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2 - The storage effect: definition and tests in two plant communities
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- By Peter Chesson, University of Arizona, Nancy J. Huntly, Utah State University, Stephen H. Roxburgh, CSIRO Sustainable Ecosystems, Marissa Pantastico-Caldas, Los Angeles Trade-Tech College, José M. Facelli, The University of Adelaide
- Edited by Colleen K. Kelly, University of Oxford, Michael G. Bowler, University of Oxford, Gordon A. Fox, University of South Florida
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- Book:
- Temporal Dynamics and Ecological Process
- Published online:
- 18 December 2013
- Print publication:
- 16 January 2014, pp 11-40
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Summary
Introduction
Nature is pervaded by variation: the physical environment is ever changing in time and in space, populations fluctuate, and no two organisms are the same. To explore natural environments is to be confronted by variation, and the science of ecology is challenged by the persistent question: is this variation more than variation itself? Environmental variation can cause population fluctuations (Ripa et al. 1998), but can it do more than this? Does it affect how organisms interact with one another? Does it shape populations and communities? How and in what ways? Biologists firmly accept that variation shapes the organisms. Heritable variation is the engine of evolution, which is fuelled by environmental change. In life-history theory, it is widely accepted that organisms show adaptations to variation in the physical environment, exemplified by evolutionary theories of iteroparity and seed dormancy (Cohen 1966, Bulmer 1985, Ellner 1985a, Real and Ellner 1992). Fundamentally, these adaptations allow species to take advantage of favourable environmental conditions without being too vulnerable to unfavourable environmental conditions.
Community ecologists have had a variety of attitudes to variation, especially variation in the physical environment (Chesson and Case 1986). Successional change after disturbance had a prominent role in the early development of plant and ecosystem ecology (Clements 1916) and now has an important role in diversity maintenance theory relying on competition–colonisation tradeoffs (Hastings 1980). Spatial variation is often assumed to provide for, and should therefore promote, species diversity (Pacala and Tilman 1994, Amarasekare and Nisbet 2001, Snyder and Chesson 2004). Although it is often assumed that regular temporal variation, such as seasonal and diurnal variation, provides for temporal niches (Armstrong and McGehee 1976, Levins 1979, Brown 1989a, b, Chesson et al. 2001), there is also much unpredictable temporal variation, such as deviations of weather and climate from seasonal averages (Davis 1986) and disturbances such as fire (Connell 1978, Bond and Keeley 2005). Should we think of this unpredictable temporal variation as disruptive to ecological processes (May 1974)? Do organisms fail to adapt to unpredictable temporal variation? Are they merely jerked around by it? Life-history theory suggests otherwise (Bulmer 1985, Real and Ellner 1992), yet conclusions are often drawn from models that reflect no such adaptations, for example Lotka–Volterra models with unpredictable environmental variation added arbitrarily (Turelli 1981, Kilpatrick and Ives 2003).
Chapter 3 - Specialized seedling strategies I: seedlings in stressful environments
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- By José M. Facelli, The University of Adelaide, Discipline of Ecology and Evolutionary Biology, School of Earth and Environmental Sciences, Adelaide, Australia
- Edited by Mary Allessio Leck, Rider University, New Jersey, V. Thomas Parker, San Francisco State University, Robert L. Simpson, University of Michigan, Dearborn
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- Book:
- Seedling Ecology and Evolution
- Published online:
- 05 June 2012
- Print publication:
- 18 September 2008, pp 56-78
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Summary
Introduction
Seedlings are particularly susceptible to harsh conditions. Indeed, the seedling stage is considered to be the most vulnerable stage in the life of the plant (Stebbins, 1971; Fenner, 1987; Fenner & Thompson 2005) because even small reductions in biomass may lead to the death of the plant (Dirzo, 1985; Fenner & Thompson, 2005). Selection has favored strategies that reduce the high risk of the seedling stage primarily in two ways: first, maternal deployment of optimal amount of reserves to ensure maximum likelihood of seedling survival (Smith & Fretwell, 1974; Westoby et al., 1992; Leishman & Westoby, 1994a; Leishman et al., 2000), and second, timing of germination to avoid emergence during periods of high environmental stress as well as during transient favorable conditions too short to ensure postemergence survivorship (Grime, 1979; Baskin & Baskin, 1989, 1998; Fenner & Thompson, 2005). However precise the mechanism to adjust germination to low-risk conditions may be, many environments present inherently high risks for seedlings because the stress is chronic or favorable conditions are intermittent and uncertain (see Table 3.1). Because the ability of the seedling to accumulate or replace biomass decreases as the environment becomes less favorable, seedlings in stressful environments are at higher risk of mortality. Furthermore, when postemergence mortality is highly probable, avoidance of stress per se is not a viable strategy and seedlings are selected to tolerate stressful conditions.