BIOL 2060 Lecture Notes - Lecture 14: Caffeine, Chemical Substance, Betula Nana
25 Feb 2016
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Grazers can change entire landscapes: affects plant biomass, usually doesn"t kill the species. Sessile filter feeders: stay in one place and feed on passing organisms, particles, etc. Herbivory may stimulate plant growth: plants adapt to grazing pressures. Ex. snowgoose grazing on salt marsh: 2 plant species make up 95% of the plant biomass in the area, geese populations rising = more grazing. Set up enclosures excluding geese to analyze the effect of grazing on grass biomass. But, enhanced total productivity in grazed areas: grasses overcompensate for grazing pressures by growing more quickly in grazing areas. Hares are highly selective in what they graze upon: eats mostly dwarf birch even though willow is more abundant. Willow may have some component making it less desirable. Structural: thorns, spines, prickles, tough leaves, thick bark, size, numbers. Chemical: quantity: chemical substance in high quantity, not very effective when only in small doses.
