How hydrology and landscape shape Odonata assemblages in marshlands crossed by ditches

Abstract

One of the major current ecological challenges is to understand how to reconcile human activities with biodiversity conservation concerns. This issue is particularly relevant in freshwater ecosystems where biodiversity is globally under severe threat. Artificial waterbodies, such as ditch networks, are part of the few remaining wetlands in agricultural landscapes and hence play a crucial role in maintaining aquatic biodiversity in these landscapes. We investigated the responses of adult Odonata assemblages at different spatial scales in a marshland crossed by ditches to two factors expected to be pivotal influences on assemblages. At the local scale, this was mainly the water regime in ditches and, at a broader scale, the composition of the landscape. Both taxonomic alpha and beta diversity, and functional trait composition were considered as response variables. Significant differences were found between the responses of the two Odonata suborders. We showed that Zygoptera species richness decreased and species turnover increased with the duration of drying episodes in ditches. Geographical distances between local assemblages as well as landscape characteristics, notably woodland cover, meadow cover and ditch network length, also significantly shaped the distribution of Zygoptera. For Anisoptera, species richness was not explained by environmental variables and beta diversity was associated only with local conditions; it increased with increasing dissimilarity in water quality and riparian vegetation. We also found evidence of functional trait syndromes (combinations of correlated traits) in Odonata assemblages, but without clear relationships to environmental gradients. This study reveals the structuring role of water regime for Odonata in ditch networks and demonstrates the need to jointly consider environmental variables at different spatial scales to properly understand the distribution of Odonata. Our findings have important conservation implications as the water regime is heavily managed in such ecosystems. Even though the relationship between functional composition and environmental gradients was found to be of limited extent in this study, we discuss how it might provide new insights for Odonata assemblage structure and be useful, locally, for stakeholders and managers. Lastly, we call for further multiscale investigations considering both the taxonomic and functional responses of Odonata assemblages (functional analyses with multiple traits and several species being scarce in this taxonomic group) in other anthropogenic freshwater ecosystems to gather more lessons for their conservation.

Morphological overdispersion supports the role of competition in the community assembly of dragonflies: drivers and spatio-seasonal variation

“…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.…”

“…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+-27.0m 2 vs 99.1+-323.6m 2 respectively).…”

“…The Odonata (with suborders dragonflies: Anisoptera, and damselflies: Zygoptera) are an insect order with rich natural history record that may be uniquely useful for understanding animal competitive interactions. The adult life of this warmadapted group is characterised by competitive encounters over limited reproductive aquatic habitats (Moore 1964), whereby the males of many species, most particularly the larger and more active dragonflies (Crabot et al 2022), allocate much of their adult time to protecting territories (Corbet 2004b). Odonata competitive reproductive encounters are targeted towards conspecifics, but also occur frequently -sometimes as intensely -interspecifically, particularly between morphologically similar species in body size, body proportions, and colour, which is likely caused by visual recognition errors (Moore 1964;Anderson & Grether 2010, 2011Chaves Resende 2010;Worthen & Phillips 2014).…”

Digital multi-scale visual planning model of spatial-geographical landscape pattern of smart parks

“…the synthesis of spatial features. In order to realize the above-mentioned automatic synthesis of multi-scale spatial information, this paper proposes a digital multi-scale visual planning model for the spatial geographic landscape pattern of smart parks, and uses reinforcement learning algorithms to establish a planning model to realize multi-scale visual planning of geographic landscapes [3] .…”