Desirable mathematical properties of indicators for biodiversity change

Numerous indicator approaches are found in the scientific literature to describe changes in biodiversity. It is however far from clear which indicators are most appropriate and which are less suitable to summarize trends in biodiversity. One reason for this lack of clarity is that so far the mathematical properties of indicator approaches have had little attention. In this paper, we derive a number of desirable mathematical properties of indicators from economic price-index theory and apply these in the form of tests to 10 metrics to summarize changes in biodiversity. The metrics species richness, Simpson index, Shannon index, Buckland's modified Shannon index and Sørensen's similarity coefficient violate the monotonicity and proportionality test. The percentage of increasing minus declining species also fails the proportionality test, and in the case where trends are assessed relative to the preceding year, this metric also violates the identity test. Most of these indicators are sensitive to spatial scale. The arithmetic and geometric mean of population indices and the mean abundance have better mathematical performance, but the first two are sensitive to appearing and disappearing species in the system surveyed. The metric mean abundance however can only be applied under particular conditions and has some undesirable properties. Unlike the arithmetic mean, the geometric mean is not sensitive to the base year chosen and has the most favourable mathematical properties of the indicators evaluated. The geometric mean can be straightforwardly extended to take into account unequal values of species if desired

Monitoring van Natura 2000 soorten en habitattypen : advies voor een landelijk meetprogramma ten behoeve van de rapportageverplichtingen in het kader van de Europese Vogelrichtlijn en Habitatrichtlijn : : rapport in het kader van het WOT programma informatievoorziening Natuur i.o. (WOT IN)

In deze gezamenlijke uitgave van CBS, VOFF en Alterra wordt aan het Ministerie van LNV advies gegeven over de toekomstige monitoring van soorten en habitattypen. Uitgangspunt bij dit advies zijn de rapportageverplichtingen in het kader van de Europese Vogelrichtlijn en Habitatrichtlijn. De Europese richtlijnen verplichten de lidstaten om op gezette tijden te rapporteren over de staat van instandhouding van soorten en habitattypen. Op basis van dit advies kunnen keuzes gemaakt worden over het wel of niet uitbreiden van bestaande monitoringsprogramma's om aan de rapportageverplichtingen te voldoe

Occupancy dynamics of wild rabbits (Oryctolagus cuniculus) in the coastal dunes of the Netherlands with imperfect detection

Context: Wild rabbits are considered a key species in the coastal dunes of the Netherlands, but populations have collapsed as a result of viral diseases. Aim: We studied to what extent population collapse led to local extinction and whether recolonisation of empty patches in the dunes happened. Methods: We investigated occupancy dynamics using data of 245 transects where rabbits were surveyed in 1984-2009. Dynamic site-occupancy models were used to analyse the data. These models adjust for imperfect detection to avoid bias in occupancy-trend estimation. Key results: The decline of the rabbit population has resulted in many local extinctions, especially in woodland and in the northern part of the coastal dunes. Most transects along grassland and mixed vegetation have recently been reoccupied. The recovery of woodland occupancy is slow, probably not because of limited dispersal capacity of rabbits, but because the quality of woodland habitats is poor. Detection probability of rabbits varied considerably over the years and among habitat types, indicating the necessity of taking detection into account. Rabbits were slightly better detected when it was cloudy, windy and rainy and when lunar phase approached new moon. Conclusion: Extinction and recolonisation of habitat patches varied considerably among habitat types. Implications: The current slow recolonisation hampers the recovery of rabbit populations in woodland habitats in the Dutch coastal dunes. Furthermore, monitoring rabbit occupancy should take imperfect detection into account to avoid biased results

Occupancy dynamics of wild rabits (Oryctolagus cuniculus) in the coastal dunes of the Nederlands with imperfect detection

Context: Wild rabbits are considered a key species in the coastal dunes of the Netherlands, but populations have collapsed as a result of viral diseases. Aim: We studied to what extent population collapse led to local extinction and whether recolonisation of empty patches in the dunes happened. Methods: We investigated occupancy dynamics using data of 245 transects where rabbits were surveyed in 1984–2009. Dynamic site-occupancy models were used to analyse the data. These models adjust for imperfect detection to avoid bias in occupancy-trend estimation. Key results: The decline of the rabbit population has resulted in many local extinctions, especially in woodland and in the northern part of the coastal dunes. Most transects along grassland and mixed vegetation have recently been reoccupied. The recovery of woodland occupancy is slow, probably not because of limited dispersal capacity of rabbits, but because the quality of woodland habitats is poor. Detection probability of rabbits varied considerably over the years and among habitat types, indicating the necessity of taking detection into account. Rabbits were slightly better detected when it was cloudy, windy and rainy and when lunar phase approached new moon. Conclusion: Extinction and recolonisation of habitat patches varied considerably among habitat types. Implications: The current slow recolonisation hampers the recovery of rabbit populations in woodland habitats in the Dutch coastal dunes. Furthermore, monitoring rabbit occupancy should take imperfect detection into account to avoid biased results

Occupancy dynamics of wild rabits (Oryctolagus cuniculus) in the coastal dunes of the Nederlands with imperfect detection

Context: Wild rabbits are considered a key species in the coastal dunes of the Netherlands, but populations have collapsed as a result of viral diseases. Aim: We studied to what extent population collapse led to local extinction and whether recolonisation of empty patches in the dunes happened. Methods: We investigated occupancy dynamics using data of 245 transects where rabbits were surveyed in 1984–2009. Dynamic site-occupancy models were used to analyse the data. These models adjust for imperfect detection to avoid bias in occupancy-trend estimation. Key results: The decline of the rabbit population has resulted in many local extinctions, especially in woodland and in the northern part of the coastal dunes. Most transects along grassland and mixed vegetation have recently been reoccupied. The recovery of woodland occupancy is slow, probably not because of limited dispersal capacity of rabbits, but because the quality of woodland habitats is poor. Detection probability of rabbits varied considerably over the years and among habitat types, indicating the necessity of taking detection into account. Rabbits were slightly better detected when it was cloudy, windy and rainy and when lunar phase approached new moon. Conclusion: Extinction and recolonisation of habitat patches varied considerably among habitat types. Implications: The current slow recolonisation hampers the recovery of rabbit populations in woodland habitats in the Dutch coastal dunes. Furthermore, monitoring rabbit occupancy should take imperfect detection into account to avoid biased results