Current data about local biodiversity is incomplete and of low quality, according to a study published in the journal Ecography. The authors from the German Centre for Integrative Biodiversity Research (iDiv) and the Martin Luther University Halle-Wittenberg (MLU) believe biodiversity information is biased and does not provide an accurate picture of how trends affect local species. The recommendation is to use local and regional biodiversity records instead of attempting to quantify global changes.
Global biodiversity loss is one of the most urgent challenges we are facing now. At the World Biodiversity Conference COP15 in Montréal, the UN Convention on Biological Diversity (CBD) adopted new rules in an attempt to reverse this trend. One of the areas covered looks for ways to improve biodiversity monitoring and evaluate trends. There are different ways to do this, but the most common is to count how many species are present in a particular location. However, these measurements do not always accurately reflect the number of species that are lost.
“There has been a heated debate on the scientific community on why major global syntheses so far have not found negative trends of local species richness,” stated Prof Henrique Pereira, head of the Biodiversity and Conservation Research Group at iDiv and MLU and last author of the study. “We show that the declines in local species richness are likely to be much smaller than many anticipated and that, in those conditions, even minor spatial biases and errors in monitoring lead to the lack of detection of global trends.”
To create an accurate picture of what happens at the local scale, data must be compiled and evaluated across time to detect changes. “The occurrence of species is recorded locally all over the world by many different people and organisations,” said first author Dr. Jose Valdez, a postdoctoral researcher at iDiv and MLU. “The problem with the data is that they were and are recorded under completely different conditions and mostly not under standardised rules. If you then pile them together, the errors and deviations add up, making the result very inaccurate.”
Monitoring results are influenced by various factors, including time intervals between sampling, the size of the sampling sites, or small errors in counting the number of species at a site. Another problem is the regional imbalance. For example, most of the data is collected in Europe and USA, primarily covering temperate deciduous and mixed forests. This means a severe underrepresentation of the tropical regions, which are areas with a high species richness but with large losses recently. As a result, global data gives a distorted view of global biodiversity.
The team simulated data from thousands of sites to assess how much biodiversity data is biased and how to compensate to get more accurate readings. The basis for these calculations involved a comprehensive compilation of data from over 32,000 sites worldwide and over 51,000 species. The results showed that global changes could be calculated using hundreds of sites within a decade and thousands of sites within three years.
However, these time periods are only valid if collections are done without any errors. This is impossible to achieve, and collection data typically has 10-30% errors due to missing or misidentifying species during sampling. However, when the team adjusted error rates to only 5%, they could no longer detect global changes accurately.
“Our results demonstrate that capturing accurate trends in local species richness would require monitoring an unfeasibly large number of perfectly sampled sites,” added Valdez. “However, the question is whether this would even be useful or meaningful for effective and responsive biodiversity conservation. Conservation strategies and measures are coordinated and implemented not on a global level but at local and national scales. Measuring biodiversity trends at these smaller scales is not only more practical but also helps in understanding the drivers of biodiversity loss and assessing the progress of conservation policies.”
As a solution, the authors suggest finding a series of representative sampling sites around the world providing local biodiversity data that can be regularly updated. This is currently being developed for the European Union with the EuropaBON project.
Valdez J, Cahhaghan C, Junker J, Purvis A, Hill S and Pereira H (2023) The undetectability of global biodiversity trends using local species richness. Ecography, https://doi.org/10.1111/ecog.06604