WK7 - INTERACTIONS: Predation: Part 2: Moderating the effects of predation

Moderating the Effects of Predation

  • By the end of this lecture, you should be able to:

    • Detail how to moderate the effects of predation.

    • Explain the role of predators as an evolutionary force.

    • Provide examples of some evolutionary responses to predation.

Refugia

  • Refugia are areas with self-sustaining prey populations without predators.

    • They can serve as a source for immigrating prey.

  • Refugia stabilize predator-prey dynamics:

    • Increase the persistence of predators and prey.

    • Increase the abundance of prey.

  • Prey populations can be maintained by immigration, even in sink environments.

Example: Banff National Park

  • Banff village acts as a refuge for elk.

    • Wolves avoid the village due to the presence of humans.

  • Elk population increases within Banff, leading to emigration into the surrounding forest.

  • Emigrating elk become a food source for wolves.

  • This example highlights the importance of heterogeneous environments for creating refugia, even in human-altered landscapes.

Lab Experiments: Gause's Protozoa

  • Gause isolated Didinium (predator) and Paramecium (prey) species.

  • Three microcosm setups:

    • Microcosm 1: No refugia, no immigration

      • Both species populations collapse over time.

      • Didinium consumes Paramecium, leading to a decline in Paramecium numbers.

      • The subsequent decline in Paramecium leads to a decline in Didinium numbers.

    • Microcosm 2: Prey refugia, no immigration

      • Paramecium numbers increase continually as they are safe from the Didinium.

      • Didinium dies out over time.

    • Microcosm 3: No refugia, immigration of prey

      • Oscillations occur where Didinium consumes Paramecium, causing a decline in Paramecium and Didinium numbers.

      • Immigration of new Paramecium restarts the cycle.

Huffaker's Mite Experiment (1958)

  • Examined predator and prey mites living on oranges.

  • Experimental setup:

    • Various arrangements of oranges separated by partial barriers (Vaseline).

  • Predatory mites disperse by crawling from orange to orange.

  • Herbivorous prey mites disperse by crawling or ballooning (aerial dispersal using silk).

  • Petroleum jelly barriers acted as refugia by hindering predator mite dispersal.

  • More complex arrangements:

    • Included wooden posts as launching pads for ballooning.

    • Fans circulated air to aid aerial dispersal.

Simple Setup

  • 40 oranges, 20 accessible to predatory mites, 20 with partial barriers.

  • Initial increase in prey numbers followed by an increase in predator numbers.

  • Crash in prey population followed by a crash in predator population.

  • Eventual extinction of both populations because predator mites eventually bypassed the barriers.

Complex Setup

  • Connections between some oranges and not others.

  • Some oranges covered in parafilm to create refugia.

  • The complex environment allowed for sustained oscillation cycles.

  • 252 oranges, with only a small portion of each exposed, created refugia for the prey.

  • Added layers of complexity:

    • Balls separating oranges.

    • Jelly barriers.

  • This complex environment allowed the cycle to persist longer before both mite populations crashed.

  • The experiments demonstrates that heterogeneous environments are needed to sustain populations in the long run.

Evolutionary Responses to Avoid Predation

Aposematism

  • Aposematism involves coloration to warn or confuse a predator.

  • Visual signals warn predators that prey are toxic or unpalatable.

Examples:

  • Lionfish: Bright stripes and spines warn predators of venom.

    • Lionfish stings can cause respiratory failure.

  • Cuttlefish: Coloration and shape changing to confuse predators.

  • Blue-ringed Octopus: Color change to yellow and iridescent blue rings when threatened to warn predators of venom.

  • Red-backed Spider: Uses red to signal danger.

  • Poisonous Frog: Contains poisonous compounds in its skin and uses red to signal danger.

Camouflage and Cryptic Coloration

  • Animals use cryptic coloration to blend in with the environment and avoid predator detection.

Mimicry

Batesian Mimicry

  • Palatable species mimic unpalatable ones to avoid predation.

  • They make themselves look like dangerous species.

  • Examples: Mantis and moth mimicking wasps.

Mullerian Mimicry

  • Convergence in appearance of unpalatable species.

  • Reinforces to predators that a coloration or patterning is dangerous, benefiting all species.

  • Predators learn quickly that they are unpalatable. So once one is eaten if species have similar appearances the predator learns that this appearance means being unpalatable.

Active Defense

  • Bombardier beetle sprays hot acid on predators and has aposematic coloring.

  • Stinging caterpillar (e.g., spitfire caterpillar in Australia) has hairs that sting, causing pain.

These examples illustrate different evolutionary responses to predation.