Journal of Animal Ecology

2009,

78

, 42–51 doi: 10.1111/j.1365-2656.2008.01467.x

© 2008 The Authors. Journal compilation © 2008 British Ecological Society

Blackwell Publishing Ltd

Access to mates in a territorial ungulate is determined by

the size of a male’s territory, but not by its habitat quality

Cécile Vanpé

1,2

, Nicolas Morellet

1

, Petter Kjellander

2

, Michel Goulard

3

, Olof Liberg

2

and A.J. Mark Hewison

1

*

1

Laboratoire Comportement et Ecologie de la Faune Sauvage, Institut National de la Recherche Agronomique, BP 52627, F-31326 Castanet-Tolosan cedex, France;

2

Grimsö Wildlife Research Station, Department of Ecology, Swedish University of Agricultural Science (SLU), S-73091 Riddarhyttan, Sweden; and

3

DYNAFOR UMR 1201, Institut National de la

Recherche Agronomique, BP 52627, F-31326 Castanet-Tolosan cedex, France

Summary

1.

Territoriality is commonly associated with resource defence polygyny, where males are expectedto gain access to females by anticipating how resources will influence female distribution andcompeting for resource-rich sites to establish their zone of dominance.

2.

We tested this hypothesis in European roe deer (

Capreolus capreolus

) by simultaneously assessingthe influence of resources on female distribution and the influence of female distribution on maledistribution and breeding success using paternity analyses.

3.

Females did not fully distribute themselves among male territories in relation to resources. As aresult, relative female abundance in a male’s territory depended on territory size, but not on its hab-itat quality. In turn, relative female abundance in a male’s territory determined, at least partially, hisbreeding success.

4.

Interestingly, male territory size, and hence access to females, was partly determined by malebody mass (all males) and by residual antler size (subadults only). The latter result suggests thatlarge antlers may be important to young males for establishing their first territory, which is thenusually retained for all subsequent reproductive seasons.

5.

To conclude, although territoriality of male roe deer has certainly evolved as a tactic for ensuringaccess to mates, our results suggest that it does not really conform to a conventional resourcedefence polygyny strategy, as males seem to gain no obvious benefit from defending a territory inan area of high habitat quality in terms of enhanced access to mates.

6.

This may explain the stability of male territories between years, suggesting that male territorialityconforms to an ‘always stay’ and ‘low risk–low gain’ mating strategy in roe deer.

Key-words:

mating tactics, reproductive success, resources, territory quality, ungulates

Journal of Animal Ecology

(2007)

>

doi: 10.1111/j.1365-2656.2007.01467.x

Introduction

In mammals (especially in ungulates), where males usuallyprovide no parental care and have the higher reproductivepotential, female reproductive success is directly constrainedby access to the resources necessary to breed and to meet theenergy requirements of gestation and lactation, whereas malereproductive success is limited more by access to potentialpartners (Trivers 1972). As a result, female distribution shoulddepend primarily on resource dispersion (modified by predationpressure and the costs and benefits of associating with otherindividuals), while males should distribute themselves in relationto females (modified by male density), at least during the breeding

period, in order to gain access to as many mates as possible(Emlen & Oring 1977).

Males can either directly compete for mates, or indirectlycompete for resources that influence female distribution(Emlen & Oring 1977). The economics of these two matingtactics depends mainly on the defensibility of females, whichis directly related to female density, distribution, range size,group size and stability, and indirectly to the distribution ofresources (Clutton-Brock 1989). When females are spatiallyand temporally predictable (e.g. when they occupy small stableranges containing clumped and high-quality food resources),the most economic mating tactic should be to adopt a ‘resourcedefence polygyny’ tactic, where males gain access to females byanticipating how resources will influence female distributionand competing for resource-rich sites to establish their zoneof dominance (Emlen & Oring 1977).

*Correspondence author. E-mail: mark.hewison@toulouse.inra.fr

Role of territory in male breeding success in roe deer

43

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Journal of Animal Ecology

,

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, 42–51

Male territoriality is commonly associated with the resourcedefence polygyny tactic (Emlen & Oring 1977). In ungulates,in which male territoriality is widespread (see Owen-Smith1977), the evolution of male territoriality as a mating tacticanalogous to resource defence polygyny has been suggestedfor various species (e.g. in Grevy’s zebra

Equus grevyi

, Klingel1974; European roe deer

Capreolus capreolus

, Putman 1988;Wahlström 1994; Johansson 1996; Liberg

et al

. 1998; hippo-potamus

Hippopotamus amphibius

, Nowak 1991; wildebeest

Connochaetes gnou

, Estes 1969; Reeves’s muntjac

Muntiacusreevesi

, Dubost 1970; sika deer

Cervus nippon

, Miura 1984).However, no study has as yet tested this hypothesis bysimultaneously assessing the influence of resources on femaledistribution and the influence of female distribution andresource dispersion on male distribution and reproductivesuccess.

The aim of this study was to investigate this issue in theEuropean roe deer [

C. capreolus

(Linnaeus 1758)], an ungulatein which only males are territorial and the spatial system of thetwo sexes is independent, so that a female’s home range mayoverlap several male territories (Hewison, Vincent & Reby 1998;Liberg

et al

. 1998). First, we expected female abundance withina male’s territory to increase with territory size (prediction 1).Second, if male territoriality evolved as a resource defencepolygyny mating tactic, females should be distributed inrelation to resources. The ‘ideal free distribution’ hypothesis(IFD; Fretwell & Lucas 1970) states that, in the absence ofconstraints on movement, individuals are expected to be distri-buted so that differences in local densities reflect differences inhabitat quality. As a result, resources are equally shared amongindividuals and fitness is equal in all habitats (Fretwell & Lucas1970). While Wahlström & Kjellander (1995) suggested thatroe does fit the IFD, Nilsen, Linnell & Andersen (2004) foundevidence for fine-scale spatial variance in fitness componentsinduced by environmental heterogeneity. Similarly, Pettorelli

et al

. (2001) reported higher fawn body weight in the richernorthern part of the Chizé forest compared to the poorer south,despite higher local density in the north. Assuming that femalesare free to distribute themselves in relation to resources, weexpected female abundance within a male’s territory to increasewith habitat quality for a given territory size (prediction 2).Third, territoriality should secure mating access to residentfemales for the territorial male. Hence, we expected a male’sbreeding success to depend on female abundance within histerritory (prediction 3). Also, males should attempt to enhancetheir mating success by either enlarging their zone of dominance,or by occupying areas particularly favoured by females, or both.Hence, we also expected male breeding success to increase withterritory size and/or territory habitat quality (prediction 4).Finally, we should expect substantial male–male competitionto occupy the ‘best’ territories (providing access to the highestnumbers of females). Hence, the best territories should beoccupied by the best competitors in male–male contests. Wetherefore expected a positive correlation between the suitabilityof the territory in terms of access to females, and male attributeswhich reflect ability to fight and dominate, such as age, bodymass and antler size (prediction 5).

Materials and methods

STUDY

SPECIES

AND

STUDY

S ITE

The roe deer is a selective feeder, preferentially feeding on forbs, seedsand deciduous browse rich in soluble nutrients (Tixier & Duncan1996), adapted to exploit the early stages of forest succession (Linnell,Duncan & Andersen 1998; Hemami, Watkinson & Dolman 2004). Itis an income breeder (Andersen

et al

. 2000), relying on food intakerather than body reserves to cope with the marked increase in energyrequirements during late gestation–early lactation. Females are con-sidered as nonterritorial, living solitarily or with their fawns duringsummer in overlapping home ranges (Bramley 1970; Strandgaard1972; Wahlström & Kjellander 1995). Adult males are considered asfully territorial, but only from early spring (March–April) until lateAugust–early September, just after the July–August rut (e.g. Bramley1970; Strandgaard 1972). Although males become sexually matureas yearlings, they usually do not defend territories until 2, 3 or 4years of age (see Liberg

et al

. 1998 for more details).The study was carried out in the 1420-ha western part of Bogesund

(59

°

23

′

N, 18

°

15

′

E), a 2600-ha mainland peninsula situated on the coastof the Baltic Sea on the inner portion of the Stockholm Archipelago,within the hemiboreal zone of east-central Sweden. The habitat isfragmented, with approximately 65% woodland, 25% fields and 10%bed rocks and bogs (Kjellander 2000; see also SupplementaryAppendix S1). The only natural predator of roe deer fawns is the redfox (

Vulpes vulpes

, Kjellander & Nordström 2003).

DATA

COLLECTION

AND

ANALYSES

The Bogesund population has been monitored intensively since 1988.Each winter, roe deer were caught in box traps, sexed and individuallymarked with plastic ear tags (see Kjellander 2000 for more details).A variable number of caught individuals were also equipped with radiocollars (TXT-2Sm, 151 or 152 MHz transmitters, Televilt Interna-tional AB, Lindesberg, Sweden). Age was either known definitively(animals first caught

<

1 year old) or estimated from tooth eruptionand wear (Cederlund, Kjellander & Stålfelt 1992) during capture orafter death. As age estimation based on tooth wear is inaccurate in roedeer (Hewison

et al

. 1999), we considered two age classes only,subadults (2 years old; all known-age) and adults (

>

2 years old; bothestimated and known-age males). Body mass was measured to thenearest 0·1 kg, while antler size was measured to the nearest 0·5 cmand standardized to the 14th of February (see details in Vanpé

et al

.2007).

Radio tracking and estimation of territory size

All deer equipped with radiocollars and older than 1 year of age wereintensively radio tracked during the ruts (i.e. from mid-July to mid-August) of 2004 (

N

=

25 males and 16 females) and 2005 (

N

=

23males and 22 females, of which 15 and 9 were the same as in 2004,respectively). Radio tracking was conducted from the ground withTelevilt RX-810 and RX-98 receivers and a four-element Yagi antenna.Animals were located by triangulation from at least three pointsalong roads or hills. An experimental study of the accuracy of ourradio-tracking fixes showed that the mean error

±

SD of localizationswas 41·0

±

41·6 m (see Appendix S1). Based on graphs of area against90% Kernel probability values (see Appendix S1), we chose to collect30 fixes per individual and per rut, which is the recommended standardproposed by Kenward (1987) and Seaman

et al

. (1999). The 30 positionsfor each individual were collected over the same number of days, with

44

C. Vanpé

et al.

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Journal of Animal Ecology

,

78

, 42–51

up to a maximum of three fixes per 24-h period, both during daytime(8 positions/individual), and during night (2 positions/individual),dusk (10 positions/individual), and dawn (10 positions/individual),and with a minimum of 3 h between successive locations to limittemporal autocorrelation.

Radio-tracking positions were digitized in a geographical informa-tion system (

arcview

3·2) and analysed using the spatial analyst andanimal movement extensions of

arcview

(Hooge & Eichenlaub 1997).Range size was estimated using the fixed Kernel method (Worton1989) with both the 90% and the 50% isoclines and the least-squarescross-validation (LSCVh) calculation for the smoothing parameter(see Appendix S1), as recently recommended by Börger

et al

. (2006).Based on measures of range overlap, we showed that a territorial malehad relatively exclusive use of his 90% Kernel area (see Appendix S1),hence 90% Kernel during the territorial period can be considered asa reliable proxy of territory size.

Pellet-group counts for estimating an index of relative female abundance in each territory

A faecal pellet-group count census (Neff 1968; Cederlund & Liberg1995) was carried out over the entire 2600-ha Bogesund peninsula,both in 2004 and 2005, in early April, immediately after snow melt.The 604 sample plots (10 m

2

) were circular and distributed every 100m along north-south transects, with 400 m between neighbouringtransects. We considered that no pellet degradation occurred duringwinter due to snow cover and low temperatures. Because new pelletsthat have deposited since defoliation could be distinguished from oldpellets in relation to dead leaves and needles that covered the latterbut not the former (Kjellander 2000), a standing crop design wasused. The total number of pellet groups (minimum of 10 pellets pergroup, which is slightly more than half the mean number of pelletsin a group) was recorded on each plot.

The number of pellet groups on each plot was interpolated usinga statistical prediction (see Appendix S1). The total number of pelletgroups was estimated within each male’s territory (based on both90% and 50% Kernels) for 2004 and 2005 as the sum of the pointestimates falling within each territory using

arcview

3·2 software.This value was used as a relative index of local roe deer abundance.It was corrected using an estimation of the local sex ratio, defined asthe proportion of mature females caught in each trap zone (

N

=

7)during winter captures, in order to obtain an index of relative abund-ance of mature females in each territory.

Vegetation sampling and identification of the specific resource attributes that reflect habitat quality for females

During both ruts, a systematic vegetation sampling was performedover the 1420 ha of the study site, comprising 357 point locations.For each point, the habitat was classified and vegetation cover wasevaluated (see Appendix S1). Vegetation sampling was carried outusing a wooden frame of 25

×

25 cm. All vegetation inside the framewas identified to the species level and cut at the following heights:0–20 cm, 20–50 cm and 50–150 cm (maximum browsing height fora roe deer). Each sample was labelled and stored frozen in a paperbag. All samples were later thawed, dried at 60

°

C for 3 days andthen weighed to the nearest 0·01 g. For each sampling point, thebiomass of crop plants (i.e. oat, wheat, and barley), berry plants(i.e.

Vaccinium

spp. and

Ribes

spp.), pasture plants (i.e.

Trifolium

spp. and

Vicia

spp.), various grasses, and the total biomass ofconsumed plants were then estimated. Plants consumed by roe deer

(see Appendix S1) were determined based on the analysis of 11 rumencontents from two females and nine males shot during the 2005 rutat Bogesund (Cécile Vanpé and Petter Kjellander, unpublished data).

Each of the 10 habitat variables (i.e. five factors: habitat, cover0–20 cm, cover 20–50 cm, cover 0–150 cm, cover of bilberry; andfive continuous variables: biomass of crop plants, biomass of berries,biomass of pasture plants, biomass of grasses, total biomass ofconsumed plants) was entered in a geographical information system(

arcview

3·2), mapped, and interpolated over the whole study area.To identify the specific resource attributes that best reflect habitatquality (in terms of attractiveness for females), habitat selection byfemales during the rut was evaluated with an ecological-niche factoranalysis (ENFA; Hirzel

et al

. 2002), using the

enfa

function of the

adehabitat

package (Calenge 2006) for the

r

2·4·1 statistical soft-ware (R Development Core Team; Ihaka & Gentleman 1996). Detailson the ENFA are provided in Appendix S1. To determine the specificresource attributes that best reflect the suitability of an area for females,we interpreted the marginality axis of the ENFA (see Appendix S1),which measures the strength of habitat selection (i.e. the mean differencebetween habitat use and availability; see Hirzel

et al

. 2002 for furtherdetails). This analysis indicated that females tended to avoid theintermediate age forest habitat with high cover of bilberry (negativevalues), while they selected crop field habitats with high biomass ofcrop plants, and high vegetation cover (positive values). A habitatsuitability map was derived from the results of the ENFA by assign-ing a numerical value to each raster map unit of the study area basedon its position in this ecological space. This map was then used toderive mean habitat quality within each male’s territory (both 90%and 50% Kernels).

Paternity analysis and estimation of male breeding success

From 1988 onwards, tissue samples were collected for DNA genotypingfrom all individuals caught for the first time and unmarked shot roedeer. From 1997 onwards, tissue samples were also collected fromneonates caught by hand in springtime, just after birth (May–June).This allowed us to sample a total of 1757 different individuals. Asmall (approximately 4

×

4 mm) piece of ear skin tissue was removedusing sheep ear-notching pliers. Mother–offspring relationshipswere elucidated by direct observations of marked fawns with theirmothers just after birth or during autumn. Genotyping of the DNAsamples was carried out using 21 microsatellite markers (see Vanpé

et al

. 2008). In this study, we focused on fawns from the cohorts 2005(

N

=

29) and 2006 (

N

=

29). We aimed to identify the father of thesefawns in order to estimate yearly breeding success of the males radiotracked during the 2004 and 2005 ruts. Parentage was assessed usinga likelihood-based approach with the program

cervus

2·0 (Marshall

et al

. 1998) and the user-defined input parameters detailed in Vanpé

et al

. (2008). For the 2005 and 2006 cohorts, we identified 57 and 73sampled candidate mothers respectively and 51 and 63 sampledcandidate fathers respectively. In total, we were able to assign 26 fawnsto the 31 different radio-tracked males. Yearly breeding success (YBS)was defined as the number of fawns assigned to a male (at the 80%confidence level) in a given year.

STATISTICAL

ANALYSES

To first describe the spatial scale of variation in pellet-group countsand habitat resources, we constructed Poisson empirical covariograms(Christensen, Moller & Waagepetersen 2000) for the 2004 and 2005

Role of territory in male breeding success in roe deer

45

© 2008 The Authors. Journal compilation © 2008 British Ecological Society,

Journal of Animal Ecology

,

78

, 42–51

pellet-group count distributions, as was described earlier for inter-polation of pellet-group count distributions, and a classical variogramfor resource distribution using the

geor

package (Ribeiro & Diggle2001).

To test our predictions, we used linear mixed-effects models (eitherGaussian or generalized) implemented in the

r

2·4·1 statisticalsoftware (R Development Core Team 2004), where male identity wasentered as a random factor to control for repeated measures of thesame individual. Model selection was performed using the smallsample size corrected Akaike information criterion (AICc) as rec-ommended by Burnham & Anderson (2002) (see Appendix S1). Theterritory size (both 90% and 50% Kernels) and the index of relativefemale abundance in a male’s territory were log-transformed to nor-malize data in models where they were the dependent variables.

To test predictions 1 and 2, we used the

lme

function (in the

nlme

r

package) for fitting linear mixed-effects models (Pinheiro & Bates2000), using the maximum likelihood estimation procedure. Toidentify territory characteristics (territory size, habitat quality) thatcould reflect territory suitability in terms of access to females formales, the model relating the index of relative female abundance in amale’s territory-to-territory size was compared with the constantmodel. The model describing the relationship between the index ofrelative female abundance in a male’s territory (corrected for territorysize) to the mean habitat quality index within the territory was alsocompared with the constant model.

To relate YBS (discrete response variable) to individual-based measuresdescribing the males’ territory (i.e. relative index of local female abundancein the territory, territory size, mean habitat quality index within theterritory) to test predictions 3 and 4, we used a generalized linearmixed model (GLMM) implemented in the glmmADMBR module(H. Skaug, D. Fournier & A. Nielsen, unpublished). YBS was modelledas a Poisson distribution (see McLoughlin

et al

. 2006 for a similarapproach) and we used a zero-inflated model (see Appendix S1).Each model including the simple effect of the index of relative femaleabundance in the territory, territory size, and the mean habitat qual-ity index within the territory was compared with the constant model.

Finally, to examine prediction 5, we tested the additive effects ofmale age class (subadults vs. adults), residual antler size (antler sizecorrected for the allometric relationship between antler size andbody mass; see Vanpé

et al

. 2007) and body mass (standardized

using the mean body mass of the corresponding age class), as well astheir two-way interactions, on territory characteristics (territory sizeand/or habitat quality index in a male’s territory) which reflect thesuitability of territories in terms of access to mates for males. Twoseparate models (one for antler size and one for body mass) wereperformed, as both data were not always available for all males.

Results

SCALE

OF

SPATIAL

VARIATION

IN

FEMALE

ABUNDANCE

AND

HABITAT

RESOURCES

The spatial autocorrelation of pellet-group counts was weakin both years and occurred over about 200 m (225 m for 2004and 235 m for 2005) (Fig. 1a and b). For resources, the spatialstructure was stronger, with spatial autocorrelation occurringover 400–600 m. Hence, the spatial structure of resourcesoccurred over a greater distance than that of pellet-groupcounts, but both varied at a spatial scale which is of the sameorder of magnitude as the average home range size of a maleroe deer on this study site [mean (

±

SD) territory size was23·1 ha (

±

13·8) and 29·5 ha (

±

12·0) in 2004 and 2005, respec-tively, based on 90% Kernel;

N

=

24 for both years].

CHARACTERISTICS

DETERMINING

THE

RELATIVE

LOCAL

FEMALE

ABUNDANCE

IN A MALE’S TERRITORY

The models including an effect of territory size on the log-transformed index of relative female abundance in the terri-tory described the data much better than the constant models(ΔAICc = 26·34 and 23·62, for 90% and 50% Kernels respec-tively). Hence, as expected (prediction 1), as territory sizeincreased, relative female abundance in the territory alsoincreased (mean slope ± SE = 0·040 ± 0·006 and 0·184 ± 0·032,for 90% and 50% Kernels respectively) (Fig. 2a and b).

In contrast, the models including an effect of the habitatquality index in a male’s territory on the log-transformed

Fig. 1. Poissonian covariograms of pellet-group count distributions in 2004 (a) and2005 (b) computed using the georglm

package. The minimum and maximumlimits were computed from generating 99simulations by permutating data values.

46 C. Vanpé et al.

© 2008 The Authors. Journal compilation © 2008 British Ecological Society, Journal of Animal Ecology, 78, 42–51

index of relative female abundance in the territory correctedfor territory size performed less well than the constant model(ΔAICc = 2·43 and 0·85, based on 90% and 50% Kernelsrespectively). However, AICc values were very similar,especially for the 50% Kernel, indicating some support for anegative effect of habitat quality on relative female abundancein a males’ territory (Fig. 2c and d), contrary to prediction 2.Note, however, that this negative effect was likely due to twoout-lying data points, since the ΔAICc was greater than 2 oncethese points were removed (ΔAICc = 2·36). These resultsindicate that the suitability of a male’s territory in terms ofaccess to females seems to be best reflected by territory size,but not by its habitat quality.

EFFECT OF RELATIVE FEMALE ABUNDANCE IN A MALE’S TERRITORY ON MALE YEARLY BREEDING SUCCESS

The constant model performed slightly better than the modelsincluding the effect of relative female abundance in a male’sterritory on male yearly breeding success (ΔAICc = 1·31 and1·25, based on 90% and 50% Kernels, respectively), but valuesof AICc were similar, indicating some support for an effect offemale abundance on male YBS. There was, thus, a trendfor an increase in male YBS with an increase in the index of

relative female abundance in their territory described by theequations: E(YBS) = (1–0·40) exp(–0·4624 + 0·0497 index ofrelative female abundance) based on the 90% Kernel andE(YBS) = (1–0·41) exp(–0·3523 + 0·2201 index of relativefemale abundance) based on the 50% Kernel (Fig. 3a and b).

EFFECT OF TERRITORY SIZE AND HABITAT QUALITY ON MALE YEARLY BREEDING SUCCESS

The constant model performed better than the model includingthe effect of territory size on male yearly breeding success, basedon both 90% and 50% Kernels (ΔAICc = 2·34 and 3·67,respectively), indicating the lack of a marked effect of territorysize on male YBS. However, there was a slight trend (2 < ΔAICc < 4;see Burnham & Anderson 2002) for an increase in male YBSwith male territory size described by the equations: E(YBS) =(1–0·3417) exp(–0·8362 + 0·0266 territory size) based onthe 90% Kernel and E(YBS) = (1–0·3456) exp (–0·4801 +0·0744 territory size) based on the 50% Kernel (Fig. 4a and b).

In contrast, the constant model performed much betterthan the model including an effect of territory habitat qualityon male yearly breeding success (ΔAICc = 4·81 for the 90%Kernel and 4·87 for the 50% Kernel, respectively). Therefore,our index of territory habitat quality had no effect on male YBS.

Fig. 2. Effect of the territory size (a and b) and of the habitat quality index in a male’s territory (c and d) on the log-transformed index of relativefemale abundance in the territory corrected for territory size, based on both the 90% Kernel (a and c) and the 50% Kernel (b and d).

Role of territory in male breeding success in roe deer 47

© 2008 The Authors. Journal compilation © 2008 British Ecological Society, Journal of Animal Ecology, 78, 42–51

EFFECT OF MALE PHENOTYPIC ATTRIBUTES ON TERRITORY SIZE

The best linear mixed models testing the effect of male bodymass (corrected for age class) and age class (subadults vs. adults)on log(territory size) were the constant models (ΔAICc = 0·21for the 90% Kernel and 2·38 for the 50% Kernel, respectively).Note, however, that the model including the simple effect ofbody mass had a very similar AICc to the constant modelespecially for the 90% Kernel, suggesting substantial supportfor this model too. Hence, body mass had a positive effecton male territory size when measured with the 90% Kernel(mean slope ± SE = 0·05 ± 0·04), but little effect on maleterritory size when measured with the 50% Kernel (0·01 ± 0·04)(Fig. 5a and b).

In addition, the best models testing the effect of male residualantler size and age class on log(territory size) were the modelsincluding both the additive effects of residual antler size andage class, as well as their interaction, for both 90% and 50%Kernels (ΔAICc = 1·74 and 0·61, respectively). Hence, terri-tory size increased with male residual antler size, but only

in subadults (mean slope ± SE = 0·29 ± 0·01 and 0·04 ± 0·01for 90% and 50% Kernels, respectively), and not in adults(0·002 ± 0·002 and 0·003 ± 0·002 for 90% and 50% Kernels,respectively; see Fig. 5c and d). Hence, these results thereforesupport, at least partly, prediction 5. Note, however, that thedata set included only three subadult individuals and thatthe effects of antler size and age class were not marked,since the constant models had very similar AICc as the bestmodels.

Discussion

Our results show that female abundance within a male’sterritory depends on the size of his territory, as expectedfrom prediction 1, but not on its habitat quality, contrary toprediction 2. In support of predictions 3 and 4, territory sizeand female abundance within the territory, in turn, seem todetermine male breeding success, at least partially. Hence, ourresults do not conform to expectations if male territoriality inroe deer was a conventional resource defence polygyny tactic(sensu Emlen & Oring 1977), because males seem to aim todefend a large territory, irrespective of its attractiveness tofemales in terms of habitat resources.

Fig. 3. Variation in male YBS with the index of relative local femaleabundance in the territory based on both the 90% Kernel (a) and the50% Kernel (b). Note: black open circles, observed data. Greystars, values predicted by the zero inflation generalized linear mixedmodel.

Fig. 4. Variation in male YBS with male territory size based on boththe 90% Kernel (a) and the 50% Kernel (b). Note: black opencircles, observed data. Grey stars, values predicted by the zeroinflation generalized linear mixed model.

48 C. Vanpé et al.

© 2008 The Authors. Journal compilation © 2008 British Ecological Society, Journal of Animal Ecology, 78, 42–51

We showed that relative female abundance in a male’s terri-tory was not related to territory habitat quality, which seemsto contrast with predictions under the resource defence polyg-yny hypothesis. These results also differ from the observationsof Johansson (1996) who reported that male mating success inroe deer was related to territory quality, but not territory size:males who occupied a territory which included clover fieldswere more successful than other males. Strandgaard (1972)also suggested that the quality of crops influenced the numberof females on a given territory. However, Johansson (1996) usedbehavioural estimates of mating success which are certainlypoor indicators of true male breeding success, particularly asmultiple mating commonly occurs and roe deer are crypticand often occupy dense forest habitat (Danilkin & Hewison1996; Liberg et al. 1998). In addition, both studies used asubjective categorical variable to describe habitat qualitybased on the assumption that clover fields were the preferredresource selected by females. To our knowledge, our study is thefirst to use a niche analysis to determine the specific resourceattributes that reflect the habitat quality of a male’s territory

in terms of access to females. Several other studies of territorialungulates have demonstrated a direct relationship betweenthe quality of male territories and access to potential mates(e.g. in American pronghorn Antilocapra americana: Kitchen1974; puku Kobus vardonii and topi Damaliscus lunatusantelopes: Balmford, Rosser & Albon 1992; impala Aepycerosmelampus and waterbuck Kobus defassa: Jarman 1974; in aterritorial population of red deer Cervus elaphus: Carranza1995). However, none of these studies had access to a reliableestimate of male breeding success to fully test the resourcedefence polygyny mating hypothesis.

The absence of a relationship between the index of habitatquality and relative female abundance in a male’s territoryobserved in our study may be due to several factors:

First, our estimation of relative female abundance within amale’s territory was based on the assumption that local femaledensity in winter was a good estimate of local female densityin summer, since female home ranges are globally stable betweenseasons (Hewison et al. 1998). However, some seasonal migra-tions can occur in yearling and 2- to 3-year-old females (see

Fig. 5. Effect of residual body mass in all males (black open triangles, black line) (a and b, subadults and adults combined) and residual antlersize in subadults (grey filled circles, grey line) and adults (black open circles, black line) (c and d) on territory size measured with both the 90%Kernel (a and c) and the 50% Kernel (b and d). Note: residual antler size is calculated as antler size standardized to the 14th of February andthen corrected for the allometric relationship between antler size and body mass (see Vanpé et al. 2007). Residual body mass is calculated as bodymass corrected for the mean body mass of that age class.

Role of territory in male breeding success in roe deer 49

© 2008 The Authors. Journal compilation © 2008 British Ecological Society, Journal of Animal Ecology, 78, 42–51

Wahlström & Liberg 1995). This may potentially result in aredistribution of young females between the winter and rutperiods, but concerns only a small proportion of the totalnumber of females. In addition, snow cover may restrict roedeer space use in winter (Cederlund & Lindstroem 1983), butsnow cover in our study area is certainly too low to constitutea problem for roe deer ranging behaviour (normal snow coverrarely exceeds 10 cm at Bogesund). To test the reliability ofour assumption, we estimated the degree of overlap betweenwinter (January–March) and summer (July–August) homeranges (90% Kernels) of 12 females of 1 year old and older,based on radio-tracking data collected from 1992 to 1995. Wefound that female home ranges were slightly larger in winter(mean = 42·15 ha, SD = 15·10) than in summer (mean = 25·36 ha,SD = 17·51), and overlap between seasons was variable andquite high, ranging from 17% to 99% of the area of the smallesthome range, with a mean of 48·2% (SD = 24·6). This suggeststhat winter female distribution should be a quite good proxyof female distribution during the rut. Note that in our study,it was not possible to obtain significant behavioural informa-tion because of the difficulties of observing roe deer in a frag-mented habitat with a large proportion of forest, such as atBogesund. However, collecting behavioural observations onfemale distribution, when possible (e.g. in a more openlandscape; see Börger 2006), would provide complementaryinformation for understanding male mating tactics.

Second, the use of pellet-group counts to reflect spatialvariation in relative deer abundance has not been fully testedat the present time. However, it has been suggested that pellet-group counts provide an informative index of relative animalabundance (e.g. Forsyth et al. 2007), especially in northernareas (such as Scandinavia), where pellet decay rate should benegligible and spatially constant during winter.

Third, although our index of habitat quality integrated anumber of habitat variables, it may still not adequately reflectthe suitability of an area for females. Fox predation, for example,is known to be a strong determinant of summer fawn survivaland variation in female reproductive success at Bogesund(Kjellander et al. 2004a). Hence, predation avoidance mayswamp the role of food resources and vegetation cover indetermining female distribution. However, a preliminary analysissuggested that the number of fox dens present within a male’sterritory has no effect on the index of relative female abund-ance in a male’s territory or on male breeding success (CécileVanpé, unpublished data).

A fourth possibility is that females may not be free to distri-bute themselves in relation to resources because of social con-straints. Indeed, the IFD model is not appropriate when someindividuals can monopolize resources by securing the highestquality areas while forcing inferior competitors into suboptimalhabitats (e.g. territoriality or dominance hierarchies). Femaleroe deer are considered as nonterritorial, except maybe duringfawning site defence (Liberg et al. 1998), because they com-monly live in overlapping home ranges. However, this overlapoften concerns close relatives (see Liberg et al. 1998), withmatrilineal associations common due to extensive femalephilopatry (see Hewison et al. 1998). Hence, we cannot rule

out the possibility that dominance relationships betweenunrelated females impose a constraint on female rangingbehaviour. Indeed, female home range size seems to decreasewith increasing population density (Kjellander et al. 2004b)and aggressive behaviours between females seem to becommon (Börger 2006).

If females do not fully distribute themselves in relationto resources, males will be unable to ‘predict’ the distributionof potential mates by anticipating how resource distributioninfluences female dispersion. Hence, in contrast to theexpectations under resource defence polygyny (Emlen & Oring1977), males would then show no interest in competing forresource-rich sites to establish their zone of dominance. Weshowed that, to some degree, local female abundance in amale’s territory increased with territory size and, as a result,had a positive influence on male YBS. This suggests that, tomaximize fitness, males should attempt to enlarge theirterritory in order to maximize their chance of encounteringreceptive females. Interestingly, a male’s territory is remarkablystable from year to year (Liberg et al. 1998), with little changeof borders and size (e.g. Bramley 1970; Johansson 1996;Linnell & Andersen 1998), even when the distribution ofresources or females changes markedly (Strandgaard 1972).Territory borders may even persist after the death of an ownerand the takeover of a new occupant (Strandgaard 1972;Cederlund, Kjellander & Liberg 1994), usually an immigratingbuck or a nonterritorial subadult (Cederlund et al. 1994;Johansson 1996). These observations suggest that males donot constantly attempt to enhance their mating success byeither enlarging their zone of dominance or by occupyingareas particularly favoured by females (Hewison et al. 1998),contrary to expectations for a conventional resource defencepolygyny strategy.

It should be noted, however, that we did not find verystrong relationships between male YBS and territory size andbetween male YBS and relative female abundance in a male’sterritory. This could be due to low sample size, but may alsobe explained by the fact that males probably do not have fullmating monopoly inside their territory. Indeed, in roe deer,30% to 50% of females make short excursions outside theirnormal home range during the rut, traversing several territories,and potentially mating with other males, before returning(see Liberg et al. 1998; Richard et al. 2008 for more details).In addition, females whose range overlaps several maleterritories move frequently between them during oestrus,being courted and mated repeatedly by one or more territoryholders (Liberg et al. 1998). The above suggests that femaleroe deer may take an active role in mate searching and matechoice, and this may explain why male breeding success is notmore closely linked to the number of females present withinthe territory.

Our results also showed that, in support of prediction 5,body mass tended to have a positive effect on territory size(90% Kernel) in all males, and interestingly, that residual antlersize had a positive effect on territory size in subadults only.Hence, among territorial males, heavy individuals with largeantlers are the best competitors, able to defend the largest

50 C. Vanpé et al.

© 2008 The Authors. Journal compilation © 2008 British Ecological Society, Journal of Animal Ecology, 78, 42–51

territories, with the highest access to mates. This also suggeststhat male phenotypic traits, and especially antler size, whichreflect the ability of males to fight are particularly importantin subadults, during the key period when males establish theirfirst territory. Because of the strong fidelity of males to theirfirst territory and the positive relationship between territorysize and YBS, the establishment of a male’s first territory maytherefore play a crucial role in determining fitness over hislifetime (note, unfortunately, we were not able to conduct ananalysis of the determinants of lifetime breeding successbecause we had lifetime breeding information and rangingdata for too few males).

To sum up, although territoriality of male roe deer hascertainly evolved as a tactic for ensuring access to mates(Hewison et al. 1998), our results suggest that it does notentirely conform to a resource defence polygyny strategy (seealso Börger 2006 for a similar suggestion). We speculate thatsocial constraints may govern, at least partly, the distributionof female roe deer at the local scale, and that variation in thenumber of females within a male’s territory probably dependsmainly on the resultant annual variation in female distri-bution (Bramley 1970; Strangaard 1972). Our results aretherefore in agreement with the view that male territorialityconforms to an ‘always stay’ and ‘low risk–low gain’ strategyin roe deer (see Linnell & Andersen 1998), where males do notcompete intensely for territories and mating (at least oncethey have established their first territory). Rather, males gainthe benefits of site familiarity and reduced frequency of dan-gerous fights with rival males by remaining in the same areawhere they are dominant (Owen-Smith 1977). As suggestedby Liberg et al. (1998) and Hoem et al. (2007), the adaptivefunction of male territoriality in roe deer is thus not themonopolization of females present within territories formating, but rather the delimitation of an area in which a buckis dominant and so can court and mate without interferencefrom other males. Roe deer territoriality seems therefore todiffer from the territorial systems of most other ungulates, forwhich previous studies have demonstrated a direct relation-ship between territory quality and mate access (e.g. in impalaand waterbuck: Jarman 1974; American pronghorn: Kitchen1974; puku and topi antelopes: Balmford et al. 1992), sug-gesting a better fit with the conventional resource defencepolygyny model than for roe deer. We therefore suggest thatresource defence polygyny should not be considered as ahomogeneous mating tactic. There are actually no discretedistinctions between the different types of polygynous matingtactics described by Emlen & Oring (1977) and, as Jarman(1974) pointed out, ‘any attempt to subdivide a continuum createsproblems’. The variability of polygynous mating tactics wouldbe probably more realistically described as a continuumextending from resource defence polygyny to female defencepolygyny, with roe deer occupying an intermediate position.

Acknowledgements

We are grateful to all the field-workers who helped in fawn capture, radio track-ing and pellet-group counts at Bogesund. Vegetation sampling was performed

by Maria Tybergsson and Per Grängstedt. We also thank Maxime Galan for hiswork with the molecular analyses, Clément Callenge for his advice concerningspatial statistics, and Hélène Verheyden for her advice concerning habitat qualityanalyses. We thank two anonymous referees for constructive comments on anearlier version of this manuscript. The study was financed by the SwedishAssociation for Hunting and Wildlife Management, the private foundations of‘Oscar och Lilli Lamm stiftelser’, ‘Olle och Signhild Engkvist stiftelser’ and aFORMAS-INRA grant.

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Received 23 August 2007; accepted 22 July 2008Handling Editor: Atle Mysterud

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