Question

Some species of rodents live on average 6 years. In the first two years of life they do not reproduce and only 20% of the females born alive reach 2 years of age. Between the third and fourth year females have 1 daughter on average and their survival is 50%, while in the las two years they have 2 daughters on average. If in an ecosystem there is initially a population of 10 females between 0 and 2 years old, 4 between 3 and 4 years and 3 with more than 4 years. After 3 years the estimated population of females will be:

Instructions: When calculating, round the result to the nearest whole number.

- females between 0 and 2 years:_____

- females between 2 and 4 years:_____

- females with more than 4 years: ____

Answer 1

Given:

Rodents live on average 6 years.  20% of the females born survive till age 2.  

Solution:

So initial population of 10 females between 0 and 2 years old will not reproduce but out of 10 only 20% will survive which is 2.

when these two reproduce on their age 3-4, on average each produce 1 rodent and their survival is 50% so on total they reproduced 1 rodent.

After 3 years for the initial population, only 2 survived from 10 females which will be in age between 3-4 and reproduced 1 rodent of age 0-2.

Now, 4 females of age 3-4 reproduce total of 2 rodents. On reaching age above 4 they reproduce 2 rodents which gives a total of 8 rodents. From this, After 3 years, there are 2 rodents of age 4 and above and 8 rodents of age 0-2.

Now, 3 females of age more than 4 will reproduce total of 6 rodents. After 3 years the parent rodents will not survive (since their average life span is 6 years) but they reproduced a total of  6 rodents who's age will be 3-4.

Result:

Females between 0 and 2 years: 9

Females between 2 and 4 years: 8

Females with more than 4 years: 2