Biol 208: Lecture 22 - Avoiding predation + Herbivory

Herbivory + predation are _____ forces in evolution

SELECTIVE forcers

What are the 2 general methods to avoid going extinct due to predation?

1. Defense

2. Take shelter

Generally describe defense, what is its main purpose

• What are the 3 methods of Defense?

Fight back

• Learning experience for the predator not necessarily death

3 methods:

1. Aposematic strategy

   1. Mullerian mimicry (type of Aposematic strategy)

   2. Batesian mimicry (type of Aposematic strategy)

Aposematic strategy

Defensive coloration and behavior

• “Don’t eat me i am not tasty”

Bright coloration or distinct patterning or appearance displayed by many toxic or distasteful potential prey species

• eg. poison dart frog or skunk

Mullerian mimicry

• Give an example

Two or more harmful or toxic species mimicking warning symbols to resemble each other. This mutual resemblance benefits all the species involved, as predators learn to avoid them due to their shared warning signals.

• Stinging Hymenoptera (Wasps, hornets + some bee) mimic each other in their coloration traits (black + yellow)

• Once stung by a member in this group a predator will most likely not feed on species with theses traits (learning effect increased)

Batesian mimicry

• what is a condition for this type of mimicry to work?

NON-toxic species resemble toxic thereby gaining protection from predators. In this case, the mimic benefits from the mistaken identity, while the model is negatively affected

• Works as long as density of model is GREATER than density of mimmicks

Spatial Refugia what is it?

• What is an example given in class?

Seek refuge + hide where predators cannot find you

• Reaching refuge costs Energy and decreases foraging BUT fitness benefits outweigh cost (better not dead than dead)

eg. Diel vertical migration

Diel Vertical Migration

Spatial refugia

= the Synchronized movement of organisms int he water column over a daily cycle

• displayed by various organisms to avoid predators

• During the day = move deeper in water to avoid predators

Protection in Numbers

Refuge

• Have populations so large that the risk of any one individual being eaten is low

Info dump: Immigration to the rescue - Gause’s predation experiments

1. Putting predator + Prey together DID NOT result in Oscillations predicted by L-V predator prey model → BOTH predator + prey went extinct

2. Creating refugia for prey: Prey was able to hide so effectively that predators Died

3. Created IMMIGRATION by restocking prey population: OSCILLATIONS OCCURED as predicted by L-V models.

• critique = immigration created artificially restocking population (masking what can happen in nature)

Info dump: Gause revisited - Hufftaker’s experiment

• Methods

• Results

Predator + prey mites

Method:

• Provided food + created Movement barriers for predators + dispersal aids for prey

Results:

• OSCILLATIONS reproduced WIHTOUT artificial restocking of populations

Spatial complexity + dispersal allow “Hide + Seek” = coexistence

Metapopulation rescue define

Refuge

• Rescue effect - individuals from larger populations may immigrate + “rescue” smaller populations

• migration of individuals can increase the persistence of small isolated populations by helping to stabilize a metapopulation, thus reducing the chances of extinction.

Metapopulation definition = in lecture 14

Refuge: size

Too big to eat = pros

Con = takes a lot of E to maintain large body size

Plant defense strategies in response to herbivory:

• What are they 2 categories of defense traits

1. Resistance = makes them less likely to be eaten

2. Tolerance = reduced harm while being eaten

What are the 2 types of Plant RESISTANCE STRATEGIES?

• give examples for each

1. Constitutive chemical defenses

   1. Toxins (tobacco) + Digestion reducing compounds (tannins tea)

2. Induced chemical defenses

   1. Volatile compound production is increased after infestation in Tomatoes (PHENOTYPIC PLASTICITY

Latitude differences in Plant chemical defenses:

• Tropical rain forest vs. boreal forest - in which do plants have more diversity of chemical defenses and WHY?

• How does herbivory change with latitude

Tropical rain forest

• Has greater biodiversity of herbivores = need more diverse types of chemical defenses

Herbivory Decreases with an Increase in latitude

True or False: PLANTS do NOT have warning colorations?

• Why or Why not

TRUE

Why?

• Herbivory normally doesn’t kill plants

  • = weaker selection pressure to evolve conspicuous visual warnings

• Warning signals only work when the effects are quick + herbivores learn quick

  • Toxins do not act as quickly in plants so the association does not form

• Many herbivores rely on chemical cues rather than vision

Toxic fruits?

Usually toxic because:

• Not ripe yet (prevent eating B4 seeds are ready)

• Reduce risk of seeds being digested

  • laxative properties

  • Digestion reducing compounds

Facilitate seed dispersal by frugivores

What is the One Plant TOLERANCE strategy?

• How does it work?

• What are the causes (5)

Overcompensation

• Increased plant growth following herbivory, compared to plants that did not experience herbivory

Taxon specific

• most common in grasses + some herbaceous plants

Causes:

1. High resource availability

2. Partial defoliation can stimulate growth (light grazing: removal of dead plant material = increase in photosynthesis)

3. Growing points - Meristems (plants with dormant buds or basal meristems are more likely to overcompensate)

4. History of grazing (grazed grass = respond more strongly than ungrazed)

5. Timing of herbivory (grazing early in summer (plants are still growing + can overcompensate)