COMMUNITY ECOLOGY

CHAPTER 8

I. Community StructureA. FOUR CHARACTERISTICS 1. Physical Appearance

Size, Stratification, Distribution of populations/ species

2. Species Diversity or RichnessNumber of different species

3. Species AbundanceNumber of individuals of each species

4. Niche StructureNumber of ecological niches

The types, relative sizes, and stratification of plants and animals vary in different terrestrial communities and biomes.

Distribution of populations and species in a terrestrial or aquatic community can be vertical or horizontal

• -In terrestrial ecosystems physical structure is usually a mosaic of VEGETATION PATCHES with sharper edges and wider ecotones

EDGE EFFECTS – Differences in the physical structure and physical properties at boundaries and ecotones.

mft

10

50

20

30100

Tropicalrain forest

Coniferousforest

Deciduousforest

Thornforest

Tall-grassprairie

Short-grassprairie

Desertscrub

Thornscrub

Community Structure: Appearance and Species Diversity

Fig. 8.2, p. 174

II. THE EXTENT of BIODIVERSITY

BIODIVERSITY- term used to indicate the number and types of organisms on the earth/in an area.

Studies indicate that the most species rich environments are…

-Tropical rain forests- low latitude forests near the equator-Coral Reefs-Deep Sea-Large tropical Lake

*Those communities with the largest number of different species generally have only a few of each species or low species abundance

A. 3 Factors That Affect Species Diversity:

1) Latitude- Position on the latitudinal line of the earth. (terrestrial)

“Latitudinal Species Diversity Gradient”

REASONS:-resource availability-higher evolution rate-parasites keep down domination-speciation greater than extinction

Spec

ies

dive

rsity

100

0

200

90˚N 60 30 0 30˚S 60

Latitude

1,000

100

1080˚N 60 40 20 0

Latitude

ANTS BIRDS

“Latitudinal Species Diversity Gradient”

Local variations within terrestrial ecosystemsDiversity tends to increase with… - increased solar radiation

- increased precipitation

- decreased elevation

- strong seasonal variations

2) Depth- How far down in an aquatic environment (aquatic)

“Depth-species diversity gradient”REASONS:

-Increased stability-Lack of nutrients in the mid-depths-Increased nutrients at bottom

3) Pollution- poisons (aquatic)REASON: -kills or impairs species

III. General Types of Species

A. Native: - Normally live and thrive in an ecosystem

B. Non-native: - Often called exotic, alien or invasive:- Migrate or Accidentally Introduced species; tend to crowd out native species

ACCIDENTAL STOWAWAYS

C. Indicator:- Serve as an early warning that an

ecosystem is being damagedEx: Birds, Trout, Frogs

D. Keystone:- Species that have a greater importance in the structure of the community

- Play role in developing habitat and key role in food chain

*Controversial among scientists

IV. Species Interactions

A) COMPETITIONB) PREDATOR/PREYC) SYMBIOSIS

1. Intraspecific:-Competition between members of the same species -Territoriality: Patrol their area

A) COMPETITION:

2. Interspecific:-Competition between 2 or more different species -Most common-Two types include… *Interference *Exploitation

Interference Competition:One species limits

another's access to a resource

Exploitation Competition:Competing species have equal access to the resources but differ in how fast they use it

The niches of 2 species cannot overlap completely or for an extended period of time

COMPETITIVE EXCLUSION PRINCIPLE:

High

Low

Rel

ativ

e po

pula

tion

dens

ity

0 2 4 6 8 10 12 14 16 18Days

Each species grown alone Both species grown together

3. Reducing Competition

Resource PartitioningDivide scarce resources so species use them at different times and/or places to live in same ecosystem to avoid excessive competitionEx: Lions/ Leopards, Owl/Hawk

B. PREDATION: (predator/prey)

Predator

Prey

Prey acquisition

Predator Avoidance

How do Prey Defend Themselves?

Quick escapeKeen sense of

smell and sightProtective shellsSpines or thornsCamouflageChemical warfare

Warning coloration

Mimicry:Imitate a dangerous species

Behavior

C. Symbiotic Species Interactions

Symbiosis: Long lasting relationship where species live together

3 types of symbiotic relationships

1. Parasitism 2. Mutualism 3. Commensalism

1. Parasitism Species feeds on part of another

organismHost is usually harmedParasite is usually smaller than the

hostRarely kills the hostEndo/Ecto parasites Ex. Fleas,

Ticks, MosquitoesEx. Tapeworms and humans

SHOW CLIP “NEVER UNDERESTIMATE THE BODY SNATCHERS”

UNITED STREAMING: TAPEWORMS BODY SNATCHERS

2. Mutualism2 species are in a relationship that is

beneficial to both(win-win)Providing Food + Protection

Examples of Mutualism-Clownfish and sea anemones -Bacteria on roots of some plants-Bacteria in the digestive system-Protozoan's in termite guts-Birds catching a ride on rhinos-Roots and Rhizoids-Lichens (algae and bacteria)

3. CommensalismRelationship that benefits one species but neither helps nor harms the other

V. Ecological Succession:

A. SUCCESSION - Defined as a gradual change in species composition of a given area.

1. Primary Succession:-Succession that occurs where no ecosystem existed before. (bare rock, lava, etc.-Initiated by PIONEER SPECIES (moss and the like) and progresses to SUCCESSIONAL SPECIES (early, mid, and late)

Primary Succession-

Time

Small herbsand shrubs

Heath mat

Jack pine,black spruce,

and aspen

Balsam fir,paper birch, and

white spruceclimax

community

Lichens and mosses

Exposed Rock

PRIMARY SUCCESSION – ALASKA, HAWAII

2. Secondary Succession:-Succession that occurs where an ecosystem previously existed

EX: Abandoned fields, polluted streams, strip mines, burned or cut forests

Secondary Succession

TimeAnnualweeds

Perennialweeds and

grasses

ShrubsYoung pine forest

Mature oak-hickory forest

SUCCESSION ON MT. MOUNT ST. HELEN

The Stages of Succession

Succession and WildlifeEarly SuccessionalSpecies

RabbitQuailRingneck pheasantDoveBobolinkPocket gopher

MidsuccessionalSpecies

ElkMooseDeerRuffled grouseSnowshoe hareBluebird

Late SuccessionalSpecies

TurkeyMartinHammond’sFlycatcherGray squirrel

WildernessSpecies

Grizzly bearWolfCaribouBighorn sheepCalifornia condorGreat horned owl

Ecological succession

B. Factors that affect the rate of succession

Facilitation

Inhibition

Tolerance

One set of species makes an area suitable for species with different niche requirements

Early species hinder the establishment and growth of other species

Species are unaffected by members of another species from earlier stages of succession

-Disturbance – a change in environmental conditions that disrupts an ecosystem or community.

-Often categorized as CATASTROPHIC or GRADUAL (natural or human-caused.)

C. Disturbances in Succession

CatastrophicNATURAL HUMAN

CAUSEDFire Deforestation

Flood or Drought Overgrazing

Earthquake Pesticide application

Volcanic Eruption Urbanization

Hurricane/ Tornado Water Pollution

Disease Loss of Habitat

GradualNATURAL HUMAN-

CAUSEDClimate Change Groundwater

depletionEcological Succession

Exotic Species Introduction

Immigration Toxic Contamination

Disease Excessive Tourism

VI. Ecological Stability Constant dynamic change in response to changing

conditions1. Inertia or Persistence: Ability to resist being disturbed or altered2. Constancy: Ability to keep its #’s within the limits imposed by

limited resources3. Resilience: Ability to bounce back after a disturbance

Precautionary Principle

When there is evidence that an activity harms the environment we should take precautionary measures

“Better Safe than Sorry”