Flight Phenology of Oligolectic Solitary Bees Are Affected by Flowering Phenology
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Linköping University | Department of Physics, Chemistry and Biology Bachelor’s Thesis, 16 hp | Educational Program: Physics, Chemistry and Biology Spring term 2021 | LITH-IFM-G-EX—21/4000--SE Flight phenology of oligolectic solitary bees are affected by flowering phenology Anna Palm Examinator, György Barabas Supervisor, Per Millberg Table of Content 1 Abstract ................................................................................................................................... 1 2 Introduction ............................................................................................................................. 1 3 Material and methods .............................................................................................................. 3 3.1 Study species .................................................................................................................... 3 3.2 Flight data ......................................................................................................................... 4 3.3 Temperature data .............................................................................................................. 4 3.4 Flowering data .................................................................................................................. 4 3.5 Combining data ................................................................................................................ 5 3.6 Statistical Analysis ........................................................................................................... 5 4 Result ....................................................................................................................................... 5 4.1 Number of observations ................................................................................................... 5 4.2 Salix caprea ...................................................................................................................... 6 4.3 Succisa pratensis and Knautia arvensis .......................................................................... 10 5 Discussion ............................................................................................................................. 14 6 Societal & ethical considerations .......................................................................................... 18 7 Acknowledgements ............................................................................................................... 18 8 References ............................................................................................................................. 18 1 Abstract Understanding the relationships between solitary bees’ flight phenology and flowering phenology is important in the context of global warming. Using Swedish citizen science data, observations of oligolectic solitary bees and flowering phenology were used together with temperature data. All five bees studied had flight period that overlapped with the flowering period their corresponding host plant. None of the species were affected by the temperature, although there was a correlation between earliest observations of flowering phenology and flight phenology. The later the flowering observation was made, the later the flight observation was made. No correlation was found between the length of flight period and length of the flowering period. Increasing temperature is not the only factor that effects flight phenology and flowering phenology. Key words: Flight phenology, Flowering phenology, Global warming, Oligolectic, Solitary bee 2 Introduction Around the world 78 % to 94 % of all flowering plants require animals to pollinate in some way for the plant to reproduce with success (Ayers et al., 2021; Ollerton, 2011). Of these animals a significant portion is bees. Not only are the plants and bees effected by this pollination relationship but also other animals and plants who rely on these services for food or other resources (Ayers et al., 2021). There are approximately 250 species of solitary bees in Sweden (Stenmark, 2016). Solitary bees are so called because they do not live in colonies as e.g. honeybees. Different species of solitary bees are active at different times of the year. Depending on the species their flight period can occur anytime between spring to early autumn (Stenmark, 2016). Phenology describes the specific date of natural occurring events that happens every year (SMHI, 2021a). These events can be both biotic and abiotic for example when the first leaves changes colour in autumn, when migrating birds return in spring or when the first snow falls in winter (SMHI, 2021a). In the current report focus is on flowering phenology and flight phenology. Flowering phenology indicate when flowering was observed. Flight phenology indicate when flying solitary bee were observed. Solitary bees can be divided in to two different groups, the oligolectic species and the polylectic species (Pekkarinen, 1997). The oligolectic bees have specialized in collecting 1 pollen and nectar from a specific plant family, or a small number of species. If a bee only collects pollen and or nectar from one species, it is called narrow oligolectic or strictly oligolectic. (Pekkarinen, 1997; Schlindwein, 2004). The polylectic bees are more general when it comes to pollen and nectar preference, this means that these bees can collect pollen and nectar from a range of different plant families. The polylectic bees can also collect pollen and nectar only within a single plant family but from more species than an oligolectic bee would collect (Pekkarinen, 1997; Schlindwein, 2004). The Intergovernmental Panel on Climate Change (IPCC, 2014) define global warming as a gradual increase of global surface temperature. This has a substantial effect on our environment. Glaciers are melting, more countries experience more intense heat waves and sea levels are rising (IPCC, 2014). Phenology is also affected by global warming (Hegland et al., 2009). The warmer temperatures can cause both plants and animals to flower or to become active earlier than they used to (Hegland et al., 2009; Kharouba et al., 2018). Because of this, with the help of phenology observations through several years, changes in climate and global warming can be observed (SMHI, 2021a). Understanding the relationships between solitary bees’ flight phenology and flowering phenology is important when climate change affects our world (Gallagher et al., 2020). Because the oligolectic solitary bees only collect pollen from specific species it is interesting to know when these bees are active and search for pollen and nectar and when the plants are flowering. The aim of this report is therefore to compare data for the oligolectic solitary bees’ flight period and the flowering of the flowers sought after. More specifically, (1) what is the relationship between solitary bees’ first flight and first flowering over different years?, (2) how does the length of the flowering period influence the flight period? I expected that both flowering phenology and flight phenology would start earlier warmer years. I also expected that the flowering period would be longer during the warmer years, which would imply an extended flight period for the bees studied. To test these assumptions, I compiled citizen science data for five oligolectic bee species and the flowering of their host plants from an 11-year period for southern Sweden. 2 3 Material and methods Three types of data were used in the present study: weather data, insect data, and flowering data. The solitary bee data and flowering data is based on Swedish citizen data while the weather data is from historical temperature data. The regions Götaland and Svealand in southern Sweden were in focus of in the present study. 3.1 Study species This report takes a closer look at five different solitary bee species Andrena vaga, Andrena praecox, Colletes cunicularius, Andrena marginata and Andrena hattorfiana. Andrena vaga, Andrena praecox and Colletes cunicularius collect pollen from Salix caprea and other Salix species which means these solitary bees are flying early in the year when most Salix flower. Andrena vaga digs holes in sandy grounds to make nests (Holmström et al., 2018a). Andrena praecox also make nests in sandy grounds and like to live close to Salix (Holmström et al., 2018b). Only the females are oligolectic for Salix caprea while the males have a more diverse diet. Flowers that males collect nectar from include Tussilago farfara and Crocus vernus, which are both also flowering in early spring (Holmström et al., 2018b). Colletes cunicularius create nests in fine sandy grounds often close to water (Cederberg et al., 2021). Andrena marginata collect pollen from several different Dipsacaceae species mainly Succisa pratensis and Knautia arvensis, though there are a few other species that are rare and with limited geographic distribution for example Scabiosa canescens, and Scabiosa columbaria (Holmström et al., 2018c). Therefore, these two plant species were not considered in the current study. Andrena marginata depends on having a good nest in close proximity to flowers like Succisa pratensis and Knautia arvensis (Holmström et al., 2018c). Andrena hattorfiana is strongly specialized in what flowers they collect pollen from (Holmström et al., 2018d). Because Andrena hattorfiana is strictly oligolectic, it only collect pollen from Knautia arvensis. Pollen collecting from Scabiosa columbaria may occur in the most southern