ANIMAL BEHAVIOUR, 2007, 73, 275e280doi:10.1016/j.anbehav.2006.08.003

Effects of patch shape and group size on the effectiveness

of defence by juvenile convict cichlids

JAE-WOO KIM & JAMES W. A. GRANT

Department of Biology, Concordia University

(Received 13 June 2005; initial acceptance 18 October 2005;

final acceptance 8 August 2006; published online 5 December 2006; MS. number: A10186R)

The causes and consequences of territory size have attracted considerable attention, but there has beenrelatively little research on optimal territory shape. We manipulated the shape of food patches, indepen-dent of patch area (square, 13.6 � 13.6 cm; rectangular, 46.5 � 4.0 cm; elongated, 93.0 � 2.0 cm),presented to small, medium and large convict cichlids, Archocentrus nigrofasciatus, in groups of varyingsize (three, six, 12 fish). We used a 3 � 3 factorial design to test the predictions that the defence andmonopolization of a food patch would decrease as both patch perimeter and group size increased. Aspredicted, with increasing patch perimeter, the ability of the large (dominant) fish to defend the patchdecreased, as reflected by a decrease in the frequency of aggression and the proportion of the aggressionby the dominant. Similarly, intruder success typically increased with increasing patch perimeter, asreflected by an increase in the proportion of intruders in the patch and the duration that an intruderremained in the patch. Group size also had the predicted effect on most response variables; in general,defender success decreased and intruder success increased as group size increased. Furthermore, the effectsof increasing the patch perimeter and group size on measures of defensibility were largely additive.

� 2006 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Keywords: agonistic behaviour; Archocentrus nigrofasciatus; competition; convict cichlid; defence and monopolization offood; freshwater fish; optimal territory size; territorial behaviour

While many theoretical and empirical studies haveaddressed the issue of the optimal size of a territory (seeAdams 2001, for a review), relatively little research hasconsidered the optimal shape of a territory (but see Covich1976; Getty 1981). The optimal shape of a noncontiguousterritory is thought to be a circle, because it has the small-est perimeter for a given surface area (Dill 1978; Hixon1980). A circle minimizes the time required for foragingand for defence against intruders, who enter across theperimeter of the territory (Covich 1976).

While circular foraging and defended areas are common(Covich 1976), a great variety of shapes are observed innature. At high population densities, when territories arecontiguous, circular territories often become hexagonal(Adams 2001). Furthermore, the patchy dispersion of re-sources or uneven topography also leads to irregular-shaped

Correspondence: J.-W. Kim, Department of Biology, Concordia Univer-sity, 7141 Sherbrooke Street West, Montreal, Quebec H4B 1R6, Canada(email: jw_kim@alcor.concordia.ca).

270003e3472/07/$30.00/0 � 2006 The Association for the S

territories (Eason & Stamps 1992; Adams 2001). In streams,for example, the one-way flow of drifting food results in ju-venile salmonid fish defending cardioidal-shaped territo-ries (Noakes & McNicol 1982).

Only a few empirical studies, however, have examinedthe effects of territory shape on the behaviour of thedefender. In high-visibility environments, juvenile lizardsdefend compact territories, whereas in low-visibility envi-ronments, they defend either small or highly elongatedterritories (Eason & Stamps 1992). Red-capped cardinals,Paroaria gularis, typically defend territories along the twoopposite sides of a lake or river rather than a longer terri-tory along only one bank (Eason 1992; Eason & Stamps2001). The observed territory shape appears to increase in-truder detectability and reduce defence costs.

Resource defence theory was originally developed topredict the occurrence of territorial behaviour (e.g. Brown1964). Nevertheless, this theory also accurately predictsthe defence of ephemeral patches of food. For example,the effectiveness of patch defence often increases witha decrease in patch size (Monaghan & Metcalfe 1985;

5tudy of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

ANIMAL BEHAVIOUR, 73, 2276

Grant & Guha 1993) and the number of intruders (Jones1983; Chapman & Kramer 1996). Round or square patchesare typically used in these studies, but we are unaware ofany experimental tests of the effects of territory shapeon the effectiveness of resource defence.

We investigated the effects of patch shape and intrudernumber on the economic defensibility of a food patch. Infish with relatively indeterminate growth, the defence andmonopolization of food is particularly interesting becauseit often leads to the increased growth rate of dominantindividuals (Magnuson 1962; Ryer & Olla 1995). Usinga 3 � 3 factorial design, we manipulated patch shapeand group size to test the following predictions: patchesbecome less defensible as (1) patch perimeter increasesand (2) as intruder number increases, leading to lowerrates of aggression, less resource monopolization andlower growth rate of the dominant. As patches becomeless defensible, (3) the foraging success of the dominantfish will decrease, whereas (4) the foraging success andgrowth rate of intruders will increase.

MATERIALS AND METHODS

Experimental Subjects and Apparatus

We chose convict cichlids, Archocentrus nigrofasciatus,for our study because they show considerable behaviouralplasticity and readily defend patches of food in laboratoryconditions (Grant & Guha 1993). We used juveniles tominimize courtship behaviour and any potential behav-ioural differences between the sexes. Prior to the study,we held the cichlids in 110-litre aquaria, filled withcontinuously filtered, dechlorinated tap water (27�C, pH7.2, 12:12 h light:dark cycle) and fed them ad libitum,twice daily, with commercial flake food. To facilitateestablishment of a dominance hierarchy and recognitionof the dominant individual, we placed one large fish(mean � SD weight ¼ 0.37 � 0.07 g), one medium-sizedfish (weight ¼ 0.28 � 0.05 g) and a group of small fish(one, four or 10; weight ¼ 0.20 � 0.05 g) in each tank.We included the medium-sized fish to act as the dominantin the unlikely event that the large fish was not dominant.In all trials, however, the large fish was always the domi-nant individual and the medium-sized fish behavedsimilarly to the small fish in the tank.

We used test tanks (92 � 47 � 38 cm; 164 litre) contain-ing a fully submerged heater, undergravel filter, light-coloured gravel to 3 cm in depth, and aged tap water.We covered the back and the sides of the tanks with whitepaper to facilitate videotaping and to minimize socialinteractions between adjacent tanks. Lighting, tempera-ture and pH were identical to the rearing tanks.

We manipulated food patch shape and group sizein a 3 � 3 factorial design. We made three differentshapes of patch of identical surface area (186 cm2) out ofopaque Plexiglas: square (13.6 � 13.6 cm), rectangular(46.5 � 4.0 cm) and elongated (93.0 � 2.0 cm). Becausethe elongated patch was longer than the tank, it wasplaced diagonally in the tank. We used group sizes ofthree, six and 12 fish, and we completed seven replicates

of each treatment, for a total of 63 trials and 441 fish.Given the number of individuals needed, we used sixfull-sibling groups and placed all fish into test tanks ran-domly, such that the six kin groups were equally distrib-uted across all treatments.

Experimental Protocol

Each trial consisted of two phases: conditioning andtesting. The conditioning phase lasted 3 days to allow fishto acclimate to test tanks and learn to feed from thepatches. To minimize growth during the conditioningphase, we fed the fish 25% of the normal ration of foodtwice a day (at 0900 and at 1400 hours). During the 7-daytesting phase, we fed fish a normal ration at 0900 each dayof 0.04 g per 1 g of fish biomass (i.e. on average 0.034,0.058 and 0.106 g for groups of three, six and 12). We in-creased the daily ration by 50% after 1 week to promotegrowth. We spread the food pellets (Fry Feed Kiowa, ap-proximately 1.0 mm in diameter) evenly on the gel-coatedpatch, made from a solution of one package of Knox gel-atine (‘The Original’; 7.354 g) in 60 ml of hot water.

At the beginning and end of each trial, we measured thestandard length (to the nearest 0.5 mm) and weight(0.01 g) of each individual. We videotaped each tank onday 5, 8 and 11 for 30 min, immediately following the in-troduction of the food patch. From the videotape, we re-corded foraging and aggressive behaviour until all foodwas consumed, typically within 5e30 min of the intro-duction of the food patch. We also recorded the total for-aging time (i.e. time until all the food was eaten) for eachtrial. Of the 189 trials, 14 lasted longer than 30 min, so weconsidered total foraging time in these 14 trials to be30 min.

To quantify monopolization, we counted the number offish that were in the patch (i.e. within one body length ofthe patch) and noted the dominance status of each fish(i.e. dominant versus subordinate) at 1-min intervalsfollowing the introduction of the food patch; the degreeof monopolization is inversely related to the number ofsubordinate fish in the patch. To quantify aggressiveinteractions, we recorded the frequency of chasing, de-fined as the pursuit of one fish by another for at least onebody length. We counted aggressive interactions only ifthey originated within one body length of the foragingpatch. More than one fish in a group was occasionallyaggressive, so we also calculated the proportion of totalaggression that was performed by the dominant individ-ual. Because the per capita rate of aggression does notdifferentiate between the number of fish present in thetank versus the number of fish in the patch, we used therate of aggressive interactions per fish in the patch as ourmeasure of aggressive rate, calculated by dividing the totalrate of aggressive interactions by the mean number of fishin the patch in a trial, and by the total foraging time.

To quantify intruder success, we recorded the first 10intrusions per trial, defined as an intruder approachingthe food patch to within one body length; only six trialshad fewer than 10 intrusions. For each intrusion, wescored whether the intrusion was successful, meaning that

KIM & GRANT: PATCH SHAPE AND DEFENCE IN CICHLIDS 277

the intruder foraged in the patch using the typical head-down foraging posture (see Foam et al. 2005) and/orlunged towards the food patch. We also scored whetherthe intruder was chased by the dominant individual orleft the food patch voluntarily, and noted how longeach intruder stayed within the food patch. If the intruderstayed longer than 60 s, the duration of intrusion was con-sidered to be 60 s; 234 of 1884 intrusions lasted longerthan 60 s. For each trial, we calculated the average ofeach variable for the first 10 intrusions.

Statistical Analysis

We quantified seven dependent variables: average pro-portion of subordinates in the patch, rate of aggression perfish in the patch, proportion of aggression by the domi-nant, proportion of successful intrusions, average dura-tion that intruders remained in the patch, and dominantand subordinate growth rate. To ensure that the variableswere sufficiently independent of one another, we calcu-lated Pearson’s correlation coefficients for all pairs ofvariables; none were greater than 0.90 (range 0.05e0.88), so multicollinearity was not likely to be a problem(Tabachnick & Fidell 2001). We analysed the seven depen-dent variables using a MANOVA. To examine the relationbetween the effects of patch shape and group size on eachof the seven dependent variables, we analysed the datausing repeated measures two-way ANOVAs (3 patchshapes � 3 group sizes � 3 times) and by two-way AN-OVAs (3 patch shapes � 3 group sizes using the mean ofthe 3 times as the dependent variable). Although the re-peated measures ANOVAs were more complex, theyyielded exactly the same qualitative results as the simpletwo-way ANOVAs, so we report the results of only thelatter here. To meet the assumptions required for paramet-ric analyses, we used the arcsine-square-root transforma-tion for all data consisting of proportions. To correct formultiple comparisons, we used a Bonferroni adjustmentby setting an alpha value at 0.007 (Sokal & Rohlf 1995).

For all of the statistical analyses, there was no significantinteraction between the effects of patch shape and groupsize. Therefore, we do not report interactions unless aninteraction appeared to be significant in a figure andhence would require an explanation.

RESULTS

The large fish was always dominant and attempted todefend the entire patch. The smaller fish independentlyattempted to gain access to the patch, typically when thedominant was busy chasing another fish. When thedominant fish was less effective at defending the patch(see below), subordinate fish occasionally defended partsof the patch for short periods of time until evicted by thedominant.

The total foraging time did not differ significantlybetween patch shapes (two-way ANOVA: F2,54 ¼ 0.16,P ¼ 0.83), but was shorter for groups of 12(X ¼ 10:75 min) than for groups of three (X ¼ 15:10 min)or six (X ¼ 15:08 min) (F2,54 ¼ 5.14, P ¼ 0.009). The food

disappeared more quickly in groups of 12, probably becausethe dominant individual was unable to exclude subordi-nates effectively from the patch (see below).

Both patch shape (Wilk’s l: F14,96 ¼ 8.27, P < 0.001) andgroup size (F14,96 ¼ 12.95, P < 0.001) had a significanteffect on the seven dependent variables. In addition, therewas no significant interaction between patch shape andgroup size (Wilk’s l: F28,174 ¼ 1.22, P ¼ 0.22). To examinethe response of each dependent variable, we present theunivariate results below.

Resource Monopolization

To quantify the degree of resource monopolization, weused the indirect method of calculating the averageproportion of subordinates in the patch (i.e. within onebody length) during the scan samples. As predicted, theproportion of subordinates in the patch, an inversemeasure of resource monopolization, increased with in-creasing patch perimeter (two-way ANOVA: F2,54 ¼ 36.20,P < 0.001) and with increasing group size (F2,54 ¼ 33.78,P < 0.001; Fig. 1).

Aggression

As predicted, the rate of aggression per fish in the patchdecreased with increasing patch perimeter (two-wayANOVA: F2,54 ¼ 9.05, P < 0.001; Fig. 2a). Although this de-crease appeared to be stronger in groups of three and sixthan in groups of 12 fish, there was no significant interac-tion between the effects of patch perimeter and group size(two-way ANOVA: F4,54 ¼ 1.62, P ¼ 0.18). The rate ofaggression per fish in the patch also differed betweengroup sizes (two-way ANOVA: F2,54 ¼ 10.51, P < 0.001);aggression was highest for groups of six, followed bygroups of three, and was lowest for group size 12 (Fig. 2a).

0

0.1

0.2

0.3

0.4

0.5

0.6

40 60 80 100 120 140 160 180 200

Prop

orti

on o

f su

bord

inat

es i

n p

atch

Patch perimeter (cm)

Figure 1. Mean � SE (N ¼ 7) proportion of subordinates within onebody length of the patch, for groups of three (C), six (-) and 12

(:) in relation to patch perimeter.

ANIMAL BEHAVIOUR, 73, 2278

As a patch becomes less defensible by the dominantfish, other fish are expected to increase their level ofaggression. Consistent with this prediction, the propor-tion of aggression by the dominant decreased with in-creasing patch perimeter (two-way ANOVA: F2,54 ¼ 12.21,P < 0.001) from an average of 0.92 in the square patchesto 0.75 in the elongated patches. This trend appeared tobe stronger in groups of six and 12 than in groups of three,but the interaction was not significant (two-way ANOVA,interaction effect: F4,54 ¼ 2.71, P ¼ 0.039; Fig. 2b). As pre-dicted, the proportion of aggression by the dominant de-creased with increasing group size (two-way ANOVA:F2,54 ¼ 59.30, P < 0.001) from an average of 0.98 in groupsof three to 0.67 in groups of 12.

Intruder Success

Contrary to the prediction, patch shape had no signif-icant effect on the proportion of successful intrusions,defined as an intruder being able to forage in the patch(two-way ANOVA: F2,54 ¼ 1.12, P ¼ 0.34; Fig. 3a). As

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

40 60 80 100 120 140 160 180 200

Prop

orti

on o

f ag

gres

sion

by

dom

inan

t

Patch perimeter (cm)

(b)

0.5

1

1.5

2

2.5

3

Rat

e of

agg

ress

ion

per

fis

h i

n t

he

pat

ch (a)

Figure 2. Mean � SE (N ¼ 7) (a) rate of aggression per fish in the

patch and (b) proportion of aggression by the dominant fish, forgroups of three (C), six (-) and 12 (:) in relation to patch

perimeter.

predicted, however, the proportion of successfulintrusions increased with increasing group size (two-wayANOVA: F2,54 ¼ 33.52, P < 0.001; Fig. 3a). The average du-ration that intruders remained in the patch increased withincreasing patch perimeter (two-way ANOVA: F2,54 ¼ 9.40,P < 0.001; Fig. 3b). The effect of patch perimeter on in-truder duration appeared to be stronger in groups of threeand six than in groups of 12, but the interaction betweenpatch perimeter and group size was not significant (two-way ANOVA: F4,54 ¼1.55, P ¼ 0.20). The average durationof intrusions also increased with increasing group size(two-way ANOVA: F2,54 ¼ 33.25, P < 0.001; Fig. 3b).

Growth Rate

Contrary to the prediction, dominant growth rate didnot differ between group sizes (ANOVA: F2,54 ¼ 2.01,P ¼ 0.14; not shown) or between patch shapes(F2,54 ¼ 1.96, P ¼ 0.15; not shown). In contrast, the

0.4

0.5

0.6

0.7

0.8

0.9

1

Prop

orti

on o

f su

cces

sfu

l in

tru

sion

s

(a)

0

5

10

15

20

25

30

35

40 60 80 100 120 140 160 180 200

Intr

usi

on d

ura

tion

(s)

Patch perimeter (cm)

(b)

Figure 3. Mean � SE (N ¼ 7) (a) proportion of intruders that success-fully foraged in the patch and (b) average duration of intrusion, for

groups of three (C), six (-) and 12 (:) in relation to patch

perimeter.

KIM & GRANT: PATCH SHAPE AND DEFENCE IN CICHLIDS 279

growth rate of subordinates differed between group sizes(F2,54 ¼ 8.25, P ¼ 0.001; Fig. 4); as expected, subordinategrowth rate was lower in groups of three than in groupsof six and 12, but did not differ significantly with patchshape (F2,54 ¼ 0.10, P ¼ 0.90).

DISCUSSION

As predicted by resource defence theory, the ability ofthe dominant fish to defend the food patch decreasedwith increasing patch perimeter and intruder number.Patch perimeter had a significant effect on four of theseven dependent variables, all in the predicted direction.While the dominant fish attempted to evict the intrudersin all patch shapes, the increasing number of intrudersin the patch caused a lower per capita rate of aggressionwith increasing patch perimeter. As defenders increas-ingly lost control of larger-perimeter patches, someintruders increased their rate of aggression, as if takingownership of a part of the patch (see Eason & Stamps1992). Interestingly, patch perimeter had contrastingeffects on intruder success at entering patches versusremaining in patches. In our high-visibility laboratoryenvironment, patch perimeter seemed to have no effecton the ability of the dominant fish to see and initiallyrepel intruders. Once in a patch, however, cryptic in-truders were able to forage longer before being detectedby the dominant fish, who was busy foraging and chas-ing other fish away. The ability of dominant fish to seeintruders in the patch may have decreased with increas-ing patch perimeter, leading to longer intruder durations(see Eason & Stamps 1992).

Curiously, these significant behavioural changes did nottranslate into a decrease in the dominants’ growth rate oran increase in the subordinates’ growth rate in patcheswith a larger perimeter. Presumably, any gains in monop-olization by the dominant individual in the square patch

0.04

0.05

0.06

0.07

0.08

0.09

0.1

0.11

0.12

40 60 80 100 120 140 160 180 200

Gro

wth

of

subo

rdin

ates

(g)

Patch perimeter (cm)

Figure 4. Mean � SE (N ¼ 7) average gain in mass of subordinates,

for groups of three (C), six (-) and 12 (:) in relation to patch

perimeter.

were offset by an increased amount of energy devoted todefence (see Noel et al. 2005), or to the social stress relatedto high rates of aggression for both dominant and subor-dinate fish (e.g. Abbott & Dill 1989).

Not surprisingly, group size had a significant effect onsix of seven variables, all in the predicted direction,supporting the hypotheses that defender success decreasesand intruder success increases with group size. As pre-dicted, increasing group size resulted in lower dominantaggressiveness and higher rates of intruder foragingsuccess and growth rate. Similar strong effects of groupsize have been observed in previous studies (Chapman &Kramer 1996; Syarifuddin & Kramer 1996; Savino & Kos-tich 2000). The effects of intruder number may be less ob-vious in field settings, where intruders are free to leave andexplore other options. Nevertheless, intruder number alsohas strong effects on territory size (Myers et al. 1979) anddefender behaviour (Jones 1983) in the wild.

In the one exception to the pattern of linear increases ordecreases in response variables with increasing group size,the per capita rate of aggression was highest at theintermediate group size of six. Resource defence theorypredicts that the rate of competitive aggression will peakat intermediate group sizes (Brown 1964; Dubois et al.2003), and previous studies suggest that the peak inaggression occurs when two fish contest a patch (Grantet al. 2000; Noel et al. 2005). In our study, the dominantfish were relatively larger than the intruders compared toprevious studies, perhaps allowing the dominant todefend effectively against five intruders (also seeChapman & Kramer 1996).

Resource defence theory predicts how changes ina single component of resource distribution affect thedefence and monopolization of resources (see Warner1980; Grant 1993, 1997). Large interactions between thesesingle factors would make applying the theory difficult inthe wild, where multiple factors are likely to be involved.In our study, the effects of patch shape and group sizewere additive. Previous studies, however, detected signifi-cant interactions between main effects that are predictedto affect economic defensibility: spatial and temporalclumping of food (Robb & Grant 1998); temporal predict-ability and spatial clumping of food (Goldberg et al. 2001);patch size and predation hazard (Kim et al. 2004). Fortu-nately, the magnitude of these interactions was small, sothat the changes in the main effects were interpretableand largely consistent with theory. Taken together, thesefactorial studies suggest that resource defence theory canbe applied in field situations.

Acknowledgments

We thank Grant Brown, Louis Lefebvre and two anony-mous referees for helpful comments on earlier versions ofthe manuscript. All work reported was conducted inaccordance with Concordia University Animal Care Pro-tocol AC-2001-GRAN. Financial support was provided bya Fonds pour la Formation de chercheurs et l’Aide a laRecherche (FCAR) team grant to J.W.A.G., Louis Lefebvreand Luc-Alain Giraldeau.

ANIMAL BEHAVIOUR, 73, 2280

References

Abbott, J. C. & Dill, L. M. 1989. The relative growth of dominant

and subordinate juvenile steelhead trout (Salmo gairdneri) fedequal rations. Behaviour, 108, 104e113.

Adams, E. S. 2001. Approaches to the study of territory size andshape. Annual Review of Ecology and Systematics, 32, 277e303.

Brown, J. L. 1964. The evolution of diversity in avian territorialsystems. Wilson Bulletin, 76, 160e169.

Chapman, M. R. & Kramer, D. L. 1996. Guarded resources: theeffect of intruder number on the tactics and success of defenders

and intruders. Animal Behaviour, 52, 83e94.

Covich, A. P. 1976. Analyzing shapes of foraging areas: someecological and economic theories. Annual Review of Ecology and

Systematics, 7, 235e257.

Dill, L. M. 1978. An energy-based model of optimal feeding-territory

size. Theoretical Population Biology, 14, 396e429.

Dubois, F., Giraldeau, L.-A. & Grant, J. W. A. 2003. Resource

defense in a group foraging context. Behavioral Ecology, 14, 2e9.

Eason, P. 1992. Optimization of territory shape in heterogeneous

habitats: a field study of the red-capped cardinal (Paroaria gularis).

Journal of Animal Ecology, 61, 411e424.

Eason, P. K. & Stamps, J. A. 1992. The effect of visibility on territory

size and shape. Behavioral Ecology, 3, 166e172.

Eason, P. K. & Stamps, J. A. 2001. The effect of visibility on space

use by territorial red-capped cardinals. Behaviour, 138, 19e30.

Foam, P. E., Harvey, M. C., Mirza, R. S. & Brown, G. E. 2005.

Heads up: juvenile convict cichlids switch to threat-sensitive forag-

ing tactics based on chemosensory information. Animal Behaviour,70, 601e607.

Getty, T. 1981. Analysis of central-place space-use patterns: theelastic disc revisited. Ecology, 62, 907e914.

Goldberg, J. L., Grant, J. W. A. & Lefebvre, L. 2001. Effects of thetemporal predictability and spatial clumping of food on the inten-

sity of competitive aggression in the zenaida dove. Behavioral Ecol-

ogy, 12, 490e495.

Grant, J. W. A. 1993. Whether or not to defend? The influence of

resource distribution. Marine and Freshwater Behaviour and Physiol-

ogy, 23, 137e153.

Grant, J. W. A. 1997. Territoriality. In: Behavioural Ecology of Teleost

Fishes (Ed. by J.-G. J. Godin), pp. 81e103. Oxford: Oxford Univer-sity Press.

Grant, J. W. A. & Guha, R. T. 1993. Spatial clumping of foodincreases its monopolization and defense by convict cichlids,

Cichlasoma nigrofasciatum. Behavioral Ecology, 4, 293e296.

Grant, J. W. A., Gaboury, C. L. & Levitt, H. L. 2000. Competitor-to-resource ratio, a general formulation of operational sex ratio, as

a predictor of competitive aggression in Japanese medaka (Pisces:

Oryziidae). Behavioral Ecology, 11, 670e675.

Hixon, M. A. 1980. Food production and competitor density as the

determinants of feeding territory size. American Naturalist, 115,

510e520.

Jones, G. P. 1983. Relationships between density and behaviour in

juvenile Pseudolabrus celidotus (Pisces: Labridae). Animal Behaviour,31, 729e735.

Kim, J.-W., Brown, G. E. & Grant, J. W. A. 2004. Interactions be-tween patch size and predation risk affect competitive aggression

and size variation in juvenile convict cichlids. Animal Behaviour, 68,

1181e1187.

Magnuson, J. J. 1962. An analysis of aggressive behavior, growth,

and competition for food and space in medaka (Oryzias latipes

(Pisces, Cyprinodontidae)). Canadian Journal of Zoology, 40,313e363.

Monaghan, P. & Metcalfe, N. B. 1985. Group foraging in wildbrown hares: effects of resource distribution and social status.

Animal Behaviour, 33, 993e999.

Myers, J. P., Connors, P. G. & Pitelka, F. A. 1979. Territory size in

wintering sanderlings: the effects of prey abundance and intruder

density. Auk, 96, 551e561.

Noakes, D. L. G. & McNicol, R. E. 1982. Geometry for the eccentric

territory. Canadian Journal of Zoology, 60, 1776e1779.

Noel, M. V., Grant, J. W. A. & Carrigan, J. G. 2005. Effects of

competitor-to-resource ratio on aggression and size variation

within groups of convict cichlids. Animal Behaviour, 69,1157e1163.

Robb, S. E. & Grant, J. W. A. 1998. Interaction between the spatialand temporal clumping of food affect the intensity of aggression

in Japanese medaka. Animal Behaviour, 56, 29e34.

Ryer, C. H. & Olla, B. L. 1995. The influence of food distribution

upon the development of aggressive and competitive behaviour

in juvenile chum salmon, Oncorhynchus keta. Journal of Fish

Biology, 46, 264e272.

Savino, J. F. & Kostich, M. J. 2000. Aggressive and foraging behav-

ioral interaction among ruffe. Environmental Biology of Fishes, 57,337e345.

Sokal, R. R. & Rohlf, F. J. 1995. Biometry: the Principles andPractices of Statistics in Biological Research. New York: W.H.

Freeman.

Syarifuddin, S. & Kramer, D. L. 1996. The effect of group size on

space use and aggression at a concentrated food source in blue

gouramis, Trichogaster trichopterus (Pisces: Belontiidae). Environ-

mental Biology of Fishes, 46, 289e296.

Tabachnick, B. G. & Fidell, L. S. 2001. Using Multivariate Statistics.

Boston, Massachusetts: Allyn & Bacon.

Warner, R. R. 1980. The coevolution of behavioural and life-history

characteristics. In: Sociobiology: Beyond Nature/Nurture? (Ed. byG. W. Barlow & J. Silverburgh), pp. 151e188. Boulder, Colorado:

Westview Press.