Introduction
Analysing biodiversity patterns is fundamental to understanding the
underlying processes and causes of diversification (Holt et al. 2013).
In comparison to plants and vertebrates, arthropods are fragmentarily
known and lack comprehensive comparative data (Decaëns 2010; Beck and
Kitching 2007; Stork et al. 2015; Nielsen 2019). This is particularly
true for biodiversity hotspots (Myers et al. 2000). Restricted dispersal
capacities of arthropods (Gálvez-Reyes et al. 2020) and their occurrence
in micro-niches result in fine scale high endemism and still unknown
patterns (Buckley and Jets 2007; Daru et al. 2020; Baselga et al. 2022).
However, data on arthropod biodiversity rely on museum collections and
suffer largely from sampling bias (Santos and Quicke 2011; Echevarría
Ramos and Hulshof 2019). This is true for even relatively large-bodied
taxa such as phytophagous scarab beetles (Coleoptera: Scarabaeidae).
Diversity patterns of phytophagous beetles are known to be generally
linked to species turnover of their host plants (Ødegaard 2006; Kemp et
al. 2017; Luo et al. 2021) and their distribution is correlated with the
region and forest type (Yotkham et al. 2021). Other guilds, such as dung
feeding beetles, respond to shade cover rather than plant species
composition. Further, their occurrence and relative abundance vary
according as responses to microclimate (light intensity, temperature,
humidity) (Davis et al. 2013) or other factors (rainfall, temperature,
and host density/diversity) varying from regional to local scale in
relation to actual local functional ecological conditions (Tshikae et
al. 2013). Such correlation of occurrence and abundance with
environmental conditions, suggest that a strong role of lineage- or
species-specific traits such as dispersal capabilities or body size
determines local community composition (Murria et al. 2017). Insect body
size is modulated by many climatic factors along species ranges,
especially when they are distributed across climatic gradients at large
spatial scales (Lira et al. 2021; Romero et al. 2016; Brehm et al.
2019). Changes in body size may affect fertility, lifespan, population
dynamics, and species composition (Garcia-Robledo et al. 2020).
In contrast to most other herbivore insects being rather host-specific,
phytophagous scarab chafers (Coleoptera: Scarabaeidae), with ca 30,000
extant species worldwide, feed unspecifically on leaves of a vast
variety of angiosperm plants as adults, on soil humus or roots as larvae
(Ritcher 1958). They have had a very successful follow-up evolution with
angiosperms (Ahrens et al. 2014). However, very little is known about
their actual assemblages responding to habitat differences (Eberle et
al. 2017). since only few studies have comparatively investigated their
quantitative composition (Ahrens et al. 2009; García Lopez et al. 2010,
2013), and often these studies include either only a part of the
assemblage (Ahrens et al. 2007), and/or consider separate localities
rather than habitats (Ahrens et al. 2009; García-Lopez et al. 2013).
To close this gap, we investigated here patterns of species diversity
and turnover in tropical phytophagous chafers in Sri Lanka, a global
biodiversity hotspot (Myers 2000) across different forest types,
elevation zones, localities, and habitats. We attempt to explore to
which extent each of these spatial components determines assemblage
composition. In this context, we also assessed their influence on
different lineages and the role of body size in shaping species
composition. If body size (as proxy of dispersal capability) had an
impact on assemblage composition, we would expect contrasting patterns
between entities of different spatial scales between smaller and larger
species assemblies, also in respect to phylogenetically partitioned
assemblages. This way, we expect to elucidate the dynamics of community
assembly and differentiation and to explain the high species richness
and endemism in tropical chafers.