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BIOC50H3 Study Guide - Exponential Growth


Department
Biological Sciences
Course Code
BIOC50H3
Professor
Marc Cadotte

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Chapter 12
Case study: snowhoe hare cycles
Hudson bay hare population cycle (fluctuations)
Lynx are the predators. Hare are major part of their diet
oTherefore, lynx population is driven by hare population
Hare population fluctuated in synchrony across Canada
oProved by birth, death, dispersal rates, reproductive, survival rates
WHY. Hypothesis:
1.Food supplies lower when hare population is high: not the best answer
though
2.Predation: 95% of death are by predators
oBut still three unanswered questions
1.Why hare birth rates drop during the decline phase of the cycle
2.Why hare numbers sometimes rebound slowly after predator numbers
plummet
3.Why the physical condition of hares worsens as hares decrease in
numbers
Introduction
Exploitation: relationship one organism benefits by feeding on and harming another
Herbivore: eats tissues or internal fluids of living plants
Predator: kills and eats other organisms (prey)
Parasite: lives in/on an organism (host)
Parasitism: insects lay eggs in another insect. After hatching they eat the host
In natural world, every single species do not fall under only one category, there are
exceptions
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Predation and herbivory
Most predators have broad diets, whereas a majority of herbivores have relatively narrow
diets
Some predators move in search of prey, others sit-and-wait
Many predators have broad diets
oResearchers provided guppies with 2 kinds of prey: fruit flies and tubificids
Guppies switched from one prey to another according to availability
Many herbivores specialize on particular part of the plant
oLeaves: most commonly eaten part (most nutritious)
oEating seeds may affect reproductivity of plant
Most herbivores have narrow diet
Adaptations
Organisms have evolved a wide range of adaptations that help them capture food and avoid
being eaten
Predators and herbivores exert strong selection on their food organisms
oHerbivore evolved defences due to selection pressure by predator
oEscaping predators: physical defences, toxins, mimicry, and behavioural
responses.
Warning (aposmatic) colouration: bright colour
Crypsis: camouflage
Example of crabs and snails: trade off between 2 different defences in
snails
oReducing herbivory: avoidance, tolerance, and defences
Masting; produce many seeds some years and less or non in other years
Compensation: removal of plant tissues stimulate production of new
tissues
Secondary compounds: sometimes toxic induced defences
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