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.