BIOB50H3 Chapter Notes - Chapter L#12: Exponential Growth, Blood Sugar, Nicotiana Attenuata
LECTURE 12: pg 272-286, 290-293
CHAPTER 12: PREDATION
- snowshoe hares are a major part of the lynx diet
- Food does not alone drive the hare cycle: 1. Some declining pop. Do not lack food, 2.
Experimental addition of high-quality food does not prevent hare pop. From declining
2nd hypothesis is predation: upto 95% of hares are killed by predators
INTRODUCTION
-predation: a trophic interaction in which individuals of one species (a predator)
consumes individuals of another species (prey)
- predation includes: carnivory (in which both prey and predator are carnivores),
herbivory (when predator is animal and prey is plant/alga), and parasitism (in which a
predator, a parasite, lives in symbiosis w/ its prey, a host, and consumes tissues w/o
killing it
some parasites are pathogens that cause disease in their hosts
- predation is not that simple eg. Sheep get food from plants, but they’re also been
known to eat the young of ground-nesting birds // eg. Conservely, some wolves will eat
berries like herbivores
-parasitoids: insects that typically lay one or a few eggs on/in another insect after they
hatch, the larvae remain w/ the host which the kill are unusually hard to classify b/c:
consume almost all of host and kill it, or only eat one indiv. Over the course of their
lives, kill it slowly)
CARNIVORE AND HERBIVORE DIETARY PREFERENCES (12.1)
- herbivores usually do not kill their plant prey // plant prey cannot hide, as well // plants
are less nutritious than animal prey
- Optimal foraging and dietary preference are dependent on 2 factors:
(1) encounter rate: a function of search time/how long it take to find prey
(2) Handling time: the time it takes to subdue and consume the prey if encounter
rate for prey is low, then it is predicted that predators should not be too narrow in
their prey choices thus: carnivorous predators are generalists: fairly broad diets,
while herbivorous predators are specialists (narrower diets)
Many Carnivores have broad diets
- can be said to have a preference for a particular prey species if it eats that species more
often than would be expected, based on that prey’s availability
eg. Lynx eat Hares 60-80% of the time for their diet, even though hares are only 20%
of the available food
some carnivores concentrate on foraging on whatever prey is most plentiful
oeg. Guppies gave them guppies or tubificids guppies ate disproportionate
amounts of what was most available
these type of preadtors tend to switch from one prey species to
another do this b/c: predator forms a search image of the most
common prey type and tends to orient toward that prey, or b/c
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learning enable it to become increasingly efficient at capturing the
most common prey type
Most Herbivores have relatively narrow diets
Specialization on Particular Plant Parts
- tissues of plant parts differ in their nitrogen content and nutritional value
- while some herbivores that are large relative to their food plant eat all parts of the
plant, most tend to specialize on particular parts
can be grouped according to whether they eat leaves, stems, roots, seeds, of
internal fluids
- most herbivores eat leaves // below ground herbivory can have major effects on plant
growth 40% reduce in bush lupine plants after 3months of herbivory by root-killing
ghost moth (Hepialus californicus) // those that eat seeds affect plant reproductive
success // aphids (fluid feeders) can make tree leaf growth decrease by 40%
Specialization on Plant Species
- most herbivores specialize on particular plant species (but that’s b/c there are mostly
insects) mostly insects (most only eat one or a few plants)
- lots of other herbivores that eat more than one species: eg. Deer (eats lots of above
ground shrubs)
MECHANISMS IMPORTANT TO PREDATION (12.2)
Some carnivores move in search of prey,
while others sit and wait
- many carnivores forage for prey
eg. Sharks, hawks, wolves etc. //
some stay: eg. Mambas, vipers,
eels, or wait until they enter a trap
(eg. Spider)
- most carnivores have unusual
features that allow them to capture
prey eg. Cheetah’s body allow it
to run fast, snakes can swallow
prey bigger than their head b/c the
bones of their skull are not rigidly
attached to one another allows it
to curve its teeth
- while some depend on physical structure, others rely on poison (Eg. Spiders), others use
mimicry, other camouflage, some predators have inducible traits that can increase
their ability to feed (eg. Ciliate protist bullinum can gradually adjust size to match that
of their preys)
some can detoxify/tolerate prey chemical defenses
oi.e garter snake can eat the toxic-rough skinned newt newt skin has TTX
(neurotoxin) trade off: locomoation speed and tolerance also: if swallow
one, are immobilized for 7h and are vulnerable to predation and heat stress
Escaping carnivores: Physical defenses, toxins, mimicry, and behaviour
- some physical features to avoid being killed: size, toxins, body armour, rapid movement
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poison have warning coloration (aposematic): brightly coloured that instinctually
tell predators to avoid them
mimicry: resemble less palatable organisms or physical features of the env, may
cause predators to mistake them for something else species that have colouration
that provides camouflage, this form of mimicry is called crypsis
other change behaviour eg. Hares: when preadators are abundant, forage less in
open areas
- trade-off between diff. types of defenses
eg. 4 species of marine snails are eatn
by the green crab species whose shells
are crushed the easiest are also the
quickest to take refuge when detected
suggests: trade-off between a snail’s
physical and behavioural defenses
Reciprocal plant-herbivore interactions
a) Reducing Herbivory: Avoidance,
tolerance, and defenses
Some make lots of seeds in some
years, and few in others big time
interval between bouts of seed
production = masting allows to hide
seeds from seed-eating herbivores
Some plants also make lots of leaves at times where herbivores are scarce
Other plants have adaptive
growth response that allow
them to tolerate herbivory
(up to a point)
compensation: when a
removal of plant tissues
stimulates a plant to
produce new tissues,
allowing for relatively rapid
replacement of the material
eaten by herbivores
oFull compensation:
when herbivory
causes no net loss of
plant tissue
oCompensation may occur when (eg. Removal of lead tissue decreases self-
shading resulting in increased plant growth) eg. Beech trees grew more
when clipped by increasing both lead production and photosynthetic rate
oSame with field gentians the timing of herbivory is critical: if in early
growing season, plant may compensate for the lost tissue
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Document Summary
Chapter 12: predation snowshoe hares are a major part of the lynx diet. Food does not alone drive the hare cycle: 1. Experimental addition of high-quality food does not prevent hare pop. 2nd hypothesis is predation: upto 95% of hares are killed by predators. Over the course of their lives, kill it slowly) Carnivore and herbivore dietary preferences (12. 1) herbivores usually do not kill their plant prey // plant prey cannot hide, as well // plants are less nutritious than animal prey. Optimal foraging and dietary preference are dependent on 2 factors: (1) encounter rate: a function of search time/how long it take to find prey. Many carnivores have broad diets can be said to have a preference for a particular prey species if it eats that species more often than would be expected, based on that prey"s availability. Eg. lynx eat hares 60-80% of the time for their diet, even though hares are only 20% of the available food.
