What does 'per capita births and deaths' mean?

Question

My book says, > If in a pond there are 20 lotus plants last year and through reproduction 8 new plants are added, taking the current population to 28, we calculate the birth rate as 8/20 = 0.4 offspring **per lotus per year**. .. >If 4 individuals in a laboratory population of 40 fruitflies died during a specified time interval, say a week, the death rate in the population during that period is 4/40 = 0.1 individuals **per fruitfly per week**. What does per lotus per year, and, per fruitfly per week imply?

Answer 1

"Per capita" refers to something per individual organism within a defined group and time period. Therefore, "per capita births and deaths" refers to the number of births and deaths for each organism within a given group and time frame. General implications of per capita births and deaths include reproductive health and population dynamics, such as population growth.

Your next question asks what the implications are for "offspring per lotus per year" and "deaths per fruit fly per week." Let's answer this one at a time by assessing the information we have, and then we will look at its implications:

1. Lotus population
2. To calculate per capita births, meaning the number of offspring from each lotus plant in the population in a year, we divide the starting population by the number of births: 8/20 = 0.4.
3. 0.4 offspring per lotus per year may imply something about the reproductive health of the lotus population, and it may also have implications for the growth of the lotus population (but more information is needed for a clearer picture on population growth such as per capita deaths). Regarding the implications for its population growth, let's say for example there are 0.5 deaths per lotus per year, but there are only 0.4 offspring per lotus per year, then the implication is that the lotus population will undergo negative population growth.
4. Lab fruit fly population
5. To calculate per capita deaths, meaning the number of deaths for each fruit fly in the laboratory population each week, we divide the starting population total by the total number of deaths in a week = 4/40 = 0.1.
6. 0.1 deaths per fruit fly per week may have implications for the general fitness of the fruit fly lab population, as well as implications for population density and growth, but more information is needed for a clearer picture of the latter such as per capita births. However, per capita deaths are pretty low, so we may consider there to be validity to the implication of the lab population not necessarily being at risk for extinction, but there may be some concerns with the potential increase in population density.