Transcript Community Ecology cont.

Predation (with parsitism and herbivory)
When one animal (a predator) eats (and kills)
another animal (a prey), the predator clearly benefits
(+) and the prey is harmed (-).
When one animal feeds from the body of another
(the host) without killing it, the interaction is called
parasitism. The parasite benefits (+) and the host is
harmed (-).
When an animal consumes plant material, the
interaction is called herbivory. The herbivore
benefits (+) and we normally assume that the plant is
harmed (-).
Now think about these interactions in evolutionary
terms. The species that is harmed is under more-orless severe selective pressure to minimize the harm.
There are an enormous variety of defensive
adaptations in both animals and plants. Here are a
few examples from the plant world:
Plants can’t run and hide, so most of their defenses
are either structural or chemical. The more
interesting ones are chemical…
1.Do you like chocolate? What gives chocolate
much of its flavor is an alkaloid (a toxin) that’s
present to protect the beans from insect herbivores.
2.Do you like cinnamon? It comes from the bark of a
tree. The ‘flavor’ is a toxin (here cinnamic acid)
again present to protect the bark from insect
herbivores.
3. Let’s save time an space. Virtually every strong
flavor we like (pepper – capsicic acid, …) has
evolved in the plant source for protection from
insects.
And the structural defenses are fairly obvious…
Thorns, hooks, spikes, or prickles in plants and
spines (porcupine quills) in animals, e.g. cactus
In animals there is a greater variety of approaches to
defense.
1.Warn a potential predator that you’re dangerous
(or even poisonous).It’s called aposematic
coloration
The warning colours are generally stripes of red and/or
yellow contrasted with black. All 3 colors are seen in coral
snakes; yellow and black are in bees and wasps.
2. Crypsis (or camouflage) – hiding in plain sight.
Think of other examples like stick insects or
insects with leaf-like wings, …
Against an artificial
background
In its natural habitat
3. Mimicry – if you can’t hide, try looking like
something the predator wouldn’t want to eat. There
are two kinds of mimicry: Batesian, where the
mimic tastes good, and the model is distasteful, or
Mullerian, where both model and mimic are
distasteful.
Batesian mimicry
Hawkmoth – left
Snake - right
Probably the most famous example of Batesian
mimicry is the Monarch (model) and Viceroy (mimic)
butterflies…
The Viceroy is not
distasteful (it may
even taste good)
The Monarch is
distasteful, even
causing bird
predators to vomit.
Blue jay vomiting after eating a noxious monarch
butterfly. The caterpiller obtains poison from its
milkweed host plant.
Photo: Lincoln P. Brower, Univ. of Florida
In Müllerian mimicry 2 different species resemble
each other, e.g., wasps & bees are both black &
yellow. The advantage to the prey is that predators
are quick to learn to avoid both species.
The model
a hornet
A beetle
mimic
fly
moth
Deceptive colouration - eyespots attract predators to
attack places on the body that do not result in fatality.
The eyespots are intended to make the prey look like a
frightening predator.
They may also have displays that at least momentarily
frighten a predator.
Animals may adopt chemical defenses, too.
Some molluscs secrete sulfuric acid, and are rejected
as food by fish
A number of animals use defensive sprays. Whip
scorpions (related to spiders) spray acid.
Skunks spray a concentrated musk (mercaptan) that
we can all agree is effective in defense against
attack.
Dendrotoxin (which blocks potassium channels in
the predator’s nerve cells) is in the skin of certain
poisonous frogs, and used by hunters in the Amazon
rainforest.
Tetrodotoxin (used in neurophysiological research)
comes from the puffer fish. It blocks sodium
channels.