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
Why is the terrestrial world green?
- they have 3 trophic levels
- predators keep herbivores low
Succession
A gradual change in community structure (e.g., species composition) over time, initiated by a disturbance
Disturbance can be
Natural and abiotic (wind storm, fire)
Natural and biotic (insect breakout, disease epidemic)
Anthropogenic (deforestation for agriculture, oil spill)
Disturbances occur on a continuum of perturbation
Frequency and intensity
Disturbance severity and leads to secondary succession
Least and most common to medium severity and rare
- windstorm, insect breakout
- fire
- agricultural clearing (middle ground on chart)
Disturbance severity and leads to primary succession
Rare and medium severity to very rare and high severity
- mining
- glaciers and volcanoes
Primary succession on newly exposed geological substrates
At first, no soil and no existing plants or other organisms (no seeds)
ex. Hawaii: 4 million years of succession and soil development
- not surprisingly, primary succession is slow
Secondary succession following disturbance that does not destroy soil (terrestrial systems)
ex. agriculture
Absent human maintenance, cities and suburbs move through rapid secondary succession: ex. 15 years after Chernobyl nuclear meltdown, Ukraine, 1986
Why is the speed of secondary succession far faster than primary succession?
- existing soil, for supporting rooted plants
- existing soil, for holding onto water
- existing soil, for nutrients (nitrogen, phosphorus)
- seed bank in soils
- often, nearby source of potential organisms (depends on spatial scale of disturbance)
Species that dominate early in succession have different traits than those late in succession
Early in succession with shorter life spans and shorter reproductive periods: r strategists
Later in succession, longer life spans and longer reproductive periods: k strategists
Succession occurs in aquatic communities, not just terrestrial ones
ex. Exxon Valdez, Prince William Sound, Alaska, march 1989
- r strategists came back in early succession
- k strategists still gone
- recovery takes around 150 years
True or false: Dominant species tend to have more of the biomass in a community than keystone species
True. Dominant species are those that are common in the community and therefore make up a great deal of the biomass. Keystone species have a very high impact on the community even though they make up a small portion of the biomass.
The connection between food web complexity and stability is more complex than once thought. Currently we think that populations are actually _________ stable when the web is complex and the aggregate whole community might be _________ stable when the web is complex.
Less, more
Beavers build dams that create flooding that creates abundant aquatic habitat. They might be considered ______________?
Keystone species
Which of the following might be considered primary succession: (You may choose one or more answers)
- Colonization of a newly formed volcanic island.
- Regrowth after timber harvest.
- Colonization after a severe hurricane.
- Colonization of exposed land after glaciation retreat.
Colonization of a newly formed volcanic island
Colonization of exposed land after a glaciation retreat
Which of the following is the correct sequence of dominant vegetation in a community undergoing succession?
Annual weed -> herbaceous perennials -> shrubs -> early successional trees -> late successional trees
Annual weed -> herbaceous perennials -> early successional trees -> shrubs -> late successional trees
Annual weed -> shrubs -> herbaceous perennials -> early successional trees -> late successional trees
Herbaceous perennials -> annual weed shrubs -> early successional trees -> shrubs -> late successional trees
Annual weed -> herbaceous perennials -> shrubs -> early successional trees -> late successional trees
Which of the following is an example of a trophic cascade?
A mountain lion preys upon deer and as a result the abundance of a grass species dramatically increases.
A large population of European rabbits grazes on an annual weed species and dramatically reduces their population.
A marine mammal feeds on baleen and significantly reduces their abundance in the Pacific Ocean.
A plant virus reduces the number of native plants in a community.
A mountain lion preys upon a deer and as a result the abundance of a grass species dramatically increases
