Damselfly community assembly

The lack of support for the role of competition on damselflies compared to dragonflies may be driven by their lower body size and mobility, lower degree of territoriality (Crabot et al. 2022), and much smaller territory size (e.g. Aromaa et al. 2019: 8.6±27.0m2 vs 99.1±323.6m2 respectively). Species mobility likely determines the scale at which animal diversity patterns emerge (Reiss 1988; Ofstad et al. 2016). The observed pattern of functional underdipersion in damselfly assemblages was neither driven by the environmental factors considered nor by species richness, stressing previously supported differences in ecological drivers between dragonflies and damselflies (Carvalho et al. 2013; Oliveira-Junior & Juen 2019; Crabot et al. 2022). Despite being closely related, both suborders differ markedly regarding their morphology, mobility, habitat use and thermoregulatory physiology (Corbet 2004a). Smaller bodied insects like damselflies have lower thermal requirements which may render their diversity patterns less dependent on thermoregulatory constrains. Additionally, their lower mobility may make them more dependent on fine microhabitat characteristics (Crabot et al. 2022) that were not assessed in this study.

Additional considerations

This study focuses on the adult stage of Odonata. While a complete understanding on Odonata community assembly would require the integration of both development stages (Grether et al. 2023), larval life may likely offer less opportunities for competitive exclusion because aquatic habitats provide a wider range of microhabitats (water column, sediments, vegetation), towards which specific lifestyle specialisation has evolved (borrower, deep borrower, clasper, hider, sprawler), allowing coexistance (Crowley & Johnson 1982). Larval interspecific predation from large to small individuals (Benke 1978) can occur between either morphologically dissimilar species or between morphologically similar species at different developmental stages (Grether et al. 2023), and therefore it is unlikely to result in the morphological overdispersion patterns reported in this study.

Conclusion and implications for climate change impacts 

By combining mechanistic-driven functional approaches with sets of ecologically-sensible defined assemblages, our study develops generalised understanding on the ecological processes driving spatial and phenological patterns of insect community assembly. More complete understanding of assembly processes is essential for addressing the challenges arising from biodiversity changes caused by climate change. Odonata are well known to respond to present climate change with strong latitudinal (Hickling et al. 2005; Hassall et al. 2007; Grewe et al. 2013; Termaat et al. 2019) and phenological shifts (Scranton & Amarasekare 2017; De Lisle et al. 2022). Our support for the role of competition in dragonflies supports previous speculations (Ott 2001) suggesting that competition may play a relevant role in mediating future climate change effects in this taxa. Hence, colonising dragonflies to newly environmentally suitable areas may impact local species through competition, or conversely, local competitors may prevent the establishment of newly colonising species (Lancaster et al. 2017). Dragonflies may therefore constitute a uniquely useful study system to understand how climate change and biotic effects interact (Poloczanska et al. 2008; Tylianakis et al. 2008; Urban et al. 2013). For this, Mediterranean range-expanding species in central and north Europe such as Crocothemis erythraea, Sympetrum fonscolombii, Thritemis annulata or T. Kyrbii may be particularly relevant study cases (Ott 2001).