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12 - Adaptive Speciation in Agricultural Pests
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- By Martijn Egas, University of Amsterdam, Maurice W. Sabelis, University of Amsterdam, Filipa Vala, University College London, Iza Lesna, University of Amsterdam
- Edited by Ulf Dieckmann, International Institute for Applied Systems Analysis, Austria, Michael Doebeli, University of British Columbia, Vancouver, Johan A. J. Metz, Rijksuniversiteit Leiden, The Netherlands, Diethard Tautz, Universität zu Köln
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- Book:
- Adaptive Speciation
- Published online:
- 05 July 2014
- Print publication:
- 02 September 2004, pp 249-263
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Summary
Introduction
Agricultural crops provide an ideal environment for adaptive speciation of pest species. They represent recently colonized habitats, harbor small incipient pest populations, and form environments in which not all the resources are already occupied [together referred to as ecological opportunity, see Schluter (2000)]. These characteristics exactly meet the conditions predicted by Dieckmann and Doebeli (1999) to favor species that split into specialists by the process of evolutionary branching (see Chapters 4 and 5). Additionally, in agricultural systems the ecological environment is constant relative to the natural world, which also favors adaptive speciation. Moreover, the economic importance of agricultural crops warrants extensive research into pest species, which increases the probability that adaptive speciation will be documented. It is therefore not surprising that the best examples of ecological speciation in sympatry involve pest species [e.g., the apple maggot fly Rhagoletis pomonella (Feder 1998), the pea aphid Acyrthosiphon pisum (Via 1999), and the two-spotted spider mite Tetranychus urticae (Gotoh et al. 1993)].
Agriculture provides a diversity of crops, and plant breeding creates a unique level of heterogeneity in both resistance and palatability within a crop species. In this world, pest species may evolve to become specialists (feeding on one or a few plant species, or even genotypes) or generalists, depending on fitness tradeoffs (Levins 1962; Egas et al., in press; Egas et al., unpublished). Such tradeoffs may be found in food conversion efficiency, detoxification, phenology, and defenses against or escape from natural enemies.
22 - Evolution of Exploitation and Defense in Tritrophic Interactions
- Edited by Ulf Dieckmann, International Institute for Applied Systems Analysis, Austria, Johan A. J. Metz, Universiteit Leiden, Maurice W. Sabelis, Universiteit van Amsterdam, Karl Sigmund, Universität Wien, Austria
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- Book:
- Adaptive Dynamics of Infectious Diseases
- Published online:
- 15 January 2010
- Print publication:
- 11 April 2002, pp 297-322
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Summary
Introduction
Why do plants cover the earth and give the world a green appearance? This question is not as trivial as it might seem at first sight. Hairston et al. (1960) hypothesized that herbivores cannot ransack the earth of its green blanket because they are kept low in number by predators. They tacitly ignored the possibility that plants defend themselves directly against a suite of herbivores and together exhibit such great diversity in defense mechanisms that “super” herbivores able to master all plant defenses did not evolve and those that overcome the defenses of some plants are limited by the availability of these plants. Strong et al. (1984) recognized both possibilities in their review on the impact of herbivorous arthropods on plants, but they also favored the view that predators suppress the densities of herbivores, and thereby reduce the threat of plants being eaten.
The two explanatory mechanisms (plant defense versus predator impact), however, may well act in concert. Ever since the seminal review paper by Price et al. (1980) ecologists have become increasingly aware that plant defenses include more than just trickery to reduce the herbivore's capacity for (population) growth. For example, the plant may provide facilities to promote the foraging success of the herbivore's enemies. This form of defense is termed indirect as opposed to direct defense against herbivores.
15 - The evolution of overexploitation and mutualism in plant–herbivore–predator interactions and its impact on population dynamics
- from Part IV - Genetic/evolutionary considerations
- Edited by Bradford A. Hawkins, University of California, Irvine, Howard V. Cornell, University of Delaware
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- Book:
- Theoretical Approaches to Biological Control
- Published online:
- 13 August 2009
- Print publication:
- 06 May 1999, pp 259-282
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Summary
Introduction
Populations of arthropod herbivores may show periodical outbreaks, large amplitude cycles, strongly bounded fluctuations or stable equilibria. At small spatial scales they may also show dynamics different from those at large spatial scales, and they may even go extinct. There is a need to experimentally test models predicting the dynamical consequences of the mechanisms underlying these patterns. In particular, what needs an explanation is the observation that plants retain a green appearance despite attacks by herbivores (Hairston et al., 1960; Strong et al., 1984). There are two possible explanations: (i) plants defend themselves effectively against herbivores, (ii) predators suppress herbivore populations to very low levels. Hairston et al. (1960) tacitly ignored the first and emphasized the latter in formulating their so-called ‘the world is green’ hypothesis. The two explanatory mechanisms, however, are not mutually exclusive; the plant may promote predator foraging success and the herbivore's enemies may use the facilities offered by the plant.
Price et al. (1980) stimulated a growing awareness that plants may defend themselves both directly against herbivorous arthropods and indirectly by promoting natural enemies, for example, by providing protection, food, and alarm signals to the enemies of the herbivore. Direct defenses include plant structures that hinder feeding by the herbivore, and secondary plant compounds that inhibit digestion, intoxicate the herbivore or deter feeding. Before Price et al. (1980) appeared, examples of indirect defenses were already well-known from ant–plant interactions (Janzen, 1966; Bentley, 1977; see also historical reviews by Beattie, 1985, and Jolivet, 1996).