Stratification studies involving Lepidoptera have been undertaken in several bioregions, focusing on particular taxa and using a variety of sampling methods. However, there is little consensus as to whether stratification of arthropods between canopy and understory in tropical subtropical forests is commonplace. It is yet not clear whether the magnitude of stratification changes across different elevations and latitudes. 

Researchers from Xishuangbanna Tropical Botanical Garden (XTBG) and Australia conducted 20 years of extensive sampling, collecting and identifying over 100,000 individual moths across elevational and latitudinal gradients. They investigated broad-scale patterns of vertical stratification of moths collected from extensive cross-continental fieldwork in a variety of forest types (tropical and subtropical rainforest in eastern Australia; tropical, subtropical and subalpine forest in Yunnan Province, China; and tropical rainforest in Panama, Vietnam, Brunei and Papua New Guinea), climates, elevations, latitudes and areas with differing biogeographical history. They investigated the generality of vertical stratification of night-flying forest Lepidoptera by using all of subsets of the canopy and understorey data sets from across continents, forest types and climates. 

The researchers sampled a total of 175,768 moths and generated 64 datasets to quantify vertical stratification of moths in terms of their species richness, using coverage-based rarefaction, and assemblage composition, using standardised hierarchical beta diversity. Based on the average temperature lapse rate, they incorporated latitudinal differences into elevation and generated ‘corrected’ elevation for each location, and analyzed its relationships with the magnitude of stratification. 

The study found that the vertical stratification was significant, with distinctive assemblages in the canopy and understory, except for three locations with small numbers of survey plots. There was an over-arching pattern of vertical stratification within forest moth assemblages across elevation, latitude and forest types. They also found differences in the direction and strength of vertical turnover across ‘corrected’ elevation between Northern and Southern Hemispheres. 

The researchers concluded that for night-flying moths, canopy assemblages were different from understorey assemblages, but not necessarily more diverse. In addition, the degree to which assemblages were stratified between canopy and understorey was not uniformly related to elevation and latitude as they found inconsistent patterns between the Northern and Southern Hemispheres. 

The study entitled “Vertical stratification of moths across elevation and latitude” has been published online in Journal of Biogeography. 

Contact:
Akihiro Nakamura, Ph.D. 
Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences,
Menglun, Mengla, Yunnan 666303, P. R. China
Email: a.nakamura@xtbg.ac.cn