Facultative Mutualism (Protocooperation)

• Nemo gets a predator-proof home.
• The sea anemone is fiercely protected--and even fed--by the clown fish.

Some species of marine arthropods will "plant" anemones on their carapace.

• Predators are deterred by the stinging anemone.
• The anemone gets food whenever the sloppy arthropod feeds.

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Competition

The Brown Anole (Anolis sagrei) was introduced to southern Florida in the 1960s.
The two species were soon in competition for habitat and food resources.

The Competitive Exclusion Principle (Gause's Law) proposes that two species competing for the same limited resource cannot coexist at constant population values.

• If one species has even a slight advantage, it will eventually dominate.
• The result will be either
  • extinction of the less competitive species OR
  • evolution of resource partitioning between the two species

In the latter case, the two species will eventually occupy different ecological niches.

Over several decades, the stockier, more aggressive Brown Anole
has displaced the native Green Anole in some physical spaces it once occupied.

• Brown Anoles are more common in low shrubbery and on the ground.
• Green Anoles are more common in high canopy.

Neutralism

• two populations exist in the same ecosystem
• neither affects the evolutionary fitness of the other

Because organisms in an ecosystem are generally interconnected in some way,
true neutralism is can be difficult to distinguish.

The term "neutralism" may be used to describe interactions
in which the effects of two populations on each other are negligible.

For example...
Two inhabitants of the Gobi Desert in Outer Mongolia are the

• Bactrian Camel, which makes its home on the arid, cold sands.
• Longtailed Tadpole Shrimp, which emerges only after a good rain.

The two species have minimal interaction,
and probably do not affect each other's Darwinian fitness.

Predation

Predation has driven the evolution of such phenomena as

• toxic or mechanical defense mechanisms
• mimicry
• crypsis (camouflage)
• aposematism (warning coloration)

Predator Categories

This effect can be even more dramatic in the case of invasive, exotic
predators introduced to an area where prey have not evolved appropriate defenses.

Herbivorous predators kill and consume entire plants or seeds.

Mesopredators consume herbivores.

• generally small

  weasel fox coyote falcon

  raccoon skunk shrew small sharks

  octopus and squid snakes insectivores seal

Top carnivores consume herbivores and mesopredators.

• generally large

  tiger lion leopard jaguar

  large shark Orca polar bear wolf

  crocodile giant snakes large raptors humans & chimps

Defense Mechanisms Against Predation:
An Evolutionary Arms Race

• mechanical barriers to predation
• chemical deterrents
• physical avoidance mechanisms

Predators can evolve mechanisms to overcome these defenses.
In turn, prey are selected for improved or different defenses.

This can result in a coevolutionary "arms race".

Predation Drives the Evolution of Crypsis

A predator that matches its background can more easily approach its prey, undetected.

A prey item that matches its background can more easily avoid detection by a predator.

Crypsis can take myriad forms

• simple color matching
• evolutionary full-body makeover

...sometimes resulting in morphologies that can be
almost unrecognizable as that of an animal.

Predation Drives the Evolution of Aposematism

An experienced predator will recognize that this particular animal is

• potentially dangerous
• not worth the risk

...and seek food elsewhere.

Know the difference:

• poisonous/toxic - harmful when eaten or touched
• venomous - delivers toxin with an apparatus such as a fang or stinger

Predation Drives the Evolution of Mimicry

A mimic has evolved resemblance to a model.

A model can be any number of things, such as

• an inedible object
• a distasteful object
• a dangerous object

...that an experienced predator will ignore or actively avoid.

Batesian Mimicry

For example,

The harmless Viceroy butterfly mimics the poisonous Monarch butterfly.

In a 1960s experiment

• Lab-raised, naive bluejays were regularly fed Viceroy butterflies.
• Offered the toxic model, a naive bluejay eagerly eats it...with unfortunate results.
• emetic cardenolides sequestered in the wing margins induce vomiting!

• After one Monarch experience, a bluejay will avoid both species.

Mullerian Mimicry

A predator need sample only one species to learn to avoid all of them.

Examples:

• Toxic Ithomiid butterflies
  • resemble sympatric Ithomiid species
  • do not resemble non-sympatric Ithomiid species

  ...thus forming mimicry complexes in regions where they co-exist.

• Many species of venomous, stinging hymenopterans (bees, wasps, etc.)
  have yellow bodies with black stripes.

• Different species of Poison Dart Frogs species resemble one another
  in areas where they co-occur. Where they are not sympatric,
  their color patterns diverge.

Parasitism

• A definitive host houses an adult parasite.
• An intermediate host houses a larval parasite.

The definitive host is usually a predator of the intermediate host.

• An intermediate host ingests parasite eggs or early larval forms.
• The parasite often encysts in the intermediate host's tissues.
• When the definitive host eats the intermediate host, the life cycle is completed.
• The larval parasite metamorphoses into the adult, takes up residence
  in the definitive host, and begins reproducing.

There is no end to the evolutionary creativity of parasite life cycles.

Parasitoidism

• metamorphosis from juvenile
• onset of reproduction

Commensalism

• species A benefits from the presence of Species B.
• Species B is neither positively nor negatively affected by the presence Species A.

Examples:

Cattle Egrets follow large grazing animals as they feed.
• As the ruminants (cows, rhinos, etc.) move through the grass,
  they stir up insects that fly to get out of the way.

• The waiting birds get an easy banquet.
  
• The large grazers are neither helped nor harmed by the presence of the birds.

Pilot Fish school around and follow a shark.

• When the shark feeds, the Pilot Fish get lots of scraps.
• The shark is neither helped nor harmed by the presence of the Pilot Fish.
• Remoras do this, too. They are not parasites.

Amensalism

• species A impedes the success of species B
• Species A is neither positively nor negatively affected by species B

Amensalism is often the evolutionary outcome of past competition.

Allelopathy is the production chemical compounds
that inhibit the growth of nearby would-be competitors.

Allelopathy is seen in some species of

• plants
• protists (e.g., Dinoflagellates, some kelps)
• bacteria
• fungi
• anthozoans

Examples:

• Black Walnut Tree (Juglans nigra) roots produce juglone,
  which inhibits the growth of other trees and shrubs.

• The ascomycete fungus Penicillium notatum produces penicillin,
  which inhibits bacterial growth by interfering with peptidoglycan synthesis.