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

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

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

I’m super venomous!

I’m just faking it!

Defense Mechanisms Even two species that are both poisonous, harmful, or unpalatable

may benefit from mimicking each other For example, the Zimmerman’s poison frog or the poison dart frog

closely resembles the mimic poison arrow frog An animal that becomes sick preying on the Zimmerman’s 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 Zimmerman’s poison frogs

This co-evolved defense mechanism is called Müllerian mimicryWe’re both

poisonous!

But we’re also

adorable!

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

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

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 can’t exist outside their host

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 don’t 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

Parasitism

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

Mutualism Mutualism is also common

in aquatic ecosystems The hermit crab and sea

anemone have a mutualistic relationship The sea anemone’s 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”

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 tree’s 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

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

Commensalism A symbiotic relationship in

which one partner benefits and the other partner is unaffected is commensalism

For example, the lemon shark doesn’t 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 shark’s 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

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 cattle’s movement

The cattle seem unaffected by the ever-present birds, neither profiting nor being harmed by the relationship

Cattle egrets don’t limit their relationships to cattle Also engage in commensalism with

other large animals such as rhinoceroses and even kangaroos

Commensalism In cases of commensalism, it’s 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

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