# Changes in Richness, Abundance, and Occurrence of Beetles in South Korea over Ten Years: Identifier Bias and Selection of Climate Change Indicators

## TL;DR

This study tracks beetle population changes in South Korean forests over ten years and identifies biases in data collection, proposing specific beetles as climate change indicators.

## Contribution

The study introduces a set of beetle taxa as climate change indicators and corrects for identifier bias in long-term ecological monitoring.

## Key findings

- Beetle abundance and occurrence declines matched climate change predictions more accurately than increases.
- Identifier bias significantly affected richness, abundance, and occurrence estimates in the initial survey.
- Four beetle families, two genera, and seven species were selected as effective climate change indicators.

## Abstract

Climate change has significant effects on insect populations, yet long-term monitoring data are limited. As part of this study, we examined changes in beetle richness, abundance, and occurrence across 273 forest sites in South Korea, comparing data collected a decade apart (2007–2009 vs. 2017–2019). We found significant underestimation of abundance of beetles during the species identification process in the first survey. After accounting for this bias, we compared changes observed with earlier predictions based on species distribution models and ecological temperature indices. Notably, taxa that declined in abundance and occurrence matched the predicted trends more accurately than those that did not, suggesting real ecological changes, likely driven by climate warming. Based on abundance, ease of identification, and temperature sensitivity, we propose four beetle families, two genera, and seven species as effective indicators for long-term climate change monitoring in forest ecosystems.

Climate change is rapidly altering the distribution and abundance of species, with significant impacts on regional ecosystems, including reduced ecosystem services and the loss of biodiversity. Accurately predicting changes in the distribution and abundance of taxa under future climate scenarios is, therefore, crucial. In South Korea, beetle data collected via pitfall traps from approximately 300 forest sites between 2007 and 2009 (30 families, 4 genera, and 150 species) were used to forecast changes in their abundance and distribution under climate change scenarios RCP 4.5 and 8.5. This study evaluated the accuracy of those predictions using data from a subsequent survey conducted between 2017 and 2019. We compared species richness, abundance, changes in abundance (i.e., number of individuals), and occurrence (i.e., number of occupied sites) using data from 273 sites that were surveyed in both the initial (2007–2009) and follow-up (2017–2019) periods. All four parameters were found to be significantly influenced by the identifiers. This identifier bias was attributed to the omission of morphologically similar species in the initial survey or the loss of individuals during the preparation process of dry specimens. As a result, increases in abundance and distribution appear to have been affected by identification errors, whereas decreases more closely reflect actual ecological changes. When the comparison between predicted and observed results was restricted to taxa with reduced abundance and distribution, the number of taxa that matched the predictions was significantly higher than that of those that did not. Based on ease of identification, abundance, and sensitivity to climate change, we selected a set of indicator taxa (four families, two genera, and seven species) for climate change monitoring.