Download III. Species Interactions

APES CHAPTER 8 NOTES
Community Ecology: Structure, Species Interactions, Succession and Stability
Case Study: Flying Foxes Keystone Species
a) Durian is a prized fruit growing in Southeast Asian tropical forest.
b) Strong odor- not allowed to transport publically.
c) Pollination of the tree depends on the bats called Flying Foxes. (mutualism)
d) Flying Fox is endangered- habit destruction- deforestation hunting- meat sold in
China.
e) Keystone Species- (important to the ecosystem because)
1.) Plant species they pollinate.
2.) Plant seeds they dispose in the droppings.
3.) Many other species depend on them.
f) Economically important because:
1.) Durian fruit
2.) Medicine
3.) Timber- fuel
4.) Fibers
5.) Dyes
g) Study illustrates:
1.) Vague Role (niche) of each species in a community
2.) How interactions between species can affect ecosystem structure and
function.
I.
II.
Role of Species in an Ecosystem- Niche
a) Community Structure: Ecologists usually describe the structure of a community of
ecosystem in terms of four characteristics.
1.) Physical appearance- size and distribution of population.
2.) Species Diversity- number of different species.
3.) Species Abundance- number of each individual species.
4.) Niche structure- species interactions.
b) Where is most of the worlds Biodiversity Found
1.) Tropical Rain Forest
2.) Coral Reefs
3.) Deep Sea
4.) Large tropical lakes
General types of Species:
1.) Native Species- Indigenous species- species that normally like and thrive
in an ecosystem.
a. Raccoon, sea oats
2.) Non-native species- Exotics, aliens- species that have been introduced
into an ecosystem by humans- some are beneficial most are not because
there is no natural control.
a. Ex. Water Hyacinths, Fire ants, Asian clams, zebra mussel’s
melaluca, cudzoo and African Bees.
Brazil
1957- imported African bees- increased honey production.
African bees have displaced regular honey- bees and lowered honey
production.
- Moved northward to Central America into US Texas,
Arizona.
3.) Indicator Species- species that serve as early warnings that a community
or ecosystem is being damaged.
a. ex. Songbirds, benthic invertebrates, trout, amphibians.
4.) Keystone Species- a species that is much more important to ecosystem
than the biomass would suggest.
a. Bats, dung beetles, sea otters, gopher tortoise, elephants, rhinos,
beavers, flying fox- fruits.
III. Species Interactions
a) Interspecific Competition:
1.) Competition among species- when they compete for food, space, or any
other unlimited resource.
2.) As long as resources are plenty- not much competition.
3.) When fundamental niches overlap one species will succeed the other
species will need to move or will die out.
b. Interference competition- one species limits another’s access to
some resource. – Territories- humming bird defends a patch of
flowers.
c. Exploitation competition- both species have access to resources, but
differ in how fast or efficiently they use the resource- humans.
d. Competitive Exclusion- once species eliminates the other due to use
of limited resources.
Ex. Fire ant- reduced 90% of native ant species.
4.) Ways to reduce competition.
a. Resource partitioning
Use resources at different times, different ways or in different places.
Negative feedback loops allow them to share the wealth.
Ex. Hawks/ Owls. Warblers- different areas of tree.
b. Character displacement
Use physical or behavioral characteristics to use different resources.
On evolutionary time scale. Ex. Birds on Darwin’s islands.
b) Predation
1.) One species feeds directly on all or part of another organism.
2.) Predator- prey relationships- positive feedback relationship for
predator- until low number of prey cause negative feedback loop.
3.) Sometimes helps the prey population by killing the sick, weak or aged
members.
4.) Predatory- not always the bad guy- cultural impact.
5.) Tactics of Predator.
a. Speed
b. Armor
c.
d.
e.
f.
g.
h.
i.
j.
Great senses
Thorns
Camouflage
Defensive chemical warfare
Warning coloration
Mimicry
Bluff
Schools, flocks, herds.
IV. Symbiosis
1.) Living together- long lasting relationship
2.) Kinds of symbiosis
a. Parasitism- one species gets nourishment from another species.
- Parasite is smaller, long time relationship, rarely kills host,
make host weaker over a long period of time.
- Two types of parasites.
1. Endoparasite- live inside ex. Tapeworm.
2. Exoparasite- live outside ex. Mosquito.
b. Mutualism- interaction where both species benefit
win- win
Ex. Lichens algae. Fungi. Pollen/ Bees. Rhizobiums- a bacteria in the
root nodules of legumes that trap Nitrogen in THE SOIL. Termites/
Protozoan. Ants/ acacia trees. Mychorrizae
- Increases when resources get scarce.
C. Commensalisms- interaction where one is benefited and the other is
unaffected.
Epiphytes- orchids.
V. Ecosystem Structure and Ecological Succession
a. Communities are in a constant state of change due to changes in vegetation in
response to changes in climate.
1.) The slow process of change is called Ecological succession.
2.) Changes form an unstable (serial community to a stable balanced
community called a Climax community. (Mature community)
3.) Succession not always predictable.
4.) Some communities never reach climax because of reoccurring disasters or
due to limiting factors.
5.) Two types of succession
a.
Primary Succession
- Starts from lifeless area- glacier, volcano
- Must build a soil first
- Soil building is started by pioneer species (lichens, mosses)
- Continued by early successional plant species – nature’s
sprinters- ground cover, reproduce fast survive harshness.
- Missuccessional plants- (100’s years) grasses/ shrubs
- Late successional plants- trees
- Rate- faster in humid tropical areas slowest in dry polar
- Also occurs in aquatic ecosystems.
b. Secondary Succession
- Begins in an area where the natural vegetation has been
disturbed.
- Ex. Farmlands, burned forest, polluted streams, floods
- Each stage brings its own species diversity, trophic
structure, niches, nutrient cycling, energy flow and
efficiency.
- Pattern of succession in SW USA is Grasses, shrubs, pines,
oaks, magnolias.
5.) 3 Factors that affect how and at what rate succession occurs
1. Facilitation- one species makes it possible for another species.
2. Inhibition- one species makes it impossible of difficult for
another species. Through competition (interference and
exploitation).
3.Tolerance- successional stages occur at the same time esp. in late
successional stages. Ex. A Birch tree growing among other trees
in a Forest.
6.) Disturbance guides succession- caused naturally and by humans
Unfavorable changes
a. Not all changes unfavorable- fire maintained ecosystems.
b. Intermediate disturbance hypothesis
- Communities that experience fairly frequent moderate
disturbances have the greatest diversity. Allows species of
both early stages in openings and late stages.
VI. Biodiversity and Ecosystem Stability
a) Stability- ability of living system to withstand externally imposed changes.
1.) Three aspects of stability.
a. Inertia/ Persistence- ability to resist disturbance
- Found in rain forest
b. Constancy- maintains a certain size, keep within limits.
c. Resilience- ability to bounce back
- Found in grasslands (fire adapted)
2.) Signs of a stressed ecosystem
a. Drop in primary production
b. Increased nutrient loss
c. Decline of indicator species
d. Larger pop of pest or disease organisms
e. Decline in species diversity
f. Contaminants
3.) Precautionary Principal: When evidence indicates that an activity can harm
human health or the environment. We should take measures to prevent harm.
“Better safe then sorry.”
4.) Map page 186-187