Beta Diversity

Differences between two sites.

Higher beta diversity = more different sites

Taxonomic

Spatial

Two communities become more dissimilar as distance increases

Temporal

Two communities may become more dis-similar as time between them increases, e.g. gain or loss in diversity

Is high beta-diversity good?

Depends on dispersal/recolonization capacity of the species and how they exist in the ecosystem

Measures

Sorensen's

Effective for Presence/Absence data (no counts needed)
!Lecture 8_Community Ecology Lecture Slides, p.55
In our example, we had 10 species that were shared between Juri and I's sample vs Ece and Lynneva's sample, we had one species not in theirs, and they had 5 that we didn't have. Therefore:
$a = 10, b = 1, c = 5$

C_{S} = \frac{2 (10)}{2 (10) + (1) + (5)} = 0.77

Bray-Curtis Index (AKA Sorenson's quantitative index)

This is similar to Sorenson's but accounts for number of individuals
$N_{j}$ is the lower abundance number of the species found in both sites
In our example, we had:
$N_{j} = 1 + 3 + 6 + 1 + 2 + 3 + 1 + . . . = 20$

C_{N} = 1 - \frac{2 N_{j}}{(N_{a} + N_{b})}

Non-taxonomic

Functional and phylogenetic metrics can be used again as in Alpha
Often partitioned into nestedness of communities and turnover of communities, although in reality beta-diversity is a result of both of these

Nestedness

Loss or gain of species/functions/phylogeny
One site has a subset of species found in another

Turnover

Replacement of species/functions/phylogeny in a community
Complete turnover = no change