which eat insect eggs that have no protection from UV radiation or pollution

WHY ARE AMPHIBIANS

VANISHING?

Gray Treefrog –

Hyla versicolor

Commonly found in the NE United States. Reports about the decline of frogs and toads in pristine environments such as nature reserves and parksgreatly concerns ecologists who look at amphibians as an indicator species, warning of environmental stress.

Warnings from Frogs

Habitat Loss and Fragmentation

Pollution

Increases in UV Radiation

Over Hunting

Parasitism

Disease

Non-native Predators

Ecological Role of Frogs

Indicators that environmental quality is deteriorating

They consume more insects than birds

Represent a storehouse of pharmaceutical products

Pharmaceutical Uses

Painkillers

Antibiotics

WHAT ARE KEYSTONE

SPECIES?

Role of a Keystone Species

Crucial in determining the nature and structure of an ecosystem.

Usually affect the available amount of food, water, or some other resource.

Usually not the most abundant species in an ecosystem.

Are the chief concern of conservation biologists.

Test for a keystone species through “removal experiments”.

Loss of keystone species cause tropic cascades.

Example of Keystone Species

Bees

Humming Birds

Bats

Great White Sharks

Leopard

Sea Otters

Lion

Alligator Frogs

Dung Beetle

Sea Stars

Activity: Movie

Watch the National

Geographic movie “The

Wolves of Yellowstone”

Write an essay

explaining the role of

wolves in the northern

coniferous forests.

WHAT ARE FOUNDATION

SPECIES?

Foundation Species Examples

Elephants push over grass or uproot trees

Mussels provide homes to invertebrate species that

do not do well in the presence of mussel

competitors, such as the sea star

Foundation Species create

and enhance habitats for

other organisms.

HOW DO SPECIES

INTERACT?

Types of Interactions

Between members of the same species

(intraspecific)

Between different species (interspecific)

High

Low

Rela

tive p

op

ula

tio

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y

0 2 4 6 8 10 12 14 16 18

Days

Both species grown together

Paramecium

aurelia

Paramecium

caudatum

Interspecific Competition

Predation ( + - )

Parasitism ( - - )

Mutualism ( + + )

Commensalism ( + 0 )

Resource Partitioning of Warblers in Spruce

Trees

Character Displacement

HOW HAVE SOME SPECIES

REDUCED OR AVOIDED

COMPETITION?

Organisms share resources to not compete.

Organisms specialize in a niche not to compete.

HOW DO PREDATOR AND

PREY SPECIES INTERACT?

Benefits of Predation

Weeds out sick, weak, and aged

Gives remaining prey better access to food supplies

Prevents excessive population growth, which can result in crashes

Helps successive genetic traits to become more dominant (directional natural selection)

Can enhance the reproductive success and long-term survival of the prey species (adaptive evolution)

Types of Predation

Herbivores (grass)

Fructivores (fruits)

Insectivores (insects)

Carnivores (meat)

Modes of Predation

Pursuit

Ambush

Pursuit Types

•Run

•Swim

•Fly

•Dive

Avoidance

Smell

Shells

Spines

Thorns

Camouflage (cryptic coloration)

Alarm Calls

Size Limitation (too big to eat)

Batesian Mimicry

A palatable or

harmless species

mimics an unpalatable

or harmful species

Chemical Warfare

Poisonous

Irritating

Foul Smelling

Bad Tasting

Common Herbivore Poisons

Cocaine

Caffeine

Cyanide

Opium

Strychnine

Peyote

Nicotine

Rotenone

Common Herbivore Repellants

Pepper

Mustard

Nutmeg

Oregano

Cinnamon

Mint

Deceptive Looks & Behavior

Puffing Up

Spreading Wings

Spreading Hoods

Mimicking a Predator

WHAT ARE PARASITES, AND

WHY ARE THEY

IMPORTANT?

Parasitism

Ectoparasitism (external parasites)

Endoparasitism (internal parasites)

Parasitoidism (laying eggs in host)

Role of Parasites

•Glue Communities Together

•Promote Biodiversity

Common Ectoparasites

Ticks

Fleas

Mosquitoes

Mistletoe Plants

Athlete’s Foot

American Dog Tick Laying Eggs

Dog and Cat Flea

Mosquitoes

Mistletoe Plants

Athlete’s Foot

Common Endoparasitic Organisms

Bacteria

Viruses

Protists

Fungi

Prions

Worms

Worm Parasites

Tapeworm

Hookworm

Pinworm

Roundworm

Schistosoma

Tapeworm

Hookworm

Ringworm

Common Water Parasites

Giardia lamblia

Cryptosporidium parvum

HOW DO SPECIES

INTERACT SO THAT BOTH

SPECIES BENEFIT?

Types of Mutualism

Pollination Mutualism

Nutritional Mutualism

Inhabitant Mutualism

Oxpeckers and black rhinoceros Clown fish and sea anemone

Mycorrhizae fungi on juniper seedlings in normal soil

Lack of mycorrhizae fungi on juniper seedlings in sterilized soil

Mutualism Extras

Sometimes require the coevolution of adaptations in

both participating species

Changes in one species are likely to affect the

survival and reproduction of the other

Many mutualistic relationships may have evolved

from predator-prey or host-parasite interactions.

HOW DO SPECIES

INTERACT SO THAT ONE

BENEFITS BUT THE OTHER IS

NOT HARMED?

Commensalistic Organisms

Redwood Sorrel

Orchids

Bromeliads

HOW DO ECOSYSTEMS

RESPOND TO CHANGE?

Types of Succession

Primary

Secondary

Types of Primary Succession

•Glaciers

•Volcanic Eruptions

•Asteroid Impacts

•Mountain Top Removal

Types of Secondary Succession

•Fires

•Hurricanes

•Earthquakes

Fireweed and glacial moraine in Alaska

Pioneer Species

Lichens

Mosses

Weeds

Grasses

Characteristics of Pioneer Species

Short-lived and reproduce frequently

Number can great.

Can withstand the lack of moisture

Can withstand extreme temperatures

Involved in soil formation

Secrete acids that break down rocks

Stabilizing nutrient cycle

Time

Small herbsand shrubs

Heath mat

Jack pine,black spruce,

and aspen

Balsam fir,paper birch, and

white spruceclimax community

Exposed

rocks

Lichens

and mosses

Characteristics of Early Successional Plant Species

Grow close to the ground

Do not require established nutrient cycles

Can established large populations quickly

Have short lives

Ecosystem Structure During Early Succesional

Stage

Plant Size

Species Diversity

Trophic Structure

Ecological Niches

Community

Organization

Small

Low

Mostly producers, few

decomposers

Few, mostly

generalized

Low

HOW DO SPECIES REPLACE

ONE ANOTHER IN

ECOLOGICAL

SUCCESSION?

Midsuccessional

Species

Elk

Moose

Deer

Ruffled grouse

Snowshoe hare

Bluebird

Late Successional

Species

Turkey

Martin

Hammond’s

flycatcher

Gray squirrel

Wilderness

Species

Grizzly bear

Wolf

Caribou

Bighorn sheep

California condor

Great horned owl

Early Successional

Species

Rabbit

Quail

Ringneck pheasant

Dove

Bobolink

Pocket gopher

Ecological succession

© 2004 Brooks/Cole – Thomson Learning

Succession of Organisms

Rate of Succession Variables

Facilitation

Inhibition

Tolerance

HOW DO DISTURBANCES

AFFECT SUCCESSION AND

SPECIES DIVERSITY?

Disturbances

Fire

Drought

Flooding

Mining

Clear-Cutting a Forest

Plowing a Grassland

Applying Pesticides

Climate Change

Invasion of Exotic Species

Yellowstone Park Forest Fire 1988.

Intermediate Disturbance Hypothesis

Dynamic Equilibrium

Promotes Heterogeneity

Promotes Evolution

Fallen trees, costal redwoods

1000

Percentage disturbance

Sp

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ity

How Disturbances Affect Species

Biodiversity

Things are Always Changing

Succession is not a linear progression

No Climax Communities

No True Homeostasis

Dynamic Equilibrium

Aspects of Stability

Persistence

Constancy

Resilience

Mature Communities

High occurrence of vegetation patches

Contain large plants

High species diversity

Well-established, efficient nutrient cycles

Many, specialized niches

High biomass

Low NPP

Low Immigration / Emigration Rate

Complex food webs dominated by decomposers

Efficient use of energy

WHY SHOULD WE

BROTHER TO PROTECT

NATURAL SYSTEMS?

Precautionary Principle

Monitor cause and effect relationships

Complete risk analysis studies before beginning

Take acceptable risks to learn

Complete independent reviews of our actions

Research Helps Us to Evaluate Environmental Issues

Agricultural Landscapes

National Parks

Reservoirs

Marine Fisheries

Grizzly

bear

NORTH

AMERICA

Spotted

owl

Black-footedferret

Kemp’sridleyturtle

Californiacondor

Goldentoad

Columbia haslost one-third ofits forest

Black liontamarin

SOUTH

AMERICA

More than 60% of thePacific Northwestcoastal forest hasbeen cut down

40% of North America’srange and croplandhas lost productivity

Hawaiianmonk seal

Half of the forestin Honduras andNicaragua hasdisappeared

Mangrovesclearedin Equador for shrimp ponds

SouthernChile’s rainforest isthreatened

Little of Brazil’sAtlantic forestremains

Every year 14,000square kilometers ofrain forest is destroyedin the Amazon Basin

Coral reef destruction

Much of Everglades National Park has dried outand lost 90% of its wading birds

ATLANTIC

OCEAN

PACIFIC

OCEAN

Manatee

Chesapeake Bay is overfished and polluted

Fish catch in the north-west Atlantic has fallen42% since its peak in 1973

Humpbackwhale

St. Lawrencebeluga whaleEastern

cougar

Floridapanther

Environmental degradation

Vanishing biodiversity

Endangered species

6.0 or more childrenper woman

EUROPE

Mediterranean

Liberia

AFRICA

Imperial eagle

640,000 square kilometerssouth of the Sahara haveturned to desert since 1940

Mali

BurkinaFaso

SierraLeone

Togo

Sao Tome

68% of theCongo’srain forestis slatedfor cleaning

Fish catches inSoutheast Atlantichave dropped by morethan 50% since 1973

Blackrhinoceros

Zambia

Angola

CongoRwandaBurundi

UgandaSomalia

Nigeria

Chad

NigerBenin Golden

tamarin

Ethiopia

Eritrea

Madagascar haslost 66% of itstropical forest

Aye-aye

YemenOman

SaudiArabia

Poland is one ofthe world’s mostpolluted countries

Many parts offormer Soviet Unionare polluted withindustrial and radio-active waste

Area ofAral Sea hasShrunk 46%

Central Asia from theMiddle East to Chinahas lost 72% of rangeand cropland

ASIA

Asianelephant

India andSri Lankahave almostno rainforest left

In peninsular Malaysiaalmost all forests havebeen cut

INDIAN OCEAN

Indonesia’scoral reefs arethreatenedandmangroveforestshave beencut in half

Giantpanda

Kouprey

Queen Alexandra’sBirdwing butterfly

Nail-tailedwallaby

AUSTALIA

Much ofAustralia’srange andcroplandhave turnedto desert

90% of the coral reefsare threatened in thePhilippines. All virginforest will be goneby 2010

Deforestation in the Himalayacauses flooding in Bangladesh

Japanese timber importsare responsible for muchof the world’s tropicaldeforestation

Blue whale

ANTARCTICA

A thinning of the ozone layer occursover Antarctica during summer

Snow leopard