2. A little bit about myself
• Hi my name is Sean Edgar.
• Today I hope will be useful
for both you and me.
• Don’t be afraid to ask me
about something you’re
unsure of.
• You’ll have the
opportunity to ask me
questions at the end of the
presentation.
• Enjoy the ride! (she sai-
3. Predators
• A predator is an animal or organism that hunts
and kills other organisms for food in an act
called predation.
• A predator may consume all or part of another
organism through a process known as “eating.”
• Definition is very broad.
• Encompasses three main groups of organism;
• Classic or “true” predators : most commonly
thought of predators including, sharks,
cheetahs, bears etc.
• These predators kill their prey soon after
catching it, normally consuming it all.
• Grazers: can be considered a predator by the
same definition but consume only part of a prey
organism.
• Parasitic species’: live on or inside a prey
organism or “host.” They may be deemed
predators as they too will obtain an energy
supply by consuming part of a prey organism,
albeit a microscopic level of consumption.
5. The importance of predators
• Although predators may sometimes be tarred
with the “bad guys” reputation, they in fact play
an important role in regulating prey
populations.
• Predator-prey interactions are cyclical. ie
repeated increase and decrease.
• Reason?
• The prey in this case, rabbits, initially rapidly
increase in numbers due to a plentiful supply of
energy from the previous trophic level to
support their growth.
• As their numbers increase the predator, the
foxes numbers’ also increase, with more rabbits
available as food.
• This causes a subsequent decrease in the rabbit
population, which too effects a decrease in the
number of foxes allowing the pattern to repeat.
• Thus, both predator and prey are linked.
6. The importance of predators: revisited
• Not only do predators curb prey populations from
spiralling out of control, but they have also been
shown to maintain species biodiversity.
• Let me give you an example:
In the 1960s an experiment was done by Robert
Paine in a community of invertebrates inhabiting
areas within the intertidal zone in the northwest
of the pacific ocean. (The intertidal zone is the
region of seashore between the water mark at
high and low tides.) The top predator in this
community is a starfish which feeds on mussels,
barnacles and other invertebrates. When the
starfish were removed, a species of barnacle and
mussel began to outcompete the other species
and eventually came to occupy almost all available
space. The species diversity decreased from 15 to
8. By keeping the numbers of the more successful
competitors in check, the starfish maintained a
diversity of species. When they were removed,
the biodiversity of species declined.
7. A closer look at prey organisms
• While I have talked about predator organisms, it
is also important to consider types of prey.
• As a predator is an animal that hunts and catches
its food, prey are the organisms to which the
former definition refers to being caught.
• Examples may include small mammals such as
rabbits, mice etc.
• Over time, predators and prey alike have evolved
in ways to make them more successful at
catching and avoiding being caught respectively.
• For predators these adaptations may be; claws,
fangs, stingers or poisons.
• However it is far better to be the hunter rather
than the hunted, and so the adaptations of
preyed animals have to be more sophisticated if
they are to survive.
Figure 1.85792: “Hey there.”
8. Camouflage etc
• Camouflage is a passive defence mechanism used
by some preyed organisms.
• It allows the prey to merge into its background,
making it difficult for predators to spot them,
especially if they have poor eyesight.
• When camouflaged the animal only needs to stay
still until they have avoided detection and the
danger has passed.
• Another mechanism of camouflage is shape
where the organism will change shape to blend in
with the shapes of its surrounding environment.
Can you spot the stonefish?!!
9. Warning colourations
• Many animals and organisms use brightly
coloured markings and patterns on the surface of
their body.
• This advertises the fact that they may be
unpleasant or poisonous to eat or merely sending
a warning to a possible predator to “stay clear.”
( a bit like how a man might get tattoos to
advertise how tough he is!!)
But not really.
• This type of colouration is known as aposematic
colouration.
• Predators will therefore have to exercise caution
should they choose to eat this type of prey as it
could potentially cause harm to them.
Figure 1.1,000,002: “Don’t eat me. I’m well hard.”
11. Mimicry etc
• Prey organisms may successfully avoid being caught
and eaten by a predator through mimicry.
• This involves the prey organism mimicking as best it
can the behaviour of another usually harmful
species so as to discourage the predator from
attacking.
• There are two types of mimicry; Batesian and
Mullerian.
• In Batesian mimicry, an edible or harmless species
mimics a poisonous or harmful one. An example of
this is the yellow and black colour patterns of the
harmless hoverfly, similar to the harmful wasp.
• In Mullerian mimicry, two or more inedible or
poisonous species have evolved to have the same or
similar warning signals. Presumably in this way each
species gains an additional advantage because once
a predator has learned to avoid a particular warning
signal or colouration with which it first cam into
contact, it would then be sensible of the predator to
avoid all other similarly patterned species. For
example, the caterpillars of the cinnabar moths.
12. Conclusion
Topics discussed:
• Types of predator
• Importance of predators
• Types of prey
• Adaptations of predators and prey, in
particular:
• Camouflage
• Warning Colourations
• Mimicry
