BIOL 2060 Lecture Notes - Lecture 14: Snow Goose, Herbivore, Overgrazing
3 May 2018
School
Department
Course
Professor
Herbivory and Mutualism
February 12th, 2016
Herbivory – a special kind of exploitation
• Change landscapes
• Mobile “grazers” usually don’t kill plants
• Sessile “filter feeders” eat entire phytoplankton
• Detritivore eat dead plants and organic material
• Many plants recover or tolerate grazing
• Herbivory may stimulate plant growth
• Herbivores cannot escape and need clever adaptations
• Herbivore specialists are used for weed control
Snow Goose Grazing on sub-Arctic Salt Marsh
• Pucinellia and Carex – 95% of plant biomass
• snow geese leave 1-2 cm carpets
• 1968-1990: geese increased from 2000 – 20,000
o overgrazing of salt marsh
o exclusion experiment testing for grazing effects
• grazing reduced the standing biomass but enhanced total productivity of plants
Herbivory
• meta-analysis across 81 studies of herbivory *
• herbivores reduce and nutrients enhance plant growth and reproduction
• recovery or compensation is similar in high and low resource conditions
• only exception is monocot herbs significant interaction
Selective Grazing
• herbivores are highly selective in their feeding
• preferences caused by secondary plant substances
Plant Defenses Against Herbivores
• structural
o thorns, spines, prickles
o tough leaves and thick bark
o size
o numbers (eg. Masting)
• chemical
o quantity
▪ digestion-reducing substances acting in high concentrations (eg. Phenolic
tannins and resins up to 60% of dry weight in leaves)
o quality
▪ toxins acting in very low concentrations that kill, repel or impair
herbivores (eg. Alkaloids; <2% dry weight)
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Herbivory: meta-analysis across 81 studies of herbivory , herbivores reduce and nutrients enhance plant growth and reproduction recovery or compensation is similar in high and low resource conditions, only exception is monocot herbs significant interaction. Selective grazing: herbivores are highly selective in their feeding, preferences caused by secondary plant substances. *both defenses can be: constitutive produced continuously induced only produced or increased when damaged. Production of secondary plant products *see diagram in slide terpenoids eg. peppermint oil and catnip: acetogenins eg. juglone (walnut tree, phenylpropanes eg. cinnamon and cloves, alkaloids eg. nicotine, morphine and caffeine. Herbivores also have adaptations: evolving enzymes to detoxify plant chemicals, altering timing of life cycle to avoid toxic plants. Tannins in oak trees: common oak (quercus robur) is dominant in western europe, attacked by larvae of >200 species of lepidoptera, from spring to summer, leaves get tougher (& shorter, amount of tannins increase, amount of protein decreases.
