Spatial α-diversity patterns of diverse insect taxa in Northern China: Lessons for biodiversity conservation
Highlights
► α-Diversity in three diverse insect families and links with environment. ► α-Diversity patterns are highly incongruous. ► Links with vegetation diversity are very weak. ► High risk that many current biodiversity conservation approaches are inadequate.
Introduction
Knowledge of spatial diversity patterns is a key prerequisite for the development of effective strategies in biodiversity conservation (Cabeza et al., 2004, Gaston, 2000, Lamoreux et al., 2005). Such knowledge is already widely available for many vertebrate and plant taxa. Nonetheless, recent estimates (Millennium Ecosystem Assessment, 2005) suggest that these taxonomic groups contribute less than 4% of global species richness. On current knowledge, insects are by far the most species-rich group, with their estimated share in global macro-biodiversity exceeding 50%, but huge knowledge gaps currently prevail in relation to their diversity and distribution.
Not least due to their enormous species richness, insects perform a multitude of fundamental roles in ecosystems. They act as herbivores, predators, pollinators and as a food resource for organisms at higher trophic levels. Insects also control many pest species and greatly aid in nutrient cycling (Summerville et al., 2004). It seems logical to conclude that the great knowledge gaps relating to insect diversity, their distribution patterns and the factors causing these patterns need to be addressed to enable the effective conservation of the global species pool and ecosystem functioning (Leather and Quicke, 2010).
One way to address the severe data scarcity on mega-diverse insect groups is to develop biodiversity indicators and surrogate taxa reflecting the overall status of biodiversity. Indeed, a range of biodiversity indicators is already being used. These indicators commonly employ vertebrate and vascular plant taxa (Butchart et al., 2010), with vascular plant diversity in particular often being suggested as an indicator of overall biodiversity (Myers et al., 2000, Xu et al., 2008). Strong positive links between plant diversity and diversity of herbivores and partly also at higher trophic levels are furthermore suggested by experimental evidence (Scherber et al., 2010, Siemann et al., 1998), while studies questioning this proposed positive relationships between plant and invertebrate diversity (Axmacher et al., 2004b, Axmacher et al., 2009; Hambler and Speight, 1995, Hawkins and Porter, 2003, Wolters et al., 2006) have been widely ignored. As Lewinsohn and Roslin (2008) point out, studies directly investigating the proposed positive links between plant diversity and diversity at higher trophic levels in the natural environment are rare, and this is especially true in relation to diverse terrestrial invertebrate taxa. It is also widely unclear if spatial diversity patterns across species-rich terrestrial insect taxa are congruent. However, this congruency forms a logical prerequisite for biodiversity surrogates to work. Consequently, further comparisons of spatial α-diversity patterns across different insect taxa and the nature and strength of their links to the vegetation are urgently needed, and this study provides important insights into these topics.
Despite our general knowledge deficits in relation to highly diverse insect taxa, more detailed data are available for several groups. One such group are ground beetles (Coleoptera:Carabidae), a species-rich family containing more than 40,000 species (Erwin, 1985) whose taxonomy, distribution and ecology are relatively well understood (Lövei and Sunderland, 1996, Niemela, 1996). Ground beetles react with high sensitivity to habitat changes, and their activity-densities can easily be recorded using pitfall traps (Bowie and Frampton, 2004, Liu et al., 2006, Liu et al., 2010, Poole et al., 2003, Thiele, 1977, Vanbergen et al., 2005). They also play important roles in biological pest control, as many ground beetles and their larvae are predatory (Kromp, 1999).
Geometrid moths are another species-rich insect family whose diversity patterns have been extensively studied for example in Southeast Asia (Beck et al., 2002, Intachat et al., 1997, Intachat et al., 1999, Willott, 1999), South and Central America (Brehm et al., 2003, Brehm et al., 2007, Hilt et al., 2006), Australia (Kitching et al., 2000) and Africa (Axmacher et al., 2004a, Axmacher et al., 2004b, Axmacher et al., 2009). More than 21,000 geometrid species are currently known (Scoble, 1999), and their caterpillars use a wide selection of food-plants, with levels of food-plant specialization apparently highly variable across species (Robinson et al., 2010).
Arctiidae are a moth family comprising about 11,000 known species (Watson and Goodger, 1986). Some studies suggest that arctiids profit from anthropogenic disturbances (Kitching et al., 2000, Nöske et al., 2008), possibly due to a high level of polyphagy in many arctiid caterpillars (Holloway et al., 2001). Arctiid moths, and especially members of the subfamily Arctiinae which dominate in our samples, tend to be morphologically more robust than geometrid moths.
Moths have very strong links with the vegetation, as caterpillars and many adult moths depend on plants as a food and nectar source, while moths in return act as important pollinators (Bawa et al., 1985). They can therefore be expected to react particularly sensitive to changes in the vegetation. Nocturnal moths can be sampled effectively on artificial light sources (Muirhead-Thomson, 1991), with weak light sources allowing for standardized sampling of highly localized species assemblages (Beck and Linsenmair, 2006).
The aim of this study is to investigate spatial patterns and correlations in the α-diversity of species-rich insect families and their links to environmental conditions. Connections between insect diversity and the vegetation form a particular focus of this study. This allows us to establish the existence and extend of the suggested positive links between plant and invertebrate α-diversity, with important implications for the validity of the widespread use of plant-based biodiversity indicators and surrogates. The soil nutrient status is well known to alter plant defence mechanisms against herbivore attack, which consequently alters the structure of the herbivore community (Campo and Dirzo, 2003, Coley et al., 1985, Siemann 1992). Soil nutrients were therefore included in our study to establish if they exert a significant influence also on the α-diversity of different insect families.
Section snippets
Study area and site selection
The study area is located in the mountain ranges stretching from Beijing in the south to the Inner Mongolian Plateau in the north. Geographically, this region falls within the transition zone between the sub-humid monsoon climate of the North China Plain and the semi-arid steppe climate of the Mongolian Plateau. Maximum precipitation is encountered during the summer months, while winter conditions are extremely cold and dry. The entire region has experienced severe habitat degradation in the
Results
A total of 410 plant species belonging to 244 genera and 69 families were recorded in the study area. The pitfall traps contained 3663 ground beetles, which were subsequently divided into 59 species and 14 morpho-species. The light traps caught 14,692 geometrid moths, which were divided into 96 species and 14 morpho-species. Light trap samples also included 1543 arctiid moths representing 19 species and one morpho-species (see Table S1 in Supporting information).
Discussion
Our results provide a clear indication that spatial α-diversity patterns diverge strongly between different insect taxa, and that they also vary significantly in relation to their associations with the vegetation and other environmental parameters. These findings lend support to the increasing number of studies reporting missing or weak positive links in diversity patterns between invertebrate taxa and other taxonomic groups (Axmacher et al., 2004b, Axmacher et al., 2009, Basset et al., 2008,
Conclusion
Overall, it appears increasingly clear that vegetation composition and phytodiversity play a subordinate role in explaining the diversity patterns of herbivorous and predatory insects. With many current approaches in terrestrial biodiversity conservation focused on plants and vertebrates, which themselves represent only a minute fraction of global species richness, we are therefore running a severe risk of completely ignoring the conservation needs of the vast majority of species. As diversity
Acknowledgements
We are very thankful to the National Natural Science Foundation of China for their financial support (30570318 and 30800150). We also want to thank Xiaotong Zhang, Xingtong Li and Ying Pan for their great help and assistance in the field and K. Bowers, J. Beck and two unknown reviewers for their helpful comments on the manuscript.
References (81)
- et al.
Testing alternative indicators for biodiversity conservation in old-growth boreal forest: ecology and economics
Ecological Economics
(2004) Carabid beetles in sustainable agriculture: a review on pest control efficacy, cultivation impacts and enhancement
Agriculture, Ecosystems & Environment
(1999)- et al.
Diversity of carabids (Coleoptera, Carabidae) in the desalinized agricultural landscape of Quzhou county, China
Agriculture, Ecosystems & Environment
(2006) - et al.
Cross-taxon surrogacy of biodiversity in the Indian Garhwal Himalaya
Biological Conservation
(2002) - et al.
Disturbance effects on diversity of epiphytes and moths in a montane forest in Ecuador
Basic and Applied Ecology
(2008) - et al.
The flora and carabid beetle fauna of a mature and regenerating semi-natural oak woodland in south-east Ireland
Forest Ecology and Management
(2003) Biodiversity hotspots
Trends in Ecology and Evolution
(1998)- et al.
Does butterfly diversity predict moth diversity? Testing a popular indicator taxon at local scales
Biological Conservation
(2002) - et al.
Forest moth taxa as indicators of lepidopteran richness and habitat disturbance. A preliminary assessment
Biological Conservation
(2004) - et al.
Soil degradation and restoration as affected by land use change in the semiarid Bashang area, northern China
Catena
(2005)