Population Growth Rate
r= b-d
G=N(1+r)^t
The formulas above work great if you are doing plug-in equations from known data. If not, here are some easy ways to understand growth rate (hey, this is straight out of your text too!)
r = b - d
b= birth rate (per capita... per head... head count)
d= death rate per capita
r = per capita growth rate
SO, if you had 2000 mice in a field and 1000 were born each month then
b= 1000 born / 2000 mice = 0.5 births/mouse/month
If 200 die each month then
d= 200 deaths / 2000 mice = 0.1 deaths / mouse / month
r= b - d
r = 0.5 - 0.1 = 0.4
The actual population growth can then be calculated with the formula
G = r x N
G = population growth
r = per capita growth rate (from above)
N = number of individuals
G=N(1+r)^t
The formulas above work great if you are doing plug-in equations from known data. If not, here are some easy ways to understand growth rate (hey, this is straight out of your text too!)
r = b - d
b= birth rate (per capita... per head... head count)
d= death rate per capita
r = per capita growth rate
SO, if you had 2000 mice in a field and 1000 were born each month then
b= 1000 born / 2000 mice = 0.5 births/mouse/month
If 200 die each month then
d= 200 deaths / 2000 mice = 0.1 deaths / mouse / month
r= b - d
r = 0.5 - 0.1 = 0.4
The actual population growth can then be calculated with the formula
G = r x N
G = population growth
r = per capita growth rate (from above)
N = number of individuals
G
The actual Population size from the last column is: 2800 by the end of the first month By the end of the second month we're at 3,920 mice 5,488 by the end of the third month!!! |
N
The population started at 2000 2800 3,920 |
r
Rate was calculated to be 0.4 x 0.4 x 0.4 |
N x r shows how many more organisms
2000*0.4 = 800 more mice per month = 1,120 = 1,568 |
Add that to the original population for the new population
2000 + 800 = 2,800 mice 2,800+1,120 = 3920 3,920 + 1,568 = 5,488 |