Ecology: Communities Part 2

absolute abundance

the number of individuals of a given species

relative abundance

the proportion of all individuals

how do you calculate relative abundance?

(individuals of one species/total individuals) x 100

Using this picture, what is the absolute and relative abundance of the dark green tree in each community?

1) absolute abundance= 3

relative abundance= 25%

2) absolute abundance= 3

relative abundance= 25%

3) absolute abundance= 16

relative abundance= 84%

If the dark green tree in a community has a relative abundance of 25%, what does that mean biologically?

the dark green tree makes up 25% of all the individual organisms in the community

evenness

how similar abundances are among the species of the community

Would this community be considered high or low evenness?

low evenness

diversity index

single number that summarizes the species richness (s) and the variation in species relative abundances of a community

Rank abundance curves

shows diversity of MULTIPLE communities by comparing species rank by relative abundance; each line is its own community

On a rank abundance curve, along the x axis what is occuring?

species are ordered from most abundant to least abundant

On a rank abundance curve, along the y axis what is occuring?

percentage of the community made up by each species

On a rank abundance curve, what does a flatter curve represent?

greater eveness meaning the species have similar numbers of individuals

On a rank abundance curve, what does a steeper curve represent?

lower evenness meaning one or few species dominate

On a rank abundance curve, what does a longer curve represent?

greater species richness meaning more species are present

Simpson’s diversity index

measures the “effective” number of species

Pictured is the simpsons diversity index formula. What does the denominator represent?

probability that two individuals drawn randomly from the population will be of the same species

the higher the simpson index number the higher the what?

the higher the diversity

If a simpsons diversity index number is 4.92, what does that mean biologically?

the diversity of the community is equivalent to about 4.92 equally abundant species

shannon (wiener) diversity index

measures how difficult it is to predict which species a randomly selected individual will belong to

the higher the shannon wiener index the higher the what?

higher diversity

If one species dominates the population, its easy to predict which species you’ll pick. Does that mean a low or high index and why?

low index because of low diversity

If all species have similar population sizes, its hard to predict which species you’ll pick. Does that mean a low or high index and why?

high index because there’s more diversity

You have a community that consists of 5 species. f your actual shannon wiener index is 1.6 and your maximum index is 1.61, what does that mean biologically?

the community is very close to the maximum possible diversity meaning all 5 species have nearly equal abundances