Predator-prey relationships
Predation is a straight-forward interspecies population interaction. One
species uses another as a food resource. Predators play an important
role in controlling prey population numbers in some systems. In simple
systems, the predator-prey relationship results in coupled population
osscilations
Classic example of predator-prey dynamics:
Canadian lynx & snowshoe hare
Coupled oscillation
• prey numbers increase, predator numbers increase…to a point where the
predation causes population decline in the prey item..
• Idealized predator-prey coupled dynamics.
•It is important to note that in most systems the food web- the web of
interactions among species- is far more complex than just a single
predator and single prey item. The relationships can become quite
complex and the “coupled” nature of the interaction becomes much
more vague.
In general, predator-prey
relationships are much
more complex than that
displayed by lynx-hare
oscillations.
Very often, but not
always, an increase in
prey density results in a
straight-forward increase
in predator population
size.
In this case often, but not always, an increase in
prey density results in a straight-forward increase in
predator population size.
The action of predators in the face of increasing
prey availability can take different forms.
In the top panel, as the number of prey items
(Microtus) increases, the number killed by the
predator increases in a linear fashion.
In the middle panel- as the density of rodents
increases, the percentage of the population killed
by weasels declines in a curvilinear fashion
In the bottom panel, as the number of available
prey items (sixth instar larvae) increases, the
number of those found in the gut of the predator
(bird) increases – the bird eats more- and then
levels off. There are various potential
explanations of this, one being that the bird
population is “satiated” at certain densities.
Prey are variable in value.
Don’t want to spend time &
energy on prey items that are
energetically expensive to
process (if other options are
available).
Predator-prey relationships can include:
pulse, lag, response, lag, response- timing
Predator-prey relationships
often have ramifications for
other parts of the ecosystem.
The hare-lynx relationship is
an example. Hares eat twigs,
more hares = more damage
to trees. More lynx = fewer
hares and less damage to
trees.
Now can you answer the wolf
songbird riddle?
• Predator-prey relationships are dynamic
• They are influenced by climate dynamics, changes in
food availability for the prey species, and dynamics in
other areas of the food web (to be discussed later in the
semester)
• Predator-prey relationships also are dynamic through
evolutionary time.
• Often involve an evolutionary “arms race.” Natural
selection simultaneously driving the predators toward
greater hunting efficiency and the prey toward traits that
help them avoid being eaten.
Tactics of the Predator
1) Invisibility Cloak (cryptic coloration/ camouflage)
http://www.youtube.com/watch?v=__XA6B41SQQ
Tactics of the Predator
2) Patience is a Virtue (Hide and Wait)
Tactics of the Predator
3) Death by Poisoning (Venoms)
Tactics of the Predator
4) “Right this Way Please”: trap-doors, nets, and other deadly devices.
Tactics of the Predator
5) Bigger, Badder, Faster
200 mph
700 lbs & built to kill
What immortal hand or eye
Could frame thy fearful symmetry?
William Blake
http://www.youtube.com/watch?v=DWsN63PRCW8
17,000 lbs, and perhaps as smart as you
Tactics of the Predator
Combinations- Invisibility Cloak; Patience; Bigger, Badder, Faster
Dr. Laurie Marker:
Dropped out of school at 20, tried
to start a vineyard- discovered
that wildlife conservation was her
life passion, became world
renown expert.
www.cheetah.org
Responses of the Prey
1) Invisibility Cloak (cryptic coloration/ camouflage)
Responses of the Prey
2) FLEE!!!!
Responses of the Prey
3) Eat me and die (poisons and aposematic coloration):
Responses of the Prey
4) “Shields up”: (armor):
Responses of the Prey
5) “Who wants fetid flesh for dinner? Surely not a proud
hunter like yourself” (play dead):
Responses of the Prey
6) Mimicry:
Batesian mimicry- looks like a toxic model- but is non-toxic
Mullerian mimicry- looks like a toxic model- AND is toxic
Responses of the Prey
6) Disguise:
Responses of the Prey
6) Strength in Numbers:
Herbivory, a special case of predation…
Not really- herbivory involves the taking of plant
material by an animal herbivore- is almost always
non-fatal, and can sometimes be an advantage
for the plant- or at least stimulate growth and
promote community diversity...
Herbivory generally becomes a problem when the
ecological system is out of balance.
E.g., invasive insects (gypsy moth)- or the loss of
predators (white-tailed deer)
Herbivore-plant relationships also can evolve into an “arms race”
Plants evolve armor (thorns, spines, prickles), toxicity, implant cells with silica,
and sometimes symbiotic relationships to defend foliage.
Plants evolve thorns, animals evolve morphology and behavioral techniques to
avoid thorns. Plants get taller, change canopy structure, animals get taller.
Plants trick animals into doing their bidding:
Plants want some parts eaten (fruits) for seed dispersal, only after the seed has
matured (thus ripening), and plants do not want foliage eaten…
The expense of herbivore defense is only worth it if the foliage is very valuable.
Plants that live it harsh conditions, can’t afford to rebuild foliage, so develop defenses.
Plants that grow in lush conditions, simply outgrow herbivores.
Predator-prey relationships