1. INTRODUCTION
Laos covers a large part of the Indochinese limestone belt and is one of the most biodiversity-rich countries of Southeast Asia (Kumar et al., 2016). Its dominant land cover is tropical dense forests, of which approximately 80% are located in mountainous areas with steep to moderate slopes. It includes several National Protect Areas (NPAs) that are considered as biodiversity hotspots, such as the Hin Nam No NPA, which has officially been submitted to become the first natural World Heritage Site of Laos. Many studies report a highly diverse fauna in the region including amphibians, reptiles, birds, bats, and over 100 species of large mammals, new species being frequently discovered (MAF & STEA, Myers et al., 2000; Ceballos & Ehrlich, 2006; Biodiversity Country Report, 2003; MoNRE, 2016). However, as of yet, no single survey has attempted to describe the diversity of Coleoptera, or even insects in general, in Laos. Until fairly recently, the insect fauna of Laos remained one of the most poorly known in SE Asia (Sekerka & Geiser, 2016) and existing knowledge mostly comes from specimens collected by foreign visitors before the 1920s. Recently, though, we observed an increase in the number of entomological expeditions, permitted by the country becoming more accessible to foreigners.
The extremely rapid economic growth that Laos is experiencing comes at the expense of biodiversity, which is facing a growing number of significant challenges associated with land-use changes (World Bank national accounts data, 2017). For example, during the 1990s and 2000s, the land area dedicated to rubber plantations has increased exponentially to reach an evaluated surface of 450,000 ha in 2015 (Smith et al., 2016). Such conversion of natural tropical forests into rubber plantations occurs in several tropical regions of the world where it is recognized to negatively impact biodiversity and ecosystems (Warren-Thomas et al., 2015). Moreover, the economic growth of the region is likely to continue or even accelerate in the near future, as the railway that connects Kunming, China to Bangkok, Thailand, passing through much of Laos, is completed (Chen and Haynes, 2017; Ng et al., 2020). Indeed, infrastructure development will increase the general appeal of the region and encourage foreign investment, contributing to direct and indirect threats to local ecosystems (Torres et al., 2016; Borda-de-Água et al., 2017). In this regard, insects, for which a global decline has been recently documented (Sánchez-Bayo & Wyckhuys, 2019), are among the taxa that are known to be affected by deforestation in a tropical context (Correa‐Carmona et al., 2022). Generally, deforestation, agricultural intensification, and climate change, including more frequent extreme weather events, have been suggested as being the major drivers of the global insect decline (Wagner, 2020; Eggleton, 2020). However, this assessment mostly comes from population trends estimated in the Global North (Sánchez-Bayo & Wyckhuys, 2019), while the current state of insect diversity in tropical contexts remains poorly known. Knowledge of the influence of human impact, through an effect on landscape structure, on insect diversity in southern Asia, and in Laos in particular, is still lacking and virtually nil (Chouangthavy et al., 2020).
Beetles (Coleoptera) are the most diverse taxonomic order on Earth. Because they exhibit rich abundance, biomass, and diversity, beetles are often used as indicator species of anthropogenic impact on ecosystems, including tropical forests (Ghannem et al., 2018; Zödl & Wittmann, 2003; Parikh et al., 2021). For example, dung beetles (Scarabaeidae: Sacarabaeinae) play an important role in the functioning of tropical forest ecosystems while being also sensitive to human disturbance and environmental changes, making them ideal focal species for investigating conservation issues (Slade et al., 2011; Spector, 2006). In southern Asia and in Laos in particular, despite the fact that beetle diversity is high (Moodley et al., 2022) and human activity is growing, the approach of employing beetle community composition, richness, and abundance as surrogates for estimating the impact of agricultural intensification and anthropogenic disturbance has never been carried out. The few studies addressing the question of beetle community richness in relation to human factors were restricted to specific local contexts (Chouangthavy et al., 2020), and were insufficient to estimate more broadly the actual impact of human pressures on beetle biodiversity in Laos. There is thus a need for large-scale assessments of beetle diversity conducted in natural vs. anthropogenic landscapes, in order to estimate the effect of Laos’ economic development on its rich biodiversity.
Besides human activity, there is evidence that beetle diversity is also partly structured by climate at large spatial scales (Andrew & Hughes, 2004; Hortal et al., 2011). Even at a more regional scale, beetle assemblages appear to be structured across elevation gradients following the corresponding climatic variation (Gebert et al., 2020; Dolson et al., 2021). This implies that (i) beetle species may be affected by climate change in the recent past and in the future (Harris et al., 2019), and (ii) any attempt to characterize the impact of anthropogenic factors on beetle diversity at a large geographical scale must also account for climatic gradients that may influence the richness, abundance, and composition of beetle communities. Therefore, it is likely that the beetle fauna of Laos, a country that covers a latitudinal gradient of ca. 900 km and hosts four different climate zones (Am, Aw, Cwa, Cwd, Essenwanger & Landsberg, 2001), is somewhat influenced by variation in temperature and precipitation across the country.
In order to understand how the rapid economic development of the region affects its biodiversity, we investigated beetle community composition, diversity, and abundance across a large spatial scale in Laos, focusing on two contrasting landscape contexts. Specifically, we made use of an unprecedentedly large inventory of beetles carried out across the entire country to compare beetle assemblages (characterized at the family level) in natural forests and in plantations, accounting also for climatic gradients that may be an additional driving force of the composition and diversity of beetle communities at macrogeographical scales. We hypothesize that beetle richness and abundance are higher in natural forests compared to plantations. This work provides the first assessment of the effect of landscape context and anthropization on beetle diversity that is carried out at such a large scale in this region of the world.