Question

How would a stochastic event lead to the extinction of population?

What are the differences of the static and cohort method of estimating parameters of a life table?

When would the net reproductive rate, reflect the geometric growth of a age structured population?

What is a metapopulation and when would somoene model a population as such?

Answer 1

1. A stochastic event includes natural calamities like floods, famines, forest fires etc. as well as the anthropogenic activities like deforestation, habitat destruction, land use for mining or megaprojects etc. All these events have a direct influence on the populations or communities occupying the area. Their effect on a given population depends on the magnitude of the event. If the event is of higher magnitude, it has an adverse effect on the habitat resilience and the subsequent effect on the oganisms that live in the specified area. Every area is occupied by different organisms, some of which have the ability to tolerate such changes while others are specific in their needs or requirements. Any change in their ecosystem can have disastrous effect on these sensitive organisms (K-selected ones) and it will also lead to a decrease in their number or complete extinction based on the magnitude of the stochastic event.

2. A life table reflects the survivorship of people. There are two methods of determining the parameters of life table: a) Static or period method b) Cohort method

In Static method, the mortality rate of a given population over a specific period of time is considered for determining survivorship while as in Cohort method, the mortality rate of a given population for the entire lifetime is considered.

out of the two methods, cohort method also known as generation method is widely used to determine the survivorship or parameters of life table. This method has an advantage over the static one in the sense that it treats population as dynamic and the results obtained can be projected to predict the future mortality rates of the population.

However, it must be noted that Static as well as cohort method are equally significant when the population is in equilibrium and environment is stable.

3. In nature, there are certain populations of the same species which are spatially distributed due to natural or anthropogenic habitat fragmentation. These small populations of the same species occupying different habitats may or may not interact with eachother at some level. such a population is known as metapopulation or we can say 'Population of populations'. The term was first coined by Richard levins. There are models to characterize such populations that include 'Levins Model' and 'Stochastic patch Occupancy model'