Discussion
We investigated here for the first time components determining the
chafer assemblage composition, comparing the impact of ecoclimatic
influences with macrohabitat and locality stochastics on the similarity
of investigated entities. Locality stochastics represent a not further
investigated multi-factor ensemble that includes all biotic and abiotic
environmental conditions at local scale such as macrohabitat,
biogeography, edaphic conditions, land use, predation, local climate,
rainfall, radiation, and others. We also explored the patterns of
lineage membership and body size resulting from assemblage composition
across larger scale entities (forest type, elevation) versus smaller
scale entities (localities, macrohabitats).
The comparison of chafer assemblage composition at different eco-spatial
scales revealed that assemblages were shaped mainly by locality
stochastics, to minor extent to the ecoclimatic conditions, and not by
macrohabitat. This was true for the entire chafer assemblage, as well as
single lineages or different body size classes. NMDS plots of faunal
similarity showed the largest overlap among macrohabitat entities. In
contrast to that, overlap for clusters of forest types, elevation zones,
and localities were limited. However, contrasts between localities were
less pronounced in medium-sized and large specimens.
Investigated macrohabitats were quite different (e.g., forest,
grassland, abandoned plantations). They are known to provide multiple
niches (Bosc et al. 2019) for chafer species, however, only a few
species were recorded that were specific to these habitats. Most species
and resulting assemblages sorted rather by locality rather than by
macrohabitat. This could be partly explained by the trapping method
(light traps) used, as fully winged chafer beetles may be attracted from
other habitats over certain distances within the same locality. However,
the fact that we found no correlation between species composition (for
total assemblage) and geographic distance (Figure 5), even for adjacent
localities situated in the same forest type also in the same mountain
range (e.g., L2, L4), may indicate either that species generally might
tend to disperse also over moderate to longer distances or that species
disperse very little. Limited dispersal is supported further by
molecular evidence (Ranasinghe et al. in review), since different, the
same here investigated localities shared almost no haplotypes. This
latter conclusion would be not surprising as previous studies have also
shown high turnover rates of assemblage composition at higher elevations
independently from geographical distance (García Lopez et al. 2010).
However, the resulting significant correlation for the assemblage of
small-bodied specimens, which is definitively linked to their limited
dispersal capacity and mirrored by their higher endemism (Fabrizi and
Ahrens 2014), might indicate that lacking significance on our study
might be a result of an insufficient number of samples and species.
Larger species were generally less common and are also less represented
in higher altitudes. Influence from palaeogeographical and
biogeographical factors should also be considered in this context (Kemp
et al. 2017) as several sampling localities are situated in the central
highlands within complex mountain systems (escarpments, ridges, or
peaks) which can act as geographical barriers. The latter can
particularly triggered geography-driven speciation, as shown by
diversification of Sericini in Asian mountains (Ahrens 2007; Eberle et
al. 2016).
Some of the divergent composition patterns retrieved for the full
assemblage (Figure 3A, F), which are in turn not encountered for any of
the single lineages, reveal that occurrences of entire lineage members
may also impact on the apparent differentiation (e.g., wet lowland
forest vs. submontane forest, EZ 1 vs EZ 2). The latter case is caused
by the more poorly sampling/ absence of larger-bodied species (e.g.,
Dynastinae), in higher elevations, since low temperatures obviously
might not favour larger species with long larval development (Danks
1992). In fact, even in mountain ranges with larger amplitudes of
elevations, the altitudinal differentiation of the fauna in phytophagous
chafers is rather poor (Ahrens 2004) compared to other insects (Mani
1968).
The strong turnover for localities is in line with the rather high
degree of endemism in many phytophagous scarabs (Ahrens and Fabrizi
2016), despite their considerable size. Their assemblage patterns across
local spatial scales can be explained not only by poor dispersal
capacities, but also by short emergence times compared to the length of
their life span: their root feeding, endogenous larvae do not disperse.
Their emergence during early night-time often falls together with heavy
monsoon rains which narrows down the time window for potential dispersal
flights.
Other lineages composed of larger species, such as Dynastinae, have
greater dispersal ability compared to smaller Rutelinae and
Melolonthinae (García Lopez et al. 2013), and this has an impact on the
faunal divergence pattern of assemblages as revealed by pronounced
larger cluster overlaps across different spatial scales.
Seasonality and weather fluctuation may strongly impact the expressed
patterns of assemblage composition in ecofaunistic analyses (De Oliveira
et al. 2021). In tropical climate, rainy seasons and dry seasons are
alternating in shorter intervals with quite constant temperature and
humidity throughout the year and food resources being continuously
available. Thus, minor fluctuations to species’ presence and numbers may
occur even in the tropical ecosystems. Many of our localities (except
L1-L3, L9) did not show a significant seasonal species turnover, while
those which did experience generally stronger dry-wet fluctuations than
other localities according to their position in the island.
In final conclusion, we need to remember that at local level all
ecological, climatical, and spatial components sum up in their effect
increasing the complexity of influences on the assemblages. This points
the way for future, more detailed studies, in which localities of
similar eco-spatial situations shall be addressed. Yet, since
phytophagous chafers are for many tropical crops common pests, and
damage can often also be caused by a multispecies autochthonous
community with endemic species, (Ahrens et al. (2009), we need more
knowledge here, as this might positively affect simultaneously pest and
biodiversity management.