Lecture 13. Anti-Predator Adaptations

Avoiding Predators - A Summary of Key Concepts

Introduction to Predator Avoidance

• Predation is a natural phenomenon; every organism has to eat, but no one wants to be prey.

Adaptations in Animals

• Adaptation: A hereditary trait that evolves through natural selection that provides a fitness benefit compared to alternative traits.

• Not all traits are perfectly adaptive; some have drawbacks.

Types of Anti-Predator Adaptations

1. Physical Speed: Animals like the Pronghorn antelope (Antilocapra ext{ }americana) can run up to 100 ext{ km/h}; Yellowfin tuna (Thunnus ext{ }albacares) can swim at 80 ext{ km/h}; while the White-throated needletail (Hirundapus ext{ }caudacutus) can fly at 170 ext{ km/h}.

2. Nocturnality: Remaining active at night to avoid visual predators.

3. Camouflage: Blending into the environment to avoid detection (e.g., peacock flounder).

4. Defensive Structures: Features such as spines or hard shells (e.g., the crested porcupine, Hystrix ext{ }cristata).

5. Autotomy: Self-amputation to escape predators (e.g., the blue-tailed skink, Cryptoblepharus ext{ }egeriae).

6. Aposematic Coloration: Bright colors indicating toxicity, warning potential predators (e.g., coral snakes).

7. Mimicry:

   • Mullerian Mimicry: Both toxic species mimic each other (e.g., various butterflies).

   • Batesian Mimicry: Non-toxic species mimic toxic ones to deter predators.

   • Emsleyan Mimicry: Less toxic species appearing less harmful than they are to create confusion.

8. Deimatic Behavior: Startling displays to scare off predators (e.g., frilled lizard).

9. Phagomimicry: Mimicking food to deter predators.

10. Distraction Displays: Drawing a predator's attention away to protect offspring (e.g., killdeer).

11. Thanatosis: Playing dead to avoid predation.

12. Pursuit-Deterrent Signals: Showing fitness to signal that catching them would be difficult (e.g., impala stotting).

13. Predator Confusion: Strategies that confuse predators about an animal's position in a group (e.g., zebras).

14. Defensive Regurgitation: Expelling stomach contents to deter attacks (e.g., northern fulmars).

15. Suicidal Altruism: Some species intentionally sacrifice themselves for their group (e.g., the Malaysian exploding ant, Camponotus ext{ }saundersi).

16. Dilution Effect: Reducing individual risk by being in larger groups.

17. Selfish Herd: Seeking a central position in the group to minimize individual exposure to predators.

18. Predator Satiation: Overwhelming predators with sheer numbers (e.g., periodical cicadas).

19. Alarm Calls: Communicating the presence of a predator.

20. Improved Vigilance: Group behaviors that enhance alertness to predators.

21. Mobbing: Group efforts to drive away predators (e.g., silver gulls).

Costs of Anti-Predator Adaptations

• Adaptations carry costs; optimal adaptations depend on cost-benefit analysis relevant to the species and their environment.

• Fitness can be expressed through direct measures (fecundity, fertility) and indirect measures (health, survival).

Examples of Adaptation Effectiveness

• Mobbing Behavior: Evidence shows decreased predation in colonies where birds mob predators, indicating a direct reproductive advantage.

• Density Impacts: High nesting density in arctic skuas suggests a fitness advantage from mobbing and dilution effects.

• Predation Risk and Group Size: Studies show that predation risk decreases with group size in butterflies, indicating an indirect fitness advantage.

The Role of Genetic Variation

• Genetic diversity within species (e.g., the peppered moth) allows populations to adapt to varying environmental factors, such as pollution.

• Phenotypic diversity can provide an advantage in different predation environments, showcasing natural selection's favoring of genetic variation.

Honesty in Displays

• Many species display fitness signals (e.g., lizard push-ups) to deter predators, usually with honest indicators to prevent deceptive signalling.

Conclusion

• Avoidance of predators drives evolutionary adaptations, but these adaptations have inherent costs. The balance of these costs and benefits, evaluated through fitness metrics, shape the survival strategies of various species in response to their environments.

Learning outcomes

1. Understanding Adaptations: Adaptations are hereditary traits that evolve through natural selection. They provide certain benefits related to fitness in a particular environment, although not all traits are perfectly adaptive, and some can have drawbacks.

2. Identifying Adaptation Types: Various anti-predator adaptations include:

   • Physical Speed: Animals like the Pronghorn antelope can run up to 100 km/h.

   • Camouflage: For example, the peacock flounder blends into its environment to avoid detection.

   • Mimicry: Such as Müllerian mimicry where toxic species imitate each other, and Batesian mimicry where non-toxic species mimic toxic ones.

3. Evaluating Costs and Benefits: Anti-predator adaptations carry inherent costs. The appropriateness of each adaptation is evaluated based on its benefits to survival and reproduction versus these costs, which are condition-dependent.

4. Exploring Genetic Variation: Genetic diversity within species allows populations to adapt to varying environmental factors. For example, variations in the peppered moth's coloration allowed it to thrive in polluted environments, showcasing how adaptation relies on genetic variation.

5. Interpreting Behavioral Strategies: Animals exhibit behaviors such as mobbing to deter predators, where a group works collectively to drive away threats, thus enhancing individual survival through cooperative strategies.

6. Connecting Fitness Metrics: Fitness can be measured both directly through reproduction (fecundity) and indirectly through health and survival metrics, illustrating how successful anti-predator strategies can lead to reproductive advantages.

7. Critical Thinking on Evolution: The avoidance of predators drives evolutionary adaptations by presenting survival challenges. The balance between the costs and benefits of these adaptations informs the evolutionary success and survival strategies of various species in their specific environments.