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Estimating the populations of three species of Volucella
in an English woodland
Roger MorrisStuart Ball
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Volucella species studied
V. inflata
V. bombylans
V. pellucens
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Study site – Old Sulehay Forest, BCNP Wildlife Trust
Reserve
• 35 hectares of ancient semi-natural woodland• Managed as hazel coppice with oak/ash standards before 1940s• Main ride is well managed and open
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Sampling sites in the wood
20 visitsfrom 7 June to 27 July 2003
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Marking
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Numbers marked and recaptured
Capture
V. bombylans
V. inflata V. pellucens
Total
1 73 158 574 805
2 22 21 87 130
3 2 3 22 27
4 3 3
Total 97 182 686 985
160 out of 985 marked flies were recaptured at least once = 16.25%
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Some practical lessons
• The consistency of paint is important - too thin and the insect gets covered (and may be fatally damaged)
• Species with hairy thoraxes are much harder to mark clearly
• Constant effort is needed to ensure that new recruits to the population are marked before they displace existing members or disperse themselves
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V. bombylans population estimates
0
20
40
60
80
100
120
140
160
180
200
Est
imat
ed p
opul
atio
n wit
h 95%
con
fide
nce
inte
rval
φ = 0.714 (0.244)
φ = estimate of daily
survival (standard error)
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V. inflata population estimates
-500
0
500
1000
1500
2000
2500
Est
imate
d p
opula
tion w
ith 9
5%
confi
dence
inte
rval
φ = 0.853 (0.027)
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V. pellucens population estimates
-400
-200
0
200
400
600
800
1000
1200
1400
Esti
mat
ed p
opul
atio
n wi
th 9
5% c
onfi
denc
e in
terv
al
= 0.765 (0.013)
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Summary of population estimates
Estimated population size with 95%
confidence interval
V. bombylans 200 (142, 339)
V. inflata 656 (468, 1097)
V. pellucens 1963 (1669, 2384)
Estimate of the total population of each speciesusing Schnabel’s method, Krebs (1989)
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Some emerging questions?
• How big is the population of V. bombylans ?
• The wood is only 35 hectares! It is difficult to believe:• There are sufficient sap runs large
enough to support the larvae of 650 V. inflata
• There are sufficient social wasps’ nests to support 2,000 V. pellucens
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Longevity
0
5
10
15
20
25
1 2 3 4 5 6 7 8 9 10 11 12 14 15 16 17 18 19 20 22 24 36
Days af ter fi rst capture
Num
ber
of
reca
ptur
es
bombylans infl ata pellucens
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Distance moved by recaptured individuals of V.
bombylans
Female Male
Recaptured at the same station
5 50% 8 32%
Moved within a ride
4 40% 13 52%
Moved between rides
1 10% 4 16%
Total recaptures 10 25
Average distance moved (m)
84 122
0%
20%
40%
60%
80%
100%
female male
Moved between rides
Moved within ride
Same station
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Behaviour of V. bombylans
• Mating strategy well known: males perch on prominent foliage and dart out at passing insects
• Our results suggest males are quite mobile. Therefore likely male does not return to the same perch each day
• Males moved more than females
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Distance moved by recaptured individuals of V.
inflata
Female Male
Recaptured at the same station
4 36% 17 65%
Moved within a ride
6 55% 6 23%
Moved between rides
1 9% 3 12%
Total recaptures 11 24
Average distance moved (m)
136 64
0%
20%
40%
60%
80%
100%
female male
Moved between rides
Moved within ride
Same station
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Behaviour of V. inflata
• Both sexes mainly captured around flowers
• Males make rapid flights around nectar sources (bramble & shrubs)
• Only one observation of copulation: male flew high round dogwood (Cornus sanguinea) and briefly coupled with female in flight
• Males moved much less than females• Some evidence that males held a territory
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Distance moved by recaptured individuals of V.
pellucens
Female Male
Recaptured at the same station
4 36% 249 78%
Moved within a ride
5 45% 45 15%
Moved between rides
2 18% 18 7%
Total recaptures 11 318
Average distance moved (m)
164 55
0%
20%
40%
60%
80%
100%
female male
Moved between rides
Moved within ride
Same station
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Details of movements of male
V. pellucens
At the same station
Moved within ride
Moved between
rides
7-14 June
17 7% 14 30% 12 55%
23-29 June
28 11% 23 49% 5 23%
7-13 July
65 26% 7 15% 5 23%
17-27 July
139 56% 3 6% 0 0%
Consecutive captures of the same individual
0%
20%
40%
60%
80%
100%
7-14June
23-29June
7-13July
17-27July
Moved between rides
Moved within ride
Same station
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Behaviour of male V. pellucens
Visiting flowers
Resting on foliage
Hovering
7-14 June
77 63% 4 3% 41 34%
23-29 June
9 5% 1 1% 161 94%
7-13 July
44 18% 2 1% 205 82%
17-27 July
20 8% 2 1% 219 91%0%
20%
40%
60%
80%
100%
7-14 June 23-29June
7-13 July 17-27 July
HoveringResting on foliageVisiting flowers
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Behaviour of V. pellucens
• Mating strategy well known: males hover and defend an air space, dart after passing insects
• Male hovering extremely sensitive to sunshine:• When the sun goes in they rapidly perch in
trees• When it comes out again, equally rapidly
resume hovering
• Copulation observed just once. Coupling appears to be very brief and in flight, like V. inflata
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Behaviour of V. pellucens (2)
• Both sexes visit flowers early during emergence and are fairly mobile
• Later on males almost exclusively caught hovering and become very immobile
• Some evidence that males hold a territory, sometimes over several days
• As season progressed, it was much more likely an individual male would be found at the same hovering post
• Suggests fierce competition for hovering posts early on leads to rapid turnover
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Potential for further study
• Our knowledge of V. bombylans population size is incomplete
• Detailed survey for potential breeding sites is needed to better understand the population dynamics of V. inflata
• Questions remain over the degree to which V. pellucens moves from breeding sites to suitable territories for mate-acquisition
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ANY QUESTIONS?