Linköping University | Department of Physics, Chemistry and Biology Bachelor thesis, 16 hp | Biology Spring term 2021 | LITH-IFM-G-EX—21/3998--SE Examining the Link between Temperature and Flight Phenology in Hoverflies (Diptera: Syrphidae) Using Swedish Citizen Science Data Malin Magnusson Rundqvist Examiner, Karl-Olof Bergman Tutor, Per Milberg 1. Abstract .......................................................................................................................................... 1 2. Introduction ................................................................................................................................... 1 3. Methods .......................................................................................................................................... 3 3.1. Syrphidae dataset .................................................................................................................. 3 3.2. Temperature data .................................................................................................................. 3 3.3. Analyses .................................................................................................................................. 4 4. Results ............................................................................................................................................ 5 4.1. Temperature data .................................................................................................................. 5 4.2. Flight phenology .................................................................................................................... 6 4.3. First flight and length of flight ............................................................................................. 9 5. Discussion ..................................................................................................................................... 13 6. Societal and ethical considerations ............................................................................................ 16 6.1. Societal considerations ........................................................................................................ 16 6.2. Ethical considerations ......................................................................................................... 16 7. Acknowledgements ...................................................................................................................... 17 8. References .................................................................................................................................... 18 1. Abstract Global warming is causing a general trend of rising temperatures worldwide. Simultaneously there is also a decline in populations of pollinators all over the world. Therefore, it is important to examine the effect warming temperatures might have on different pollinator species. The focus of this study was to look at how flight phenology of hoverflies in southern Sweden is affected by rising summer temperatures using two regions differing in temperature, and 11 years of citizen science data on hoverfly observations. Summer temperature and observations of 13 species were used. Although four species had a significantly earlier first flight in years with warmer weather, there were overall no apparent trends toward earlier or longer flight periods due to temperature deviation. However, geographical location had a strong impact on flight behaviour of hoverflies in Sweden with hoverflies in Götaland having an earlier first flight compared to Svealand (located further north). This might be the result of an earlier onset of spring and summer in Götaland than in Svealand. The results of this study indicate that more factors than temperature affect flight phenology in hoverflies. Keywords: climate change, hoverfly, phenology, pollinator, Sweden, Syrphidae. 2. Introduction The global climate is under change due to anthropogenic effects, and it can be seen on every continent of the world. Temperature is rising globally, and weather conditions are becoming more extreme (IPCC, 2014). In Europe, springtime is advancing on an average of 2.5 days per decade, and it is apparent that both animal and plant phenology adjust accordingly (Menzel et al., 2006). Phenology is a term used to describe the study of how recurring events in nature occurs in relation to seasonal weather changes i.e., time for bird migration, leafing of trees, flowering of plants as well as freezing of lakes (Lechowicz, 2001). An extensive study with data from over two centuries in England (Sparks & Carey, 1995), found that some species were leafing and blooming earlier in spring, while others came on later. Sparks and Carey (1995) predict that most phenological events would start earlier in the year due to climate change. Some birds have also been found to lay their eggs earlier in spring in the United Kingdom (Crick & Sparks, 1999). Although there seems to be many factors contributing to the decline of pollinator biodiversity all over the world, three important factors that seem to stand out are habitat loss, climate change, 1 and the changing of plant phenology (mainly length of growth season) (Vasiliev & Greenwood, 2021). In Sweden pollinators are almost solely insects. Of the 299 anthophilan species (wild bees) in Sweden 33 % is on the national red list, 20 % of 2 645 lepidopteran species (butterflies and moths) and 11 % of the 400 Syrphidae species (hoverflies) also appears on the national red list (Bergström et al., 2018). Almost all Swedish adult hoverflies are generalists, in contrast to bees and butterfly species, meaning they pollinate a wide variety of flowers. The relatively low percentage of species found on the national red list is likely due to the fact that most adult hoverfly species are generalists (Bergström et al., 2018). Since most hoverflies are generalists with good flying capacity, they can visit many flowers and are effective pollinators (Bergström et al., 2018). Therefore, hoverflies is one of the most important families of pollinators in Sweden (Bartsch, 2009a; Bartsch, 2009b) and hence the focus of the current study. Studies regarding rising temperatures in Europe and the response of different hoverfly species, have led to the conclusion that hoverflies in general emerge earlier each year (Graham-Taylor et al., 2009; Hassal et al., 2016; Olsen et al., 2020). Despite their importance as a pollinator in Sweden, there is a paucity of knowledge about their phenology and response to the Swedish weather (Bergström et al., 2018). In 2009 the Encyclopaedia of Swedish flora and fauna (Bartsch, 2009a; Bartsch, 2009b) was published and made it significantly easier for amateurs to identify different hoverfly species. This resulted in an increase of reported sightings of hoverflies, both red-listed and non-threatened all over Sweden (Bergström et al., 2018). The aim of the current study is therefore to address whether rising summer temperatures affects flight phenology of hoverflies in Sweden. This is studied in two Swedish regions using 11 years of temperature data as well as observational citizen science data on hoverflies. 2 3. Methods To examine if there is a connection between flight period of hoverflies and temperatures, observational reports from Swedish citizen science data as well as historical temperature data were used. These were divided into two geographical regions of southern Sweden: Götaland and Svealand. Götaland is located at approximate latitude 55.40 to 59.20 while Svealand is located north of Götaland at approximate latitude 58.70 to 62.20. 3.1. Syrphidae dataset The observational data for different hoverfly species were obtained from the open database available on Artportalen.se (SLU Artdatabanken, 2021). Artportalen.se is a website hosted by the Swedish University of Agricultural Sciences and funded mainly by the Swedish Environmental Protection Agency. In total there are over 56 million reported observations of plants, animals, and fungi, starting at the late 1990s (SLU, 2016). The data uploaded to Artportalen.se is reported by both professionals and amateurs (SLU Artdatabanken, 2020). The number of observed hoverfly species per year varied, and only the years 2010-2020 were deemed to have sufficient number of observations for meaningful analyses. In April 2021, I downloaded the data from Artportalen.se filtered by species name, years 2010- 2020, months March-October and Imago/adult. I chose period March-October to remove outliers outside of the general flight period for hoverflies in Sweden. The different species were chosen based upon three criteria: 1) how common they were in Sweden, 2) total number of observations reported during 2010-2020 and 3) species found in both Götaland and Svealand. The third Swedish province Norrland was initially considered, but there were too few observations to be useful in the current analysis. The minimum number of observations 2010-2020 was set to 900, as lower numbers is unlikely to work well when broken down per year and region. I also considered the number of observations in each region and set 250 as the minimum. Among the many potential species, 13 were selected for this study. 3.2. Temperature data Temperature data was compiled from the website of Swedish Meteorological and Hydrological Institute, SMHI, and open data for year- and monthly statistics (SMHI, 2021). I downloaded 3 monthly weather data (temperature and wind) from March-October, and 2010-2020, from all active weather