Farrah Ansari | Monday Lab
A population is a group of individual species that all reside in the same general area. These individuals rely on each other for resources because the same resources are used by every member of the group. Populations evolve for time due to natural selection favoring heritable traits within the group. Different populations of a single species may be isolated due to geographic barriers which causes exchanging materials only rarely. Members of a population typically breed with one another and this on average are more closely related to each other than to members of other populations. A gene pool characterizes a population’s genetic makeup by showing the alleles that are present within the population. If only one allele is exists within a population is said to be fixed in the gene pool. Each allele frequency has a frequency in the population. If there are no differences within the population we can conclude that the real population is evolving. The gene pool of population that is not evolving can be described by the Hardy-Weinberg principle. This states that the frequencies of alleles and genotypes in a population will remain constant from generation to generation provided that only Mendelian segregation and recombination of alleles are at work, these gene pools is said to be in Hardy-Weinberg Equilibrium.
In order to study the relationship between population and the environment there is a separate field of study called population ecology. Within this field is population dynamics, which is the study of long and short term changes in the size and age of a population. This is done by correlating the birth rates, death rates, immigration, and emigration and how these factors affect a population. Population dynamics is based on three fundamental characteristics, density, dispersion, and demographics.
Density is the number of individuals per unit are or volume. Different patterns affect the density of a population. Additions to a population occur when there are births and individuals immigrate into boundaries. Subtractions can also occur within a population through deaths and individuals emigrating out. The population size and density can be determined by simply counting the number of individuals that are present within the boundaries but conducting studies this way would be impractical. In order to study density in a practical way scientist a method called mark-recapture method. This method is used for sampling a population density with mostly mobile individuals by capturing, marking, then releasing the individuals. By collecting data through this method the scientists can have an estimated population number. The calculations are done by multiplying the first and second samples together then dividing them by the number of marked individuals in the recaptured sample. The only time this method can be used is when the population is fairly static, meaning the migration and mortality rates are known. Another method that is also used is called the Lincoln-Petersen method which is another sampling technique but the population that is studied is assumed to be a closed population, meaning no immigration or emigration occurs. The method combines two visits to a population which are close enough in time where no deaths or births occur.
Dispersion is the pattern of spacing among individuals within the boundaries of the population. Variations among local density are crucial for ecologist because they allow a closer view to the environmental and social interactions that occur within a population. There are three different patterns to dispersion; clumped, uniform, and random. Clumped dispersion, the most common, is when individuals accumulated themselves in particular areas; these patches may be associated with mating behaviors. Uniform dispersion occurs when there is a direct interaction between majorities of individuals in a population; this form is a result of aggressive social interactions. The