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Evolutionary Significance of Predation
Relevant Publications:
Langerhans and DeWitt 2002 EER, DeWitt and Langerhans 2003 J. of Sea Research,
Langerhans et al. 2004 Evolution, Langerhans and DeWitt 2004 American Naturalist,
Langerhans et al. 2005 PNAS, Langerhans 2006 in Predation in Organisms,
Losos et al. 2006 Science, Langerhans et al. 2007 Evolution
Langerhans and Gifford 2009 Evolution, Langerhans 2009 J. of Evolutionary Biology
Langerhans 2009 Biology Letters, Langerhans and Reznick in press (Chapter in Fish Locomotion)
Langerhans et al. in press (in Viviparous Fishes II)
Predation is one of the most important and obvious forces shaping organismal traits. Prey have evolved diverse means of enhancing the probability of survival in the face of predation, comprising two major classes of antipredator strategies: (1) avoidance of predatory encounters, and (2) escaping after encountering a predator. A range of antipredator defenses—including behavioral, morphological, physiological, and chemical defenses—serve to either reduce the probability of detection by a predator or enhance the probability of surviving after detection by a predator. However, the recognition that reproductive strategies (e.g., offspring number, reproductive lifespan) are typically strongly influenced by mortality regimes induced by predators, highlights that most but not all “antipredator traits” fall into one of these two categories—that is, some life history traits influence only fecundity, not survival. Emphasizing a conceptual link between life histories and predation broadens and refines our current understanding of predation’s role in phenotype evolution.
The table below presents a framework for understanding antipredator traits based on the manner in which traits directly influence prey fitness and the chronological stage of the predatory encounter in which they are employed. Acronyms are as follows, ASF: avoiding a predator’s sensory field, DSF: avoiding detection within a predator’s sensory field, ATD: attack deterrence, CPD: capture deterrence, CND: consumption deterrence, Y: yes. Table from Langerhans 2006.
A varied history exists for the study of predation’s role in influencing evolutionary change. Despite the wealth of antipredator adaptations present in organisms, research investigating the significance of predation in biological evolution has received considerably less attention than other ecological factors (e.g., competition, mate attraction). However, predation can generate divergent selection among prey populations in several different ways (Figure to right), and is predicted to represent a major source of evolutionary change.
The figure on the right illustrates three common ways in which predators can drive phenotypic divergence among prey populations (or species). Solid arrows in A-C depict selection on a prey trait. The sign beside each arrow indicates the direction of the optimal phenotype in relation to the population mean. Divergent selection arising from (A) divergent predator regimes, (B) competition for enemy free space within a given predator regime, and (C) an interaction between predation and the prey’s selective regime. (D) Hypothetical fitness functions resulting from each scenario depicted in A-C, with trait distributions for the two prey populations represented by the shaded areas. Arrows in D illustrate the direction selection is pulling trait means for each population. Figure from Langerhans 2006.
The figure below illustrates a common theme for morphological differences between populations inhabiting low- and high-predation environments. In both of these distantly related fish species, populations inhabiting high-predation environments exhibit a smaller anterior/head region and a larger caudal region. Figures represent results of thin-plate spline deformations from the grand mean in each species, and are magnified 2× to aid visualization. A) Threespine stickleback, Gasterosteus aculeatus, from 40 lakes in Alaska, USA (data from Walker and Bell 2000). B) Western mosquitofish, Gambusia affinis, from six ponds in Texas, USA (data from Langerhans et al. 2004). Figure from Langerhans and Reznick in review.
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(An undesirable fate.)
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