Article by Shreya Dasgupta.
A biodiversity crisis is looming upon us. We are now in the middle of a “sixth great extinction” of animal species, scientists warn, with loss of species about 1,000 times higher than it would have been without human impact.
Nearly every country in the world has committed to reducing the rate of loss of biodiversity under the Convention of Biological Diversity (CBD) 2010 and 2020 biodiversity targets. One of the first steps to achieving this is to understand the changes in animal and plant populations in the wild over time.
However, population monitoring surveys are often poorly designed, scientists report in a new study published in Biological Conservation. And this could pose a serious challenge to halting species loss, they warn.
“To understand the changes in biodiversity and develop conservation programs that will be suitable to mitigate or reverse the losses, it is critical to have good quality surveys that satisfy criteria to produce reliable trends in biodiversity,” Stephen Buckland of the Centre for Research into Ecological Environmental Modelling at the University of St Andrews, U.K., said in a statement.
Asian small clawed otter. Photo by Rhett A. Butler.
Well-designed surveys should satisfy five criteria, Buckland and Alison Johnston of Cornell Lab of Ornithology, New York, write in the paper. First, monitoring programs must choose sample locations that are representative of the region that the researchers are interested in and not biased towards particular habitats or locations. Second, conservation practitioners must sample a “sufficiently large” number of sites. Sampling too few sites can lead to high bias and low precision of population change estimates, the authors write.
Third, monitoring programs must ensure that every target species — both common and rare — are adequately counted. Fourth, species that the practitioners select for monitoring should be representative of all the species in the community they are interested in. Choosing only common and easily detectable species for monitoring, for instance, can lead to misleading trend estimates, the authors write. Finally, the researchers call for repeated surveys over time (for example, every year or once every three years) to help arrive at reliable long-term population trends.
“If a scheme produces population trend estimates, policymakers tend to assume that these are accurate and precise,” Buckland told Mongabay. “In reality, the populations monitored may not be at all representative of the community for which inference is required, and so the estimated trends may be highly misleading.”
Take the Living Planet Index (LPI), for example. The LPI measures global population trends of mammals, birds, fish, reptiles and amphibian species by using data from sources like government reports, scientific articles and research programs. While cost-effective, LPI suffers from several biases, a study published in January found. Some regions like Europe are heavily over-represented relative to others, for example, as are temperate bird and mammal species while several tropical species and marine fishes remain under-represented.
“There are still many places and species for which we do not have good information on biodiversity,” Johnston said. “In some cases there are statistical tools that we can use to account for this missing data, but statistical methods can only take us so far. It is essential that we also assess the ways we collect data.”
Goodman’s mouse lemur (Microcebus lehilahytsara). Photo by Rhett A. Butler.
While good quality, long-term monitoring surveys are critical, such surveys are not always feasible due to constraints like unavailability of resources. “To conduct a completely watertight survey of a nation’s biodiversity with high precision would require a level of resource that is not feasible even for the wealthiest nations,” Buckland said.
The level of expertise required to survey species reliably is also often lacking, he added. Given the constraints with respect to resources and expertise, practitioners frequently compromise on survey designs.
Buckland and Johnston are, however, hopeful that survey designs can be improved. Accessible technologies in particular can help individuals and groups collect reliable data on species population trends.
“Technologies such as camera traps, acoustic detectors, high-resolution images, drones, etc mean that it is feasible to collect data across wide regions for more taxa than has been possible to date,” Buckland said.
Existing monitoring programmes that have been in place for decades, and where strong biases have been identified, also need to be improved, he added. “I think it is necessary to review methods, and implement new approaches. This was done for example for monitoring breeding birds in the UK. The Common Birds Census, which monitored a biased set of locations, was replaced by the Breeding Bird Survey in the 1990s. The two schemes overlapped for several years, allowing bias in the old scheme to be assessed.”
Johnston added: “Environmental decisions rely on accurate information about the state of biodiversity. We should continue to collect high quality data and create the best measures we can about the natural world. However, it’s also important that we recognise the weaknesses of each metric and that we continually search for ways to improve the data we collect and the statistical methods used to analyse them.”
Camera traps are increasingly becoming more accessible. Photo by Rhett A. Butler.
McRae L, Deinet S, Freeman R (2017) The Diversity-Weighted Living Planet Index: Controlling for Taxonomic Bias in a Global Biodiversity Indicator. PLoS ONE 12(1): e0169156. https://doi.org/10.1371/journal.pone.0169156
Banner image: A blue-and-yellow macaw (Ara ararauna) in Colombia. Photo by Rhett A. Butler.