Formulas Summary
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Name |
Formula |
Interpretation |
Fundamental equation of population growth |
Nt+1=Nt+Bt−Dt+It−Et |
Nt = population size at time t B = births; D = deaths; I = immigrants; E = emigrants |
Net reproductive rate - average total number of female offspring per female over the course of her lifetime |
R0=Ixmx |
increasing pop: R0 > 1 stable population: R0 = 1 decreasing pop: R0 < 1 |
Generation time |
T=xIxmxR0 |
T = average age of reproduction |
Intrinsic/ per capita growth rate |
r=Tln(R0) |
increasing pop: r > 0 stable population: r = 0 decreasing pop: r < 0 |
Rule of 70 |
t=70(100r) |
t = time (in years) for population size to double |
Fx |
Fx=Sxmx+1 |
age-specific fecundity |
Tx |
Tx=xLx |
Tx = years left to live |
Ex |
Ex=Txnx |
Ex = life expectancy |
Lx |
Lx=(nx+nx+1)/2 |
Lx = number surviving |
Geometric population growth - growth rate of population with pulsed (seasonal) reproduction patterns |
λ=Nt+1/Nt |
increasing pop: > 1 stable population: = 1 decreasing pop: < 1 |
Geometric growth model future population estimation |
Nt=N0λt |
Nt = population size at time t |
Exponential population growth - growth by a population with continuous reproduction (rate of population size change over time) |
dN/dt=rN |
increasing population: r > 0 stable population: r = 0 decreasing population: r < 0 |
Exponential growth model future population estimation |
Nt=N0ert |
N = population size at time t (e≈2.71828) |
Logistic population growth - exponential growth limited by carrying capacity |
dNdt=rN(K−Nt)K |
increasing pop: N < K stable population: N = K decreasing pop: N > K |
Bioenergetics model |
S=IE−(FE+UE)−M |
S = energy storage (growth and reproduction) |
Lincoln-Peterson Index (Mark-Recapture Model) |
N=(M∗S)R |
N = population size estimate M = # of animals marked and released S = # of animals recaptured R = size of sample on 2nd visit |
Leslie Matrix formula |
Nt+1=L∗Nt |
Nt+1 = population size at time t L = Leslie Matrix Nt = age-specific population at initial start time |
Simpson’s Index of Diversity (measure of probability): the less diversity, the greater the probability that two randomly selected individuals will be the same |
D=∑Si=1(niN)2 |
ni = number of individuals of species i N = total number of individuals of all species 1 - D: if D is closer to zero, then less diversity; if D is closer to 1, then more diversity |
Shannon-Wiener Diversity Index (measure of certainty): more common species, more uncertain which one will be selected |
H=−∑Si=1pi∗lnpi |
ni/N=pi = proportion of individuals of species i H = 0 in the absence of diversity |
Species richness |
Hmax=ln(S) |
Hmax = maximum number of different species H can reach S = number of different species |
Species evenness |
J=HHmax |
if J is closer to 0, then less evenness; if J is closer to 1, then more evenness |
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