community ecology
TRANSCRIPT
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
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
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
ecie
s D
ivers
ity
Sp
ecie
s D
ivers
ity
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”?
Species Classification
Native (indigenous)
Nonnative (invasive)
Indicator
Keystone
Foundation
Pioneer
Animals Native to Georgiahttp://georgiawildlife.dnr.state.ga.us/
U.S. Invasive Species
African Bees
Cane Toads
Zebra Mussels
Sea Lamprey
European Starling
Bull Frog
Flat Head Catfish
Ragweed
Japanese Maple
Kudzu
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
100
1 10 100 1,000 10,000 100,000
Area (square miles)
Nu
mb
er
of
am
ph
ibia
n a
nd
rep
tile
sp
ecie
s
10
SABA MONTSERRAT CUBA
Hispaniola
Puerto Rico
Jamaica
Cuba
Montserrat
Saba
Redonda
© 2
00
4 B
roo
ks/C
ole
–T
ho
mso
n L
ea
rnin
g
Map of US National Parkshttp://www.nps.gov
How are national
parks like islands;
how are they
different?
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.
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.
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
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
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.
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.
Types of Interactions
Between members of the same species
(intraspecific)
Between different species (interspecific)
High
Low
Rela
tive p
op
ula
tio
n d
en
sit
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 )
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)
Avoidance
Smell
Shells
Spines
Thorns
Camouflage (cryptic coloration)
Alarm Calls
Size Limitation (too big to eat)
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
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.
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
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
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
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
Things are Always Changing
Succession is not a linear progression
No Climax Communities
No True Homeostasis
Dynamic Equilibrium
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
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