The Fossil Record of Predator-Prey Arms Races: Coevolution and Escalation Hypotheses

Abstract

Arms races between predators and prey may be driven by two related processes—escalation and coevolution. Escalation is enemy-driven evolution. In this top-down view of an arms race, the role of prey (with the exception of dangerous prey) is downplayed. In coevolution, two or more species change reciprocally in response to one another; prey are thought to drive the evolution of their predator, and vice versa. In the fossil record, the two processes are most reliably distinguished when the predator-prey system is viewed within the context of the other species that may influence the interaction, thus allowing for a relative ranking of the importance of selective agents. Detailed documentation of the natural history of living predator-prey systems is recommended in order to distinguish the processes in some fossil systems. A geographic view of species interactions and the processes driving their evolution may lead to a more diverse array of testable hypotheses on how predator-prey systems evolve and what constraints interactions impose on the evolution of organisms. Scale is important in evaluating the role of escalation and coevolution in the evolution of species interactions. If short-term reciprocal adaptation (via phenotypic plasticity or selection mosaics among populations) between predator and prey is a common process, then prey are likely to exert some selective pressure over their predators over the short term (on ecological time scales), but in the long run predators may still exert primary “top-down” control in directing evolution. On the scale of evolutionary time, predators of large effect likely control the overall directionality of evolution due to the inequalities of predator and prey in control of resources.

Threat-protection mechanics of an armored fish

“…Predator-prey interactions are widely thought to lead to socalled "evolutionary arms races" in which predators evolve enhanced weapons and prey evolved improved defensive capabilities (Vermeij, 1987;Agrawal, 2001;Dietl and Kelley, 2002). The process leads to progressive elaboration of weapons and defenses, and in some may result in "adaptive stalemates" due to costs, tradeoffs, and constraints (Vermeij, 1987;Agrawal, 2001;Dietl and Kelley, 2002).…”

“…The process leads to progressive elaboration of weapons and defenses, and in some may result in "adaptive stalemates" due to costs, tradeoffs, and constraints (Vermeij, 1987;Agrawal, 2001;Dietl and Kelley, 2002). For example, interactions between snails (gastropod mollusks) and crabs that prey upon them, can lead to the evolution of thicker, larger shells, external shell ornamentation, and variable macroscopic shell geometries in prey and strong, geometrically-specialized claws of the crab (Vermeij, 1987;Seed and Hughes, 1995;Dietl and Kelley, 2002).…”

“…It has been hypothesized that environmental and predatory threats are critical factors in the protective functional design of biological exoskeletons or "natural armor", which arise through processes such as co-evolution and escalation between predators and prey (Vermeij, 1987;Dietl and Kelley, 2002). Evidence for predator-related exoskeletal damage and repair has been reported extensively in the literature Wang et al, 2009).…”

“…are investigated. Such a mechanistic approach to predator-prey offensive and defensive interactions is relevant to elucidating universal principles that direct ecological interactions and resulting evolutionary outcomes (Herre, 1999;Dietl and Kelley, 2002) and also can provide insights in the design of synthetic protective systems.…”

“…Based on these results, a summary of advantageous and disadvantageous design strategies for the offensive threat and defensive protection was formulated. Studies of such a system where the offensive threat and defensive protection are comparable may lead to insights into adaptive phenotypic plasticity of tooth and scale microstructure, predator-prey "adaptive stalemates" and the so-called evolutionary "arms race" (Agrawal, 2001;Dietl and Kelley, 2002).…”