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Colonisation/local extinction rates

  • Biodiversity

  • Function

Summary

Turnover indices reflect colonisation and extinction, they capture biodiversity changes that are not captured by species richness (Hillebrand et al. 2018). Turnover integrates information on species identity and abundance (Hillebrand et al. 2018). Spatial changes in habitat structure/composition and changes in external pressures can drive changes in colonisation and extinction (Sirami et al. 2008).

Colonisation and extinction impact the homogenisation and heterogeneity of communities, capturing the processes underlying changes in beta-diversity (Tatsumi et al. 2021).

For rare species, lower probability of detection can make it harder to accurately determine whether they are occupying a site (Lindenmayer et al. 2020).

Methodology summary

Local colonisation and extinction metrics can be derived from data on species richness and abundance which can be obtained using methods for the richness, abundance and diversity metrics (see Invertebrate biomass, Mammal biomass, Vegetation biomass, Species diversity for methodologies). However, for rare species, there will be lower confidence that these methods accurately represent species occupancy. Community survey data in the form of site x species matrices is required to calculate these metrics.

Estimates of biodiversity turnover, rates of extinction and immigration are reported as a closed range of values between 0 and 1 (Hillebrand et al. 2018).

  • Richness-based species exchange ratio (SERr) = (immigrations + extinctions)/total number of species. SER measures gross change in species composition – where 0 means all species persist and 1 means all species are exchanged.
  • A more robust approach would consider changes in proportional abundances over time. Proportional abundance species exchange ratio (SERa), where 0 means identity and dominance structure unchanged and 1 means all species replaced. (Complements Wishart’s similarity ratio and Simpson’s diversity index).

Metric threshold or direction of change

Thresholds and direction of change will be context dependent, with desirable loss/gain of species depending on the project aims.

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  • Agricultural
  • Forest
  • Grassland
  • Heathland
  • Other
  • Peatland
  • Saltmarsh
  • Wetland

Scale

  • Community

Cost

  • High

Tier

  • Future

Technical expertise

  • High

Standardised methodology

  • Partial