Lecture 13 + 14 Flashcards
Species richness
The total number of species in a community
An island is newly formed by a volcanic eruption. You want to follow what happens with plant communities on the island. What type of succession is this?
Primary succession
Anthropologists have long wondered what happened to the inhabitants of Easter Island. It is clear that part of the island was land used for farming. What likely occurred after the island was depopulated?
Secondary succession
What term describes structured analyses that use large numbers of data sets to discern consistent trends?
A meta-analysis
Any species that has a low abundance but exerts strong effects upon the community through multiple trophic levels would be considered what?
A keystone species
What do you call a series of similar communities that are in different stages of succession all in order?
Chronosequence
If all trophic levels are being controlled by the abundance of resources available to plants it would be called _____________.
Bottom up control
Some marine mussel communities do not change even after strong storms. They might be considered ______________?
Resistant
Two major ways ecologists think about food webs:
- relation to community structure
- energy flow
Trophic level
Position in food web as determined by number of energy transfer steps
Carnivores (2º consumers)
Omnivores
Herbivores (1º consumers)
Primary producers
Food Web Complexity Varies among Communities
In part because of how ecologists study and represent communities
- not all species and not all species interactions are equally important
Strong interactors
Species that play a major role in determining community structure and function
- the loss or introduction of a strong interactor results in significant community changes
Foundation species
A strongly interacting species that comprises a large amount of the biomass in a community
ex. Douglas fir in PNW old growth forests, blue mussels in PNW rocky intertidal zone
Keystone species
A species whose impact on the community is large and disproportionately great relative to its biomass
ex. pisaster starfish in rocky intertidal zone of PNW US coast
Removing the keystone species (starfish)
Results in a loss of biodiversity
ex. following the removal of Pisaster, number of species fell. Pisaster promotes species diversity by preventing competitive exclusion by Mytilus (the blue mussel, a dominant species). Limiting resource is space.
Beavers –another keystone species
Due to habitat modification rather than grazing/exploitation
- few wetlands when beavers were almost extinct
Consider the interaction between phytoplankton and zooplankton. Would you expect:
A) the control by phytoplankton on zooplankton is most important (ie, more phytoplankton production leads to more zooplankton, because zooplankton are food limited).
B) the control by zooplankton on phytoplankton is most important (ie, more zooplankton leads to less phytoplankton, due to grazing).
C) the interaction is weak, with phytoplankton controlled mostly by light and nutrients, and zooplankton controlled by fish predators.
D) the control by zooplankton on phytoplankton is strong only when primary productivity is low.
E) the interaction is strong, but sometimes zooplankton control phytoplankton while other times phytoplankton abundance regulates zooplankton.
The interaction is strong, but sometimes zooplankton control phytoplankton while other times phytoplankton abundance regulates zooplankton
Bottom up effect in food webs
Zooplankton biomass increases with increasing algal biomass (measured as chlorophyll) suggesting bottom-up control
Primary producers -> primary consumers (herbivores) -> secondary consumers
Trophic cascade
Chains of interactions extending among multiple trophic levels through top-down effects
Indirect effects
Effects that are transmitted via the food web to species beyond those with which the exploiter immediately interacts
ex. increase in zooplanktivores, decrease in zooplankton, increase in algae
ex. decrease in zooplanktivores, increase in zooplankton, decrease in algae
Arrows flip
Why were some ponds more green than others? Note that all ponds have the same inputs of nutrients (fertilizer).
Minnows were present in ponds that were more green. Increase in minnows, decrease in zooplankton, increase in algae -> more green
What might happen if we add a fourth trophic level (large predatory fish eating the smaller fish)?
More large fish, less minnows, more zooplankton, less algae
-> arrows flip
-> tertiary consumers, top down effect to secondary consumers, primary consumers, then finally primary producers
Dramatic top-down effects of cod fishing off Nova Scotia
- cod fishing increased leading to a crash in the stock
- cod food increased in abundance
- zooplankton declined in abundance
- phytoplankton increased
Whistling thorn-tree savannah
With native ants, elephants didn’t eat the trees. The invasive ants replaced the native ants and trees were being eaten.
Low visibility, better for lion activity and zebra kill occurrence, worse for zebra density
High visibility scenario, worse for lion, worse for zebra kill occurrence, better for zebra density