In the Light of Evolution Volume III: Two Centuries of Darwin (2009) / Chapter Skim
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7 Human-Induced Evolution Caused by Unnatural Selection Through Harvest of Wild Animals--Fred W. Allendorf and Jeffrey J. Hard
7 Human-Induced Evolution Caused by Unnatural Selection Through Harvest of Wild Animals--Fred W. Allendorf and Jeffrey J. Hard
Pages 129-148
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From page 129... ...
hArD‡ Human harvest of phenotypically desirable animals from wild populations imposes selection that can reduce the frequencies of those desirable phenotypes. Hunting and fishing contrast with agricultural and aquacultural practices in which the most desir able animals are typically bred with the specific goal of increasing the frequency of desirable phenotypes.
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From page 130... ...
H umans have exploited wild populations of animals for food, cloth ing, and tools since the origin of hominids. human harvest of wild populations is almost always nonrandom.
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From page 131... ...
regulations that restrict harvest based on size or morphology of weapons under sexual selection Timing of selective harvest of Altered distribution harvest reproduction seasonally early or of reproduction throughout late reproducers (truncated or altered reproductive seasonality) season Behavior harvest of more reduced boldness implement harvest active or aggressive in foraging or methods less likely or bolder (more courtship behavior, to impose selection vulnerable potentially reduced on activity to predation)
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From page 132... ...
Hard activity in contrast to natural selection. Unnatural selection generally acts at cross purposes to the long-term goal of sustainable harvest of wild populations and can reduce the frequency of phenotypes valued by humans.
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From page 133... ...
Modified natural selection Change in phenotypic frequencies Reduction in frequency of Change in Modified sexual desirable phenotypes and Human harvest population selection reduced genetic "quality" dynamics Increased mortality Selective change for earlier maturity FiGUre 7.1 human harvest can have a variety of direct and indirect genetic effects on populations, and it has the potential to affect the future yield and viability of exploited populations.
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From page 134... ...
. sustainable harvests will eventually require that fisheries and wildlife managers incorporate genetic principles into the management of wild populations.
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From page 135... ...
exploitative selection imposed by fishing tends to reduce the frequency of desirable phenotypes through directional selection for alternative phenotypes, unlike other human-induced forms of selection, such as domestication, which often produce maladapted phenotypes indirectly by favoring alternative optima through alteration of the natural selection regime [e.g., Araki et al.
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From page 136... ...
. Total selection estimates that combined natural and sexual selection intensities tended to be smaller, in general, and sexual selection on morphology was often stronger than natural selection.
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From page 137... ...
We expect that hunting selection could have a considerable effect on the evolution of adult characteristics, particularly those in prime-aged adults under sexual selection because hunting mortality is often substantially higher than natural mortality for adult game animals (Festa-Bianchet, 2003; Gaillard et al., 2003)
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From page 138... ...
several key population characteristics can affect genetic variability and adaptive potential. in most ungulates, for example, breeding population size, generation length and adult longevity, and mating structure, including the breeding sex ratio and harem size, can have a large influence on the dynamics of genetic and phenotypic variation under exploitation (ryman et al., 1981; Martinez et al., 2002; Mysterud et al., 2002; Wade and shuster, 2004)
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From page 139... ...
0 1830 1850 1870 1890 1910 1930 Year FiGUre 7.2 reduction in frequency of the silver morph of the fox in eastern Canada resulting from the preferential harvest by hunters of the more valuable silver morph (elton, 1942; haldane, 1942)
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From page 140... ...
Both ram weight and horn size are undoubtedly subject to sexual selection through male-male competition during the rut, but it is unclear to what extent such sexual selection can alter the rate of evolution under hunting selection because sexual selection gradients have not been estimated. however, they must be high for some heavily hunted populations, where heritabilities for traits under selection are high and observed temporal declines in breeding values for
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From page 141... ...
(2008) Another human activity that can impose exploitative selection on wild populations is specimen collecting, whether for private, commercial, or scientific use.
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From page 142... ...
For example, if larger individuals enjoy greater reproductive success, sexual selection for increased body size could counter selection against larger size imposed by fishing. selective harvest can directly affect mating and have a strong effect on subsequent recruitment because it tends to remove individuals with particular characteristics, such as large size or elaborate weapons from those of the breeding pool (Kingsolver et al., 2001)
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From page 143... ...
in this case, combined natural and sexual selection impose a selection gradient on a bivariate phenotype that opposes the selection gradient imposed by exploitation. As a result, a suboptimal phenotype in the wild breeding population can increase in frequency as the effectiveness of natural and sexual selection is reduced.
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From page 144... ...
44 / Fred W Allendorf and Jeffrey J
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From page 145... ...
natural and sexual selection impose a selection gradient on the bivariate phenotype, which tends to oppose the selection gradient imposed by selective fishing. The result is a suboptimal phenotype in the wild breeding population that might deviate substantially from A
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From page 146... ...
Although we cannot be certain that many of the observed phenotypic trends in a variety of exploited animals are solely the result of exploitative selection, it would be imprudent to assume that such selection has not had an effect. The coupling of such trends with evidence for reduced productivity and yield is reason enough to adopt a risk-averse approach in considering sustainable harvest practices.
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From page 147... ...
. no-take protected areas have considerable potential for reducing the effects both of loss of genetic variation and harmful exploitative selection.
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