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”