Quiz 10: Population Dynamics
The population of species in the flowing water bodies such as the rivers and the streams is highly dynamic. It is governed by the water current, along with the other environmental factors. The water currents cause the movement of the organisms downstream. A downstream movement or a drift can also be cause due to the floods or the active downstream movement of organisms. To maintain the population, the organisms show an active upstream movement. Thus, the balance between downstream and upstream dispersal of the organism maintains the population of the organism that is also called as the colonization cycle by Karl Müller. The freshwater snail Neritina latissima lives in the clear streams. It shows the dispersal at a very slow step that can be monitored visually in the clear stream. The members of a population of Neritina latissima migrating upstream may migrate out to the local subpopulations. In the same way, members from the local subpopulations can join the migrating population. The survey of the different subpopulations of the snail in the study area can be carried out. The shells of the snails of each subpopulation can be marked by different colors. The members of the colonization wave can also be marked by a different color. The migration into or out of the colonization wave can be visually observed by the mixing of snails with different-colored shells.
The probability of rejecting a hypothesis when it is true is called a significance level. A significance level of 0.05 indicates a 5% probability of rejecting the hypotheses that are correct. Let us consider a population showing random distribution of individuals. There is a probability of 5% to reject the hypothesis that the individuals are randomly distributed in the population. The probability to accept the correct hypothesis would be 95% of the time. Another significance level employed in statistical studies is 0.01. It indicates 1% probability to reject a correct hypothesis. Hence, 99% of the time we can accept the correct hypothesis.
Cohort and static life tables are used to estimate patterns of survival within a population. A group born at the same time is called cohort. The life table made is from the data collected from a large number of people born at the same time and maintains a record of them from birth to death is known as cohort life table. Another way to estimate patterns of survival in wild population is to record the age at death of a large number of individuals. This method produces a static life table, which needs to estimate the age at which individual dies. The static life table involves a snapshot of survival within a population during a short interval of time. The cohort is used to study a group of plant seedlings that germinated at the same time or all the lambs born into a population of mountain sheep in a particular year. While, the static life table differs from cohort approach as the sample born at different times is considered. For instance, mountain sheep can be aged by counting the growth rings of their horns.