Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Energy transfer through food webs / Predator control of herbivory (trophic cascade)
Predator control of herbivory (trophic cascade)
How predators change plant biomass indirectly by reducing herbivore numbers or altering herbivore feeding behavior.
Boundary: where this process starts
Starts with: Spiders reduce grasshopper density
Boundary: where it ends
Ends after: Less herbivory leaves more plant biomass
Line thickness = size of impact (1 to 5)% on a line = chance a fork takes that branch📄 = pieces of evidence on a stepNegative effectLoops backHypothesisResource used up (arrow into the step)Resource used, not used upResource made or released (arrow out of the step)
What am I looking at? The concepts on every map
- Participant
- Someone or something that takes part in a process or influences it: a plant, a microbe, a river, a machine, a force. Participants are the rows of a map.
- Resource
- Something a step uses or uses up: water, oxygen, sunlight, a tool. Each step has an arrow down to the resources it uses.
- Step
- One thing that happens in a process. Every step has at least one participant and carries evidence.
- Decision fork
- A step where the process can go several ways. Every outcome is labeled with a percentage, and the percentages add up to 100%. It is not limited to yes or no.
- Loop
- A line that carries the process back to an earlier step. We record whether it reinforces or balances, how strong it is (weak, moderate, strong), and its gain (0 to 1): the share of the effect that returns on each pass.
- Size of impact
- Every line says how much the earlier step affects the next one (1 to 5), in which direction (+, -, 0), and why. Thicker lines mean bigger impact.
- Evidence
- The support for a claim: a source and what it shows. Every step, line, change and vote needs it. Click any step or line to read its evidence.
- Boundary
- Where a process starts and where it ends. Every process, and every subprocess, has a start and an end.
- Subprocess
- A step that is itself a whole process, with its own boundary, steps and lines. Click a step marked ↘ to open it. Subprocesses nest as deep as the evidence goes.
- Description
- A plain-language summary of what a process is and what it covers.
- Hypothesis
- A proposed new connection between two parts of the map that nobody has linked. It carries a prediction, a way to test it, and a count of papers on each topic and on both. It is an unverified idea until someone tests it.
Every step, with its evidence
The same information as the map, as a list you can search and share. Click a participant or resource to see everywhere it appears.
Spiders reduce grasshopper density
Evidence (1) · added by Verity
- Beckerman 1997, Experimental evidence for a behavior-mediated trophic cascade in a terrestrial food chain, PNAS, doi:10.1073/pnas.94.20.10735: Predators of herbivorous animals can affect plant populations by altering herbivore density. (confidence 0.8)
Risk of predation alters grasshopper feeding behavior
Evidence (1) · added by Verity
- Beckerman 1997, Experimental evidence for a behavior-mediated trophic cascade in a terrestrial food chain, PNAS, doi:10.1073/pnas.94.20.10735: Risk spiders with glued mouthparts could not kill prey, isolating behavioral effects from density effects. (confidence 0.8)
Less herbivory leaves more plant biomass
Evidence (1) · added by Verity
- Beckerman 1997, Experimental evidence for a behavior-mediated trophic cascade in a terrestrial food chain, PNAS, doi:10.1073/pnas.94.20.10735: The experiment tested the indirect effect of predators on plants through herbivores. (confidence 0.7)
Aquatic prey subsidies redirect spiders and change herbivory
Evidence (1) · added by Verity
- Graf 2017, Contrasting effects of aquatic subsidies on a terrestrial trophic cascade, Biology Letters, doi:10.1098/rsbl.2017.0129: Aquatic insect subsidies can enhance predator abundance or cause prey switching, increasing or decreasing herbivory depending on herbivore type. (confidence 0.75)