Herbivory Notes

Herbivory Herbivory is similar to predation but usually not the whole of the plant is eaten; because of this, and in contrast to predation where a single predator eats a single prey item or partitioning between carrion eater, this leads to plant diversification. Herbivory is much more common than predation - it is much more efficient energy transfer, Energy is lost at every trophic levels. Would not be stable to have more predators than herbivores. 99% of herbivores are insects, the most numerous group of animals on earth. Insects tend to be herbivorous in general (52% of all described species). Many ways to be herbivorous and this is reflected in the plant structure. You can eat fruit, seeds, nectar, pollen, leaf eaters, root eaters, miners between cells, phloem/sap feeders like aphids. Stick stylet into plant phloem, which is a poor resource in general (sugar but not much else) and just exits the aphid. The other difference between predation and herbivory is that whereas predation is always negative (if something is preyed upon, it is dead), herbivory is not necessarily always negative and in many cases it can result in mutualistic interactions and so can be on occasion positive. Plant defences Plants are stationary so why is it they persist in the face of onslaught? Different possibilities 1. herbivores are self-regulating prudent predators and so will not exhaust their resource. Doesn't typically work. 2. Top-down regulation - predators are regulating herbivore numbers 3. Not everything green is edible - plants keep themselves protected Self -regulation Reindeer released into islands in Alaska - rapidly increased then declined. Clearly no self-regulation as if they were, would see a saturation. This hasn't happened as resource is lichen, which grows slower than reindeer. If this was in a different location then the reindeer could have moved on, but these were trapped on an island and so resources were limited - no niche partitioning. The way that regulation happens is that there is some sort of system where once resource decreases below a certain level, it not longer remains profitable to search for that resource and they search for something else. This can be seen here: On the top is grass and then three herbivores: zebra, wildebeest and gazelle. Largest tends to be at location when grass highest. When length decreases, appearance of different herbivore, so there is some sort of partitioning of the resource so many can utilise it. Also potentially facilitation between herbivores - smaller things exclude the bigger things. The zebra facilitates foraging by the wildebeest. Zebra 

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