Food webs Flashcards
Define a food web
A representation of feeding relationships in a community that includes all of the links revealed by dietary analysis.
Give the 2 main ways a food web can be formed.
By observation
By molecular analysis of stomach content
Are there consistencies between completely disparate communities ?
Yes
Pisaster and Sea otters are examples of what ?
Keystone species
How do Pisaster engineer their ecosystems ?
Pisaster preys on starfish
This creates a habitat for competitively inferior species
Mussels are competitively dominant, exclude all organisms
Pisaster mediates co-existence
What happened when Pisaster was removed from its ecosystem for an experiment ?
Diversity dropped from an average of 15 to 8 species.
Destabilisations at the highest trophic level induce….
Structural changes in the ecosystem
When the removal of one species occurs, does the whole ecosystem usually collapse ?
No, very rare that this happens. Will only occur in non-robust ecosystems.
What affect did the fur trade on the otter ecosystem ?
Otters were removed in large numbers
Consume sea urchins which were no longer controlled
Allowed to feed unchecked causing damage to ecosystem
What entices ants to participate in seed dispersal ?
The seed has a fatty deposit, encouraging the ant to remove the seed away from the parent plant
Give an example of a robust ecosystem.
Common seed dispersal ant, (65%) was removed
Self healing network, other species stepped in to fulfil role
Maintaining dispersal.
What is Connectance ?
A measure of complexity
actual no. of interaction/
Possibl no. of interactions
Give the 6 measures of an ecosystem
Robustness Quantitative connectance Vulnerability Nestedness Evenness
How would you make a web of a paristoid network ?
Choose a plot Quantify plant abundance, Sample herbivore with transect Collect all herbivores on trans. Taxonomy Analyse Data.
How many trophic levels do communities usually have ?
3 to 4
Give the 3 reasons trophic levels are limited to 3-4 per community.
Energy flow hypothesis
Dynamic fragility
Constraints on predator design and behaviour
What is the energy flow hypothesis ?
That a maximum of 30% of energy per trophic level can be transferred as food to the next level.
What is dynamic fragility ?
Food webs with long chains are much more prone to severe population fluctuations.
Extinction of the top predator is also more.
Can dynamic fragility be measured in an ecosystem ?
No, requires a computer model of the species and population dynamics
What are the constraint on predator design and behaviour ?
No organism can evolve to outcompete the current top predator in a community (become too big)
Do top predators have predators ?
Not on a trophic interaction
Do have parasites.
Give some of the uses of food webs
Monitor effect of alien species Organic farming pest control Pollination Landscape scale conservation Effectiveness of restoration
Give an example of the use of food webs in the restoration of a landscape
Removal of the Hornwort
ant pollinated alien species in Avon gorge
Food web showed they are deeply embedded in a network of pollinated species
Currently weeding them out.
