Photo: Madrone trees, Guadalupe Mountains, Texas. © 2017 Delena Norris-Tull
Fluctuation dependent mechanisms: Their role in maintaining diversity
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, July 2020.
Chesson, 2000, states that, “Some stable coexistence mechanisms critically involve the fluctuations in the system, that is, without the fluctuations, the mechanism does not function. Thus, they are termed fluctuation dependent.”
Letten, et al., 2018, points out that fluctuation-dependent mechanisms include both “the temporal storage effect, which formalizes the concept of temporal niche partitioning, and relative nolinearity of competition, which can mediate coexistence through the asymmetric effects of nonlinear averaging on population growth rates.”
Letten, et al., 2018, point out that temporal niche partitioning “was originally presented as a solution to the so-called paradox of the plankton, the seemingly inexplicable coexistence of numerous species on just a few limiting resources. The proposed explanation was that environmental fluctuations could afford each species a period of competitive superiority, thus avoiding any one species being excluded.”
“For stable coexistence to arise via temporal niche partitioning, species at low density have to capitalize on low levels of competition during periods favorable to their growth, whereas the potential gains made by high-density species during favorable periods are constrained by high levels of intraspecific competition” (Letten, et al., 2018).
The temporal storage effect suggests that the coexistence of diverse species is facilitated by environmental fluctuations that enable different species to access the same resource at different times. For example, environmental conditions that are temporal, such as the temporal nature of availability of sunlight, and the seasonal nature of flower and seed production, are fluctuation-dependent mechanisms. Seasonal variations in nutrient concentrations in plants (e.g., amino acids and sugars) are another example. Normal seasonal variations in temperature and precipitation are additional examples. These temporal variations do not destabilize the system, but rather become a necessary aspect of the ecosystem, facilitating species coexistence.
Letten, et al., 2018, state that, “Relative nolinearity of competition differs from the temporal storage effect in that it relies on fluctuations in the intensity of competition, rather than fluctuations in the environment itself. Due to nonlinear averaging on population growth rates, species with sharply saturating (more concave) functional responses to resource concentrations will be more harmed by variability in a limiting resource than their less concave competitors. This difference can reduce fitness inequalities between species and also benefit species at low density if the more concave species increases resource fluctuations while the more linear species dampens fluctuations.”
References:
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Fluctuation dependent mechanisms: Their role in maintaining diversity
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, July 2020.
Chesson, 2000, states that, “Some stable coexistence mechanisms critically involve the fluctuations in the system, that is, without the fluctuations, the mechanism does not function. Thus, they are termed fluctuation dependent.”
Letten, et al., 2018, points out that fluctuation-dependent mechanisms include both “the temporal storage effect, which formalizes the concept of temporal niche partitioning, and relative nolinearity of competition, which can mediate coexistence through the asymmetric effects of nonlinear averaging on population growth rates.”
Letten, et al., 2018, point out that temporal niche partitioning “was originally presented as a solution to the so-called paradox of the plankton, the seemingly inexplicable coexistence of numerous species on just a few limiting resources. The proposed explanation was that environmental fluctuations could afford each species a period of competitive superiority, thus avoiding any one species being excluded.”
“For stable coexistence to arise via temporal niche partitioning, species at low density have to capitalize on low levels of competition during periods favorable to their growth, whereas the potential gains made by high-density species during favorable periods are constrained by high levels of intraspecific competition” (Letten, et al., 2018).
The temporal storage effect suggests that the coexistence of diverse species is facilitated by environmental fluctuations that enable different species to access the same resource at different times. For example, environmental conditions that are temporal, such as the temporal nature of availability of sunlight, and the seasonal nature of flower and seed production, are fluctuation-dependent mechanisms. Seasonal variations in nutrient concentrations in plants (e.g., amino acids and sugars) are another example. Normal seasonal variations in temperature and precipitation are additional examples. These temporal variations do not destabilize the system, but rather become a necessary aspect of the ecosystem, facilitating species coexistence.
Letten, et al., 2018, state that, “Relative nolinearity of competition differs from the temporal storage effect in that it relies on fluctuations in the intensity of competition, rather than fluctuations in the environment itself. Due to nonlinear averaging on population growth rates, species with sharply saturating (more concave) functional responses to resource concentrations will be more harmed by variability in a limiting resource than their less concave competitors. This difference can reduce fitness inequalities between species and also benefit species at low density if the more concave species increases resource fluctuations while the more linear species dampens fluctuations.”
References:
- Chesson, P. (2000). Mechanisms of maintenance of species diversity. Annual Review of Ecological Systems, 31, 343-366.
- Letten, A.D., Dhami, M.K, Ke, P, & Fukami, T. (July 26, 2018). Species coexistence through simultaneous fluctuation-dependent mechanisms. Proceedings of the National Academy of Sciences of the United States of America (PNAS), 115 (26), 6745-6750.
Next Sections on the role of diversity:
Next Sections on research on the success of invasive species: