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Unformatted text preview: Consumption (predation and herbivory) Today's questions: I. II. III. IV. How does predation affect prey populations? p y p p How do prey respond to predators? How do predators affect communities of species? Why is the world green? Why is the world green? I. How does predation affect prey populations? Question: Do predators reduce prey populations below the level that can be supported by available resources? level that can be supported by available resources? Predator removal experiments: Wolves, cougars, coyotes removed from the Kaibab l f h b b plateau 19071937 Start: 1920: 920 Predator addition experiments: Restoring wolves to the d dd l h Greater Yellowstone Ecosystem
Ca alves pe er 100 co ows Wolves were extirpated in the 1920s and reintroduced in 1995; i t d d i 1995 elk are the main prey. Create a hypothesis to explain these data: Prewolf Postwolf Pre wolf Post wolf What does this graph mean? Proport tion vigil lant Distance to wolves (km) Distance to wolves (km) How does this connect How does this connect to the observation in the previous graph? p g p II. How do prey respond to predators? A. Standing defenses are always present e.g. Design an experiment to test the hypothesis that stingers are an effective standing defense in honeybees. ff ti t di d f i h b B. Inducible defenses are produced in response to predation d i e.g. blue crabs (predator) and mussels (prey) Low predation in high tidalflow areas; high l fl h h predation in lowtidal flow areas flow areas
A Average shell thickness High Low predation predation These data are correlational in nature, and there are other reasonable interpretations, besides induced defenses. p , Hypothesis: Mussels increase shell thickness and attachment strength in response to evidence of predation. An experimental test: A i l III. How do predators affect communities of species? A keystone species has an extraordinarily large impact on the surrounding community, relative to its abundance. the surrounding community, relative to its abundance. e.g. Pisaster removal experiments
Spe ecies rich hness Time (years) Trophic cascades in the Greater Yellowstone Ecosystem
Hawks, owls, eagles Coyotes Wolves Rabbits Mice Elk Deer Moose Beaver Grasses, forbs Aspen Willow IV. Why is the world green? H1: The topdown hypothesis H2: The poornutrition hypothesis (Nlimitation) (on a per gram basis, plants contain 10% of N found in (on a pergram basis, plants contain <10% of N found in animals) H3: The plant defense hypothesis Example: Nicotine as an inducible defense Synthesized in roots in response to attack by herbivores S th i d i t i t tt k b h bi and transported to trichomes ("leaf hairs") Experiment: Study 3 populations of wild tobacco. For many generations, each has been exposed to different levels of herbivory (low medium or high) (low, medium, or high). 1. Grow individuals from each population in the same environment. 2. Induce nicotine production in each (same stimulus). 3. Measure: number of seeds produced. NOTE: individuals from each population show about the same response to induction (same nicotine production). i d i ( i i d i ) Data on avg. # seeds produced per plant Data on avg. # seeds produced per plant
Source population history Induced Control (not induced) Low herbivory Medium herbivory High herbivory High herbivory 4,494 6,047 5,314 7,335 4,860 4,505 4 860 4 505 ...
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This note was uploaded on 03/08/2012 for the course BIOL 180 taught by Professor Freeman during the Fall '07 term at University of Washington.
- Fall '07