Week 9 - Biological interactions Flashcards
What are Ecosystems ?
- A self-contained unit
- Biological community + abiotic environment
- Trophic levels and energy flows
(Primary Producers to Top Predators) - Biogeochemical cycles
(Nutrients e.g. nitrogen, phosphorus)
What is commensalism?
1 species benefits and the other is unaffected
What are symbionts?
Cannot survive in the short or long term without the other species
What do competitive interactions generally need?
Spatial and temporal co-occurrence
Increases in intensity as the:
- density,
- phylogenetic similarity, and
- niche overlap
of competing species increases
What is interference competitive ?
When individuals directly interact with each other to compete for resources, often by fighting, chasing, blocking access, or some kind of aggressive behaviour.
What is exploitation competition ?
Indirect e.g. use of resources depletes the amount available to others
What is apparent competition?
Occurs indirectly between two species which are both preyed upon by the same predator.
What is a contest competition outcome ?
Individuals compete for resource but one outcompetes the other and monopolises the resource – but the outcome is unequal asymmetrical
What is a scramble competition outcome?
When everyone competes for the same resource at the same time, but no one actively fights — instead, the resource gets used up quickly, and everyone may suffer
What is the competitive exclusion principle?
If two species have similar needs, competition happens.
If too similar, one species can outcompete the other — this is called the competitive exclusion principle.
What is bottom up control ?
The amount of resource at the bottom of the food chain is determining population size
What is top down control?
Where predation influences prey numbers this is referred to as top down control
What is a food web ?
A representation of feeding relationships in a community that includes all the links revealed by dietary analysis
What is meant by predator mediated co-existence?
The co-existence of many species is reliant on a predator eating the most dominant of the inferiors e.g. mussels
What happens to seaweed if otters decrease?
Urchins increase so seaweed decreases
What is a keystone species?
Change in one key species leads to cascading effects across whole community e.g. beavers
What does connectance measure?
A measure of complexity
What is the equation for connectance?
Actual number of interactions / Possible number of interspecific interactions
How to actually calculate connectedness?
Actual links / possible links (top x bottom )
What are the 3 explanations for why food chains are so short (only 3/4 trophic levels)?
- Energy flow hypothesis
- Dynamic fragility
- Constraints on predator design and behaviour
What is the energy flow hypothesis?
A max of 30% of energy consumed at one trophic level is available as food to the next
What is dynamic fragility ?
Longer chains are prone to severe fluctuations in population size
What is meant by constraints on predator design and behaviour ?
Not really anything that can kill the top predators, so how can it get any longer?
What are alien plants?
Alien plants (also called non-native, exotic, or introduced plants) are plants that have been brought by humans, intentionally or accidentally, to areas where they do not naturally occur.
