Transcript Community Properties - University of Oklahoma

Community Properties
Definitions
• What is the definition – quick review…
• An area where plants, animals and
microbes interact with each other
Examples
• Within a grassland biome, you have
grassland ecosystems, river ecosystems, etc.
• Within a grassland ecosystem, you can have
a short grass community, a tall grass
community, a riparian (area next to stream)
forest community
Community Structure
• If we look at a grassland community, we can look
at what organisms fill the producer role
– Big Bluestem, Little Bluestem, Switchgrass,
Indiangrass, Dropseed, Lovegrass
• What organisms fill the herbivore or primary
consumer role
– Bison, grasshoppers, mice, voles, prairie dogs
• What organisms are carnivores
– Coyotes, snakes, hawks, skunks, racoons, etc.
Communities and Food Webs
• Food webs show the
interconnection
between the organisms
in a community
• See that in “real
world” there is no
such thing as a food
chain
More Community Structure
• Food webs deal only with one type of
interaction between organisms – predation
• Other interactions are also important
–
–
–
–
Competition
Symbiosis
Commensalism
Parasitic
Definition of Interactions
Interaction Type Organism 1
Organism 2
Competition
negative
negative
Symbiosis
positive
positive
Commensalism
positive
neutral
Parasitic
positive
negative
Predation
positive
negative
Community change over time -- succession
• If you have a community that is disturbed
by some agent (e.g. fire, plowing, landslide,
flooding), the community structure in that
community is altered. Gradually the
community will rebuild itself, tending
towards a more stable structure that can be
supported by the environment in that
particular climate – The Climatic Climax
Forest Succession
Pioneer
Comm.
Climax
Comm.
Secondary Succession
• Succession that occurs following a
disturbance is called Secondary Succession
Community change over time -- succession
• Organisms also invade spaces that did not
previously support life, e.g. bare rocks, sand
dunes, volcanic flows.
• This is known as
Primary
Succession
Comparison of Primary and Secondary
Succession
Primary
• Pioneer organisms are
lichens and mosses
• Takes very long to
reach climatic climax
community stage
because soil must be
created through
physical and biotic
interactions
Secondary
• Pioneer organisms are
typically small, weedy
plants
• Time it takes to reach
climatic climax stage
variable, dependant on
climate (short in
tropics, long in arctic)
Details on Succession
• Intervening communities found in
succession after pioneer and before climax
community are known as “seres”.
• Types of communities that area grows
through during succession are important,
will work on during group exercise
• Succession is driven by competition
between organisms in each sere.
Community Structure Details
• Each sere has a different structure than the
one preceeding it.
• Pioneer sere tends to be made of small
plants with little control over their own
“microenvironment”.
• How do ecologists quantify community
structure?
Dominance
• Dominance – how prevalent a species is,
how many individuals there are.
• The most dominant species are usually the
ones whose name is given to the
community, e.g. redwood forest
• The redwood forest has lots of species in it
besides redwoods, but redwoods are the
dominant tree.
Diversity
• Diversity = how many different kinds of
species are present.
• Usually find highest diversity in tropical,
moist areas and lowest diversity in arctic or
dry areas.
Diversity & Stability
• There is a huge controversy in ecology right
now about whether or not diversity
increases ecosystem stability.
Diversity & Stability
• Stability in an ecosystem is defined as
– Resistance: The ability to resist change
– Resilience: The ability to recover from change
Diversity & Stability
• If you look at two extremes, a corn field and
a tallgrass prairie, which is most diverse?
• Which would be the most stable if a virus
attacked the dominant plant species?
Diversity & Stability
• We see that stability
does not increase with
the addition of more
and more species, but
rather there is a point
above which – more
species make a system
less stable.
S
t
a
b
il
it
y
Species number
Species distribution
Random
Uniform
Clumped
Odum’s laws about succession
Ecosystem/Com
munity property
Control over
abiotic environ.
Species
diversity
Productivity
Pioneer
Climax
Low
High
Low
High
High
Low
Production
Low
High
Leakiness of
High
Nutrient Cycles
Low
Group Exercise Assignment 1
• Succession can take over 100 years to reestablish a climax community. You are a
young assistant professor wanting to get
tenure at a major University. You have 6
years to publish several interesting and
important papers to accomplish this. How
could you possibly figure out what the
successional seres are for a grassland in
Central Oklahoma in time to get tenure?
Group Exercise Assignment 2
• You are interested in determining what
types of interactions are going on among
several coral reef fish species. It’s too
expensive for you to go to the Bahamas all
the time, so how would you determine what
interactions they have in aquariums here in
Central Oklahoma? (remember you need to
keep enough alive to do multiple
experiments).
The steps in a good experiment
• Observe the system
• Make a hypothesis on how it works
• Design a method that will determine
whether or not that hypothesis is false
• Implement your methods & collect data
• Analyze data
• Conclusions
• Share your information with others