Defense Mechanisms Most organisms have adaptations that help
protect them against their predators Cacti have thorns Porcupines
have quills Monarch butterflies have toxins and protective
colouration The interactions between producers and consumers
typically result in co-evolution Ex: The milkweed plant produces
bitter-tasting chemicals that discourage many herbivores, but some
have adapted to tolerate the toxin
Slide 2
Defense Mechanisms Many organisms use protective colouration as
a natural defense mechanism This can include camouflage, mimicry,
and warning colouration For example, the dead leaf butterfly is
nearly invisible to predators When it remains motionless, its brown
colouration and the veined pattern on its wings camouflage it from
predators
Slide 3
Defense Mechanisms Some species use warning colours, such as
red, yellow, and black The highly venomous eastern coral snake has
red, yellow, and black stripes Yellow jacket wasps are black and
yellow Other species that are not toxic or poisonous use these
colours to their advantage The non-venomous Scarlet king snake has
red, yellow, and black stripes similar to the eastern coral snake
The syrphid fly has a similar yellow and black colouration to a
yellow jacket This type of mimicry, where a species looks like
another species that has an effective defence strategy, is called
Batesian mimicry Im super venomous! Im just faking it!
Slide 4
Defense Mechanisms Even two species that are both poisonous,
harmful, or unpalatable may benefit from mimicking each other For
example, the Zimmermans poison frog or the poison dart frog closely
resembles the mimic poison arrow frog An animal that becomes sick
preying on the Zimmermans poison frog will avoid all frogs with
that colouration, including the mimic frog Scientists hypothesize
that the converse is also true Predators finding the mimic frog
distasteful, will also avoid Zimmermans poison frogs This
co-evolved defense mechanism is called Mllerian mimicry Were both
poisonous! But were also adorable!
Slide 5
Symbiotic Relationships Close interactions between two species
living in direct contact often result in an ecological relationship
called symbiosis Symbiosis means living together Symbiotic
relationships have one organism, the symbiont, which lives or feeds
in or on another organism, the host There are 3 forms of symbiosis:
Parasitism Mutualism Commensalism
Slide 6
Parasitism In parasitism, a symbiont (the parasite) benefits
from the relationship but the host is harmed by it Mistletoe is a
parasite that obtains food by growing roots directly into the host
tree and gaining nutrients from its sap The interactions weakens
the tree and predisposes it to disease
Slide 7
Parasitism Parasites include: Viruses Unicellular organisms
Insects Various types of worms Ectoparasites live outside their
hosts Ex: Mistletoe, ticks Endoparasites live inside their hosts
Ex: Viruses, tapeworms Usually depend on their interactions with
their hosts to survive and cant exist outside their host
Slide 8
Parasitism The parasite-host cycles are similar to
predator-prey cycles and show a direct relationship to population
density An increase in the host population results in an increase
in the parasite population The increase in parasites eventually
reduces the host population growth, either through decreasing the
hosts abilities to reproduce or by reducing survivorship The cycle
continues as the survivors in a now-reduced population of hosts
dont have to compete with as many individuals for resources Figure
11.37 shows the population cycles of one host-parasite
relationship: the adzuki bean weevil and its wasp parasitoid The
adult female wasp lays her eggs into or on the host bean weevil The
larva hatches and eats the tissue of its host This type of wasp
parasite that kills their host is called a parasitoid
Slide 9
Parasitism
Slide 10
Mutualism When both partners in a symbiotic relationship
benefit from the relationship, or depend on it to survive, their
relationship is called mutualism Such relationships are common in
nature A lichen, for example, is actually a combination of an alga
and a fungus Their mutualistic relationship allows them to grow on
exposed, bare rock, where neither would survive on its own While
the algal partner in the relationship carries out photosynthesis to
feed both organisms, the fungus protects the alga from drying out
or blowing away The fungus also produces an acid that dissolves
rock, releasing minerals the alga requires
Slide 11
Mutualism Mutualism is also common in aquatic ecosystems The
hermit crab and sea anemone have a mutualistic relationship The sea
anemones stinging tentacles protect the crab from predators The
crab provides the sea anemone with a ready source of food, the
detritus from its meals The crab also provides a mobile home
Slide 12
Mutualism Animal behaviour is an important part of most
mutualistic relationships For example, in Latin America, bull-horn
acacia trees show mutualism with stinging ants The leaves of the
Acacia produce a sugary liquid that the stinging ants consume The
stinging ants also find protection inside the trees hollow thorns
The ants are beneficial to the tree because they attack any other
herbivores that land on it The ants also cut down the branches of
other plants that come in contact with the Acacia, ensuring the
Acacia has adequate light for photosynthesis
Slide 13
Mutualism How do mutualistic relationships affect the growth of
the populations involved? Because both partners have co-evolved,
growth in one population typically spurs growth in the other
population Similarly, if one population decreases in size, the
other population tends to do the same
Slide 14
Commensalism A symbiotic relationship in which one partner
benefits and the other partner is unaffected is commensalism For
example, the lemon shark doesnt appear to benefit or suffer from
its relationship with the remora The remora uses a modified,
sucker-like dorsal fin to hold fast to the sharks body It receives
protection and bits of food from the shark and gains a source of
transportation The remora is clearly benefiting, while the shark
seems unaffected
Slide 15
Commensalism Another example of commensalism is the
relationship between the cattle egret and cattle The birds follow
the cattle around, feeding on insects roused by the cattles
movement The cattle seem unaffected by the ever-present birds,
neither profiting nor being harmed by the relationship Cattle
egrets dont limit their relationships to cattle Also engage in
commensalism with other large animals such as rhinoceroses and even
kangaroos
Slide 16
Commensalism In cases of commensalism, its often difficult to
determine how each species is affected Some ecologists argue that
there are few true cases of commensalism They believe both partners
in symbiotic relationships are usually affected in some way, making
the relationship a mutualistic one Although how both organisms are
affected is not always clear If true commensalism does exist Growth
of the host population would affect growth of the symbiont
population in a positive way Growth of the symbiont population
would have no effect on the host population whatsoever
Slide 17
Summary Nature of Relationship between Populations Effect of
Growth in One Population on the Other Population Competitive-/-
(both are negatively affected) Predator-prey or herbivore-plant+/-
(one population gains at the expense of the other) Host-parasite-/+
(one population gains at the expense of the other) Mutualistic+/+
(both are positively affected) Table 11.2: Interspecific
Interactions