Ch. 6
Natural Selection & Adaptation:
The most important of these consequences for the study of ecology is evolution by natural selection. The term evolution pertains to any change in a population’s gene pool. When genetic factors cause differences among individuals in survival and reproductive success, evolutionary change comes about through natural selection. Individuals whose traits enable them to achieve higher rates of reproduction leave more descendants, and therefore the alleles responsible for those traits increase in the gene pool of the population. The traits themselves are referred to as adaptations, or evolutionary adaptations, and the process itself is often referred to as adaptation. The process of evolution by natural selection has three main ingredients:
1. Variation among individuals
2. Inheritance of that variation
3. Differences in survival and reproductive success, or fit- ness, related to that variation
Types of selection:
Over the next hundred years, this dark form became increasingly common in forests near heavily industrialized regions, which is why the phenomenon is often referred to as industrial melanism. In the absence of factories and other heavy industry, the pale, or typical, form of the moth still prevailed.
The capacity to respond to environ- mental variation, which is called phenotypic plasticity, can itself be an adaptation that enhances the individual’s fitness. Environments change over time and space, and individuals adjust to these changes by altering their behavior, their physiology, and even their structure.
Animals are free to move about their environment, and at any given time they may choose that part of the environment that best enhances their survival or reproduction because of its temperature, moisture, salinity, or other conditions. Parts of the environment that can be distinguished by their conditions are referred to as microhabitats or microenvironments.
Growing thicker fur in winter, producing smaller leaves during the dry season, increasing the number of red cells in the blood at high elevations, producing enzymes with different temperature optima or lipids that remain fluid at different temperatures— all of these are forms of adaptive phenotypic plasticity referred to as acclimatization. Acclimatization may be thought of as a shift in an individual’s range of physiological tolerances.
Whether differences between populations are due to genetic differences, phenotypic plasticity, or genotype– environment interactions can often be revealed by reciprocal transplant experiments. Transplant studies com- pare the observed phenotypes of individuals kept in their native environment with those of individuals transplanted to a different environment (Figure 6.19). Reciprocal trans- plants involve the switching of individuals between two localities. When the phenotypic values of native and trans- planted individuals are the same, we can conclude that the traits of interest are genetically determined— that is, that the trait values reflect the population of origin (genotype) rather than the local conditions (environment)
Natural Selection & Adaptation:
The most important of these consequences for the study of ecology is evolution by natural selection. The term evolution pertains to any change in a population’s gene pool. When genetic factors cause differences among individuals in survival and reproductive success, evolutionary change comes about through natural selection. Individuals whose traits enable them to achieve higher rates of reproduction leave more descendants, and therefore the alleles responsible for those traits increase in the gene pool of the population. The traits themselves are referred to as adaptations, or evolutionary adaptations, and the process itself is often referred to as adaptation. The process of evolution by natural selection has three main ingredients:
1. Variation among individuals
2. Inheritance of that variation
3. Differences in survival and reproductive success, or fit- ness, related to that variation
Types of selection:
Over the next hundred years, this dark form became increasingly common in forests near heavily industrialized regions, which is why the phenomenon is often referred to as industrial melanism. In the absence of factories and other heavy industry, the pale, or typical, form of the moth still prevailed.
The capacity to respond to environ- mental variation, which is called phenotypic plasticity, can itself be an adaptation that enhances the individual’s fitness. Environments change over time and space, and individuals adjust to these changes by altering their behavior, their physiology, and even their structure.
Animals are free to move about their environment, and at any given time they may choose that part of the environment that best enhances their survival or reproduction because of its temperature, moisture, salinity, or other conditions. Parts of the environment that can be distinguished by their conditions are referred to as microhabitats or microenvironments.
Growing thicker fur in winter, producing smaller leaves during the dry season, increasing the number of red cells in the blood at high elevations, producing enzymes with different temperature optima or lipids that remain fluid at different temperatures— all of these are forms of adaptive phenotypic plasticity referred to as acclimatization. Acclimatization may be thought of as a shift in an individual’s range of physiological tolerances.
Whether differences between populations are due to genetic differences, phenotypic plasticity, or genotype– environment interactions can often be revealed by reciprocal transplant experiments. Transplant studies com- pare the observed phenotypes of individuals kept in their native environment with those of individuals transplanted to a different environment (Figure 6.19). Reciprocal trans- plants involve the switching of individuals between two localities. When the phenotypic values of native and trans- planted individuals are the same, we can conclude that the traits of interest are genetically determined— that is, that the trait values reflect the population of origin (genotype) rather than the local conditions (environment)