Species Turnover Calculators

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Species turnover refers to the change in species composition between locations (spatial turnover, i.e., beta diversity) or over time (temporal turnover). It is a central concept in biogeography, macroecology, and conservation — reflecting how different the biological communities are across space or time. Spatial species turnover is measured by beta diversity metrics including Whittaker's beta (βW = γ/α − 1), Sørensen dissimilarity (1 − QS), and Bray-Curtis dissimilarity. Beta diversity can be decomposed into two components: true turnover (species replacement) and nestedness (loss or gain of species from a richer to a poorer community).

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Beta Diversity Metrics

Whittaker's β: βW = γ/ᾱ − 1 (where ᾱ = mean alpha diversity of sites). β = 0: all sites have identical species composition. β = S − 1: complete turnover (each site has unique species).

Sørensen dissimilarity: βSOR = 1 − QS = 1 − 2C/(A+B). Ranges 0 (identical) to 1 (no shared species).

Turnover vs. Nestedness

Baselga (2010) decomposition: βSOR = βSIM + βSNE. βSIM = true turnover (species replaced by different species as you move along a gradient). βSNE = nestedness (poorer communities are subsets of richer communities — no replacement, just loss). If βSNE dominates: poorer sites are just subsets of the richest site → conservation priority = protecting the richest site. If βSIM dominates: each site has unique species → all sites needed for regional diversity → different conservation strategy.

Temporal Turnover

Species list at time 1 vs. time 2 for the same site: temporal β. Colonizations + extinctions drive temporal turnover. Climate change signal: compare historical and current species lists to detect range shifts.

Glossary

Species Turnover (Beta Diversity)
Change in species composition between sites or over time; Whittaker's βW = γ/ᾱ − 1; Sørensen βSOR = 1 − QS; drives gamma diversity; decomposes into turnover (replacement) + nestedness.
Whittaker's Beta (βW)
βW = (γ/ᾱ) − 1; γ = total regional species; ᾱ = mean site species richness; βW = 0 (no turnover); higher βW = more compositional variation across the landscape.
Nestedness
A component of beta diversity where poorer communities are subsets of richer ones; no species replacement — just species loss; βSNE in Baselga decomposition; when dominant, protecting the richest site is most efficient.

Frequently Asked Questions

Species richness (alpha diversity) measures how many species are present at a single location. Species turnover (beta diversity) measures how much species composition changes between locations or through time. A landscape can have low alpha diversity at each site but high beta diversity if each site has completely different species (leading to high gamma diversity). Conversely, if all sites have the same species, beta = 0 regardless of how many species each site has. Beta diversity is crucial for conservation: to protect total regional biodiversity (gamma), you need to account for how much turnover exists across sites, not just the richness of individual sites.

Whittaker's beta (βW) = (γ/ᾱ) − 1. γ = total species in all sites combined (gamma diversity). ᾱ = mean alpha diversity across sites. Example: 3 sites with S₁ = 10, S₂ = 12, S₃ = 8 species; total unique species γ = 22 (many unique to each site): ᾱ = (10+12+8)/3 = 10. βW = 22/10 − 1 = 1.2. Interpretation: βW = 0 → no turnover (identical communities). βW = 1 → each species found in only half the sites on average. Higher βW = more compositional variation among sites. Alternative: Sørensen dissimilarity (βSOR = 1−QS) for pairwise comparisons between two sites.

Beta diversity can be decomposed into two distinct mechanisms: True turnover (βSIM, Simpson's dissimilarity): species in one community are replaced by different species in another — driven by environmental gradients, niche differences. Example: different bird species in alpine vs. lowland forest. Nestedness (βSNE): poorer communities contain only a subset of species from richer communities — no replacement, just a loss. Example: island communities with fewer species than mainland due to random colonization/extinction. Baselga decomposition: βSOR = βSIM + βSNE. Conservation implications: if β is driven by nestedness → protecting the richest site captures most species. If β is driven by turnover → need to protect multiple sites with different species complements.

Temporal turnover: change in species composition at the same site over time. Measure by resurveying the same plots or species lists: apply same beta diversity metrics to time 1 vs. time 2 data. Temporal turnover = (number of colonizations + extinctions) / mean(S at time 1, S at time 2). Decompose into: extinctions (species lost from the site); colonizations (new species arriving). Ecological significance: natural temporal turnover (community succession); climate change-driven turnover: thermal specialists lose range → thermophilic species gain range → net change in composition. Biotic homogenization: in many regions, native species are being replaced by common generalist and invasive species → β decreasing globally. Long-term biodiversity monitoring: compare species lists across decades to detect temporal turnover driven by climate change, habitat change, and invasive species.