Ecology: Lecture 5 Flashcards
What are communities?
A set of species within an ecosystem
Function of communities?
- Species interactions
- Energy and nutrient flows
Structure of communities?
- Species richness (number of species)
- Composition (relative abundance of species)
Dynamics of communities?
- Change in structure or function over time
Species interactions (types)
- Competition ( - - )
- Mutualism ( + + )
- Commensalism ( + 0 )
- Trophic interactions ( + - )
- Predation
- Herbivory
- Parasitism
What are trophic interactions?
- Related to feeding. Transfer of energy from one species to another (prey-predator).
Ex. Predation, herbivory and parasitism
Food webs represent?
They represent simplifications of trophic interactions.
Trophic levels?
The vertical position in the food web is called the trophic level.
Food webs are made up of?
Food chains.
Food web arrows represent?
The direction of energy flow.
Ex. Squids ~> leopard seals
Collared lemmings?
They eat most plants and are eaten by most predators.
This makes them “important” for the food web.
Large impact species?
Some species play a disproportionate role in the food web.
Dominant species- Large impact?
They are a food source for many predators
- Large impact die to high biomass - many of them and high abundance
Ecosystem engineers - Large impact?
Large impact because they alter the physical environment.
Keystone species - Large impact?
- Large impact despite low biomass and abundance
- Usually predators
Are predators really important?
Sea otters
- eat sea urchins, mussels, etc.
- not “apex” predators
Atlantic cod
- eat crustaceans, herring, other small fish.
Top-down control?
High trophic level reduces abundance or biomass of lower trophic level.
affect of top-down control?
More plants without herbivores.
- More herbivores means less plants
Directions of energy flow vs. direction of impact?
IMPACT: Herbivores ~> PP
ENERGY: PP ~> Herbivores
Trophic cascade?
Impact of top predators extends to lower trophic levels.
- Effect cascades down the levels.
Trophic cascade impact - visual?
Predators impact herbivores and then the herbivores have reduced grazing.
- Fewer herbivores and MORE plants
Trophic cascade impact - ecosystem structure?
Predators are important in terms of ecosystem structure because they impact directly through predation and indirectly through trophic cascades
- extensively impact ecosystem’s look
British Colombia 1960s?
No sea otters.
Sea urchins eat kelp, causing them to be very scarce. High density of urchin barrens.
British Colombia 1970s?
Sea otters return.
Top down control.
- Sea otters lower sea urchin population which increases kelp population. Re-established kelp forests.
- A transition in the environment was brought by top-down control and trophic cascade.