Lecture 11 Flashcards
How does community composition work?
- Natural process that some communities are species rich while others are species poor
Species richness
- How many species are present in the comunity?
Evenness
How abundant are the species
ex. How many of each animal
Species diversity
- Combines species richness (# species) and evenness (# of animals in each species).
Rank abundance
X-axis = species rank (how many in the species) (species richness)
y= relative biomass (sum measure of how many organisms)
(# of how many)
Community has low evenness when the species have very different amounts of abundance
Dominant species
- species that is present in the largest quantities of individuals or in the highest biomass
- Dominant species is
the most abundant in a
community - Large influence on community structure
- can be dominant species on each trophic level
Keystone species
- Species that has a disproportionate effect on the ecosystem
- Not most abundant or dominant but has large effect, you see this when that species is removed
ex. Star fish
- Not abundant
- prey abundant
-They graze on muscles
- Control the muscle population size
ex. beaver
- influence habitat
diversity as ecosystem
engineers
- small number of individuals outside effect
Niche at the beginging
All environmental
factors that limit a species’ distribution, growth, and reproduction
Thinking about biotic and abiotic factors…
It’s the physical space occupied by organism
Fundamental vs realized niche
*Fundamental niche: total range of conditions under which a species can establish, grow, and
reproduce
- Realized niche: actual range of conditions, influenced by competitors
Niche definition by G Evely Hutchinson
A multidimensional
space of environmental
factors that a species can tolerate (the
fundamental niche),
within which it lives (the
realized niche), and to
which it is well adapted
- Multidimensional space of environmental factors
y axis temperature
x axis moisture
Nutrient available makes it three dementional
Niche overlap
- One you account for all the environmental factors, you realize that these niches don’t actually overlap
- This is how different species can live in the same ecosytem
What is the Competitive exclusion principle?
Competitive exclusion: Species with identical niches cannot coexist
- One species would be outcompeted and disappear from the community if they had the exact same niche.
- No two species can occupy the exact same niche
ex. yeast populations
ex. Galium saxatile
dominates at acidic sites
and Galium sylvestre
dominates at basic sites
- Competitively exclude each other on either side of the eco tone.
What is Competitive release?
- A species can spread out, and occupy a broader niche when a
competitor is eliminated
ex. If meadow
voles are removed from
an area, mountain voles
experience competitive
release, and expand to
their wetter habitats.
Fundamental vs realized niche
Realized niche is the range after restriction by competitors
ex. fundamental
niche of two cattail
species extends to dry
land; realized niche
restricted by competitor
- competitive exclusion principle
ex. ant birds, each in a specific niche (each has one area of ant swarm)
Do wood warblers defy
the competitive
exclusion principle?
- No fighting
- Separate realized niches (same resource but different areas of tree)
- each species was adapted to particular parts of the tree
- Resource partitioning
allows warblers to
coexist.
What is facilitation? Give me examples.
Facilitation: one organism’s present enhances the opportunity for other organisms to exist there
- Typically mutualism
Ex. Hemlock uses fallen logs to grow in moss-rich forests
-It’s growth is facilitated by the organism that came before it
Ex. flowers that time their flowering so they all flower at the same time so they can attract more pollinators
Ex. Nitrogen-fixing species promotes growth of other species
Intermediate disturbance hypothesis
- Species richness is the
highest at intermediate
levels of disturbance. - At high levels of
disturbance, many
species fail to establish (disturbance too frequent) - At low levels of
disturbance,
competitively superior
species suppress others
ex. algal community in the intertidal zone
- when rocks are small, each wave makes them completely flip (completely scraped)
- medium rocks move a bit (most plants on rocks that experience intermediate levels of disturbance)
- giant rocks never move
ex. plant species diversity in plots that
experience different degrees of browsing by
rabbits in a sand-dune community, most species richness at intermediate level of disturbance
Top-down vs bottom-up
Top-down hypothesis
(consumer control):
abundance of a
species is limited by
consumers
ex. decrease of carnivores= increase in herbivores
- Bottom-up hypothesis
(resource control):
consumer abundance
determined by food
limitation
ex. more acorns= more rodents
Don’t just look at one, we should combine both!!
Trophic cascade
Serial changes in
species abundances and
distributions at lower trophic levels, occurring in response to
changes at a
higher level
