# Life tables in population ecology

1. Jul 9, 2014

### atomant

1. The problem statement, all variables and given/known data
http://imgur.com/OInF6O2

The blue table shows the mortality and offspring production rates per year per age class by individuals of an unnamed species. The orange tables shows the starting population at time t, I have to find the number of individuals at T+1 (next year)

2. Relevant equations

Not sure if relavent but an equation is given: r = ln (NT+1)/NT)/T

3. The attempt at a solution
http://imgur.com/pilNkOP

Would love if someone could check the workings though or see if this makes sense

2. Jul 10, 2014

### Staff: Mentor

How did you get the first value?
I agree with the others.

3. Jul 11, 2014

### atomant

Well the basic idea was to calculate the Mx values for the age groups that had an initial population at times t, which means age groups 2 and 3 which has Mx values of 3 and 2 respectively. Therefore the number of 0 age offspring should be 5 (I think)..don't really know how I got 7. Is this correct?

4. Jul 12, 2014

### Staff: Mentor

Those mx values are "offspring per individual and year". It mean a single individual at age 1 will (on average) get 2 children.

How many do 10 at age 2 get then? And the other groups?

5. Jul 12, 2014

### atomant

Ah, I see - so the 10 at age 2 will on average have 30 offspring at t+1 (10 individuals and mx of 3).

The question now then is do I assume that all 10 individuals are alive at t+1 to reproduce? i.e- at age 2 the have a mortality rate of 10%, which means 9 individuals will survive at t+1 to become 3yr olds so do I assume that reproduction occurs after the death based on mortality rate happens or do I assume that these 2yr olds will reproduce before dying? Depending on these assumptions the offspring will either be 30 or 27. The question doesn't specify so I am unsure which is the most logical assumption to take.

6. Jul 13, 2014

### Staff: Mentor

I would read the table in a way that mortality does not have to be taken into account - in other words, they get children before they can die.

7. Jul 13, 2014

### atomant

Thank you so much for your help, you have been amazing!