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Week 8 study questions
Terms in this set (14)
Describe in words what alpha and beta in the Lokta-Volterra competition equations mean.
Alpha: effect of species 2 on 1
Beta: effect of species 1 on 2
What components of the Lotka Volterra (L-V) competition equations represent intra- v. inter- specific competition? Which parameters govern the strength of interspecific competition?
Alpha and Beta. If Alpha and Beta are less than one, they will have less effect on species 1 and 2. When equal, the effects are the same.
We talked about asymmetric competition in class: some species are competitive "winners" and some species are competitive "losers." Give a set of alpha & beta values in the L-V competition equations that show asymmetric competition, as well as a set of alpha and beta values that show symmetric competition.
One species is harmed more than the other. One is going to drive one to extinction.
Describe the four outcomes of L-V competitive dynamics using a phase-plane diagram. Explain what inequalities have to be true to get each of the four outcomes.
-non intersecting isocline lines:
-species 2 at the top = species two dominating over species one, leading species one to extinction
-species 1 at the top = species one dominating over species two, leading species two to extinction
-with two arrows pointing away, species 1 and 2 cannot coexist, one will win and one will lose
-all arrows facing in, species 1 and 2 can coexist
Name two ways in which predation imposes different evolutionary & ecological constraints on predators/ prey than herbivory does on herbivores/ plants.
Herbivores feed on things but do not kill them. It is easy for an herbivore to find food, but harder to digest because plants have different nutritional makeup. Food quality for herbivores is much more important. Plants are sessile prey- they do not move.
What limits a predator's ability to reduce prey numbers at high prey densities?
The predator can get too full.
Describe two reasons why a predator might exert very weak effects on prey populations at low density. Why is this important for sustaining the predator population?
Prey switching: switch up what they eat depending on availability of prey. Learning how to hunt the prey takes time as well.
1. population growth: numerical response
2. Behavioral response
Give three examples of the putative costs of being vigilant. How might a prey species avoid or minimize these costs?
Fear hormones make them stressed, have to eat in subprime habitat areas where they CAN be vigilant (e.g., impala example in class), must spend time being vigilant rather than eating. To minimize: can look for refuges or whoever is on watch can rotate.
Prey use defense and vigilance, as well as refuges, to minimize predation. How do these tactics minimize predation risk, and how might predators respond to these different tactics?
Predators can become sneaky to get prey who are vigilant, and search for prey who are refuges.
Explain three reasons that otters exert strong control over kelp populations.
They engage in prey-switching: otter pop'ns remain high even when sea urchin populations are low
Otters have a high metabolic rate b/c they don't have blubber to keep them warm
They prefer sea urchins and will consume them when available
Sea urchins hide when they smell other sea urchins getting eaten & reduce feeding of kelp
Give an example of a trophic cascade not discussed in the book or in class.
Effective predation: Lizards- ate spiders and had strong effect on prey
Also, killer whales & sea otters
Wolf eating elk, elk eating aspen trees, the beaver not having habitat.
Describe the difference between top-down v. bottom up control using the lynx-showshoe hare example discussed in your book (or another ecosystem of your own choosing). How would you design an experiment to test these different hypotheses of ecosystem control?
The lynx eats the hare which eats the grass. Hare populations decrease as their vegetation supply decreases being bottom up control. Lynx kills more Hares when they are at peak population causing top-down control.
Describe what each of the components of the L-V predator prey equations represent.
PREY: dV/dt= rv(birth) -p(habitat)Vp)(death due to predation)
PREDATOR: dP/dt= cpVp(birth)-dpp(death rate of predator)
Use the L-V predator prey isoclines, drawn on a phase plane diagram, to describe why cyclic dynamics are common in predator prey interactions.
Not enough prey, decline in predator. Not enough predators, increase in prey. Vice-versa.
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