Lecture 11

Question 1

How does community composition work?

Answer 1

• Natural process that some communities are species rich while others are species poor

Question 2

Species richness

Answer 2

• How many species are present in the comunity?

Question 3

Evenness

Answer 3

How abundant are the species
ex. How many of each animal

Question 4

Species diversity

Answer 4

• Combines species richness (# species) and evenness (# of animals in each species).

Question 5

Rank abundance

Answer 5

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

Question 6

Dominant species

Answer 6

• 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

Question 7

Keystone species

Answer 7

• 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

Question 8

Niche at the beginging

Answer 8

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

Question 9

Fundamental vs realized niche

Answer 9

*Fundamental niche: total range of conditions under which a species can establish, grow, and
reproduce

• Realized niche: actual range of conditions, influenced by competitors

Question 10

Niche definition by G Evely Hutchinson

Answer 10

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

Question 12

Niche overlap

Answer 12

• 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

Question 13

What is the Competitive exclusion principle?

Answer 13

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.

Question 14

What is Competitive release?

Answer 14

• 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.

Question 15

Fundamental vs realized niche

Answer 15

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)

Question 16

Do wood warblers defy
the competitive
exclusion principle?

Answer 16

• 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.

Question 17

What is facilitation? Give me examples.

Answer 17

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

Question 18

Intermediate disturbance hypothesis

Answer 18

• 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

Question 19

Top-down vs bottom-up

Answer 19

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!!

Question 20

Trophic cascade

Answer 20

Serial changes in
species abundances and
distributions at lower trophic levels, occurring in response to
changes at a
higher level