Habitat associations of day-flying Lepidoptera and their foodplants within nature reserves in Bedfordshire, UK

Species often associate with specific habitat characteristics, resulting in patchy distributions, whereby they only occupy a proportion of available habitat. Understanding which characteristics species require is a valuable tool for informing conservation management. We investigated the associations of eleven species of day-flying Lepidoptera larvae and their foodplants with habitat characteristics within calcareous grassland reserves in Bedfordshire, UK, across two scales relevant to land managers and target species: the reserve (cardinal aspect, vegetation type) and foodplant patch scale (foodplant height and density). We investigated whether ecological traits (habitat specialism, as defined at a national-scale, and overwintering life stage) influenced the strength of associations. At the reserve scale, we found variation in associations with habitat characteristics across species, with species that overwinter at non-adult life stages having more restricted associations, indicating that they may be more vulnerable to environmental change. Associations were generally stronger with vegetation type than aspect, which can be manipulated more easily by land managers. Seven species had similar associations with habitat characteristics to their foodplants, implying that management to benefit foodplants will also benefit larvae. However, the remaining four species had different associations to their foodplants, and may require alternative management approaches. At the foodplant patch scale, four species were associated with foodplant characteristics, which could be used to inform effective fine-scale management. Implications for insect conservation: Diverse habitat associations imply that topographic and vegetation variation are valuable for supporting diverse assemblages of butterflies and their foodplants

Oviposition behaviour and emergence through time of the small blue butterfly (Cupido minimus) in a nature reserve in Bedfordshire, UK.

ABSTRACT: Climate change affects butterflies in many ways, influencing the timing of emergence and reproduction, habitat preferences, and behaviour. The small blue (Cupido minimus Fuessley, 1775) is highly specialised in its host plant requirements, feeding on the seeds of a single species, kidney vetch (Anthyllis vulneraria), on which the larvae occur singly to avoid cannibalism. The butterfly is likely to be vulnerable to temperature-related changes in oviposition, adult emergence, and host plant flowering times, and is, therefore, a good model species for investigating climate change-related impacts. Using 26 years of data from the national UK Butterfly Monitoring Scheme (1993-2019) from one nature reserve, and 4 years of targeted egg searches (2006, 2007, 2008, 2020) from three reserves in Bedfordshire, UK, we investigated the effects of local temperature on small blue emergence date and total abundance, whether flowerhead or local environmental characteristics predicted small blue oviposition behaviour, and whether this changed between years. Small blue adults emerged on earlier dates over time, and earlier in years with higher maximum February temperatures. Total adult abundance was not predicted by monthly temperatures or total abundance in the previous year. Oviposition behaviour was broadly consistent across years, with egg presence more likely and egg abundance higher on kidney vetch flowerheads that were taller than the surrounding vegetation, and surrounded by taller vegetation and fewer mature flowerheads. The effect of solar radiation differed between years, with a negative effect on the probability of egg presence in 2007 and 2008, but a positive effect in 2020. Egg abundance per flowerhead was highly variable between years, with 2006 having four times more eggs per flowerhead than other years. This was likely driven by high adult abundance in 2006, which could have increased competition for flowerheads. IMPLICATIONS FOR INSECT CONSERVATION: Our results indicate that management for greater availability of taller kidney vetch amongst taller vegetation would encourage small blue oviposition on a greater number of flowerheads, providing a possible means of reducing competition and increasing larval survival, and that this would be effective despite variation in adult abundance between years. The high level of competition we observed in the year with the highest adult abundance indicates that higher numbers of host plants should be encouraged to reduce competition and larval cannibalism in peak years, increasing the likelihood of long-term population persistence and growth. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10841-021-00360-5.SITA Trust Landfill Community, Bedfordshire and Northamptonshire Butterfly Conservation, Balfour Browne fund, Natural England, Isaac Newton Trust/Wellcome TrustISSF/University of Cambridge Joint Research Grants Scheme (RG89529

Thermoregulatory ability and mechanism do not differ consistently between neotropical and temperate butterflies

Climate change is a major threat to species worldwide, yet it remains uncertain whether tropical or temperate species are more vulnerable to changing temperatures. To further our understanding of this, we used a standardised field protocol to (1) study the buffering ability (ability to regulate body temperature relative to surrounding air temperature) of neotropical (Panama) and temperate (the United Kingdom, Czech Republic and Austria) butterflies at the assemblage and family level, (2) determine if any differences in buffering ability were driven by morphological characteristics and (3) used ecologically relevant temperature measurements to investigate how butterflies use microclimates and behaviour to thermoregulate. We hypothesised that temperate butterflies would be better at buffering than neotropical butterflies as temperate species naturally experience a wider range of temperatures than their tropical counterparts. Contrary to our hypothesis, at the assemblage level, neotropical species (especially Nymphalidae) were better at buffering than temperate species, driven primarily by neotropical individuals cooling themselves more at higher air temperatures. Morphology was the main driver of differences in buffering ability between neotropical and temperate species as opposed to the thermal environment butterflies experienced. Temperate butterflies used postural thermoregulation to raise their body temperature more than neotropical butterflies, probably as an adaptation to temperate climates, but the selection of microclimates did not differ between regions. Our findings demonstrate that butterfly species have unique thermoregulatory strategies driven by behaviour and morphology, and that neotropical species are not likely to be more inherently vulnerable to warming than temperate species

Cool as a caterpillar: Understanding the responses of butterflies to temperature across the life cycle

Anthropogenic effects, including land-use and climate change, have had dramatic and wide-ranging impacts on the natural world. The impacts of these changes have already been detected in many systems, with global biodiversity and abundance of many taxa declining across spatial scales. The loss of biodiversity has knock on impacts to human society, which are only just beginning to be understood. Only with a detailed understanding of how species will respond to environmental changes, and with effective dissemination of this knowledge, can we hope to slow and halt biodiversity loss. In this thesis, I use butterflies as a model taxon to understand the responses of insects to changing habitat and microclimatic conditions. Insects are a diverse and globally distributed group of organisms that play fundamental roles in ecosystem processes, many of which are critical to human societies. Despite this, there is growing evidence that insects are declining at rapid rates around the world, and many of these declines have been attributed to anthropogenic change. Butterflies show detectable responses to environmental change, including spatial responses, such as range shifts, and temporal responses, such as changes to timing of life cycle events. They are diverse, wide-spread, and ecologically sensitive, with complex life cycles that differ in morphology, behaviour, and ecology, and therefore differ in their sensitivities and requirements. In my first data chapter, I use a systematic mapping method to screen, quantify and discuss current knowledge on butterfly responses to temperature. I found that Nymphalidae were the most studied family, likely owing to their high number of species, including large, charismatic and common species of cultural importance. In contrast, Riodinidae were rarely studied, likely due to their elusive nature and being concentrated in the tropics. The tropics were less studied than temperate regions, and more studies reported the responses of butterflies at the adult life stage compared to all other life stages combined. I found that of the responses recorded, behavioural responses were the least common. I found that *in situ* studies were more common than *ex situ*. Taken together, there is an incomplete understanding of butterfly responses to temperature, which may lead to ill-informed decisions. I make suggestions for how to resolve these knowledge gaps, including calling for an increased focus on the tropics, the establishment of more butterfly monitoring schemes, particularly in the global south and South America, incorporating non-adult life stages into butterfly monitoring schemes, and conducting more studies on species from under-represented families. In my second data chapter, I investigated the habitat associations of 11 species of day-flying Lepidoptera as larvae and their foodplants from four nature reserves in Bedfordshire, UK. These study sites were the focus of fieldwork for three data chapters (Chapters 3, 4, and 5). These associations were tested across two spatial scales relevant to both Lepidoptera and land-managers; the reserve-scale and the foodplant patch-scale. I also assessed whether these associations were related to ecological traits. At the reserve-scale, I found substantial variation across species, with a tendency for species that overwinter at non-adult life stages to have stronger habitat associations. The majority of species shared similar habitat associations as their foodplants, indicating that management that benefits foodplants will also benefit these Lepidoptera. However, there were notable exceptions to this, with some species (*Erynnis tages*, *Cupido minimus*, *Polyommatus coridon*, *Aglais urticae*) having conflicting habitat associations with their foodplants, and therefore requiring focused management. At the foodplant scale, four species were associated with specific foodplant characteristics; two with taller foodplants (*C. minimus*, *Anthocharis cardamines*), and two with dense foodplant patches (*Aglais io*, *A. urticae*). These habitat associations can be used to manage for these species and their foodplants. In my third data chapter, I use a single species approach to highlight how citizen science data from butterfly monitoring schemes can be used alongside habitat use data to provide a more complete picture of how species change over time, focusing on the small blue (*C. minimus*). I used 26 years of data from the national UK Butterfly Monitoring Scheme and four years of targeted egg surveys across 14 years to investigate the effects of local temperature on small blue emergence date and total abundance, and whether foodplant characteristics predicted oviposition behaviour. I found that adult small blues were emerging earlier over time, which correlated with higher maximum temperatures in February. In contrast, total abundance was not related to temperature, or abundance in the previous year. Oviposition behaviour was broadly consistent across time, with females selecting foodplants that were tall and apparent, surrounded by taller vegetation, and in low density patches. These results imply that management for greater availability of tall foodplants surrounded by tall vegetation would encourage oviposition across a greater number of flowers, reducing competition and improving larval survival in this rare and declining species. In the fourth data chapter, I investigated the capacity of 14 species of day-flying Lepidoptera to thermoregulate, whether this was influenced by morphological or ecological traits, and whether this capacity differed between adults and larvae. I also investigated what mechanisms species used to thermoregulate, and whether this differed between life stages. I found that larvae were worse at thermoregulating than adults, and that thermoregulatory capacity differed between families, species, and with body length, whereby Pieridae were better at thermoregulating than Nymphalidae, and large larvae were better at thermoregulating than small larvae. I found that adults relied on behavioural thermoregulation, whereas larvae relied more on microclimate selection. This implies that larvae are more dependent on their immediate area to thermoregulate than adults, and that management should maintain or protect vegetation surrounding butterfly foodplants to allow larvae to thermoregulate effectively under climate change. Finally, in the last data chapter, I investigated the impacts of temperature on tropical butterflies. I collected field data on 54 butterfly species in Panama, and also conducted heat knockdown assays on a subset of these species (24) in the lab, to determine whether ecological traits influenced the ability of tropical butterflies to thermoregulate, whether similar ecological traits also influenced thermal tolerance, and whether there was an interaction between the capacity to thermoregulate and thermal tolerance. Thermoregulation and thermal tolerance were influenced by family, wing length, and wing colour, with Pieridae, and butterflies that were large or dark having the strongest ability to thermoregulate, but Hesperiidae, small and dark butterflies tolerating the highest temperatures. There was also an interaction between capacity to thermoregulate and thermal tolerance, whereby species better at thermoregulating had lower thermal tolerance, and vice versa. This implies that species with more stable body temperatures in the field may be more vulnerable to increases in ambient temperatures than previously thought, particularly extreme temperatures such as heatwaves. Butterflies make a valuable taxon to investigate responses to environmental change. Though there are gaps in our understanding, I have started to address these, and made suggestions for future research directions. I have identified species, life stages, and ecological traits that make some butterflies more vulnerable to change than others. I have demonstrated that sensitivity to change differs across the life cycle, and these differences will require different management strategies. Crucially, this highlights that butterfly responses to environmental change can be predictable, and therefore can be managed for to improve butterfly conservation.Cambridge Conservation Initiative (CCI) Evolution Education Trust (EET

Heatwave predicts a shady future for insects: impacts of an extreme weather event on a chalk grassland in Bedfordshire, UK

Climate change is set to become one of the leading causes of biodiversity loss worldwide, with extreme weather events projected to increase in frequency. Ectothermic animals such as insects are at particular risk, especially when they are isolated and unable to move through the landscape to track suitable climate. To protect such taxa, it is important to understand how they are impacted by extreme weather events and whether management could provide effective microclimate refuges. However, potential management interventions remain untested for many species. Here, we show that the extreme high temperatures experienced in the UK on 19th July 2022 resulted in a community of butterflies becoming inactive, but that shaded areas, including artificial slopes created as part of conservation management for climate change, provided a refuge during this period. Our results indicate that future high temperatures could force butterflies to shelter in the shade, potentially being unable to fly, feed or mate during these periods, with possible long-term impacts, particularly if multiple consecutive high temperature days are experienced. Implications for Insect Conservation Producing artificial slopes and integrating patches of scrub within grassland could create an array of microclimates that allow butterflies and other invertebrates to thermoregulate, providing a refuge during extreme weather events. Our findings highlight the dramatic effect of extreme temperatures on insect communities, as well as simple management solutions that could be implemented widely and relatively easily by conservation managers, to counter some of the negative impacts of rising temperatures and extreme weather events.We thank the People’s Postcode Lottery Nature-based Solutions Fund for supporting the "Banking on Butterflies" Project associated with this work. MPH was funded by the David and Claudia Harding Foundation through a Harding Distinguished Postgraduate Scholarship. EAJ and her collaboration with the Wildlife Trust was supported by an Evolution Education Trust Knowledge-Exchange Studentship grant, administered by the Cambridge Conservation Initiative. The Isaac Newton Trust/Wellcome Trust ISSF/University of Cambridge Joint Research Grants Scheme grant (RG89529) supported the work of AJB and ECT in establishing this project. AJB was funded by the NERC Highlight topic GLiTRS project NE/V007173/1

Day‐flying lepidoptera larvae have a poorer ability to thermoregulate than adults

Funder: Cambridge Conservation Initiative, Evolution Education Trust (EET)AbstractChanges to ambient temperatures under climate change may detrimentally impact small ectotherms that rely on their environment for thermoregulation; however, there is currently a limited understanding of insect larval thermoregulation. As holometabolous insects, Lepidoptera differ in morphology, ecology and behaviour across the life cycle, and so it is likely that adults and larvae differ in their capacity to thermoregulate. In this study, we investigated the thermoregulatory capacity (buffering ability) of 14 species of day‐flying Lepidoptera, whether this is influenced by body length or gregariousness, and whether it differs between adult and larval life stages. We also investigated what thermoregulation mechanisms are used: microclimate selection (choosing locations with a particular temperature) or behavioural thermoregulation (controlling temperature through other means, such as basking). We found that Lepidoptera larvae differ in their buffering ability between species and body lengths, but gregariousness did not influence buffering ability. Larvae are worse at buffering themselves against changes in air temperature than adults. Therefore Lepidoptera may be more vulnerable to adverse temperature conditions during their larval life stage. Adults and larvae rely on different thermoregulatory mechanisms; adults primarily use behavioural thermoregulation, whereas larvae use microclimate selection. This implies that larvae are highly dependent on the area around their foodplant for effective thermoregulation. These findings have implications for the management of land and species, for example, highlighting the importance of creating and preserving microclimates and vegetation complexity surrounding Lepidoptera foodplants for larval thermoregulation under future climate change.</jats:p

Day-flying Lepidoptera larvae have a poorer ability to thermoregulate than adults

Changes to ambient temperatures under climate change may detrimentally impact small ectotherms that rely on their environment for thermoregulation, however there is currently a limited understanding of insect larval thermoregulation. As holometabolous insects, Lepidoptera differ in morphology, ecology, and behaviour across the life cycle, and so it is likely that adults and larvae differ in their capacity to thermoregulate. In this study we investigate the thermoregulatory capacity (buffering ability) of 14 species of day-flying Lepidoptera, whether this is influenced by body length or gregariousness, whether it differs between adult and larval life stages. We also investigated what thermoregulation mechanisms are used; microclimate selection (choosing locations with a particular temperature) or behavioural thermoregulation (controlling temperature through other means, such as basking). We found that Lepidoptera larvae differ in their buffering ability between species and body lengths, but gregariousness did not influence buffering ability. Larvae are worse at buffering themselves against changes in air temperature than adults. Therefore Lepidoptera may be more vulnerable to adverse temperature conditions during their larval life stage. Adults and larvae rely on different thermoregulatory mechanisms; adults primarily use behavioural thermoregulation, whereas larvae use microclimate selection. This implies that larvae are highly dependent on the area around their foodplant for effective thermoregulation. These findings have implications for the management of land and species, for example highlighting the importance of creating and preserving microclimates and vegetation complexity surrounding Lepidoptera foodplants for larval thermoregulation under future climate change.EAJ was supported by the Cambridge Conservation Initiative (CCI) Evolution Education Trust (EET) Knowledge-Studentship. AJB was funded by a NERC Highlight topic grant (GLiTRS project NE/V007173/1), and the project was developed from an Isaac Newton Trust/Wellcome Trust ISSF/University of Cambridge Joint Research Grants Scheme grant (RG89529) to AJB and ECT

Habitat associations of day-flying Lepidoptera and their foodplants within nature reserves in Bedfordshire, UK

Species often associate with specific habitat characteristics, resulting in patchy distributions, whereby they only occupy a proportion of available habitat. Understanding which characteristics species require is a valuable tool for informing conservation management. We investigated the associations of eleven species of day-flying Lepidoptera larvae and their foodplants with habitat characteristics within calcareous grassland reserves in Bedfordshire, UK, across two scales relevant to land managers and target species: the reserve (cardinal aspect, vegetation type) and foodplant patch scale (foodplant height and density). We investigated whether ecological traits (habitat specialism, as defined at a national-scale, and overwintering life stage) influenced the strength of associations. At the reserve scale, we found variation in associations with habitat characteristics across species, with species that overwinter at non-adult life stages having more restricted associations, indicating that they may be more vulnerable to environmental change. Associations were generally stronger with vegetation type than aspect, which can be manipulated more easily by land managers. Seven species had similar associations with habitat characteristics to their foodplants, implying that management to benefit foodplants will also benefit larvae. However, the remaining four species had different associations to their foodplants, and may require alternative management approaches. At the foodplant patch scale, four species were associated with foodplant characteristics, which could be used to inform effective fine-scale management.The research was funded by a Cambridge Conservation Initiative/Evolution Education Trust (CCI/EET) grant to EAJ. We thank the Isaac Newton Trust / Wellcome Trust ISSF / University of Cambridge Joint Research Grant (RG89529) for funding ECT and AJB to establish the larger research project, within which this study was based. AJB was supported by a NERC Highlight topic grant (NE/V007173/1) to the GLiTRS Project. JA and SW were supported by the Balfour-Browne Fund, and JA was supported by Kings College, University of Cambridge

Hot topics in butterfly research: Current knowledge and gaps in understanding of the impacts of temperature on butterflies

1. As small poikilotherms, insects are largely dependent on their environment for thermoregulation, and so are particularly vulnerable to changing temperatures. 2. Butterflies are a well-studied group often used as models to investigate insect responses to temperature. However, little has been done to synthesize and present this large volume of literature in an accessible format, particularly with reference to knowledge gaps and areas rich in information. Using a systematic mapping method, we synthesized the last 40 years of research on the topic of butterfly responses to temperature. 3. We identified and coded 451 research papers, in which butterfly species were studied 3,198 times. We identified taxonomic groups, regions, and experimental designs that were well or poorly represented. 4. We found that there was a relatively good balance of representation across butterfly families in relation to the number of species within each family. The tropics were less frequently studied than temperate regions, and there were more studies reporting outcomes on adults than at any other life stage. Finally, in situ studies were more common than ex situ studies. 5. Taken together, the higher representation of certain regions, life stages and approaches could lead to an incomplete understanding of the impacts of temperature on butterflies, potentially resulting in ill-informed decisions. 6. We make suggestions for how to resolve these discrepancies in representation, including calling for an increased focus on the tropics, the establishment of butterfly monitoring schemes in the global south, a greater focus on the effects of temperature on non-adult life stages, an increase in experiments investigating fluctuating thermal regimes, and the incorporation of more behavioural responses to temperature in future research. Only by addressing these disparities can we gain a complete understanding of how butterflies will respond to climate change.EAJ was supported by a Cambridge Conservation Initiative/Evolution Education Trust Knowledge-Exchange Studentship. AJB was funded by a NERC Highlight topic grant (GLiTRS project NE/V007173/1)

Hot topics in butterfly research: Current knowledge and gaps in understanding of the impacts of temperature on butterflies

Publication status: PublishedFunder: Cambridge Conservation Initiative; doi: http://dx.doi.org/10.13039/501100014746Abstract As small poikilotherms, insects are largely dependent on their environment for thermoregulation and so are particularly vulnerable to changing temperatures. Butterflies are a well‐studied group often used as models to investigate insect responses to temperature. However, little has been done to synthesise and present this large volume of literature in an accessible format, particularly with reference to knowledge gaps and areas rich in information. Using a systematic mapping method, we synthesised the last 40 years of research on the topic of butterfly responses to temperature. We identified and coded 451 research papers, in which butterfly species were studied 3198 times. We identified taxonomic groups, regions and experimental designs that were well or poorly represented. We found that there was a relatively good balance of representation across butterfly families in relation to the number of species within each family. The tropics were less frequently studied than temperate regions, and there were more studies reporting outcomes on adults than at any other life stage. Finally, in situ studies were more common than ex situ studies. Taken together, the higher representation of certain regions, life stages and approaches could lead to an incomplete understanding of the impacts of temperature on butterflies, potentially resulting in ill‐informed decisions. We make suggestions for how to resolve these discrepancies in representation, including calling for an increased focus on the tropics, the establishment of butterfly monitoring schemes in the global south, a greater focus on the effects of temperature on non‐adult life stages, an increase in experiments investigating fluctuating thermal regimes and the incorporation of more behavioural responses to temperature in future research. Only by addressing these disparities can we gain a complete understanding of how butterflies will respond to climate change. </jats:p