Determinants of diversity in afrotropical herbivorous insects (Lepidoptera: Geometridae): plant diversity, vegetation structure or abiotic factors?

Abstract

Aim This study was conducted to investigate the potential of predicting alpha diversity and turnover rates of a highly diverse herbivorous insect family (Geometridae) based on vascular plant species richness and vegetation structure. LocationThe study was carried out on the south-western slopes of Mount Kilimanjaro within a wide range of habitats between 1200 and 3150 m elevation.Methods The floristic and structural composition of the vegetation was recorded at 48 plots of 400 m 2 . Geometrid moths were sampled manually at light sources located at the plot centres. Principal components analysis, redundancy analysis and multiple linear regression were used to explore how alpha diversity and species turnover of geometrid moths are related to vegetation structure and plant species richness.Results Alpha diversity of geometrid moths was significantly correlated with species diversity patterns in the most common vascular plant families (R 2 = 0.49) and with plant structural parameters (R 2 = 0.22), but not with overall floristic diversity. Species turnover of geometrid moths was strongly linked to diversity changes in a range of plant families (40% explained variance), less strongly to changes in vegetation physiognomy (25%), and only weakly to overall floristic diversity (5%). Changes in elevation were a better predictor of both alpha diversity and species turnover of geometrid moths than any principal component extracted from the vegetation data.Main conclusions Vegetation composition, diversity and structure all showed significant correlations with the diversity and species composition of geometrid moth assemblages. Nevertheless, in most cases relationships were indirect, via environmental parameters such as temperature and humidity, which influenced both vegetation and moth fauna. Possible direct links between geometrid diversity and potential food plants were much weaker. The lack of a significant correlation between overall plant species richness and geometrid diversity indicates that tropical geometrid moths may not be very selective in their food plant choice. Accordingly, a clear correlation between floral diversity and herbivore species richness must be regarded as overly simplistic, and the diversity of vascular plants cannot universally be used as a suitable biodiversity indicator for diverse insect taxa at higher trophic levels.

Determinants of moth diversity and community in a temperate mountain landscape: vegetation, topography, and seasonality

“…While some studies have reported that overall plant diversity is not a good indicator of overall moth diversity (Axmacher et al 2004, Brehm et al 2007, others have suggested that plant diversity is a good predictor of macromoth diversity (Novotny et al 2006). Known host-plant diversity was not a good predictor of macromoth richness, diversity, evenness, or abundance in this study, but a more general physiognomic description of the vegetation communities were good predictors, akin to the findings of Axmacher et al (2009). Known host-plants in this area carry different loads of caterpillars.…”

“…Because of their dependence on host-plants, the abundance and distribution of macromoth species may reflect vegetation distribution patterns as well as plant phenology (Novotny et al 2005(Novotny et al , 2006, although some studies found that plant diversity did not predict macromoth diversity , Axmacher et al 2004, Beck and Chey 2007. Nocturnal macromoth species distribution and diversity have been related to the presence of rare habitats , vegetation disturbance (Holloway 1985, Kitching et al 2000, Kuussaari et al 2007, land use and habitat shifts (Erhardt and Thomas 1991, Ricketts et al 2001, Baur et al 2006, habitat size and distribution (Usher and Keiller 1998, Ober and Hayes 2010, and topographic influences on temperature and predation , Beck and Chey 2008, Axmacher et al 2009). …”

Determinants of nocturnal Lepidopteran diversity and community structure in a conifer-dominated forest

“…A similar inverse relationship between elevation and moth species richness was reported in forests of South Korea (Choi 2008). In Tanzania, elevation was a better predictor of a-diversity of geometrid moths than characteristics relating to vegetative species richness or structure (Axmacher et al 2009). These results collectively suggest that unmeasured environmental factors associated with elevational changes are more influential to the richness of moth species than abundance or diversity of vegetation.…”

Ecological integrity assessment as a metric of biodiversity: are we measuring what we say we are?

“…For example, Kirkman et al (2012) found that species richness of vascular plants at wetland sites was not a good predictor of species richness of the other groups, probably because biotic and abiotic processes act at different scales for different taxa, and other factors such as the number of species in neighboring patches and the number of neighboring patches also need to be accounted for. In another empirical study, Axmacher et al (2009) found that alpha diversity of 279 geometrid moth species was not significantly correlated with overall vascular plant species richness, and hence ''the diversity of vascular plants cannot universally be used as a suitable biodiversity indicator for diverse insect taxa'' at the community level. While it is certain that animal species assemblages are influenced by vegetation, among other drivers, what is not so clear is the nature of the relationship between vegetation and diversity, and the degree to which the former can serve as a surrogate for the latter.…”

“…Gollan et al (2009) tested environmental factors (vegetation structure, soil) and found that none were reliably correlated with species diversity across four invertebrate orders, and hence could not be adequate proxies for the diversity of multiple invertebrate taxa. In another empirical study, Axmacher et al (2009) found in a principal components analysis that vegetation structural attributes overall (cover, tree crown diameter, leaf shape, height, epiphyte cover) accounted for less than one-quarter of the variation in diversity patterns of 279 geometrid moth species. Because habitat-based measures tend to be specific to a given taxon, they may correlate well with occurrence of that particular species or group [such as birds and overstory vegetation richness ; arboreal marsupials and hollow trees ; see review by McElhinny et al (2006) for fauna of Australian woodlands)] but are unlikely to be suitable as proxies for diversity of biota across multiple taxa.…”