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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

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defense mechanisms
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 mechanisms1
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 mechanisms2
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 mechanisms3
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 mimicry

We’re both poisonous!

But we’re also adorable!

symbiotic relationships
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
  • 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
  • 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
  • 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
  • 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 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”
  • 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
  • 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
  • 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
  • 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
  • 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

Table 11.2: Interspecific Interactions