Step 4 defenses Prevent attack

Detected prey can avoid an attack by way of warning signals (aposematism), for example, bright coloration as a sign of toxicity. Such warning signals are the opposite of camouflage but are also widespread. An example is shown in Figure 5. Several poisonous prey species have evolved similar warning-coloration patterns, so-called Mullerian mimicry, which increases recognition and avoidance by the predator, for example, black-and-yellow stripes in wasps and bees. Aposematisms offer opportunities for 'cheating species which are not poisonous but show the same color pattern, so-called Batesian mimicry. For instance, hover flies are similarly colored as wasps and bees but harmless. Acoustic warning signals are produced by rattlesnakes and several other species. A further type of warning signal is aggressiveness and readiness to fight, indicating the predator that an attack might come with serious wounds.

Figure 5 Striped skunks (Mephitis mephitis) have a black-and-white warning coloration that indicates their chemical weapon to predators, an example for a permanent step 4 defense. © Jeschke.

Step 5 defenses: Prevent consumption

Defenses in this final class reduce predator attack efficiency, that is, the probability that a predator attack is successful. Typical examples are flight behavior (as in antelopes or gazelles), armor (as in turtles, mussels, or Daphnia, Figure 2), weapons (such as cnidocytes in corals and other cnidarians, Figure 6), and fighting. The latter is especially effective for grouped prey, as is famously exemplified by musk oxen (Ovibos moschatus) forming a defense wall against wolves. Aggregated prey may also confuse the predator: many moving individuals cause information overload of the predator and thus reduce its ability to attack successfully (Figure 7).

Some predators cannot mechanically handle individuals beyond a certain size. For example, many aquatic predators are gape-limited: pike (Esox lucius) cannot ingest fish that exceed a certain height or breadth. Crucian carp

Figure 6 Charged and discharged cnidocytes. They are effective weapons of cnidarians against predator capture and exemplify permanent step 5 defenses. © Laforsch.
Figure 7 Prey swarms often confuse a predator, thereby reducing its attack efficiency, an example for a step 5 defense. Here is a Queensland grouper (Epinephelus lanceolatus) surrounded by a swarm of silversides (Atherinomorus lacunosus). © Tollrian.

(Carassius carassius) with a deep body are therefore effectively defended against this piscivore. Similarly, Daphnia can allocate energy into growth instead of reproduction in order to outgrow the prey-size spectrum of Chaoborus larvae (Figure 8), Leptodora kindtii, and other gape-limited invertebrate predators. This energy-allocation strategy is also an example for a life-history defense (Figure 9).

Step 5 defenses could in principle be further classified into defenses that prevent capture (e.g., flight) and those

Figure 8 Phantom midge larvae (Chaoborus spp.) are gape-limited predators. © Laforsch.

Figure 9 Daphnia adaptively change their resource allocation between somatic growth and reproduction in response to cues from fish and invertebrate predators. Fish consume larger size classes, so Daphnia invest less energy in somatic growth and more in reproduction if fish predation dominates. On the other hand, gape-limited invertebrate predators consume smaller Daphnia, so outgrowing their prey-size spectrum by investing much energy in somatic growth is an effective defense if invertebrate predation dominates. This resource-allocation shift is an example for an inducible step 5 defense that affects the prey's life history. © Tollrian.

Figure 9 Daphnia adaptively change their resource allocation between somatic growth and reproduction in response to cues from fish and invertebrate predators. Fish consume larger size classes, so Daphnia invest less energy in somatic growth and more in reproduction if fish predation dominates. On the other hand, gape-limited invertebrate predators consume smaller Daphnia, so outgrowing their prey-size spectrum by investing much energy in somatic growth is an effective defense if invertebrate predation dominates. This resource-allocation shift is an example for an inducible step 5 defense that affects the prey's life history. © Tollrian.

that prevent consumption (e.g., armor in turtles or mussels) but this distinction is often unclear. Recall that step 5 defenses also increase predator handling time, so they are also step 1B defenses.

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