Determining the extent of human adaptation to climate change, known as climatic variation, is important in identifying the potential environmental causes of the changing climate and in determining the best course of action for conservation planning and policy. In a well-designed research programme, quantitative methods can be used to examine the magnitude and nature of climatic variation and to examine the effects of climatic variation on adaptation. A variety of models are used in such investigations, and these can include those of the general population (the “population genetics”), of populations isolated from others (genetic isolation models) or of individuals only (genetic evolution models).
Fluctuating selection refers to a particular mode of evolutionary selection characterized by a fluctuating tendency of variation on an organism over a relatively short period of evolution, usually between a few generations and several hundred thousand years. The most common forms of fluctuating selection have been called the “gene-culture coevolutionary model”. In this model, natural genetic variation within a culture is balanced by variations caused by gene-culture interactions within the culture. This model has been used to explain the evolution of cultural traits such as language and religious beliefs. These models may also be used to study the process of adaptation to climate change and to predict its future consequences.
In a general population model, the genetic drift model, the fluctuating selection model, and the gene-culture coevolution model have all been used to describe the history and the dynamics of genetic variation among natural populations. The gene-culture coevolution model can also be used to evaluate whether the climate change scenario is likely to result in a more rapid rate of population change than those seen in the past.
The size of an ecological niche has been shown to depend on the degree of fluctuating selection. In this model, the selection has been shown to occur at the level of species. This may be due to a biological factor such as a dominant genetic trait, to the existence of different selective pressures acting on different species, or both.
Gene flow between environments, on the other hand, is sometimes used to identify the role of fluctuating selection. In this approach, a specific genetic type, that is dominant in one environment but not in the other, is selected in one habitat but not in the other. {s. These results in a gene-culture coevolution effect whereby the genetic type that is dominant in one environment becomes dominant in the other environment (due to its higher frequency in one).
Fluctuating and gene-culture coevolution effects on ecological niche size can also be studied using population genetic models (such as the Kullback-Nilsson theory), genetic isolation models (which involve genetic isolation of animals from other habitats, and the genetic distance effect (which are related to gene flow between genetic isolating environments). An ecophysiological perspective has also been applied to the problem by using quantitative techniques and simulations to examine the effect of gene flow on ecological niches.
Another aspect of fluctuating selection that has not received much attention is the relationship between environmental influences and climatic variation. Two environmental factors, temperature and precipitation, are known to have varying effects on the viability of specific types of plant species. The occurrence of a temperature gradient in a plant species can determine its ability to adapt to the environment. However, whether such gradients are present in a particular species, how they interact with other environmental influences and the magnitude of such gradients can differ among different species. A number of studies have shown that some plant species have a greater capability to cope with increasing temperature than others.
It is important to identify which type of climatic variation is dominant in a species so that a suitable management strategy can be implemented in the event of future climate change. Using a variety of genetic models, for example, and using the same environment as a control, it may be possible to identify the dominant environmental variation in the long-term. This could then be used to predict the impact of future climate change on populations and communities and thus determine how to best protect species and habitats. Some models have already provided good estimates of the potential impacts of climate change on certain species, while others have suggested that some species may not be able to adapt to the expected future changes in climate because they are genetically resistant to these changes. Thus, identifying the dominant environmental variation in species and the genetic variation in ecological niche sizes could help researchers to better manage the effects of climate change on species.
