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1988 Evolution of competitive ability
CHAPTER FIFTY FIVE
1988 Evolution of competitive ability The concept The expansive elaboration of r- and K-selection by MacArthur and Wilson (1967) predicted that, at high population densities, competitive ability would be at a premium and under strong natural selection for improvement. This prediction was tested experimentally by Mueller (1988a) by keeping replicated populations of Drosophila melanogaster at high and low population sizes. After 128 generations of evolution at these extreme densities, the populations adapted to high densities had competition coefficients that were 58% greater than the populations kept at low density. This finding was consistent with basic models of density-dependent natural selection.
The explanation Mueller (1988a) initiated an experiment to examine the outcome of density-dependent natural selection by using replicated populations of Drosophila melanogaster. In Chapter 35 a trade-off in density-dependent population growth rates was described (Mueller and Ayala, 1981). The finding that Drosophila had adapted to different levels of crowding motivated further investigation on competitive ability. In these laboratory-selected populations, crowding has the largest impact on the mortality of the larvae. Drosophila larvae compete through a scramble competition for food. Consequently, a good measure of competitive ability is to allow larvae to compete for carefully controlled amounts of food (live yeast). Phenotypically the populations adapted to low and high densities were wild type. Thus, each of these different density-adapted populations was competed against a standard population carrying the X-linked white allele, which results in flies with white eyes, at 10 different yeast levels. The survival of the lab-adapted larvae relative to the white competition stock can be used to infer competitive ability from models of Drosophila competition (Mueller, 1988b). The average high-density adapted population had a competition coefficient of 1.14 while the coefficient for the Conceptual Breakthroughs in Evolutionary Ecology ISBN: 978-0-12-816013-8 https://doi.org/10.1016/B978-0-12-816013-8.00055-7
© 2020 Elsevier Inc. All rights reserved.
129
j
130
Conceptual Breakthroughs in Evolutionary Ecology
low-density populations was 0.72. That is, the competitive ability of the high-density adapted populations was 58% greater than the low-density populations. A phenotype tightly correlated with competitive ability is the larval feeding rate (Bakker, 1961; Mueller, 1988b). Joshi and Mueller (1988) showed that the high-density adapted populations fed 15% faster than the low-density adapted populations.
Impact: 8 An intuitive but important component of the theory of densitydependent natural selection is the prediction that competitive ability for resources in short supply in a crowded environment will increase by natural selection. The experiments conducted by Mueller (1988a) provide direct evidence for this important theoretical prediction.
References Bakker, K., 1961. An analysis of factors which determine success in competition for food among larvae in Drosophila melanogaster. Arch. Neerl. Zool. 14, 200e281. Joshi, A., Mueller, L.D., 1988. Evolution of higher feeding rate in Drosophila due to densitydependent natural selection. Evolution 42, 1090e1093. MacArthur, R.H., Wilson, E.O., 1967. The Theory of Island Biogeography. Princeton Univ. Press, Princeton, NJ. Mueller, L.D., 1988a. Evolution of competitive ability in Drosophila due to densitydependent natural selection. Proc. Natl. Acad. Sci. U.S.A. 85, 4383e4386. Mueller, L.D., 1988b. Density-dependent population growth and natural selection in food limited environments: the Drosophila model. Am. Nat. 132, 786e809. Mueller, L.D., Ayala, F.J., 1981. Trade-off between r-selection and K-selection in Drosophila populations. Proc. Natl. Acad. Sci. U.S.A. 78, 1303e1305.
1988 Evolution of competitive ability The concept The expansive elaboration of r- and K-selection by MacArthur and Wilson (1967) predicted that, at high population densities, competitive ability would be at a premium and under strong natural selection for improvement. This prediction was tested experimentally by Mueller (1988a) by keeping replicated populations of Drosophila melanogaster at high and low population sizes. After 128 generations of evolution at these extreme densities, the populations adapted to high densities had competition coefficients that were 58% greater than the populations kept at low density. This finding was consistent with basic models of density-dependent natural selection.
The explanation Mueller (1988a) initiated an experiment to examine the outcome of density-dependent natural selection by using replicated populations of Drosophila melanogaster. In Chapter 35 a trade-off in density-dependent population growth rates was described (Mueller and Ayala, 1981). The finding that Drosophila had adapted to different levels of crowding motivated further investigation on competitive ability. In these laboratory-selected populations, crowding has the largest impact on the mortality of the larvae. Drosophila larvae compete through a scramble competition for food. Consequently, a good measure of competitive ability is to allow larvae to compete for carefully controlled amounts of food (live yeast). Phenotypically the populations adapted to low and high densities were wild type. Thus, each of these different density-adapted populations was competed against a standard population carrying the X-linked white allele, which results in flies with white eyes, at 10 different yeast levels. The survival of the lab-adapted larvae relative to the white competition stock can be used to infer competitive ability from models of Drosophila competition (Mueller, 1988b). The average high-density adapted population had a competition coefficient of 1.14 while the coefficient for the Conceptual Breakthroughs in Evolutionary Ecology ISBN: 978-0-12-816013-8 https://doi.org/10.1016/B978-0-12-816013-8.00055-7
© 2020 Elsevier Inc. All rights reserved.
129
j
130
Conceptual Breakthroughs in Evolutionary Ecology
low-density populations was 0.72. That is, the competitive ability of the high-density adapted populations was 58% greater than the low-density populations. A phenotype tightly correlated with competitive ability is the larval feeding rate (Bakker, 1961; Mueller, 1988b). Joshi and Mueller (1988) showed that the high-density adapted populations fed 15% faster than the low-density adapted populations.
Impact: 8 An intuitive but important component of the theory of densitydependent natural selection is the prediction that competitive ability for resources in short supply in a crowded environment will increase by natural selection. The experiments conducted by Mueller (1988a) provide direct evidence for this important theoretical prediction.
References Bakker, K., 1961. An analysis of factors which determine success in competition for food among larvae in Drosophila melanogaster. Arch. Neerl. Zool. 14, 200e281. Joshi, A., Mueller, L.D., 1988. Evolution of higher feeding rate in Drosophila due to densitydependent natural selection. Evolution 42, 1090e1093. MacArthur, R.H., Wilson, E.O., 1967. The Theory of Island Biogeography. Princeton Univ. Press, Princeton, NJ. Mueller, L.D., 1988a. Evolution of competitive ability in Drosophila due to densitydependent natural selection. Proc. Natl. Acad. Sci. U.S.A. 85, 4383e4386. Mueller, L.D., 1988b. Density-dependent population growth and natural selection in food limited environments: the Drosophila model. Am. Nat. 132, 786e809. Mueller, L.D., Ayala, F.J., 1981. Trade-off between r-selection and K-selection in Drosophila populations. Proc. Natl. Acad. Sci. U.S.A. 78, 1303e1305.