1. Assessing the hoverfly populations at Primley
Meadow and Clennon grassland and their
interactions with the wildflower communities
Hannah Sutton1, 2 and Tracey Hamston2
1 University of Plymouth, Plymouth, PL4 8AA, UK
2Whitley Wildlife Conservation Trust, Paignton, TQ4 7EU
5. Aims: To compare the hoverfly communities and
foraging patterns of the two grassland sites
Questions:
1. Do the hoverfly communities of calcareous grassland and semi-
improved grassland differ?
2. What are the foraging preferences of the hoverflies present at
the sites?
6. Method: Setting up transects
Hoverfly transects Flower transects
Three 50m transects were set up on each site
Environmental variables were recorded
Record every individual present in the transect
(Tally counter used for flowers)
Identification to genus level Estimated the flowers on flowering
trees like hawthorn
Collection pots used for closer
identification
Photos were taken and wildflower
guides used for identification
Data analysis - Bipartite Package in R
7. Aerial map of the 50m transects
B
A
E
Clennon Grassland
D
C
F
Primley Meadow
8. Results: Numbers of foraging hoverflies
W = 31.5
p-value = 0.002
No.ofhoverfliesforaging
Site
No.ofhoverfliesforaging
Habitat
No significance
p-value = 0.571
9. Results: Clennon Visitation Networks
Many of the interactions were only with one
individual which is reflected in the thickness of
the bands.
PlantSpecies
Hoverfly Species
Total no. of foraging hoverflies = 24
10. Results: Primley Visitation Networks
Total no. of foraging hoverflies = 182
• A Total of 13 different hoverfly species
interaction with 6 flower species.
• Multiple interactions with meadow
buttercup.
• Some hoverfly species were interacting with
5 flower species.
PlantSpecies
Hoverfly Species
I
I
I
I
I
I
I
I
I
I
I
I
I
11. Results: Generalised linear models
Variable Df LRT (χ2) Pr(>Chi) Significance
<none>
Site 1 110.592 < 2.2e-16 High (0***)
Cloud cover (%) 1 92.440 < 2.2e-16 High (0***)
Flower diversity (Simpsons, D) 1 28.164 1.115e-07 High (0***)
Temp:Abun.flowers (Nested) 1 34.941 3.399e-09 High (0***)
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
• Likelihood ratio test table
• Compared hoverfly abundance with four variables
• They are all highly significant
• Nested terms – temperature and abundance of flowers
12. Aims: To compare the hoverfly communities and
foraging patterns of the two grassland sites
Questions:
1. Do the hoverfly communities of calcareous grassland and semi-
improved grassland differ?
2. What are the foraging preferences of the hoverflies present at
the sites?
13. Discussion
• As a whole both sites had a similar number of hoverfly species with eight species seen at
both sites.
• Many more foraging individuals at Primley than Clennon.
• Melanogaster sp. frequently fed on buttercup species at Primley, in comparison to
Clennon where only 3/5 foraging individuals fed on buttercup.
• Many of the other species, like Cheilosia sp., were recorded on multiple flowering species
at both sites.
• It seems that the hoverflies vary in their foraging patterns and looks to feed on what is
available and in the case of Primley, the most abundant flower source.
• Looking at hoverfly species diversity other influences could play a part.
14. Further Research
• Setup more or longer transects to get an more even representation.
• Compare to other grassland sites, especially calcareous to see if Clennon is representative
• Could look at specific species and follow individual foraging routes, which would achieve
more detailed data.
• Prolonged data collection period to observe more changes in the flowering communities.
• Further research will be able to highlight the most important flower species for hoverfly
communities which can be taken in consideration when site management is carried out.
I’m Hannah and I have am one of the ecology placement students who has been looking at our hoverfly communities at both reserves over the last six months.
Here are my two sites, Primley Meadow and Clennon Grassland.
They are owned and managed by WWCT and are situated in and around Paignton Zoo.
Both sites are grasslands with Primley being a semi-improved meadow and Clennon being a limestone grassland.
Clennon has a unique flower community with the likes of spurge-laurel being present.
Management takes place at both sites with Primley having a annual hay cut and Clennon with scrub clearance.
There are currently 283 species in the British Isles as of 2015.
Like bumblebees pollen grains will stick to them and get transferred between flowers.
Insectivore larvae, like the one in this picture, will feed on aphids and other plant sucking insects and are great for farming and biological pest control.
They also have short tongues like many of the bumblebees so need to get up close to there food sources, hence the picture on the right where the hoverfly’s face and eyes covered in pollen grains.
They are regularly seen cleaning their faces.
Much less is known about hoverfly foraging preferences than other pollinators such as bees.
We were interested in what species we had on the WWCT sites and how the two sites compared in terms of both species diversity and abundance. As we had no data on hoverfly communities, this study was also useful in developing some baseline data for future research.
The two questions we asked were….
I surveyed two sets of transects at each site one for the hoverflies and the other for the flowers.
Two of the transects were in open grassland and the other along the scrub edge, visualise representation will be shown next.
All possible environmental variables were recorded similar to the butterfly transects – don’t survey in the rain and within a narrow temperature range.
All hoverfly individuals were recorded whether they were foraging, basking or hovering in the transect.
It is near impossible to count every flower on a flowering tree so a estimation was calculated for the abundance.
I used the bipartite package in R to create ecological networks
Transect C & F –Grassland
Transect D – Scrub
The routes were chosen so we had a comparison between an open area of grassland and a scrub line and representation of the site.
Just to note that Clennon is a much smaller site than Primley so naturally the grassland transects were closer together.
A mann-whitney test of the foraging data (only hoverflies actually seen on the flowers) to compare the abundance of foraging individuals at both sites and in both habitats showed that there was…
Significantly more foraging individuals at Primley than Clennon, (24 individuals in comparison with 182 individuals at Primley) however we didn’t find any difference between the grassland and scrub of both site combined. We will be carrying out further data analysis to determine the effects of other variables such as the abundance of particular flowers and environmental factors (temp, wind etc)
On to my Visitation networks….
The data from the hoverfly and flower transects was combined to create an interaction table and network.
These are the results from the calcareous grassland at Clennon
Every time a hoverfly was seen on a particular flower species an interaction was recorded. This chart shows the frequency of those interactions and gives us a summary of the flower preferences of different hoverflies.
Meadow buttercup looked to be the most favoured flower with these two species (point) however we can see that the Marmalade hoverfly preferred bramble (point) and Cheilosia sp. had the strongest interactions with a range of flowers, in particular Smooth hawks beard flower, which is similar to a dandelion flower but smaller in size.
If we want a more detailed picture of the interactions we can create a network.
The black bars represent abundance with hoverflies species on top and flower species at the bottom.
The length of the bar indicates how abundant the species were.
The grey bands show the foraging interactions between the hoverflies and flowers.
Here we are looking at a lot of single or infrequent interactions. We see that different hoverflies feed on different flowers and there is no real dominance of flowering species. There is a slight trend of the more common hoverflies feeding on more species – perhaps more generalist but due to there being few sightings it is difficult to draw firm conclusions.
At Clennon we observed mostly the same hoverfly species but we did record the Marmalade Hoverfly and Rhingia campestris both feeding on bramble.
Here we have the results for Primley.
Many more foraging hoverflies were recorded on this site, 182 individuals in comparison to 24 (semi-improved grassland)
Again the chart shows the strength of the interactions.
The strongest interaction is shown between meadow buttercup and Melanogaster sp.
The network from the Primley data shows a quite different pattern.
The key things to note are the popularity of meadow buttercups which were very abundant - 3552 individual recorded over the data collection period (in contrast to Clennon where only 18 flowering individuals were recorded)
10 of the 13 hoverfly taxa foraged on meadow buttercup, including the less common species like Baccha elongata, which may indicate that the hoverflies were drawn to the more abundance flowering species however more data analysis is required.
Performed a Poisson GLM looking at hoverfly abundance and the influence on four variables on the abundance.
All were significant which gives more areas to focus on in future study.
I nested the variables temperature and abundance of flowers.
This meant that the abundance of flowers influenced the abundance of hoverflies and temperature impacted the flowers.
I also did a binomial GLM looking at hoverfly diversity, however this achieved no significant results
A quick reference back to my questions…..
So lets see if I have answered them…..
14 species at Primley
13 species at Clennon
8 species seen at both sites
Some site specifics were…. Primley = Eristalis sp. & Clennon = Volucella sp. (bumblebee mimic)
The boxplot showed there were more foraging individuals at Primley than Clennon, which you wouldn’t think would be the case with Clennon having 30 flower species recorded and Primley only 18 species. There is topography to take into considered so Clennon is an elevated site which is very exposed and can have high winds. Most of the plants are short in stature and tend to have closed flowers which are not ideal for hoverflies.
Whereas Primley is sheltered in comparison and have tall blooms of flowers and tend to have high abundance of open flowers like meadow buttercup. This is potential why more were foraging at Primley.
Just to highlight some of the key differences between the hoverfly species….
Melanogaster sp. – so many more recorded at Primley they weren’t as common at Clennon.
Differences between species and the sites. With further analysis, we will be able to see whether the environmental variables had an affect on hoverfly and flower abundance at the sites.
The species diversity could be explained by the lack of data and other influences that we didn’t take into account like larval habitats, foraging distances and overwintering habitats.
A few recommendations for future research:
It would be beneficial to setup more or longer transects in Primley, as it is so much larger in size than Clennon which would get an more even representation.
Wider study sample to validate initial findings.
See a wider range of flowers and limited seasonal variation, for example making sure the bramble flowering season was within data collection, it our study bramble flowered later this year and combined with bad weather I only managed to record it for one week at the Clennon site.
Here are my acknowledgments and references and thank you for listening.
