Ecological Networks Flashcards
What are interaction networks
Descriptions of how species are connected by antagonistic or mutualistic interactions, e.g. food webs or pollination networks
What is Darwin’s tangled bank metaphor
A description of complex interdependent interactions among species in nature
Do species exist in isolation
No, they are embedded in networks of interactions that shape community structure
What are antagonistic interactions
Predator-prey, parasite-host, herbivore-plant, pathogen-host
all interactions where one species benefits at the expense of another
What are mutualistic interactions
Interactions where both species benefit, e.g. pollinators and flowers, seed dispersers and fruits
What are linkage networks
Networks showing which species interact with which
What are energy flow networks
Networks that show how much energy flows between species
What are functional/interaction strength networks
Networks highlighting key interactions that structure the community, often identified via experiments
What is Connectance (C)
The fraction of possible links in a web that are realised.
Formula: C = L / [S(S–1)/2] where L = number of links, S = number of species.
What happens to the total possible links if a species eats itself
Then total possible links become S²
What does ‘small world’ mean in ecological networks
On average, species are two links apart, with >85% within three links of each other
Why is the ‘small world’ property important
Changes in one species’ abundance propagate quickly
Ecosystem dynamics are highly connected
Impacts of biodiversity loss, overharvesting, or invasions may be wider than expected
Why are ecological networks useful
They help summarise complex community interactions, giving insight into species rarity, abundance, and community structure
Name 3 methods to study food webs
- Observation
- Modelling
- Experiments
Give 4 issues that affect observed food web patterns
- Taxonomic bias
- Lumping species (e.g. ‘plankton’)
- Omnivory underestimation
- Missing rare links
What consistent pattern is seen in food webs
Short food chains (typically 3–4 levels)
Why are food chains short
Productivity limits: Energy lost at each level
Instability: Random variations are amplified at higher levels
Prediction: More productive or efficient ecosystems should have longer chains
How is robustness measured
By simulating extinctions and recording secondary extinctions
What increases robustness in real food webs
Higher connectance
What happens when you remove weakly connected species
Generally, little effect on network structure
What are ‘rivet-like’ thresholds
Points where removal of certain species causes disproportionate impacts
What did May, Lawton and Pimm do
Extended LV models to test food web stability
What did May’s model predict
More species (S) = less stability
Higher connectance (C) = less stability
Complexity reduces stability
What was Elton’s opposing view to May’s model
Complexity increases stability, by buffering fluctuations through multiple links
