Define genetic drift in biology In wild populations, there are always relatively common and relatively rare alleles. Small populations are at risk of losing genetic variation much faster than large populations. While common alleles generally tend to remain common, rare alleles are likely to be randomly lost in subsequent generations. Consider how each parent only …
Demographic stochasticity Population stochasticity (also known as demographic change) refers to random variations in the demographic characteristics of a population (eg. sex ratios, birth rate, death rate), the cumulative effect of varying the fitness of individual organisms. In any natural population founded by only a few individuals by definition start off with low genetic diversity, …
In some taxa, such as butterflies, annuals, and amphibians, population size varies dramatically from generation to generation. In recent years, populations may be so large that they seem in little danger of extinction. However, years of abundance can be misleading when followed by subsequent years of low abundance. Typically, in a population of individuals experiencing …
Large populations have many ecological, behavioral, and physiological mechanisms that prevent hybridization, the production of offspring among genetically distant taxa, whether they be individuals of different species, or individuals of the same species but with different adaptations (the latter being intraspecific hybridization). As with inbreeding depression, these mechanisms may fail in small populations, leading to …
Mating among closely related individuals, which occurs in small populations, often results in lower reproductivesuccess and weaker offspring. In large populations, a variety of instinctive mechanisms are in place to promote heterosis, which occurs whenoffspring have a level of genetic variation that improves their individual evolutionary fitness. Some species are predisposed to disperse from their …
Thermal pollution describes localized human-induced temperature changes in the natural world. Aquatic ecosystems represent one of the ecosystems most vulnerable to thermal pollution. For example, when water is released from big dams, it comes from the colder middle and lower strata of the reservoir, leading to rapid cooling of aquatic ecosystems further downstream. The opposite …
Many people find a sense of freedom when they are in natural surroundings, with peace and quiet facilitating a much-needed connection to nature. These experiences are increasingly being threatened by noise pollution. Noise Pollution and Its Sources; noise pollution (also called acoustic pollution)—caused by human activities, such as industrial, military, and transportation systems—is harmful and …
Light pollution describes the addition of excessive, prolonged, or poorly designed artificial light to the natural world. As a consequence of an increasingly industrialized world, light pollution has increased dramatically over the past decades as more people have gained greater access to electricity. Behavioral disruption is perhaps the most well-known consequence of increased light pollution—consider …
Soil pollution occurs when the soil encounters foreign chemicals and other pollutants. This type of pollution is often associated with industrial activities that extract agricultural and land resources, runoff, pesticide use, oil spills, acid rain, improper sewage treatment, and improper waste disposal. People and wildlife can therefore become ill through direct contact with contaminated soils, …
Air pollution by hydrocarbons often manifests itself in the form of photochemical smog. Hanging like a thick cloud over industrial areas, people sometimes confuse it with natural mist in the early morning. In the past, people and industries believed that the atmosphere was so vast that it contained gases or particles released into the air, …
