Biology 2483A Study Guide - Final Guide: Prey Switching, Optimal Foraging Theory, Body Armor

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15 Dec 2017
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You would have thought that covering up pitchers would be a problem  didn’t make a
difference so why do they compete for nutrients???
Take away their neighbours (reduce competition) open pitchers is a huge advantage
oIn the experiments on pitcher plants, the results suggested little competition for soil nutrients between
them and non-carnivorous neighbors.
oCompetition for light was more important. When shaded by neighbors, pitcher height increased at the
expense of pitcher volume.
oPitcher plants compete with neighbors for light but avoid competition for soil nutrients by eating animal
prey.
oIn low light they grow little and require few nutrients, thus prey deprivation has little effect.
oIn high light, they grow more and require nutrients, thus prey deprivation matters.
oHabitat is prone to fire  tolerates it well uses changes in light levels as growth cue
Grows mostly when other competitors are reduced from fire  allows to escape competition for
nutrients by reducing demand for scarce nutrients when competition is more intense i.e. in
years without fires.
Basically it increases nutrient demand when there’s a fire because other plants aren’t as
good
Chapter 13: Predation and Herbivory
Over half the species on Earth get energy by feeding on other organisms, in a variety of types of interactions
oAll are exploitation: a relationship in which one organism benefits by feeding on, and directly harming,
another
Categories
Herbivore: eats tissues of living plants or algae
Predator: kills and eats other organisms, referred to as prey
Parasite: lives in or on another organism (its host), feeding on parts of it. Usually doesn’t kill the host. Some
parasites called pathogens cause disease
*Not all organisms fit neatly into these categories i.e. some predators e.g. wolves also eat berries, nuts & leaves
Parasitoids: insects that lay an egg on or in another insect host. After hatching, larvae remain in the host, which
they eat and often kill
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Predators and Herbivores
Predators and herbivores both tend to feed on multiple individuals of prey or food plants in their lifetimes
Herbivores don’t usually kill the food organisms as predators do
Predators
Some predators forage throughout their habitat in search of food.
Others are sit-and-wait predators, remaining in one place and attacking prey that move within striking distance.
oThese include sessile animals, such as barnacles, and carnivorous plants
Predators tend to concentrate effort in areas that yield abundant prey
oE.g. wolf packs follow seasonal migrations of elk herds
Sit-and-wait predators relocate from areas of scarce prey to areas where prey are abundant
oE.g. spiders
Most predators eat a broad range of prey species, but specialist predators show a preference
oE.g. lynx eat more hares than expected based on abundance of hare
Some predators concentrate on whatever prey is most abundant
oE.g. when researchers provided guppies with two kinds of prey, they ate disproportionate amounts of
whichever prey was most abundant
Straight line shows how they would have acted based on availability
Curved line shows that they switched to the more abundant prey
oThese predators may form search image of most common prey type and orient toward that prey
oOr learning enables them to become increasingly efficient at capturing the most common prey
oIn some cases, prey switching is consistent with optimal foraging theory
Herbivores
Herbivores eat different parts of the plant
oLarge herbivores may eat all aboveground parts, but most specialize on particular plant parts
oLeaves are most commonly eaten, because they are often the most nutritious part, except for seeds
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Shows relative nitrogen content  animal bodies>seeds>leaves>sap
Herbivores can reduce the growth, survival, or reproduction of plants
Herbivores that eat seeds can impact reproductive success of those plants
Some herbivores feed on plant fluids by sucking sap etc.
Belowground herbivores can also have an impact
Most herbivores feed on a narrow range of plants. Most insect herbivores feed on only one or a few plant
species
Shows distribution of how many plant species these flies feed on  most feed on less than 5
Other herbivores feed on a wide range of species e.g. grasshoppers
Large browsers such as deer often switch from one tree or shrub species to another
Adaptations to Exploitative Interactions
Organisms have evolved a wide range of adaptations that help them obtain food and avoid being eaten
History
Life changed radically with the appearance of macroscopic predators about 530 million years ago
Within a few million years, prey had evolved defenses to being eaten
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