Mar 27: Predation Defenses: Traits and Problems

Approaches to Adaptation Trait-oriented • Starts with questions about a puzzling trait--What is the problem (the challenge to survival) that it solves for the animal? • Thus the answers to trait-oriented questions are the problems that the trait allows the animal to solve • The answers may lead to new questions: e.g., are those traits used only for those problems? why do the traits have the particular properties that they do?

Problem-oriented • Starts with questions about how animals solve some major challenge to survival • Thus, the answers to problem-oriented questions are the traits that animals use to solve the problem • The answers may lead to new questions: e.g., why do animals use those particular solutions and not others? why do those traits have the particular properties that they do?

In both cases, we are looking for an association between traits and the selection pressures that may have been involved in shaping the trait’s evolution

Mar 27: Predation Defenses: Stages of predation

A (Mainly) Problem-Oriented Approach to Predation The problem: how to survive in a world in which a lot of other living things are trying to eat you? Stages of predation • Detection • Attack • Capture • Consumption For predator: fitness is maximized by traits that ensure that the sequence goes to completion For prey: fitness is maximized by traits that interrupt sequence (and do so as early as possible)

Mar 27: Predation Defenses: Consumption

Research On Predator Defense Strategies Illustrates Power of Both Comparative and Experimental Approaches to Study of Function Experiments: • Create extreme or rare circumstances to study what aspects of environment affect fitness • Do “phenotypic engineering” • Control confounding variables Comparisons--among species or populations (Example: predator-defense strategies in ground-nesting and cliff-nesting gulls) • Comparisons are a sort of natural experiment: ecological differences between species create different experimental situations • Observe how the outcome of natural selection differs as a function of ecology • Important: comparisons should be among closely related species (otherwise you can’t know whether the differences are a result of current ecological differences or instead of some ancient phylogenetic difference)

Mar 27: Predation Defenses: Detection

Reducing Likelihood of Detection Be rare (or leave town) Crypsis: • be hard to see

Mar 27: Predation Defenses: Detection

Reducing Likelihood of Detection Be rare (or leave town) Crypsis: • be hard to see • note importance of behavior in crypsis

Peppered moths (2 morphs) 3-toed sloth

Mar 27: Predation Defenses: Detection cont’d

Reducing Likelihood of Detection Be rare (or leave town) Crypsis Masquerade: • be visible, but look inedible • again, appropriate behavior helps

Stick insect

Frog

Mar 27: Predation Defenses: Attack

Making Attack Less Likely Flee (but you need to be fast, and there are energy costs) (see Alcock Fig. 8.29) Tree frog Send a signal •Aposematism: warning signaling (visual, auditory, or chemical) • Exploit ability of predator to develop conditioned aversions • Conspicuous signals are learned faster!

Wasps Monarch butterfly and larva

Mar 27: Predation Defenses: Attack

Making Attack Less Likely-- cont’d Run away (but you need to be fast, and there are energy costs Send a signal • Aposematism: warning signaling • Batesian mimicry: be tasty, but look like something nasty (and benefit from conditioned aversions of predators)

Experimental test of Batesian mimicry • Show that naïve predator finds mimic palatable • Show that predator learns to avoid nasty-tasting, aposematic model • Show that experienced predator subsequently avoids palatable mimic • Note that mimic benefit but aposematic model potentially loses out

Mar 27: Predation Defenses: Attack

Making Attack Less Likely-- cont’d Flee (but you need to be fast, and there are energy costs) Send a signal • Aposematism: warning signalling • Batesian mimicry: be tasty, but look like something nasty (and benefit from conditioned aversions of predators) • Mullerian mimicry: be nasty, and look like something else that is nasty

Viceroy butterfly

Monarch butterfly

• Viceroy was once thought to be Batesian mimic of monarch • But, birds don’t like Viceroys, develop conditioned aversions to them, and subsequently avoid Monarchs--thus these are Mullerian mimics

Mar 27: Predation Defenses: Attack

Protective mimicry (cont’d) Mimicry Rings: West African butterflies have evolved complex networks of Batesian and Mullerian mimics

= same species found in two different morphs (all others are diff. species) = nasty-tasting

Mar 27: Predation Defenses: Attack

Making Attack Less Likely-- cont’d Run away (but you need to be fast, and there are energy costs Send a signal • Aposematism: warning signalling • Batesian mimicry: look like something nasty • Mullerian mimicry: be nasty, and look like something else that is nasty • Advertise uncatchability: tell the predator you’re on to him Consider alternative hypotheses: • Warning signal • Social cohesion signal • Confusion effect

“Stotting” in Thomson’s gazelles (Alcock Fig. 9.20)

Mar 27: Predation Defenses: Capture

Making Capture Less Likely Confuse predator momentarily (to gain opportunity to escape) • Visual illusions to misdirect attack (NOTE: Alcock classifies this as an anti-consumption defense)

Alcock Fig. 9.35

Mar 27: Predation Defenses: Capture

Making Capture Less Likely Confuse predator momentarily (to gain opportunity to escape) • Visual illusions to misdirect attack • Startle cues

Mar 27: Predation Defenses: Capture

Making Capture Less Likely--cont’d Anti-predator strategies associated with group living • Vigilance (and alarm calls to warn others in group)

Alcock Fig. 9.22

Mar 27: Predation Defenses: Capture

Making Capture Less Likely--cont’d Anti-predator strategies associated with group living • Vigilance (and alarm calls to warn others in group) • Selfish herd: physical protection from predators (try to get to center of group, so someone else is between you and predator)

Mar 27: Predation Defenses: Capture

Making Capture Less Likely--cont’d Anti-predator strategies associated with group living • Vigilance (and alarm calls to warn others in group) • Selfish herd: physical protection from predators (try to get to center of group, so someone else is between you and predator) • Dilution effect: statistical protection from predators

Alcock Fig. 9.27

Mar 27: Predation Defenses: Capture

Making Capture Less Likely--cont’d Anti-predator strategies associated with group living • Vigilance (and alarm calls to warn others in group) • Selfish herd: physical protection from predators (try to get to center of group, so someone else is between you and predator) • Dilution effect: statistical protection from predators • Mobbing: aggressive group response to predator Alcock Fig. 9.3

Alternative Hypotheses for mobbing (trait-oriented) • Advertise uncatchability • Distract predator • Warning of others in group • Lure predator away • Educate offspring • Injure predator • Attract larger predators (see Alcock Table 9.1)

Mar 27: Predation Defenses: Consumption

Making Consumption Less Likely Fight back (or be noxious) Attract predator’s enemies to distract him “Schreckstoff” in fish: •Signal to conspecifics of prey? (von Frisch) •Or signal to competitors of predator? (see Alcock)