1. What herbivores do to plants. Bioe 147/247 Often ASSUMED herbivory is not important because: Herbivore damage looks low Herbivory: A Special Case of Predation Or Why is the World Green? (and when isn’t it?) 1. What herbivores do to plants. Some herbivore damage isn’t seen: some insects such plant juices: Often NOT observed because: Herbivores might kill a plant Plant parts die and drop off: Most conspicuous damage: Or bore through wood Leaf chewers Gall formers 1
Sporadic: very high herbivore abundance Herbivores can cause heavy plant damage in some terrestrial systems Sometimes damage is extensive: California oak moths on campus: Grasslands Defoliate plants Pupal cases In many marine systems: Intertidal Why do we suspect that even low herbivory can affect plants and communities? Types of Evidence: Subtidal 1. The oak spraying experiment (Crawley) already done in lecture (near shore) 2. Biological control of invasive plants: compare - before and after control - home and away Oceanic Cactus ( Opuntia ) invaded woodlands and pastures in Australia in 1800s. Chemical control (arsenic pentoxide) worked a bit. 2
In Australia: Ecologists went to Opuntia ’s native range (South America) to Cactoblastis reared; understand its ecology. Eggs distributed to Opuntia habitats. They found herbivory by moths 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 ….which was very effective and rapid. Today – small, remnant populations of Opuntia and Cactoblastis 2. What plants do to herbivores: Mechanical defenses Back to lecture notes Chemical defenses 3
Behavior /Physiology ……… + …….. Ecology The moral of plant/herbivore interactions: Herbivores can fight back: a) Detoxify compounds b) & sometimes use them for their own defense Evolution 4
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