1 Sporadic: very high herbivore abundance Herbivores can cause - - PDF document

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Bioe 147/247 Herbivory: A Special Case of Predation Or Why is the World Green? (and when isn’t it?)

• 1. What herbivores do to plants.

Often ASSUMED herbivory is not important because: Herbivore damage looks low

• 1. What herbivores do to plants.

Often NOT observed because: Herbivores might kill a plant Plant parts die and drop off: Some herbivore damage isn’t seen: some insects such plant juices: Most conspicuous damage: Leaf chewers Gall formers Or bore through wood

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Herbivores can cause heavy plant damage in some terrestrial systems Grasslands Sometimes damage is extensive: California oak moths on campus: Defoliate plants Pupal cases Sporadic: very high herbivore abundance In many marine systems: Intertidal Subtidal (near shore) Oceanic

Why do we suspect that even low herbivory can affect plants and communities?

Types of Evidence:

• 1. The oak spraying experiment (Crawley)  already done in lecture
• 2. Biological control of invasive plants: compare
• before and after control
• home and away

Cactus (Opuntia) invaded woodlands and pastures in Australia in 1800s. Chemical control (arsenic pentoxide) worked a bit.

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Ecologists went to Opuntia’s native range (South America) to understand its ecology. They found  herbivory by moths Cactoblastis In Australia: Cactoblastis reared; Eggs distributed to Opuntia habitats. ….which was very effective and rapid. Today – small, remnant populations of Opuntia and Cactoblastis In South America, Opuntia  not very abundant;  not much herbivore damage. In many introduced locations:  no native herbivores use this plant. So differences – may be due to impacts of herbivores. Plants in native ranges may be relatively rare  in part because of herbivores

Back to lecture notes

• 2. What plants do to herbivores:

Mechanical defenses Chemical defenses

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Behavior /Physiology ……… + …….. Ecology

Herbivores can fight back: a) Detoxify compounds b) & sometimes use them for their own defense The moral of plant/herbivore interactions:  Evolution