Estimating the populations of three species of Volucella
in an English woodland
Roger MorrisStuart Ball
Volucella species studied
V. inflata
V. bombylans
V. pellucens
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
Sampling sites in the wood
20 visitsfrom 7 June to 27 July 2003
Marking
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%
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
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)
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)
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)
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)
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
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
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
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
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
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
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
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
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
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
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
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
ANY QUESTIONS?
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