Dragonfly Assemblages Research Articles

Human‐modified habitats imperil ornamented dragonflies less than their non‐ornamented counterparts at local, regional, and continental scales

AbstractBiologists have long wondered how sexual ornamentation influences a species' risk of extinction. Because the evolution of condition‐dependent ornamentation can reduce intersexual conflict and accelerate the fixation of advantageous alleles, some theory predicts that ornamented taxa can be buffered against extinction in novel and/or stressful environments. Nevertheless, evidence from the wild remains limited. Here, we show that ornamented dragonflies are less vulnerable to extinction across multiple spatial scales. Population‐occupancy models across the Western United States reveal that ornamented species have become more common relative to non‐ornamented species over >100 years. Phylogenetic analyses indicate that ornamented species exhibit lower continent‐wide extinction risk than non‐ornamented species. Finally, spatial analyses of local dragonfly assemblages suggest that ornamented species possess advantages over non‐ornamented taxa at living in habitats that have been converted to farms and cities. Together, these findings suggest that ornamented taxa are buffered against contemporary extinction at local, regional, and continental scales.

Seasonal variation in dragonfly assemblage colouration suggests a link between thermal melanism and phenology

Phenology, the seasonal timing of life events, is an essential component of diversity patterns. However, the mechanisms involved are complex and understudied. Body colour may be an important factor, because dark-bodied species absorb more solar radiation, which is predicted by the Thermal Melanism Hypothesis to enable them to thermoregulate successfully in cooler temperatures. Here we show that colour lightness of dragonfly assemblages varies in response to seasonal changes in solar radiation, with darker early- and late-season assemblages and lighter mid-season assemblages. This finding suggests a link between colour-based thermoregulation and insect phenology. We also show that the phenological pattern of dragonfly colour lightness advanced over the last decades. We suggest that changing seasonal temperature patterns due to global warming together with the static nature of solar radiation may drive dragonfly flight periods to suboptimal seasonal conditions. Our findings open a research avenue for a more mechanistic understanding of phenology and spatio-phenological impacts of climate warming on insects.

The balance of common vs. rare: a study of dragonfly (Insecta: Odonata) assemblages in the Brazilian Pampa biome

ABSTRACT We surveyed dragonflies (Odonata) at 87 sites in the anthropologically modified Pampa biome of southern Brazil to evaluate how regionally rare and common species form species assemblages in habitats with different water physiochemistry, habitat structures, and other environmental variables. We classified 9 out of the 90 species encountered as regionally common and 59 as regionally rare. A discriminant analysis confirmed that localities with only a few common species were characteristic in the set of rare species present, while localities housing more common species showed no clear pattern. A PCA revealed that a subset of the common species were strongly positively associated with water temperature, turbidity, dissolved O2 and pH but negatively associated with desertification. In contrast, rare species were positively associated with grassland habitat, but negatively with agriculture, salinity, and conductivity. In general, the associations of the rare species were weaker than those of common species. Finally, a correlation suggested that sites with six or more common species present had a reduced number of rare species compared to sites with fewer common species. It is possible that common species reduce the available niche space for weaker competitors among the rare species. We conclude that the original species assemblages in the biome may have been species poor with few regionally common species. Current anthropogenic change has increased the number of common species, which in turn has negative effects on the survival possibilities of rare species.

Natural and anthropogenic determinants of peatland dragonfly assemblages: Implications for management and conservation

Natural and anthropogenic determinants of peatland dragonfly assemblages: Implications for management and conservation

Species‐specific responses to warming alter community composition

Abstract Species are responding to global climate change in varied and nuanced ways. However, how species‐specific responses to climate change= affect interactions among species remains poorly understood. It is important to understand species interactions under potential climate change scenarios because those interactions can in turn alter community dynamics. In this study, we conducted two complementary experiments to examine how simulated warming might alter larval intraguild predation (IGP) rates and resulting adult assemblage composition in three species of North American dragonflies: Pachydiplax longipennis, Plathemis lydia and Libellula luctuosa. First, using both P. longipennis and L. luctuosa, we isolated interspecific and intraspecific pairs of larval dragonflies of different size differentials to determine how the size and species identity might influence IGP rates. In tandem, we conducted a year‐long mesocosm experiment with all three species to assess how simulated warming and heat waves influenced the resulting adult dragonfly assemblages. IGP trials revealed that P. longipennis individuals were much more likely to engage in IGP than L. luctuosa, regardless of size differential. In the mesocosm experiment, emerging adult assemblages were dominated by P. longipennis individuals, a pattern that was most pronounced in the control treatment. Our results indicate that while P. longipennis may be the competitively dominant species under current ambient conditions, warming may alter this dynamic and lessen the dominance of this species on the resulting assemblage composition.

32 years of essential management to retain value of an urban dragonfly awareness pond

Pond construction in urban areas can mitigate loss of aquatic insects by providing refuges. Urban ponds are also an interface between civil society and aquatic insects, especially via charismatic dragonflies. Ponds have therefore been constructed specifically for dragonfly conservation awareness in many countries. Yet they require regular management, especially when an inflow to a shallow pond supplies inorganic and organic material, leading to vegetation overgrowth and natural infilling, rendering a pond back into a stream, unsuitable for many lentic species. Here, we assess changes in dragonfly diversity over a 32-year period at a pond constructed for dragonfly conservation awareness, and which underwent system changes: stream→pond→vegetation overgrowth and infilling and then following restoration from stream→pond. Adult male dragonflies and 13 environmental variables were recorded along 31 transects, and compared with previous data collected at the same sites before pond construction and then in the short- and medium-term after. Years when the system comprised a pond had higher dragonfly abundance and species richness than when a stream, and both increased after the pond was restored. Shortly after restoration, the dragonfly assemblage closely resembled that of the earlier pond. Vegetation cover and alien vegetation presence were significant drivers of dragonfly assemblage change and decreased dragonfly abundance and species richness. Lessons learned here for maintaining a dragonfly awareness pond include periodical dredging to remove excessive vegetation overgrowth and infilling from organic and inorganic matter, and aim for high microhabitat heterogeneity using selective management of marginal vegetation, alongside a range of flow regimes.

A Review of the Impacts and Opportunities for African Urban Dragonflies.

Simple SummaryThe expansion of urban areas in combination with climate change places great pressure on species found in freshwater habitats. Dragonflies are iconic freshwater organisms due to their large body sizes and striking coloration. They have been widely used to indicate the impacts of natural and human-mediated activities on freshwater communities, while also indicating the mitigation measures required to ensure their conservation. Here, we review the major threats to dragonflies in southern Africa, specifically those in urban areas. We also provide information on effective mitigation measures to protect dragonflies and other aquatic insects in urban spaces. Using three densely populated areas as case studies, we highlight some of the greatest challenges for dragonflies in South Africa. More importantly, we give a summary of current mitigation measures which have maintained dragonflies in urban spaces. In addition to these mitigation measures, public involvement and raising awareness contribute greatly to the common cause of protecting dragonflies around us.Urban settlements range from small villages in rural areas to large metropoles with densely packed infrastructures. Urbanization presents many challenges to the maintenance of freshwater quality and conservation of freshwater biota, especially in Africa. There are many opportunities as well, particularly by fostering contributions from citizen scientists. We review the relationships between dragonflies and urbanization in southern Africa. Shifts in dragonfly assemblages indicate environmental change, as different species are variously sensitive to abiotic and biotic water and bank conditions. They are also conservation umbrellas for many other co-occurring species. Major threats to southern African dragonflies include increasing infrastructure densification, frequent droughts, habitat loss, pollution, and invasive alien vegetation. Mitigation measures include implementation of conservation corridors, maintenance of healthy permanent ponds, pollution reduction, and removal of invasive alien trees. Citizen science is now an important approach for supplementing and supporting professional scientific research.

Webs of well-designed conservation corridors maintain river ecosystem integrity and biodiversity in plantation mosaics

Landscape transformation and subsequent habitat loss locally extirpate populations and threaten ecosystem health. Timber plantations are a major threat to grassland ecosystems globally. An effective mitigation measure is the instigation of webs of large conservation corridors as ecological networks in plantation mosaics. These ecological networks incorporate natural water courses along with their matrices of natural grassland. Dragonflies are highly sensitive to habitat condition and are effective bioindicators of water quality. Here, we compare dragonfly diversity in conservation corridors, with nearby protected areas as controls, to determine the effectiveness of ecological networks for maintaining river ecosystem integrity, in the KwaZulu-Natal Midlands, South Africa. We also investigate the effect of ecological network corridor width on dragonfly assemblages. Lastly, we explore the importance of 18 environmental variables as drivers of dragonfly diversity. Dragonfly abundance, species richness, and Dragonfly Biotic Index scores (a scoring system based on dragonfly range of extent, threat status, and environmental sensitivity) did not differ between ecological network and protected area sites. Dragonfly abundance and species richness were positively correlated with ecological network corridor width. Landscape and water variables were the most important drivers of dragonfly assemblage composition in both ecological networks and protected areas. Management variables and those related to anthropogenic disturbance were not as important. This highlights the conservation success of these well-managed ecological networks for maintaining dragonfly biodiversity in forestry plantations, provided that corridors are wide enough. Implementation of ecological networks as a mitigation measure for plantation forestry is highly effective for lotic systems, and should be implemented more widely in environmental protection plans for transformed landscapes.

Dragonfly assemblages in four Mediterranean wetlands of Samos Island, Greece (Odonata)

Dragonflies (Odonata) are considered to be valuable indicators of hydroecosystems. This study reports the composition of the dragonfly assemblages in four wetlands of Samos Island, Greece, in a geographic area especially vulnerable to climate change where a trend towards a drier climate has been observed in the last decades. Dragonfly assemblages have not yet been studied on Samos. The analysis based on the number of different species and their autochthony revealed clear differences among the wetlands. The eutrophic Glyfada Lake, despite its variable hydrology resulting from drought – the seasonal decrease in water availability – harboured the largest diversity of dragonflies, larger than the oligotrophic Mesokampos Lake. The assemblage of the spring and rivulet at Mytilini, although also influenced by drought, had its own set of species of high autochthony. The seasonal brackish lake and marsh of Psili Ammos had the lowest number of species and was dominated by one very abundant breeding species. Drought was the main factor affecting the number and composition of species. The collected data create a reference for the future monitoring of trends in the composition of odonatofauna under the changing climate of Samos Island.

Odonatans in lowermost Cenomanian Kachin amber: updated review and a new hemiphlebiid damselfly

Odonatans are rare in Cretaceous amber deposits, and only four fragmentary specimens were recorded in Lebanese, Jordanian, Charentes and South Dakota ambers except for Kachin amber. This study reviewed the odonatans in lowermost Cenomanian Kachin amber and commented 11 odonatans, which were previously placed in the family level. Until now, over 350 odonatans have been found in Kachin amber, including 38 species of three extant suborders, and representing the most diverse and abundant dragonfly assemblage in amber inclusions. The dominated odonatans include the damselflies Burmahemiphlebia zhangi and Mesomegaloprepus magnificus, and the damsel-dragonfly Burmaphlebia reifi, accounting for ca. 79% of all odonatans. The Kachin odonatans include the earliest records of the damselfly Perilestidae, Platycnemididae and Platystictidae, and the youngest records of the true dragonfly Araripegomphidae and Stenophlebiidae, contributing to exploring the origination and evolution of these families.Hemiphlebiidae is the dominant family in Kachin amber, represented by the species Burmahemiphlebia zhangi with ca. 160 species been recorded. It is surprising that the hemiphlebiid damselfly is abundant, but the diversity is very low with only two species been previously reported. Herein, a new hemiphlebiid damselfly, Kachinhemiphlebia lini gen. et sp. nov., is described by the unique characters: Arc slightly distal of Ax2 in both fore- and hindwings; and a well-defined AA ending on posterior wing margin below Ax2. This is the second genus of the Hemiphlebiidae in Kachin amber.

Development of a new continental-scale index for freshwater assessment based on dragonfly assemblages

Abstract African freshwater ecosystems are increasingly being impacted by humans, requiring an effective tool to assess these impacts for future conservation action. Such a tool, the Dragonfly Biotic Index (DBI), was earlier developed to assess the quality of South Africa’s freshwater ecosystems and is based on combining the scores of three sub-indices (geographical distribution, threat status, and habitat sensitivity) for each South African dragonfly species. The sum of the DBI scores for all the species recorded at assessed sites indicates the relative quality of these sites. The International Union for the Conservation of Nature/Species Survival Commission (IUCN/SSC) has assessed the threat status of certain aquatic taxa in Africa, including dragonflies. These assessments, coupled with the latest information on the geographical distribution of each species, makes it possible here to geographically expand the South African DBI into a continental-scale assessment index (the African Dragonfly Biotic Index (ADBI)) by adapting the South African DBI sub-indices. We develop this continental index here. However, there are challenges when undertaking an assessment at the continental scale compared to a national scale. In particular, the habitat sensitivity sub-index of the South African DBI is a relative, quantitative measure based on numbers of individual dragonflies recorded from natural versus human-modified or artificial freshwater systems. While the data for the two sub-indices, species’ geographical distribution and Red List threat statuses, are available across the continent, this is not the case for the habitat sensitivity sub-index at this large spatial scale. This meant that an alternative sub-index measure was required. We overcame this challenge by exploring an alternative sub-index, i.e. the ‘species vulnerability sub-index’, based on knowledge of the vulnerabilities of the species to certain types of landscape transformation. Then, the species vulnerability sub-index scores were calculated and combined with the geographical distribution and Red List threat status sub-index scores to develop ADBI scores for a core of 604 dragonfly species with adequate data across the African continent. These ADBI scores provide a workable framework and baseline for determining freshwater quality, both lotic and lentic, relative to human disturbance at a continental spatial scale. The ADBI enables the monitoring of quality changes, for better or worse, over the continent in years to come. Overall, the ADBI also has the potential to help identify threats to, and sensitivities of, African freshwater ecosystems, leading to conservation action.

Restoration of raised bogs–Land-use history determines the composition of dragonfly assemblages

Even though bogs function as the most important terrestrial carbon store on Earth and play a crucial role in the conservation of highly endangered species, the area covered by peatlands is declining globally. Consequently, numerous restoration efforts within degraded bogs have been realized. In many cases, however, it is unknown whether the conservation measures have been successful.We used Odonata (hereafter referred to as dragonflies) as ecological indicators to evaluate the restoration success of rewetting measures in central European degraded raised bogs. Depending on their land-use history (rewetted industrial peat cuts with and without former agricultural use), two types of bog restoration were compared with rural peat cuts (control).Our study demonstrated that restored bogs are important habitats for dragonfly conservation. Both types of restored bogs were as diverse in overall species richness as the control plots. However, land-use history had a strong effect on restoration success. All raised-bog species of the study area were able to recolonize at least some of the nutrient-poor restored bogs. The situation was different for the nutrient-rich restored bogs. Due to the high nutrient content – caused by the former agricultural use – the characteristic dragonfly fauna of raised bogs will be unlikely to be able to recolonize in these locations in the long term. Nevertheless, the nutrient-rich restored bogs represent an important secondary habitat, especially for transition-bog species. In conclusion, the conducted restoration measures created a network of small oligo- to mesotrophic water bodies, which fosters aquatic macroinvertebrate diversity in bogs.

Environmental variables drive differences in the beta diversity of dragonfly assemblages among urban stormwater ponds

Stormwater ponds are beneficial to urban landscapes because these man-made systems can reduce the negative effects of flooding in urban areas and restrain the distribution of pollutants. In additio ...

Dragonflies community assembly in artificial habitats: Glimpses from field and manipulative experiments.

Several factors act on community structure, so determining species composition and abundance patterns. Core processes operating at local scales, such as species-environment matching and species interactions, shape observed assemblages. Artificial habitats (simplified structure) are useful systems for assessing the main factors affecting community composition and disentangling their assembly rules. Drinking troughs (brickwork tanks for free-ranging cattle watering) are widespread in Italy and represent a suitable aquatic habitat for colonization by various aquatic organisms. Dragonflies larvae are usually found in drinking troughs and often exhibit strong species interactions and striking community assembly patterns. Our primary aim was to search for Odonata communities exhibiting non-random co-occurrence/segregation patterns in drinking troughs. We performed null-model analyses by measuring a co-occurrence index (C-score) on larval Odonata assemblages (13 species from 28 distinct troughs). Overall, we found a non-random structure for the studied dragonfly assemblages, which, given their fast generation time, must have been generated by short-term ecological processes (i.e. interspecific interactions). We thus analyzed potential competition/predation among and within ecological guilds. From the field data, we speculated that interactions within the sprawlers’ guild is likely among the main drivers structuring the studied assemblages, especially the effect of intraguild predation between C. erythraea and Sympetrum spp larval stages. We then experimentally tested these interactions in laboratory and demonstrated that intraguild predation among larvae at different development stages may result in an effective exclusion/negative impact on density pattern, representing one of the processes to take into consideration when studying dragonfly assemblages.

Complementarity among dragonflies across a pondscape in a rural landscape mosaic

Abstract Networks of ponds (pondscapes) are becoming increasingly significant for resilient landscape planning in rural areas. Farmland and forestry ponds are habitat islands that support heterogeneous communities of aquatic organisms. Species richness, Dragonfly Biotic Index (DBI), Shannon's index, and species composition are used here to assess the complementary conservation value of adult dragonfly assemblages associated with forty ponds across a protected area‐sugarcane‐forestry mosaic. Despite differences in environmental variables among the various ponds, dragonfly species richness, DBI, Shannon index scores, as well as responses to particular environmental variables, did not differ between ponds in sugarcane, plantation forestry, and protected areas. Dragonfly composition differed in response to vegetation cover. Our results highlight the importance of catchment and regional management for all ponds within the pondscape, and show that ponds in the transformed areas (i.e. sugarcane and forestry areas) are important contributors to regional conservation. As the various ponds were complementary in their dragonfly assemblages, we recommend conservation focus at the level of the pondscape rather than on individual ponds.

Egg‐laying traits reflect shifts in dragonfly assemblages in response to different amount of tropical forest cover

Abstract Oviposition site selection by aquatic insects is usually influenced by both aquatic and terrestrial cues. Landscape changes (e.g. native vegetation loss) can affect the level of the reproductive success in aquatic insects, changing local species composition and richness. We investigate whether forest cover loss around streams influences the number of species with exophytic (species which lay eggs directly on the water surface), endophytic (species which lay their eggs directly into plant tissue), or epiphytic (species which lay eggs on the exposed surface of rocks, leaves, trunks or other substrates protruding from the stream surface) oviposition behaviour in dragonfly assemblages. We sampled adult dragonflies in 116 streams in a Neotropical savanna region in Brazil. The relationship between species richness for each behavioural category, and the proportion of forest cover around the streams, was tested using regression analysis. We collected 2413 dragonfly (Anisoptera and Zygoptera) individuals, belonging to 8 families, 30 genera, and 63 species. Of these, 25 species were classified as exophytic, 28 as epiphytic, and 10 as endophytic. Our results show that the number of species with exophytic or epiphytic behaviour was strongly related to riparian forest loss. Forest loss changes the habitat, and here, specifically changes site suitability for oviposition. We highlight the importance of using behavioural traits as a bioindicator tool for the assessment of anthropogenic impacts on tropical forest.

Stormwater ponds promote dragonfly (Odonata) species richness and density in urban areas

The loss of global biodiversity is one of the major challenges of our time and urbanisation is seen as a main cause of this. The aim of this study was to determine whether artificial stormwater ponds, designed to control water flow, can act as refuges for Odonata in urban areas. Moreover, we analysed the influence of habitat and landscape quality on dragonfly species richness and density of 35 stormwater ponds (STOPON) in comparison to 35 control ponds (CONTROL).Our study revealed significant differences in environmental conditions between STOPON and CONTROL. At the habitat level, STOPON were larger, had a warmer microclimate, and lower concentrations of phosphate. STOPON were predominantly situated in suburbs, while CONTROL occurred mostly in rural areas. Accordingly, at the landscape level, STOPON had greater cover of built-up area as well as a lower cover of arable land and woodland. In line with this, the dragonfly assemblages at STOPON and CONTROL differed. Overall species richness was greater at STOPON than at CONTROL, and indicator species were only identified for STOPON. Especially threatened species benefited from STOPON, having higher species richness as well as higher adult and exuviae densities than CONTROL.In conclusion, our study shows that stormwater ponds in urban areas play an important role in the conservation of dragonflies in general and threatened species in particular. At STOPON, as a result of regular management, the habitat quality was high and compensated for the low landscape quality stemming from significant urbanisation effects.

Canopy cover affects habitat selection by adult dragonflies

The mechanisms structuring aquatic communities across environmental gradients are often difficult to distinguish from one another and can produce similar patterns of species distributions. In freshwater systems, the amount of canopy cover from surrounding trees is often associated with transitions in local community structure. These community changes could be driven by habitat selection prior to colonization of the aquatic habitat and/or species-sorting post-colonization. To assess the contributions of pre- versus post-colonization processes in structuring larval dragonfly assemblages, we tested the impact of artificial and natural canopy cover on the selection of experimental aquatic mesocosms by adult dragonflies, and monitored the performance (i.e. growth and survival) of larval dragonflies that were placed in mesocosms under a gradient of natural canopy cover. We found that greater levels of canopy cover resulted in fewer adult visits to mesocosms, and more natural canopy cover decreased the species richness of visitors. There were no effects of canopy cover on the growth and survival of larvae added to the mesocosms. Our results suggest that adult habitat selection plays a dominant role in structuring larval dragonfly assemblages across a canopy cover gradient, and that canopy cover can be an important environmental filter on species distributions.

How difficult is it to reintroduce a dragonfly? Fifteen years monitoring Leucorrhinia dubia at the receiving site

Conservation translocations (including reintroductions) are potentially powerful tools for wildlife conservation, and their use has increased worldwide. However, most studies have focused on vertebrates, with the long-term impact and ecological progress of translocations being neglected. Moreover, such projects rarely target insects. The present study reports the long-term persistence of a population of Leucorrhinia dubia (Odonata: Libellulidae) reintroduced to artificially created bog pools in the Czech Republic. Eighty (pen)ultimate instar L. dubia larvae were translocated in 2001, and the dragonfly assemblage at the reintroduction site was monitored for 15years following larvae release. In 2015–2017, the capture-mark-recapture method, the Jolly-Seber model, and exuviae collection were used to evaluate the demography of the translocated population. Microsatellite analysis was performed to assess the genetic variability of source and reintroduced populations. Over the monitored period, population size increased (80 larvae released vs. 108–115 exuviae and 75 adults at the end of the study) and L. dubia became a dominant species, whereas the composition and abundance of the local dragonfly assemblage were not substantially changed. These results indicate that reintroductions are effective measures for dragonfly conservation, as translocating a relatively small number of individuals led to the establishment of a self-sustaining population. Using (pen)ultimate instar larvae was optimal for dragonfly translocation, but the availability of a high-quality habitat and the active collaboration with nature conservation authorities were vital for the successful outcome. Genetic analysis suggested that the translocated population might serve as a source of genetic variation for the original population, if depleted.

Evolutionary processes, dispersal limitation and climatic history shape current diversity patterns of European dragonflies

We investigated the effects of contemporary and historical factors on the spatial variation of European dragonfly diversity. Specifically, we tested to what extent patterns of endemism and phylogenetic diversity of European dragonfly assemblages are structured by 1) phylogenetic conservatism of thermal adaptations and 2) differences in the ability of post‐glacial recolonization by species adapted to running waters (lotic) and still waters (lentic). We investigated patterns of dragonfly diversity using digital distribution maps and a phylogeny of 122 European dragonfly species, which we constructed by combining taxonomic and molecular data. We calculated total taxonomic distinctiveness and mean pairwise distances across 4192 50 × 50 km equal‐area grid cells as measures of phylogenetic diversity. We compared species richness with corrected weighted endemism and standardized effect sizes of mean pairwise distances or residuals of total taxonomic distinctiveness to identify areas with higher or lower phylogenetic diversity than expected by chance. Broken‐line regression was used to detect breakpoints in diversity–latitude relationships. Dragonfly species richness peaked in central Europe, whereas endemism and phylogenetic diversity decreased from warm areas in the south‐west to cold areas in the north‐east and with an increasing proportion of lentic species. Except for species richness, all measures of diversity were consistently higher in formerly unglaciated areas south of the 0°C isotherm during the Last Glacial Maximum than in formerly glaciated areas. These results indicate that the distributions of dragonfly species in Europe were shaped by both phylogenetic conservatism of thermal adaptations and differences between lentic and lotic species in the ability of post‐glacial recolonization/dispersal in concert with the climatic history of the continent. The complex diversity patterns of European dragonflies provide an example of how integrating climatic and evolutionary history with contemporary ecological data can improve our understanding of the processes driving the geographical variation of biological diversity.