ZoologicalJoumal ofthe Linman Society (198 l), 72: 69-92. With 8 figures
The activity budget and use of territory
by a tropical blenniid fish
J . R. NURSALL
Department of Zoology, University of Alberta,
Edmonton, Alberta, Canada T6G 2E9
Acceptedfor publication June 1980
Both sexes of Ophioblennius adanticus (Valenciennes) maintain permanent territories, intermixed
without pattern. They occur at a density of about 1.9 individuals per mp on shallow coral rock and
comprise a significant portion of the benthic fish biomass. They are diurnal; about 60% of their time
is spent resting, 15% swimming and 8.5% feeding. Feeding is concentrated in the afternoon and is
time-minimized. Territory is used exponentially, about 50% of time being spent in about 15%of the
territory. The relatively infrequent use of peripheral parts of a territory suggest that it is potentially
compressible or expansible. This, in turn, leads to a conclusion that an optimum size can only be
defined as a range and that, normally, a territory includes more resources than the minimum for
survival. Competition may be reduced between aegis corrivals of different species.
KEY WORDS:- Ophioblennius - Blenniidae - activity budget - territory - feeding
competition - Pomacentridae - aegis principle.
- coral reef -
CONTENTS
Introduction . . . . . . . . . . . . . .
The redlip blenny as an important component of the community
Theestablishmentofanactivitybudget . . . . . . .
Analysis of the activity budget . . . . . . . . . .
Time-minimized feeding may reduce competitive interaction .
Total activity and the boundazy of a territory. . . . . .
The Aegis Principle. . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . .
Acknowledgements. . . . . . . . . . . . .
References . . . . . . . . . . . . . . .
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69
70
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80
84
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91
INTRODUCTION
“The challenges of tropical environments stem chiefly from the intricate mutual
relationships among the inhabitants.” These are the words of Dobzhansky ( 1950)’
and their importance is becoming clearer as more investigators examine the
complexities of communities in the tropics. Bradbury ( 197 7 ) considered
‘connectedness’ as a fundamental property of an ecosystem, defining it loosely as
“a measure of a system’s relational complexity.” ‘Connectedness’ provides a
useful reference against which to examine ecological data. Nursall ( 197 7a)
69
0024-4082/8 1/050069 + 24$02.00/0
0 1981 The Linnean Society of London
J. R. NURSALL
70
discussed ‘biotic interaction’ as a general and pre-eminent control of community
relationships in marine tropical environments.
This paper details many of the die1 activities of Ophioblennius atlanticus
(Valenciennes), the redlip blenny, a common benthic, shallow-water, territorial
fish of the Caribbean. The work represents part of a continuing investigation of
this and ecologically associated species, in an attempt to comprehend community
complexity, energetics and evolution, by examining in detail how certain fish
spend their time and trying to recognise the significance of the activities
recorded.
Nursall(l97 7b) outlined the general territorial behaviour of the redlip blenny.
Here emphasis is placed upon analysis of individual activities and the establishment of an activity budget. The work was done at Bellairs Research Institute of
McGill University, St. James, Barbados.
THE REDLIP BLENNY AS AN IMPORTANT COMPONENT OF THE COMMUNITY
Ophioblennius atlanticus is highly successful as a benthic resident of shallow coral
rock. Counts along 14 transects during 1978 showed a mean population of 1.9
redlip blennies m-* (range 0.6-4.0) on suitable substrate, which corresponds
closely to the mean measured area of 0.5m2 for a territory reported by Nursall
(1977b). Moreover, in August, 1978, it was possible to make rough
measurements of biomass. Two coral heads, each isolated in a large sand patch
in the Bellairs fringing reef, St James, Barbados, were sampled by poisoning. A
high concentration of poison was used; several collectors spent several hours
making collection as complete as possible. The fish collected were those that were
benthic or cryptic in their behaviour. Transient or vagile species were not
collected; these included labrids, pomacentrids, pomadasyids, acanthurids,
scarids, mullids, ophichthids and muraenids. Most of them reappeared within
hours or days following poisoning.
Table 1 shows the results of collection from the two heads. ‘Other species’
include clinids, gobiids, tripterygiids, apogonids, dactyloscopids, tetraodontids,
cirrhitids, as well as juvenile labrids, acanthurids, pomacentrids and scorpaenids.
Table 1 . Biomass figures for benthic and cryptic fishes collected from two
isolated coral heads, StJames, Barbados
No. Ophioblennius atlanticus
Weight 0. atfanticus(g)
Mean weight 0. athnticus (g)
Sex distribution
No. other species
No. other individuals
Weight other individuals (g)
Isolated head M
25August 1978
Isolated head A
31 August 1978
19
38.9
2.05
8 9 ; 8 6 ; 3imm
I 5*
24’
18.2
3.26t
109; 116; 3imm
24t
31
71
15.6
40.6
* One redlip blenny (not recorded here) was seen to be captured by a wrasse as it drifted incapacitated away
from the poisoned head.
t It is not clear why the redlip blennies on head A were larger than those on head M. Comparisons of the
figures overall suggest the population of fish on M to be younger or less stable than that on A. M was within 2 m
of the main body of the fringing reef; A was about 8 m distant from the nearest large reef.
Identification not possible in all cases.
*
BLENNIID ACTIVITY AND TERRITORY
71
The two coral heads were more or less columnar in form, but highly irregular
in surface topography. Head M stood about 1.5m high, topped with a narrow
spire; head A was somewhat taller and broader. Their relative sizes are reflected
in the numbers of redlip blennies collected from their surfaces. What is of
interest in the data of Table 1 is the fact that the wet weight of 0. atlanticus is from
about 2 times (A) to 2.5 times (M) the wet weight of all other benthic and cryptic
specimens collected.
However, it is difficult to gauge accurately the success in kill and capture by
poisoning from coral. So complex and numerous are the interstices of coral that
the failure of rotenone to penetrate completely and the disappearance of
specimens within the coral cavities places a degree of error on population
estimates that is probably impossible to calculate. An estimate for surfacedwelling species may be made by repetitive re-examination of the treated area at
short intervals, say half a day, for a few days following treatment. That method
simply fails for species that spend most of their time within coral cavities. It is
however, useful for the redlip blenny which spends most of the daylight hours in
the open. No redlip blennies were seen on the treated heads on daily
examination from 25 (M) or 31 August (A) until I left Barbados on 5 September
1978. They were still absent on 11 September 1978. Two, assumed to be new
colonists, were seen on each head on 4 October 1978. The last two sets of
observations were made by Ruth Dubin at my request. Other species absent until
5 September included hbrisomus guppyi (Norman), Malacoctenus triangularis
Springer and Acanthemblemaria spinosa Metzelaar (Clinidae). These absences give
Table 2. A table of biomass proportions for estimation of relative biomass of
Ophioblennius atlanticus and other benthic species from the same location.
Italicized numbers are the actual weights recorded
a
b
c
d
e
f
g
h
Collection
as estimated
percentage
of actual
biomass
Isolated head M
Isolated head A
Weight (g)
Weight (g)
0.atlanticus
100
90
80
70
60
50
25
10
38.9
43.2*
48.6
55.6
64.8
77.8
155.6
389.0
0 ther
species
15.6
17.3
19.5
22.3'
26.0
31.2*
62.4
156.0
0.atlanticus
0ther
species
78.2
86.9'
97.8
111.7
130.3
156.4
312.8
782.0
45.1
50.8
58.0'
67.7
81.2'
162.4
406.0
40.6
Combine figures for estimated percentage collection (recovery) to determine biomass of 0.atlanticus relative to
other species, e.g.:
Apparent biomass ratio
ala
bld'
bIP
ck
Isolated head M
Isolated head A
38.9/15.6=2.5
43.2/22.3= 1.9
43.2131.2= 1.4
48.6162.4 =0.8
78.2/40.6= 1.9
86.9/58.0= 1.5
86.9/81.2= 1 . 1
97.8/162.4=0.6
etc.
* Presumed success in poisoning and collecting (see text).
72
J . R . NURSALL
some assurance of completeness in poisoning, but some specimens may not have
been collected for a variety of reasons, so even the biomass figures for these are
subject to error.
Table 2 illustrates how one can manipulate the figures to approach an estimate
of biomass. One may combine the calculated figures in whatever ratio is thought
best to represent the proportion of poisoned specimens collected. In the
examples of coral heads A and M, estimates of the population made visually
before poisoning and disappearance of the fish after poisoning lead to my belief
that recovery of 0. atlanticus was better than 90% and of other species of benthic
and cryptic fish from 50-70%. Thus, one arrives at a biomass proportion of
c. 1.1-1.9, the redlip blenny providing at least as much mass as other species in
question, and perhaps nearly twice as much.
T H E ESTABLISHMENT OF A N ACTIVITY BUDGE?
Fifteen redlip blennies were each watched for long periods during May and
June, 1976 and 1977, on reefs from about 0.5 to 3.0m deep, near Bellairs
Research Institute. The territory of each fish was mapped accurately beneath a
metre-square grid subdivided into 16 sections. Twelve of the territories were
photographed vertically by means of a Nikonos 15mm, wide-angle, deep focus
(‘fisheye’)lens, to enhance mapping. The fish were watched during 17 1 periods of
observation. The mean length of the periods of observation was 1399s (23.3min)
(range 810-2700s; S, 338.37; S, 26.34). That is to say, more than 65 h were
spent gathering data.
The smallest number of periods of observation of an individual was five, made
during a session of four days for specimen B9. The greatest number was 19, made
during a session of 16 days, for specimen A3. Visits to the experimental area were
irregular, though not formally randomized. They took place throughout the
daylight hours, from before sunrise until after sunset. Redlip blennies are
entirely diurnal; I have never seen one when diving or sampling at night. About
sunset, redlip blennies disappear for the night into holes in the coral. At about
sunrise it is possible to see a redlip blenny emerging from the same hole into
which it was seen to move the previous evening.
Figure 1 is a graphic log of observation times for individual specimens.
Observations were made while snorkelling. Activities were recorded on
underwater paper in code marks on a grid diagram corresponding to the metresquare grid placed over each territory, thus being located fairly accurately within
the territory.
The fish studied comprised eight females, four males and three of uncertain
wx. The uncertainty arises from the fact that the sexes are indistinguishable
without examination of urinogenital papillae, which requires collection of the
specimens at the end of sessions of observation. The fish were collected by fine
spear, to minimize local disturbance. If a specimen could not be speared in two,
or at most three attempts, the possibility of collection became practically nil. The
fish rapidly learned the danger of the new predator, and its evasive tactics
precluded collection. A wary fish being stalked might disappear as soon as the
snorkeller came into sight, even when five or more metres distant, even after a
lapse of four or five days in attempts to capture it. Before an attack a slowmoving observer could approach the fish within a metre or two and stay without
4
L
L
I
L
L
L
C
~
+
L
L
L
L
L
L
&
~
>
5
L
L
L
L
Figure 1. The distribution of periods of observation of activity for each of 15 specimens of redlip
blenny. A 1-6 are specimens watched during 1976; B 1-9 are specimens watched during 197 7 . Along
the lower margin are the clock times from 05.00-19.00 hours. Periods 1-13 are hours, distinguished
lor purposes of analysis. N=noon; SR=sunrise; SS=sunset; F=female; M=male; ?=sex
unknown. The lengths of the horizontal bars in the figures represent the time spent in each period of
observation.
74
J . R. NURSALL
disturbing i t ; after an attack by the observer, the specimen would no longer
tolerate him.
I n terms of their behaviour I think that two of the uncertain specimens were
female and one male. I t is known that the sexes are equally distributed without
pattern in permanent territories over dead coral rock substrate (Nursall, 197 7b;
Marraro, 1978). The specimens studied were on widely separated territories of
variable aspect, but amenable to mapping and observation. Nest-guarding males
may be behaviourally slightly more cryptic than females, which may have had
some influence on the preponderance of females reported. In 1977, males
guarding nest holes were sought specifically, in order to bring the sex ratio in
observations closer to equality. The purpose of the observations was to record
the distribution of activities of 0. atlanticus temporally and spatially, which would
allow proportional analysis of activity as well as definition of sexual distinctions
and the use made of the territory as living space. Records were taken rapidly and
regularly during each period of observation.
A simple recording code for a limited number of activities was devised. Six
major activities were recorded; they are explained below.
I t proved difficult to record at regular intervals of a few second’s duration.
Miniature devices that ticked or flashed metronomically had very short sealives;
we are experimenting by using battery-powered light-emitting diodes. For the
purposes here I tried to establish rhythmic repetition of code entry by singing
repetitious measures silently to myself as I worked. Starting and stopping times
for each period of observation (223.3min) were accurately taken ( + 2 s ) . A mean
interval could then be calculated. Overall, the mean spacing of coded entries was
3.6 s (range 1.8-5.8s; .li. 0.66; S, 0.05). The total number of coded entries
was 65,948.
I t was not possible to impute purpose to any of the activities as they were being
recorded, for two reasons. First, the purpose of an action could often only be
determined (if at all) after the event, e.g. swimming could lead to feeding, or
boundary antagonism, or reproductive behaviour, or retreat to shelter, or
shifting of resting spots. The second reason is complication of recording.
Possibly one could distinguish, say, feeding for sustenance from feeding as
displacement activity, from feeding as agonistic advertisement, but that
distinction trebles the coding of one simple function, which makes decision in
coding more complex and liable to error. That, in turn, slows down the
recording process and coarsens the temporal analysis.
It is, of course, important to keep the recording as rapid as possible because
many of the redlip blenny actions are speedy and short-lived. For example,
within five seconds it is quite possible for a fish to dash out from rest, graze with
two or three nibbles at the algal lawn, return to rest, then move off again,
perhaps for entirely different ends. Such a sequence might be recorded only as
’rest’ and ‘swim’, marking just the first and last of five activities. It is the
expectation that by recording regularly and rapidly the statistical pattern of
activity will emerge, despite loss of detail in any given sequence of behaviour
[Altmann, 1974). The maintenance of relatively steady levels of the activities
described as ‘resting’ and ‘swimming’suggests that there was no great fluctuation
of frequency of activities throughout the day (Fig. 2).
The descriptions of the activities recorded are as follows:
( 1) Resting: the redlip blenny spends most of its time resting on the substrate,
BLENNIID ACTIVITY AND TERRITORY
75
noon
Figure 2. Mean distribution of activity of Ophioblennius utlunticus as percentage of time spent during
the day. The periods are hourly intervals from 05.30-18.30 hours. 0 , Represents ‘resting’. 0,
‘swimming’,A, ‘feeding’,0, ‘out of sight’.
commonly on a prominence or a part of the territory that permits a broad view.
The position of its body ranges from horizontal to vertical, head up or down.
The head is generally raised in relation to the trunk, the pectoral fins being used
as props. An individual may have several preferred resting spots within its
territory, and it moves from one to another of these. If disturbed, a redlip blenny
may seek refuge in a depression, a hole, or beneath an overhang. When in refuge
it usually flattens its body to the contours of the substrate. ‘Resting’ here refers to
any record of a redlip blenny in contact with the substrate. It does not imply
immobility, for a resting redlip blenny may shift its body, move its head or jaws
or look about.
(2) Swimming: a redlip blenny patrols its territory sporadically (Nursall, 197 7b).
The fish lacks a swimbladder; it stays close to the substrate and does not swim
far, unless chased or engaged (as female) in reproductive activity. I t swims when
changing resting location, making a feeding foray, being attracted to antagonistic
or reproductive encounters, or attempting to escape a predator. Locomotory
activity for any of these purposes was recorded as ‘swimming’.
(3) Feeding: 0. atluntzcus is wholly herbivorous (Randall, 1967).The gut seems
invariably to be filled with the green remains of algae, but die1 studies of gut
76
J. R. NURSALL
contents are yet to be made. Feeding is accomplished by grazing the dead coral
surface, the comb-teeth being used to cut and rake filamentous or fleshy algae
and diatoms. The feeding motion is distinctive, a combination of head-bobbing
and jaw movement. Most often feeding consists ofjust a few nips at the substrate,
fdlowed by movement away from the feeding place. Sometimes it is more
prolonged, in a small area. In ‘exaggerated grazing’ (Nursall, 1977b) feeding is
part of an agonistic activity, related to boundary definition. At other times it may
have a displacement quality, e.g. as when the sea urchin, Diadema antillarum
(Philippi), moves onto a redlip blenny resting spot or across the opening of a
nest- hole, or when a yellowtail damselfish, Microspathodon chrysurus (Cuvier),
forces a blenny to move from its path as it goes on its own feeding round. Any of
these ingestive actions, caught in recording, was shown as ‘feeding’. N o search
component, in the sense of foraging, is included.
(4)W h i n crevice: redlip blennies go into holes for several reasons. They retire
to them at night; they duck into them to escape danger; males, when brooding,
guard and clean them; females enter them to spawn. All are recorded in the same
way. I t refers to small holes, within which the fish could be seen, or from which
thkre was not an exit hidden from view.
( 5 )Interaction: 0 . atlanticus is not a strongly aggressive fish, except to territorial
transgressions of its own species. I t will chase juvenile yellowtail damselfish
(jewelfish; M . chrysurus).Nest-guarding males will respond aggressively to various
wrasses and damselfish. Some other damselfish, particularly Eupomacentrus
dorsipunicans (Poey), will occasionally chase redlip blennies. Blennies will move
away from cruising predators that come within a metre or so. ‘Interaction’
includes all these things, but is chiefly a record of intraspecific boundary
reactions.
(6) Out Of sight: there is a significant proportion of the time of observations
during which the fish is out of sight. Irregularities in the topography of the
territory sometimes resulted in the fish moving over a ridge or behind a spur for
a few seconds or a few minutes. Since a principle of observation is for the
observer to remain relatively motionless, I rarely attempted to keep the fish
always in sight as long as the boundaries of the territory were in view. Sometimes
the fish left the territory (required of spawning females), and sometimes it was
absent when a period of observation began. The method of recording allowed
location and activity of a specimen to be noted, even if it were away from its
territory, when it could be identified. However, an individual commonly was
soon lost to the observer when away from its home ground, as it mingled with its
neighbours or travelled more than about a metre away. Observations at dusk
also made it sometimes difficult to keep the fish in sight, because of the increased
shadow in hollows and under ledges. Any absence from sight, or uncertainty of
location, therefore was marked ‘out of sight’.
ANALYSIS OF T H E ACTIVITY BUDGET
Table 3 gives the basic distribution of time for the activities described. Figure 2
5unirnarizes some of these activities arithmetically during the course of the day.
This plot shows that resting is the chief activity throughout the day, that
swimming makes up a relatively constant proportion of the day’s activity, that
feeding seems to increase in proportion as the day progresses, and that there is a
BLENNIID ACTIVITY AND TERRITORY
17
Table 3. Percentage of time spent by Ophioblennius
atlanticus at different activities (data for males and
females combined-see
text for numbers and
nature of observations)
Activity
Mean percentage
of time
Resting
Swimming
Feeding
Within crevice
Interaction
Out of sight
60
15
8.5
5
2.5
9
Total
100.0
decline in the proportion of time that individuals are out of sight, at least during
the ,morning.
The question may be raised as to whether or not the proportion of time ‘out of
sight’ distorts the values for other activities. Of the other activities, feeding is the
most important in the analysis here. A detailed examination was therefore made
of the effect of ‘out of sight’ on feeding activity, by returning to detailed notes
and records for each period of observation. N o distortion of the figures
tabulated could be demonstrated. The fish were in sight for more than 90%of the
time in 80% of the periods of observation. For most of those periods during
which the fish was out of sight for more than 10% of the time, it was either
engaged in spawning activity off the territory in the early morning before feeding
became a significant activity, or it had retreated out of sight in the failing light at
the end of day, or I confused it momentarily with neighbours (two or three
instances), or, in one case, I probably disturbed it because of my movements
compensating for a particularly strongly surging sea. In only four instances out
of 17 1 were fish lost to sight for more than 10%of the time in a late morning or
afternoon period when feeding was most important. Assuming a 15% feeding
rate (nearly twice as much as the mean recorded), these lost observations would
have provided only another 93 counts of feeding activity. That represents about
0.15% increase in proportion of time spent feeding, which is well within
experimental error.
That the figures for feeding in the early morning are not distorted by the proportionally large numbers of absences at that time is known from independent
observations. Among those fish that did not wander in the early morning,
feeding was uncommon until mid-morning; among those that were followed as
they wandered and engaged in reproductive activities, feeding was practically
never undertaken; for those that wandered unseen in early morning, then were
watched after their return, feeding did not take place consistently until long after
the return to the home territory. The general accuracy of the figures is satisfactory.
The arithmetic plot of levels of activity (Fig. 2) does not reveal much. More
detailed analysis is necessary to show significant variations in the observed levels.
For this purpose the tabulated data (numbers of each activity) were reduced to
proportions. These proportions were subjected to angular transformation
4
J. R. NURSALL
78
Table 4. The significance of changes in activity of Ophioblennius atlanticus that
occurred during the day. The time periods are listed in order of increasing levels
of activity. Periods underlined are not significantly different from one another
P<O.Ol
Activity period (hourly from 05.30 hours)
Feed rig
1
1
3
2
4
3
5
6
8
9
7
1 0 1 1 1 2
Period (two-hourlyfrom 05.30 hours)
P<O.Ol
P < 0.05
Feeding
1
2
3
4
5
6
1
2
1
4
5
6
Rcbring
6
4
1
2
3
5
6
4
1
2
3
5
Swimming
1
2
5
4
3
6
1
2
5
4
3
6
lntei action
5
6
4
3
1
2
5
6
4
3
1
2
Out ol +$it
6
4
5
3
2
1
6
4
5
3
2
1
fi),
(arcsine
and are reported in radians. The original percentages extended
from c. 0.1 to >90 between activities, and nearly as widely within. The
transformation expanded the distributions to allow two-way analysis of variance
and significance testing by Duncan’s stepwise multiple range test, using APL
library programmes.
One interesting result of the analysis of transformed data is that, in general,
significant sexual differences did not appear. The recorded ‘out of sight’
incidents increase in early morning as females leave their territories on sexual
adventures, but statistical significance ( P = 0 . 0 5 ) could not be demonstrated for
differences between the sexes. The category ‘within crevice’ was recorded
significantly more often ( P < 0.05)for males than females throughout the day and
significantly more often (P<0.05)in 1977 than 1976. Such a difference is seen
because nest-guarding males stay close to the nest-hole, and an effort was made
in 197 7 to redress the unbalanced sex ratio of the observations by choosing males
at holes, as that is the only way easily to identify them. Since those males would
be in a special reproductive state. some bias was introduced, and recognized as
shown above.
Initially, in the analysis of transformed data, records were summed at hourly
intervals, but it was found that if they were opened to two-hourly intervals the
curves were smoothed and significant differences became more apparent. Table 4
shows the significance of changes that occurred in levels of activity throughout
the day. The intervals are two-hourly, except in the case of feeding, where hourly
intervals are included for purposes of comparison. Figures 3-7 illustrate the data
tabulated for ‘feeding’, ‘swimming’, ‘interaction’ and ‘out of sight’. Results for
the two sexes are combined. The category ‘within crevice’ showed no significant
change during the course of the day, so is neither tabulated nor plotted.
These distributions of activity are readily explainable biologically. The earliest
morning activity of redlip blenny is reproduction, especially at times of full
BLENNIID ACTIVITY AND TERRITORY
I9
noon
0.d
02
c
0.2
.
0.1
I
3
5
7
9
I1
13
Period
Figure 3. Levels of feeding activity of Ophioblennius allantims. Periods are hourly from 05.30 to 18.30
hours. P,= proportion of time measured in radians from angularly transformed data.
moon (Marraro, 1978). Reproductive activity begins to be reduced by 08.30
hours (period 2 in the two-hourly analysis) and ceases shortly thereafter.
Reproductive behaviour required the migration of females from their territories
to that of a male, hence females tend to be lost from sight then. I t also involves a
series of female-male and female-female interactions, as well as antagonistic
responses when migrating females transgress neighbouring territories as they
seek a receptive male. The morning rate of interaction is also increased by the
efforts returning females often made to chase transgressors from their
temporarily abandoned territories.
Feeding commences slowly in the morning. It increases in rate to late
morning, then remains more or less constant during the afternoon. The
arithmetic and hourly plots illustrate one feature that is less sharp in the twohourly plots, namely, that during the very last hour of daylight, redlip blenny
activity is markedly reduced. Movements, feeding and interactions are much
reduced; about 75%of time is spent ‘resting’. The fish goes in and out of the hole
J . R. NURSALL
80
noon
ss
04
./
03
c
02
A
01
I
2
3
4
5
6
7
Period
Figure 4. Levels of feeding activity of Ophiobfmniuc aflantinrc. Periods are two-hourly from 05.3018.30 hours. P , =proportion of time in radians from angularly transformed data.
within which it will spend the night. I t disappears about sunset, usually shortly
afterward.
The pattern of swimming activity resembles that of feeding. While
reproductive behaviour does involve movement across a distance, there is less
protracted swimming and more ‘interaction’ and ‘within crevice’ behaviour once
the site of reproductive activity is reached. On the other hand, feeding is usually
the concomitant or termination of a foray from a resting spot, i.e. feeding and
swimming are commonly directly associated.
TIME-MINIMIZED FEEDING MAY REDUCE COMPETITIVE INTERACTION
The proportion of time spent feeding by 0. atlunticus may seem to be small,
particularly for a herbivore. Examination of recent literature for examples of
comparable activity or time budgets does not provide many data. Table 5 lists
some measurements and estimates that have been made. The data for
Table 5. Examples of time spent feedingby various vertebrates
Animal
Diet
Proportion of
time (%)
Fish
Redlip blenny (Ophioblenniusatlanticus)
Northern pike (Esoxlucius)
Kelp perch (Brachyistiusfrenatus)
White seaperch (Phanerodonfurcatus)
Senorita (Oxy~ulis
cal~oonica)
Redband parrotfish (Sparisomaaurofrenatum)
Algae
Fish
Copepods; gammarids
Bryozoans; polychaetes
Mostly bryozoans
Algae
Reptiles
Chuckwalla (Sauromalusobesw)
Egernia cunninghami
Herbivorous
Primarily herbivorous
8.5
<< 10'
c. 20'
c. 4'
c. 1*
Tph 147
Iph 20t
c. 4-7'
9'
Author
This paper
Christiansen, 1976; W. C. Mackay&J. S . Diana(pers. comm.)
Bray& Ebeling, 1975
Bray& Ebeling, 1975
Bray & Ebeling, 1975
R. E. Dubin (pers. comm.)
Nagy, 1973
Wilson&Lee, 1974
Side-blotchedlizard (Utaslawburiana)
Anolis polylepzs
Insectivorous
c. 10'
Insectivorous Foraging 986.3
Alexander&Whitford, 1968
Andrews, 197 1
Desert iguana (Dzpsosaurusdorsalis)
Feeding
Herbivorous
< 1.0'
c. 5'
Porter, Mitchell, Beckman &DeWitt, 1973
10-35
Wolf, Hainsworth & Gill, 1975
Dickcissel(3)(Spiza americana)
Marsh wren (3)
(Telmatodylespalwtns)
Ducks
Nectar and small
components of insects
Insects
Insects
ChieHyherbivorous
Lesser Hamingo (Phoenzconazasminor)
Blue-green algae
319.5
Birds
Hummingbirds and sunbirds
Mammals
Dairy cows
Sheep
Moose (Akes alces)
Herbivorous
Herbivorous
Herbivorous
>
Schartz&Zimmerman, 1971
Verner, 1965
D y e r , 1975; Folk, 1971;
Klima, 1966; Siegfried, 1974;
Siegfried, Burger&Van Der Menve, 1976
est. 50-80 Pennycuick & Bartholomew, 1973
17-21
61.2
20-70
30
58
Blaxter, 1962
Blaxter, 1962
Belovsky & Jordan, 1978
48? 13
__
* Author's calculations based on published graphs, tables or statements and their interpretation
t Tph, terminal phase ( 3 )Iph,
; initial phase (8or 0).
zU
J. R. NURSALL
82
0.45.
noon
Period
kigii1.c 4. I.cvr4s 01 tecding atrivity of Ophioblennius a~lanticus. Periods are two-hourly from
0i.SO-18.30 h o u ~ - \P. , = pr-opoi-tionof time in radians from angularly rransformed dara.
homoiotherms, especially birds, are more numerous than those for
poikilothernis. The limited data reported suggest that poikilotherms spend much
less of their time feeding than do homoiotherms, and that the redlip blenny is
not unusual in the proportion of time so spent. However, these data are
extremely sparse, so must be taken only as suggestive. The problem of distinguishing ‘foraging’ and ‘feeding’, as defined herein, complicates comparison,
as was recognized by Schoener ( 1969)and as is exemplified by foraging taking up
to 77% of the daily activity of the teiid lizard Cnemidophorus murinus (Bennett &
Gleeson, 1979) or up to 86%in Anolzs polylepis (Andrews, 197 11, with actual feeding
taking up very little time (Table 5 ) .
Nonetheless, it is clear that the redlip blenny does spend only a small
proportion of its time feeding. I t is also periodic in that activity (Figs 3, 4). What
are the consequences of this use of time?
In Schoener’s (1971) terms, the redlip blenny would seem to be a Type I feeder
and tinie-minimizer. It possesses a territory within which sufficient food grows.
The food comprises sessile plant forms almost entirely. Having its food in a
particular form in a limited space allows the fish to reduce both energy and time
costs when foraging. I t should be noted that the energetics of this fish are yet to
be quantified.
The redlip blenny will defend its territory against conspecifics, but not usually
against other species (unless it is a nest-guarding male), with the notable
exception of antagonism towards the juvenile M . chrysurus. That is to say, energy
expenditure in agonistic activity is reduced relative to that of more aggressive
fishes. The damselfishes E . dorsipunicans (= Pomacentrus fuscus in Randall, 1967)
and adult M . chrysurus eat the same algae as 0. atlanticus, though not exclusively
BLENNIID ACTIVITY AND TERRITORY
83
(Randall, 1967). By minimizing time spent feeding and by showing periodicity in
feeding, 0. utlunticus not only conserves energy, but it presumably reduces its
competitive interaction with other grazers (and might well be reducing its
exposure to predators), leading to further energy conservation. Such a reduced
demand in the food resources allows use of them by other consumers which
means that niche space has been left for other species.
Pough (1980) has considered the advantages of ectothermy for tetrapods. He
concludes that low energy requirements make it possible for amphibians and
reptiles to utilize small size, attenuated shape and relatively harsh environments,
thus making available more habitats and developing more niches. On the other
hand, coral reef fishes with low energy requirements have the potential to
develop new niches because their warm-water environment does not make high
energetic demands on its inhabitants or force them into torpor periodically. That
is to say, there are strong evolutionary advantages to possession of low energy
metabolism in favourable as well as unfavourable environments. The arguments
of Bennett & Ruben (1979) on selective factors in the evolution of endothermy
seem to be largely teleological. High energy metabolism may counter
unfavourable abiotic conditions, but low energy metabolism is still the mode of
most organisms. I daresay that the proliferation and diversity of poikilothermous
animals across the planet is in large part owing to their reduced demands upon
organic sources of energy and consequent increased sharing of them by
competitors or corrivals.
noon
0.11
0.11
Q-
0.IG
A
O
L
0
;
0.1I
o,o\
0.11
I
2
3
4
5
6
Period
Figure 6. Levels of activity for interaction by Ophioblenniw utlanticus. Periods are two-hourly from
05.30-1 7.30 hours. P,=proportion of time in radians from angularly transformed data.
J. R. NURSALL
84
TOTAL ACTIVITY A N D T H E BOUNDARY OF A TERRITORY
Nursall ( 1977b) described non-reproductive activity of the redlip blenny
within its territory by means of isopleths (isochrons) on a map of the territory.
With finer data now available from the more detailed recording of activity as
discussed herein, such graphic presentation may be refined. For instance, by
plotting total activity and feeding separately, one can see that the fish does not
necessarily feed in those parts of the territory where it spends most of its time.
However, since both the geography and pattern of events of each territory is
different from that of all others, it is more satisfactory to generalize in ways other
than mapping.
Total activity and feeding may be compared across a territory in a number of
ways. Here, three sets of relationships have been examined:
( 1) Total activity (TA): the total activity recorded in a given square of the grid (i.e.
a given part of the territory marked by a superimposed grid) as a proportion
of the total activity recorded for the whole territory. This is calculated as
l/n
n
1 OOU
C 1 A
where n = n o . ofperiods ofobservation (tests);u=activity/square/test; A = total
activi ty/test.
( 2 ) Feeding actiuity ( F A ) : the number of times feeding was recorded in a given
noon
0
o\
I
I
I
2
3
4
5
6
Period
kigurr 7. Proportion of time Ophioblennius atianticu out of sight to observer. Periods are two-hourly
Lion1 05.30-1 7.30 hours. /',=proportion of time in radians from angularly transformed data.
BLENNIID ACTIVITY AND TERRITORY
85
square as a proportion of the total feeding recorded for the territory as a
whole. This is calculated as
n
1 oog
(29,
l/n C G
1
where n=no. of periods of observation (tests); g=no. of records of
feeding/square/test;F= total record of feeding/test.
(3) Feeding as a proportion of activity (FP): the number of times feeding was
recorded in a given square as a proportion of the activity recorded in that
square. This is calculated as
n
g
(3).
l/n C 7
1
The figures for TA for all 15 sets of observations, i.e. blennies Al-A6 of 1976
and Bl-B9 of 1977, were ranked from most used to least used grid square
(territorial location), then the results for each averaged. Table 6 gives these
ranked values. That the number of tests (n)for the last four ranked areas falls
below 15 means simply that the territories vary in size so that in smaller
territories there may have been fewer than 12 grid squares covering utilized
areas. Larger territories may have records from more than 16 areas, but n is small
and the results vary irregularly and insignificantly. They make no difference to
the analysis so are left out of it.
The results are plotted in Fig. 8 where TA forms an exponential curve of
decreasing activity. By inspection of Fig. 8 or Table 6 , it can be shown that a
redlip blenny may be expected to spend 50%of its time within about 2.4 squares
or about 15%of the area of the territory.
Feeding activity (FA) is relatively constant, with a mean of about 12% of the
time in each of the four most actively used squares. It then declines, roughly
following the decline of total activity. The curve for feeding as a proportion (FP)
Table 6 . Total activity ranked by use of areas of the territory (grid squares)
Ranked
area
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Mean total
activity (TA)
each area
Sample
standard
deviation
(4
( Q"-' )
(EX)
27.84
16.05
11.72
8.24
6.47
4.78
3.80
2.71
1.94
1.48
1.17
0.86
0.63
0.52
0.50
0.37
11.853
4.026
2.951
2.730
2.587
2.109
1.879
1.388
1.037
0.895
0.894
0.747
0.781
0.759
0.772
0.609
417.64
240.80
175.85
123.57
97.04
71.63
56.93
40.60
29.16
22.20
17.54
12.94
8.78
7.34
7.05
3.74
Sum of
values
No. tests
(n)
15
15
15
15
15
15
15
15
15
15
15
15
14
14
14
10
J. R. NURSALL
86
1.63.2
28
24
Ir
i
9 36.3
Y -
OTA
20
16
12
FP
A
FA
8
4
0
4
8
12
16
Rank
Figure 8. The distribution of activity of OphiobLentuuJ nLlantzcur across its territory. Total activity (TA)
declines exponentially from the most-used region of the territory. See text for explanation of other
curves. The vertical bars represent the range of variation of total activity for each of the 16 ranked
grid squares.
BLENNIID ACTIVITY AND TERRITORY
87
measures the relative importance of feeding in each square. Feeding makes up a
relatively minor part of the activity of the most-used area of the territory, then
becomes much more important relatively in those parts of the territory that are
little used; some regions seem to be used almost entirely for feeding, although
they might be visited only rarely. Put another way, almost one half of the feeding
activity takes place in the four most used squares but its proportion of the activity
in those squares is small.
It must be kept in mind that all three curves of Fig. 8 are based on means of
results from 15 territories, so that variations and fluctuations, apparent when
each territory has its own results plotted, are reduced. Examination of plots for
different territories shows that fluctuation is very wide for FP. This is because
certain locations in a territory may be used almost exclusively for feeding, while
other places may be seldom or never used for feeding, though visited just as
often. The distinction arises from the nature of the local substrate and its algal
cover.
‘Feeding activity’ also varies widely from territory to territory, although with
less oscillation than FP. In Fig. 8 the curve FA is seen to follow the curve TA fairly
closely as it declines, but for many single territories, the conjunction is slight, and
reflects variation in FP. That is to say, in some territories there are quite welldefined feeding areas, which may be quite separate from the chief areas of ‘total
activity’. Those distinctive TA areas are primarily the chosen resting spots of the
inhabitant, commonly possessing prominences for perching, but not necessarily
having nearby feeding surfaces.
‘Total activity’ does not fluctuate as widely from territory to territory as the
other two proportions. In some cases, the curve TA for a given territory is more
nearly linear than exponential, but it always declines. Although the use of the
territory is differential, with favoured resting and feeding spots, it is not certain
that the same areas are always favoured by the resident. Much of the less-used
area may be lying fallow, in a sense, to be used at other times. Moreover, one
individual replacing another as resident will not use the same parts of the
territory in the same way. This was seen in 1977 with specimen B7, which
succeeded B 1, removed after study. The territory of B 7 was at the same place, but
not of precisely the same outline as that of B 1 and use of regions of the territory
differed from one fish to the other. In general, Fig. 8 describes the territory as
being intensively used centrally and less intensively used peripherally, although
intensively used locations were not always geographically central; they could be
close to the territorial boundary.
The exponential decline in use of the territory, from more to less favoured
areas, suggests that the area of a territory may be changed readily. A territory
would seem to be compressible, the long tail of the curve representing a low level
of utilization, i.e. a part of the territory that could be surrendered without serious
consequences to the food supply. In the curve TA of Fig. 8 each of the lowest six
regions makes up only about 1%or less of the use of the territory, and each of the
last eight squares represents less than 2% utilization. Furthermore, it is within
these areas that curve FP shows its greatest variability. Such variability represents
mostly opportunistic, incidental, or behaviourally motivated feeding by the
resident (e.g. exaggerated grazing at a boundary). The chief effect of having a
compressible margin would be felt during the recruitment of juveniles when
larvae, returning from the plankton year-round, take up interstitial territories
88
J. R. NURSALL
(Nursall, 197713; Marraro, 1978). Inflexible boundaries would make it impossible
for recruitment to begin, except by means of direct replacement.
Of course, the boundaries are also expansible (Nursall, 197713). Indeed, the
pressure seems to be outward, i.e. each fish being prepared to expand its territory
whenever resistance against it is reduced. I t is not clear what the limits are either
to expansion or compression. Expansion may be limited by vision to the
boundary and a reasonable radial distance of travel to it for defensive purposes.
Compression should be limited by absolute requirements for grazing space,
which includes the necessary food supply plus some perhaps immeasurable
psychic requirement for space. In the territories as measured here, food supply is
not a limiting function, but space appears to be. The limit will only be defined by
the degree of compressibility of the territory that can be shown to exist.
Covich (1976) discussed shape and use of foraging areas, and although he
could suggest optimal shapes for contiguous territories, he was forced to
conclude that permanently held territories might develop irregular outlines and
sizes and that the ultimate control of equilibria1 boundaries lay in the
heterogeneity of the habitat. The results with 0. atlunticus support those
conclusions. The long tail of the curve TA of Fig. 8 suggests the possibility of
flexibility and irregular re-arrangement of boundaries given differences in size
and aggressiveness of neighbours. Huxley’s ( 1934) figure of speech, the ‘elastic
disc’, seems to have been very well chosen.
Verner ( 197 7 ) has proposed the occurrence of ‘super-territories’, within which
somewhat more than enough resources are available for the support of the
resident. This seems to me to be a reasonable formulation, on the grounds that
making optimum and minimum requirements equivalent would necessitate
constant application of energy for resource utilization and territorial defence,
with catastrophic loss of territory given any relaxation of attention. Either that or
highly ritualized and predictable behaviour would be necessary to maintain any
degree of territorial stability. Certainly, neither of these is the case with
0 . attunticur, which spends only about 11%of its time in feeding and interaction
with other fishes (Table 3). The territory of 0. atluntim provides much more than
its minimal needs.
The balance of resources (food and space) in a territory may be shown as :
Min< Opt<Max,
or substituting actual utilization for optimal :
Min<Act <Max,
which in life has actual utilization fluctuating between minimum and maximum:
Min f Act 2 Max.
The limits to the oscillation of actual utilization of resources are expressed at
the minimum by failure of resources, i.e. too little food; insufficient space; and at
the maximum by energetic constraints, i.e. the excessive effort to defend a large
space. There is no reason to believe pragmatically that the actual utilization of
the territory by its holder is at any time at a definable optimum. Such
perfectibility of adaptation seems to me to be highly improbable. Given the
nature of the community and the competitive forces operating in it, actual
utilization must slide around the ‘optimum’, which itself probably exists as a
range slightly narrower than that of actual utilization. Optimality then is difficult
or impossible to measure as an absolute quantity (Getty, 1979).
BLENNIID ACTIVITY A N D TERRITORY
89
Pyke (1979) demonstrated that calculation of the optimum territory size as a
boundary condition (i.e. maximum or minimum) may be made using an
hypothesis of minimization of daily energy costs. It is intended that
measurements of parameters of energy be made for the redlip blenny, which will
allow calculations to be made to test all of Pyke’s hypotheses on energy costs.
Meanwhile, I think the proposal of Verner ( 1977), that territories may
encompass an excess of resources, is reasonable, at least among some
permanently territorial coral reef fishes. I t is accurate for 0. utlunticus. Though
the data are far from complete, I believe it will be applicable to the territory of
E. dors@unicans and the permanent territories of other pomacentrids. The proposal is, however, somewhat overstated. The term ‘super-territory’ implies
extra competitive activity, whereas, in the examples dealt with here, the territory
is normally larger than its resource minima require for survival of the resident.
Both compressibility and expansibility to minimum and maximum respectively
can be tested by controlled addition or removal of competitive neighbours.
THE AEGIS PRINCIPLE
Ophioblennius utlunticus is a territorial herbivore that spends less than 10%of its
time feeding. It is not particularly aggressive towards other species. It is highly
successful as measured in terms of numbers and biomass. What are the
components of its success?
The numerical data of activity are misleading if they give an impression of
immobility because of the large proportion of time spent resting. Redlip blennies
are found on exposed surfaces of coral rock, generally on resting spots from
which most of the individual’s territory can be surveyed. Head movements and
responses to intrusion demonstrate their visual acuity. They are cautious or
timorous in the presence of predators or more aggressive species. They are less
curious than some other species. For instance, tapping on coral rock will bring
several species of labrids and pomacentrids and sometimes other fish flocking
around, presumably seeking dislodged or uncovered food. Redlip blennies do
not respond to that signal. They are also cryptic to a certain degree, their range
of cream to grey to chocolate-brown colours fitting the substrate colours and the
sharp light-dark contrasts that are found across the rugose surface of the rock. A
redlip blenny is highly familiar with its own territory. One often sees repetitive,
though not periodic or regular, patterns of swimming; there are favourite routes
to and fro, but they are not exclusive. Knowledge of the territory is also shown by
the nature of territorial defence and the mappable boundaries (Nursall, 197 7b).
They are fierce in defence against others of their own species. Undoubtedly
sharp-eyed caution is important to the survival and success of the redlip blenny.
Its territory provides sanctuary and an abundance of food. Presumably, if food
were not abundant, the fish would spend a greater part of its time feeding. Use of
the territory is to some extent selective in that a small part of the territory is
relatively heavily used. Foraging and patrolling are minimized, which conserves
energy and reduces exposure. The territorial boundary is elastic (but not slack),
which provides some security against the pressure of population expansion.
In Caribbean coral reefs the damselfish E . dorsipunicuns has territory about
twice the size of the redlip blenny territory on exactly the same sea floor and
superimposed on it quite randomly. There is a large overlap in the algal diet of
90
J . R. NURSALL
the two species (Randall, 1967) though the damselfish is omnivorous, being only
50-60% dependent upon algae. Overlying, or stacked upon the territories
of E . dorsipunicuns and 0. utlanticus is the feeding area of the pomacentrid
M . ch~ysurus,another herbivore, about 90% dependent on algae, many species
of which are the same as those used by the two other fishes. The three species of
fish are therefore using the same space and food, which would seem to be
direct competition.
In the crowded conditions that are found on coral reefs, competition between
species for shared resources sometimes leads to the formation of guilds (Sale,
1975) wherein several species may react with one another as if their competition
were intraspecific. The response is different in the species considered here. The
redlip blenny does not interact at all closely with the damselfishes, because of its
benthic habits, its lack of interspecific aggressiveness and its modest (‘timeminimized’) use of the algae. Both the damselfishes are aggressive, especially
E. dorsipunicuns.The activities of these fish seem to be sufficient to protect not only
their own territories, but also that of 0. atlanticus from the depredations of roving
grazers such as acanthurids and scarids, scavengers such as labrids, and possibly
some predators. Thus the inoffensive redlip blenny with its territories contained
within the damselfish territories, is protected to some extent by the damselfishes
from extraspecific competition and aggression. This is a working of what may be
termed the Aegis Principle, whereby one species is sheltered under the behaviour
of another, without corporeal contact. It is possible only because of mutual
tolerance between the species concerned. Its operation may be found to cover the
still smaller territories on the same substrate of, e.g. clinids and gobiids. As an
example of biotic interaction (Nursall, 1977a) or connectedness (Bradbury,
19771, it suggests one mechanism to support the intensive use of space by overlap
(Luckhurst & Luckhurst, 1978). Its precise definition by experiment will be
difficult, but it should be possible by combining the sheltered and the shielding
species in different ways under different circumstances to seek behavioural
changes in the sheltered species, or changes in survivability as measured, for
instance, by abundance. The Aegis Principle is probably not a strong one, i.e. not
an invariable requirement for survival for any participant but it seems plausible as
a contributor to a species’ welfare, and it is invoked for the redlip blenny of
Barbados. At this time, it is not at all’clear what benefits, if any, accrue to
E. dorsipunicuns, except that the blenny is not a strong competitor, whose presence
may inhibit the activities of some other herbivore or space-claimer, perhaps invertebrate. Perhaps blenny and damselfish could be described as aegis corrivals.
SUMMARY
This paper began by suggesting that the biological relationships between
organisms were the chief ecological controls in tropical marine communities.
This proposition is not proved, but detailed, autecological examination of the
activities of the abundant, territorial herbivorous redlip blenny shows
behavioural components and sets of intra- and interspecific reactions that lead to
further questions about community relationships, e.g. matters of energetics, the
flexibility of a territory, the reduction of competition between species, etc., which
themselves seem not to change the nature of “the challenges of tropical environments” (Dobzhansky, 1950). The questions must be pursued; it is expected
that their answers will reinforce tentative conclusions reached here: that many of
BLENNIID ACTIVITY AND TERRITORY
91
the fish in a coral reef community are time-minimizers in feeding which allows
large overlaps in resource use; that permanent territories are tautly elastic, their
'optimal' size and use being a range within the boundaries of maximum and
minimum; and that there is a relaxation of competition between aegis corrivals,
for reasons not absolutely clear, but probably related to time-minimization and
periodicity in food use.
ACKNOWLEDGEMENTS
Dr Finn Sander and the staff at Bellairs Research Institute of McGill University,
Barbados, have been of great assistance with studies there. I am grateful to
numerous students and investigators at Bellairs for help with diving and
collecting. Ruth Dubin, Mary Nursall and Chris Marraro have willingly
participated in field work and discussion. I am especially grateful to Barbara
Chernick for her invaluable role in statistical analysis and computer operation.
Some of the analysis was done while in residence at Queen Elizabeth College,
London; I thank Professor G. Chapman and his staff for thoughtful help. P. L.
Forey and R. Winterbottom criticized early drafts of this paper. The work was
supported by an operating grant from the National Research Council of Canada.
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