2
$\begingroup$

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?

Improve this question
$\endgroup$
6
  • $\begingroup$ Please rewrite the quote. Images are not searcheable and can pose problems to visually impaired people $\endgroup$
    – Remi.b
    Commented Jan 2, 2018 at 18:17
  • $\begingroup$ 0.4 offspring per lotus per year means that each lotus produces on average 0.4 offspring every year. $\endgroup$
    – Remi.b
    Commented Jan 2, 2018 at 18:18
  • $\begingroup$ @Remi.b All should be good now. :) $\endgroup$
    – user22020
    Commented Jan 2, 2018 at 20:44
  • $\begingroup$ Thanks! +1 You might want to comment on my answer if something is still unclear to you. $\endgroup$
    – Remi.b
    Commented Jan 2, 2018 at 20:50
  • $\begingroup$ I'm not the OP. =P $\endgroup$
    – user22020
    Commented Jan 2, 2018 at 21:00

1 Answer 1

Reset to default
2
$\begingroup$

I will use an ever so slightly more specific scenario than what your book offers.

At the beginning of 2017, there were twenty lotus plants in a pond. By the first day of 2018, eight of those twenty lotus plants reproduced. Using this information, we now want to describe the birth rate of lotus plant population.

To do this, we need the number of plants that produced offspring, and, the population size at the beginning of 2017.

$$\frac{no. \ of \ parent \ lotus \ plants}{initial \ population \ size} = \frac{8}{20} = .4$$

This means that, when considering the twenty lotus plants that first existed at the beginning of 2017, each of those twenty plants contributed an average of 4/10s of a lotus plant offspring for that year.

To generalize this, we say, "a birth rate of .4 offspring per lotus plant per year."

The same method and persective can also be applied to the fruitflies, however, they're considering death rate.

Improve this answer
$\endgroup$
3
  • 1
    $\begingroup$ Hey Thanks, this was comprehensible. Could you please explain the meaning of 'per capita' also please? $\endgroup$
    – Shreya Varshney
    Commented Jan 3, 2018 at 11:24
  • $\begingroup$ @ShreyaVarshney Per capita is just another way of saying Per lotus plant. :) $\endgroup$
    – user22020
    Commented Jan 3, 2018 at 11:27
  • $\begingroup$ @Charles , the numerator should be the "number of offspring." Per capita birth rate is the average number of offspring at the next time step produced by mothers at a particular time. Your equation is the proportion of number mothers to total population at a particular time. $\endgroup$
    – Chris Moore
    Commented May 8, 2019 at 16:54

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .