Alpha-diversity, Beta-diversity and host-specificity of wood-boring longhorn beetle (Cerambycidea) in Asian tropical and subtropical forests

A long-debated question in ecology is whether the hyper-diversity of
tropical plant-feeding insects is a direct consequence of high tropical
plant diversity and/or should be attributed to increases in host plant
specialization. To address this debate, we used the longhorn beetle as a
study system because their larval stages feed on the xylems of trees and
lianas. We hypothesized that longhorn beetles show higher host-specificity
in tropical forests than in other forests; alternatively, the high
longhorn beetle diversity in the tropics may simply be owing to more
diverse host plants. We therefore designed an investigation in tropical
and subtropical forests to test these hypotheses. We adapted several
analyses (i.e., non-metric multidimensional scaling analysis,
alpha-diversity, beta-dissimilarity indices comparisons, and variation
partitioning based on redundancy analysis) to compare the species
diversity of plants and longhorn beetles in different forests. Our results
show that both the plant and beetle species in the tropical and
subtropical areas were well-stratified (non-metric multidimensional
scaling analysis). The beetle alpha-diversity in the tropical forests was
significantly higher than that in the subtropical forests, but the plant
alpha-diversity in the two types of forests were not significantly
different. The beta-dissimilarity comparison showed that the plant species
exerted a significant influence on beetle compositional assemblage in the
tropical forests, but not in the subtropical forests. Finally, the
variation partitioning results showed that both plant species and plant
phylogenetic beta-diversity possessed significant explanatory power for
beetle assemblage composition in the tropical forests, but not in the
subtropical forests. We conclude that wood-boring longhorn beetles show
higher host-specificity in tropical forests than in subtropical forests,
and the high diversity of wood-boring longhorn beetles in tropical forests
might be explained to a large extent by their more finely partitioned
diet-breadth.