The importance of locally sourced data in identifying population trends: Insights from Iberian vertebrates

Abstract

Understanding species population trends is key for assessing their conservation status and proposing measures to ensure their future persistence amid recent biodiversity loss. However, studies are reporting contrasting biodiversity trends over time. These discrepancies can be partly attributed to biases in global datasets, which might not capture the representativeness of local processes. Here, we aimed to address this gap of knowledge by complementing data included in the Living Planet Database (LPD), one of the largest repositories of population time-series, with locally sourced data from the Iberian Peninsula. The study aim: (i) to assess the state of wildlife Iberian vertebrates using population time-series across taxonomic groups and (ii) to determine differences between locally sourced data and LPD (evaluating also the differences between data sources). To supplement LPD, we conducted a review, analysing over 6000 peer-reviewed manuscripts and grey literature documents. We obtained 999 population time-series for 294 vertebrate species compiled in an Iberian Vertebrate (IbeV) database, two times the number of populations as the LPD includes. Our results indicate contrasting population trends across taxonomic groups, with freshwater amphibians and bony fishes showing steep declines. Moreover, the LPD shows a positive trend and IbeV indicates no net change over time. Threatened species did not exhibit net changes in population trends, while non-threatened species showed positive trends. We showed that local databases can provide distinct population trends compared to global databases. This approach highlights the need to bridge the gap between global and local datasets, to support context-specific management and conservation programmes.