TERRITORIAL AGGRESSION AMONG MALES OF THREE SYRPHID SPECIES by SHEILA M ...

150 Pages·2009·8.17 MB·English

TERRITORIAL AGGRESSION
AMONG MALES OF THREE SYRPHID SPECIES
by
SHEILA M. FITZPATRICK
B.Sc.(Agr.), University of British Columbia, Vancouver, 1979
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE
in
THE FACULTY OF GRADUATE STUDIES
(Department of Plant Science)
We accept this thesis as conforming to the
required standard
THE UNIVERSITY OF BRITISH COLUMBIA
November 1981
© Sheila M. Fitzpatrick, 1981
In presenting this thesis in partial fulfilment of the
requirements for an advanced degree at the University
of British Columbia, I agree that the Library shall make
it freely available for reference and study. I further
agree that permission for extensive copying of this thesis
for scholarly purposes may be granted by the head of my
department or by his or her representatives. It is
understood that copying or publication of this thesis
for financial gain shall not be allowed without my written
permission.
Department of
The University of British Columbia
2075 Wesbrook Place
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ABSTRACT
Among t e r r i t o r i al syrphids, Eumerus tuberculatus (Rond.)
males are always less aggressive than Merodon equestris (Fab.)
and E r i s t a l is tenax (L.) males. This aggressive gradient is
maintained despite the fact that the aggressive intensity of
a ll three species increases with the density of conspecifies,
varies with insect age and stage, and ceases if temperatures
f a ll below a certain c r i t i c al level or if sunlight disappears.
Possible reasons for the difference in the inherent level of
aggression are discussed.
Males of a ll three species recognized conspecifie females
through a combination of visual and behavioural cues. A
t e r r i t o r i al male approached a ll other intruders aggressively
but attempted to mate with them i f, like females, the intruders
did not respond to the male's approach.
Differences in behaviour patterns among species are
tentatively traced to different energy budgets and mating
strategies. Within each species, males and females show
different temperature thresholds for activity. This finding
is discussed in terms of energy requirements and reserves.
The final two sections of the thesis deal with the agricultural
implications of these results and with possibilities for future
studies.
i i i
TABLE OF CONTENTS
ABSTRACT ii
LIST OF TABLES vi
LIST OF FIGURES . . . v ii
ACKNOWLEDGEMENTS . . vi i i
Introduction 1
T e r r i t o r i a l i ty defined 3
Insect t e r r i t o r i a l i ty 6
Materials and Methods 22
The Narcissus Bulb F l y, Merodon equestris 30
Importance 30
Biology and Life History 30
Results 39
Characteristics of a Territory 39
Territorial Behaviours 43
Variations in Territorial Behaviour Patterns 47
1. Sunlight and temperature 50
2. Additional weather effects 51
3. Crowding by conspecifics 52
4. Insect age and stage 54
Recognition of Intruders 62
The Lesser Bulb F l y, Eumerus tuberculatus 64
Importance 64
Biology and Life History 65
Results 73
i v
Characteristics of a Territory 73
Territorial Behaviours 74
Variations in Territorial Behaviour Patterns 81
Recognition of Intruders 83
The drone f l y, E r i s t a l is tenax 84
Importance, Biology and Life History 84
Results 89
Characteristics of a Territory 89
Territorial Behaviours 91
Variations.in Territorial Behaviour Patterns 97
1 . Sunlight and temperature 97
2. Crowding by conspecifics 98
3. Territory type 100
4. Insect age and stage ' 101
Recognition of Intruders 102
Discussion 104
Variation in Aggression 104
Recognition of Females 111
Other Differences Between Species 113
Implications for Agriculture 116
Areas for future study 117
Literature cited 120
Appendix I. Solar elevation 131
Appendix II. Behavioural data 132
A1 133
A2 1 34
A3 135
V
Bl. . ... . . . . . . 1 36
B2. 137
B3. . .. . 1 38
C1 1 39
C2. ..140
C3 . . . . .... .141
vi
LIST OF TABLES
Table I. Behaviours of male syrphids 25
Table I I. Time allocation by an M. equestris male 50
Table I I I. Responses of M. equestris males.to intruders .. 53
Table IV. Responses of E. tuberculatus males to intruders 77
Table V. Time allocation by an E. tenax male 94
v ii
LIST OF FIGURES
Figure 1. Merodon equestris and bumblebee . . ...... 32
Figure 2. Mating M. equestris pair 34
Figure 3. M. equestris: Stages in mating 37
.Figure 4. Map of the study site 41
Figure 5. Behaviours of t e r r i t o r i al M. equestris males ... 44
Figure 6. Patrol routes of M. equestris males 48
Figure 7. M. equestris territory size in response to
crowding 55
Figure 8. Newly-emerged M. equestris male 58
Figure 9. Eumerus tuberculatus and h a l i c t id 66
Figure 10. E. tuberculatus male 68
Figure 11. Mating E. tuberculatus pair 71
Figure 12. E. tuberculatus territory 75
Figure 13. Behaviours of t e r r i t o r i al E. tuberculatus males
78
Figure 14. E r i s t a l is tenax and Apis me11ifera ..85
Figure 15. A mating E. tenax pair 87
Figure 16. E. tenax hovering 92
Figure 17. E. tenax male on horizontal territory 95
vi i i
ACKNOWLEDGEMENTS
In order to do this study, I had to stop "looking" at
insects and begin "seeing" what they were doing. My guide to
the realm of seeing was Dr.W.G. Wellington, who also provided
me with a study site, an elaborate combination of camera and
flash units, moral and financial support, and much good humour.
He took many of the photographs which appear here, and readily
changed hats from photographer to able-bodied field assistant.
He and his wife Margret, daughter Kathy, and son Stephen were a
continual source of sustenance and encouragement; I am
extremely grateful to them a l l.
I also had several teaching assistantships in the
department of Plant Science. I am grateful to Drs. Copeman,
E l l i o t t, Myers, Todd and Runeckles for these positions and
their moral support.
I thank Deborah Henderson for sharing her field plot at
U.B.C. with me, Mark Ridgway and Lee Gass for helpful
discussions about analyzing behavioural data, Laura Richards
for allowing me to quote her unpublished work, and Dave Zittin,
whose inexaustible computer wizardry was much appreciated. I
have enjoyed the wit and companionship of the graduate student
population at the Institute of Animal Resource Ecology and, in
particular, of Peter Morrison and Ken Lertzman, who were always
uncannily supportive at just the right moment. Finally, I
thank Peter Cahoon, who helped me to see what was really there.
1
INTRODUCTION
Territorial aggression has often been studied in an
evolutionary context, where hypotheses deal with the
reproductive success or fitness of t e r r i t o r i al animals. The
evolutionary approach facilitates interesting theoretical
comparisions and many now-familiar optimality arguments (e.g.,
Parker, 1978). But other, more immediate aspects of t e r r i t o r i al
aggression are of equal interest. A t e r r i t o r i al animal is
continually faced with a dynamic environment and must respond
appropriately in order to survive. In this f i e ld study, I
investigated the responses of t e r r i t o r i al males to changing
external and internal factors by observing changes in patterns
of t e r r i t o r i al behaviour and subsequent fluctuations in
aggressive intensity.
I observed three species of syrphid f l i e s: Merodon
equestris (Fab.), Eumerus tuberculatus (Rond.), and Eristalis
tenax (L.). Preliminary observations showed that males of the
first and third species were always more aggressive than males
of the second. These observations led to the formation of my
first hypothesis, namely, that males have a species-specific
inherent level of t e r r i t o r i al aggressiveness which varies in
response to changes in external factors, such as weather and
population density, and internal factors, such as insect age.
My second hypothesis arose from the combination of my own
field observations and a controversy among entomologists who
study insect t e r r i t o r i a l i t y. The controversy concerns the
intent of a t e r r i t o r i al male as he approaches intruders on his