Predator-Prey Relationships: Coevolution versus Escalation
Species on Earth interact in many different ways (Abrams, 2000). These interactions have evolved over millions of years to become an incredibly complex web of inter-species relationships and understanding these relationships enables science to model future species interactions (Abrams, 2000). From symbiosis to parasitism, Earth seems to have every type of relationship imaginable (Dietl and Kelley, 2002). One of the most intriguing and commonly studied relationships is that of predator and prey. The predator-prey relationship can manifest itself in many forms, be it two animals, an insect and a plant or a parasite and its host (Dietl and Kelley, 2002). Predators evolve different offensive mechanisms such as speed, large canines and claws, or resistances to toxins, while prey develop defensive mechanisms such as camouflage, bright colours, toxins, burrowing or behaviours such as ‘playing dead’ (Ebner, 2006). The main topic of study within this relationship is discovering how this relationship develops between two species (Ebner, 2006). The two main hypotheses for its occurrence are coevolution and escalation (Ebner, 2006). Coevolution is the process by which beneficial evolutionary changes in one species, that increase the species’ fitness, influence evolutionary changes in the other (Ottino-Lofler et al., 2007). The two species (predator and its prey) selectively influence each other’s characteristics through an evolutionary ‘arms race’, each attempting to gain the upper hand through genetic mutation, drift and random chance (Ottino-Lofler et al., 2007). This is a very circular process, causing cyclic fluctuations in predator and prey populations, with a lag time in between (Ottino-Lofler et al., 2007). One species, for example the prey evolves a new defense mechanism enabling it to better escape its predator; there will be a lag time as the predator either evolves a new predation method or learns a way around the new defense mechanism (Marrow et al., 1992). The development of the defense mechanism allows prey populations to increase, until the predator develops a method to capture its prey once again, causing the predator population to rise, and prey population to fall, until the prey develops a new defense mechanism and the cycle repeats (Ottino-Lofler et al., 2007). There are usually three possible outcomes of coevolution in predator-prey relationships: 1) the prey evolves an impenetrable defense and the predator goes extinct, 2) the predator evolves an unstoppable offense which drives the prey to extinction and 3) the evolution of defensive and offensive strategies by prey and predator balance each other leading to the aforementioned cyclic population fluctuations (Marrow et al., 1992, Ottino-Lofler et al., 2007). The third outcome is known as the Red Queen effect (Marrow et al., 1992, Ottino-Lofler et al., 2007), after Lewis Carroll’s Through the Looking Glass in which the Red Queen says, “Now here you see it takes all the running you can do, to keep in the same place. If you want to get somewhere, you have to run at least twice as fast as that” (Carroll, 1871). The cyclic nature of the struggle between predator and prey to maintain their existence epitomizes the Red Queen’s line, in that defenses developed by prey are counteracted by offenses by predators, leaving the two species in the same place as before (Marrow et al., 1992, Ottino-Lofler et al., 2007). Alternatively, escalation is entirely predator determined (Marrow et al., 1992, Ottino-Lofler et al., 2007). Prey evolves defense mechanisms to its predator; however that predator does not evolve based on the changes in its prey (Marrow et al., 1992, Ottino-Lofler et al., 2007). The predator evolves based on its own predator, creating a ‘trophic escalated’ evolutionary arms race (Rikvold and Zia, 2003). While both processes may occur in the wild, coevolution is the more dominant force,...
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