genetic relatedness and home-range overlap among female black bears ( ursus americanus...

Genetic relatedness and home-range overlapamong female black bears (Ursus americanus) innorthern Ontario, Canada

Anita Schenk, Martyn E. Obbard, and Kit M. Kovacs

Abstract: The degree of philopatry exhibited by females in an unhunted black bear (Ursus americanus) populationoccupying the Chapleau Crown Game Preserve in northern Ontario was examined. A truncated kernel estimator wasused to identify home-range use. Pairs of adult females were categorized as having home ranges that had moderateoverlap or low overlap or were adjacent and non-overlapping or non-adjacent and non-overlapping. Females had lowoverlap with 6.4 other females, on average, and moderate overlap with 1.5 females. The degree of philopatry wasassessed using two methods, each of which was used in an attempt to examine home-range overlap and averagegenetic relatedness. Relatedness among bears was determined from DNA fingerprints, using an alkaline phosphataselabelled multilocus probe and chemiluminescence detection. The first method involved choosing the 3 oldest females inthe region to represent potential matriarchs, and all neighbouring females were identified (n = 8, 8, and 11). DNAfingerprints from each matriarch were compared with those of her neighbours. Average band-sharing coefficients andrelatedness estimates within the groups did not reveal patterns of close kinship. The second method involved band-sharing comparisons among pairs of females from each of the 4 home-range categories (n = 12, 57, 80, and 21).Again, no relationship between spatial proximity and average genetic relatedness (range 0.032–0.120) was suggested.The extensive home-range overlap exhibited by this population is not a consequence of natal philopatric tendencies.

Résumé: Nous avons étudié l’importance de la philopatrie chez des femelles d’une population protégée d’Ours noirs(Ursus americanus) dans la réserve de Chapleau, dans le nord de l’Ontario. Un coefficient d’estimation avec contrainte(truncated kernel estimator) a permis de délimiter les domaines. Les domaines de paires de femelles adultes sechevauchaient moyennement, se chevauchaient peu, ou alors étaient adjacents et ne se chevauchaient pas, ou encoren’étaient pas adjacents et ne se chevauchaient pas. Le chevauchement a été estimé faible en moyenne entre le domained’une femelle et celui de 6,4 autres et moyen entre le domaine d’une femelle et celui de 1,5 autre. Deux méthodes ontété utilisées pour évaluer l’importance de la philopatrie, les deux destinées à estimer le chevauchement des domaines etle degré moyen de parenté génétique. Le degré de parenté a été déterminé à l’aide d’empreintes d’ADN identifiées aumoyen de sondes multilocus marquées à la phosphatase alcaline et par détection à la chimioluminescence. Dans lapremière méthode, les 3 femelles les plus âgées de la région représentaient les matriarches probables et toutes lesfemelles voisines ont été identifiées (n = 8, 8 et 11). Les empreintes de chacune des matriarches étaient comparées àcelles de ses voisines. Les coefficients de similarité des bandes et les estimations de la parenté au sein d’un groupe ontdémontré que les femelles étaient peu apparentées. Dans la seconde méthode, il s’agissait d’évaluer la similarité desbandes entre des paires de femelles de chacune de quatre catégories de domaines vitaux (n = 12, 57, 80 et 21). Encorelà, il n’y avait pas de relation particulière entre la proximité spatiale et la parenté génétique moyenne (étendue 0,032–0,120). Le chevauchement important des domaines vitaux chez cette population n’est donc pas une conséquence detendances philopatriques congénitales.

[Traduit par la Rédaction] Schenk et al. 1519

Spatial patterns within mammalian populations are influ-enced by ecological factors as well as the dispersal charac-teristics of males and females (Crook 1970; Crook et al.1976). Sex-biased differences in dispersal patterns dependon the relative cost and benefit of dispersal to each sex andare associated with the mating system displayed by a popu-lation or species (Greenwood 1980; Pusey 1987). Male-biased dispersal is most prevalent in mammals (Packer1979; Greenwood 1980; Dobson 1982; Waser and Jones1983). In a promiscuous mating system, such as that foundin black bears (Ursus americanus) (Rogers 1987; Schenkand Kovacs 1995), parental investment by males is minimaland their reproductive success is limited by the number of

Can. J. Zool.76: 1511–1519 (1998) © 1998 NRC Canada

1511

Received August 11, 1997. Accepted March 4, 1998.

A. Schenk1 and K.M. Kovacs.2 Department of Biology,University of Waterloo, Waterloo, ON N2L 3G1, Canada.M.E. Obbard.3 Wildlife and Natural Heritage ScienceSection, Ontario Ministry of Natural Resources, P.O. Box7000, 300 Water Street, 3rd Floor North, Peterborough, ONK9J 8M5, Canada.

1Present address: Biological Data Services, 954242, R.R. #5,Orangeville, ON L9W 2Z2, Canada.

2Present address: UNIS (University Courses on Svalbard),Box 156, 9170, Longyearbyen, Svalbard, Norway.

3Author to whom all correspondence should be addressed(e-mail: [email protected]).

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females they encounter and with whom they successfullybreed (Trivers 1972). Dispersal by subadult males reducescompetition with male relatives for mating opportunities andincreases the probability of mating with unrelated females(Waser and Jones 1983). Further, dispersal may exposemales to a larger number of available female mating partners(Trivers 1972). In contrast, dispersal may cause females toincur heavy costs (Johnson 1986a). The reproductive suc-cess of female black bears is tightly linked to resource avail-ability (e.g., Bunnell and Tait 1981; Kolenosky 1990;Stringham 1990) and is proportional to the amount of energyavailable to rear young (Trivers 1972; Sandell 1989). If theenergy costs of dispersal are high, the onset of first repro-duction may be delayed in female mammals that are forcedto disperse, and may result in reduced lifetime reproductiveoutput (Johnson 1986a). The predominant energy cost ofdispersing for female black bears is probably that associatedwith foraging in unfamiliar areas (Rogers 1987).

Resource dispersion influences carnivore social structureand spatial organization (Macdonald 1983). Among bears,knowledge of food resources is developed through experi-ence (Rogers 1987; Mattson 1990). A nondispersing youngfemale can benefit directly from the continued use of hermother’s range (Waser and Jones 1983). This behaviour,termed natal philopatry, is widespread among female mam-mals (Packer 1979; Greenwood 1980; Dobson 1982) and hasbeen found in both gregarious and solitary species. Femaleblack bears have been documented to remain and be toler-ated within their natal areas beyond the age of independence(e.g., Rogers 1987; Elowe and Dodge 1989; Schwartz andFranzmann 1992). Although conspecifics may deplete foodsources and reduce foraging efficiency (Sandell 1989),philopatry may be a long-term maternal investment strategy(Johnson 1986b) that serves to maximize a female’s lifetimeinclusive fitness (Rogers 1987).

Natal philopatry could influence a female black bear’s re-productive output, as it is strongly correlated with nutritionalstatus (Rogers 1976; Bunnell and Tait 1981; Eiler et al.1989; Elowe and Dodge 1989; Kolenosky 1990; Stringham1990). For adult females, age is also positively correlatedwith reproductive rate (e.g., Kolenosky 1990; Stringham1990); younger individuals experience a greater decrease inreproductive success during food shortages (Stringham1990). This evidence suggests that for females, increasedforaging efficiency on established home ranges is importantfor success (Kolenosky 1990; Stringham 1990). Philopatrymay increase an offspring’s foraging efficiency (Rogers1976), resulting in a faster increase in body mass than in itsnonphilopatric counterparts (Rogers 1987). This results inearlier sexual maturity and larger litters for female blackbears that do not disperse (Rausch 1961; Jonkel and Cowan1971; Rogers 1976; Reynolds and Beecham 1980).

A correlate of natal philopatry, particularly among long-lived species, is that several generations of females may liveclose together (Waser and Jones 1983; Johnson 1986a). Thespatial configuration and utilization of home ranges are twomeasures that indicate philopatric behaviour (Waser andJones 1983). A system of overlapping home ranges suggeststhat portions of maternal home ranges are being shared withoffspring (Waser and Jones 1983). Black bear home-rangespatial patterns appear to be highly variable. Some studies

report territorial behaviour (Young and Ruff 1982; Rogers1987), while others have documented extensive overlapamong adult females (e.g., Lindzey and Meslow 1977;Garshelis and Pelton 1981; Horner and Powell 1990). Thisvariation has been attributed largely to habitat quality, whichis related to the abundance, concentration, and seasonalavailability of food (Macdonald 1983; Elowe and Dodge1989; Sandell 1989). The relationship between the spatialstructure and relatedness among females is largely unre-ported in these studies.

Traditional methods of assessing the degree of philopatryinvolve tracking subjects from birth to adulthood or examin-ing age differences in neighbouring individuals (Waser andJones 1983). Among bears, mother–daughter relationshipshave been followed from the birth of the offspring (Rogers1987), but are generally inferred from age differences(Garshelis and Pelton 1981; Pelchat and Ruff 1986). The re-cent application of molecular genetics to behavioural andecological postulates provides an opportunity to examine so-cial relationships within a reduced time frame. This studydescribes the spatial organization of females within a popu-lation of black bears in northern Ontario, using DNA finger-printing to estimate relatedness.

Study siteThis study was conducted within the Chapleau Crown Game

Preserve (CCGP) in northern Ontario (48°10´N, 83°20´W). Since1925, hunting and trapping have been prohibited within the pre-serve. The CCGP is located at the southern end of the boreal forestregion. The boreal forest experiences extreme seasonal variation inclimate, with a 3- to 4-month growing season and low rates of pri-mary productivity compared with temperate forests (Art and Marks1978; Bonan and Shugart 1989).

This study was part of an ongoing Ontario Ministry of NaturalResources research program examining the population dynamics ofblack bears. Bears were captured in barrel traps from mid-May toJuly in 1989–1991. The animals were immobilized, standardmorphometric measurements were taken, and a first premolar toothwas extracted for age estimation by cementum annuli counts(Stoneberg and Jonkel 1966). Females were fitted with radio col-lars and blood samples were collected and stored at –20°C untilDNA analyses were performed.

Radio-tracking and home-range analysisHome-range analysis was conducted on radio-tracking data col-

lected principally in 1991. One exception was the inclusion of datafor 2 females that died in the fall of 1990. Their home ranges wereestimated from 1990 radio-tracking data. Daily attempts weremade to locate collared bears using vehicle-mounted 3- to 5-element Yagi antennas from the time of den emergence or capturein the spring until den entry in late fall. Compass bearings weretaken either from two stations within 15 min or from more thantwo stations within 20 min, in order to minimize error due to bearmovement. Locations were estimated by maximum-likelihood esti-mators (Lenth 1981) using Locate II software (Pacer 1990) andwere recorded as Universal Transverse Mercator (UTM) coordi-nates to the nearest 50 m. Telemetry accuracy and errors associatedwith collecting radio-tracking data, such as observer and equip-ment error, were examined using blind tests, with radio collarsplaced throughout the study area in locations that were unknown tothe people performing the radio-tracking tests (Schenk 1994). Asubset of data from 15 bears across the study area was extracted to

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examine bearing variability due to topographical signal bounce.For each bear, 25 radio locations and bearing standard deviationswere estimated from those sessions that used 3 or more bearings.Differences among bears were tested.

Average error distance and bearing error standard deviationwere used to establish criteria for eliminating inaccurate locationsand as parameters for home-range analysis. Ground radio-trackingdata and visual observations were supplemented with fixes ob-tained from fixed-wing aircraft (Cessna 172 or Cessna 185) whensignals could not be received adequately from a road or when bearsranged outside of the study area. Locations separated by at least12 h were considered to be independent. Distinctive wide-rangingforaging excursions in mid to late summer (typically 6 to >20 kmfrom the home-range area) and consecutive locations within theaverage error distance from an individual animal’s den site in latefall were not included as locations for annual home-range analysisin this study.

Kernel density estimation (Worton 1987, 1989) is well suited foranalyzing range use (Harris et al. 1990; Seaman and Powell 1996).This method makes no a priori assumptions about the probabilitydistribution. Rather, the data set determines its own probabilitydensity function (Worton 1987). For this study, home ranges wereestimated using a truncated kernel estimator (Naef-Daenzer 1993a)using GRID software (Naef-Daenzer 1993b).

Home ranges were analyzed for each bear by superimposing a0.1 × 0.1 km grid onto the study area. Location densities were esti-mated at each grid intersection using kernel estimation. The contri-bution of each location to the density estimate was calculatedaccording to a bivariate normal distribution. The distribution wastruncated so that at each grid cell intersection, only locationswithin a radius of 1.5× bearing error standard deviation were in-volved in that particular density estimate (564 m; Schenk 1994).This truncated estimator improved the overall spatial resolution byremoving the influence of distant location fixes. Home-range over-lap among bears was estimated by examining areas of overlap de-fined by contours representing approximately 5 and 50% ofmaximal density. Four categories were defined to describe differentdegrees of home-range overlap: (1) non-adjacent, non-overlapping(NA-NO); (2) adjacent, non-overlapping (A-NO); (3) low degreeof overlap (LO; 5% of maximal density contour); and (4) moderatedegree of overlap (MO; 50% of maximal density contour). A pairof bears was considered non-adjacent if its home-range boundaries,defined by contours representing an area encompassing 5% ofmaximum density, were separated by 6 km (greater than 3× the av-erage home-range width (1.8 ± 0.45 km,n = 32)) or more. Pairsthat had non-overlapping ranges but were within 6 km of eachother were considered to be adjacent.

A known mother–daughter pairHome-range information for known mother–daughter pairs

within the CCGP population is limited, owing to the length of thestudy, yearling mortality, and dropped yearling radio collars. How-ever, the spatial relationship between one mother and her daughterwas examined in detail over a 3-year period (yearling home rangeuntil it was 3 years old). This radio-tracking information was col-lected from 1993 to 1995.

Preparation of DNA fingerprintsThe validity of using DNA fingerprinting to identify relation-

ships among black bears was confirmed using a blind test ofknown mother–offspring and sibling samples (n = 12) that werecorrectly identified (Schenk 1994).

The relationship between the spatial organization of females andtheir genetic relatedness was examined using two different meth-ods. The first was based on age. The 3 oldest females in the popu-lation in 1990 (aged 14, 16, and 20 years) were chosen to represent

possible “matriarchs.” Putative “matriarch groups” comprised allfemales occupying ranges categorized as having low or moderateoverlap with that of the matriarch, and those females that werecaptured within a matriarch’s range but otherwise lacked detailedhome-range information. DNA fingerprints of all 3 matriarchgroups (8, 11, and 8 bears; Table 1) were compared with those ofeach matriarch (3× 3 gels).

The second design involved comparing the DNA fingerprints ofbears with different degrees of home-range overlap (NA-NO,n =21; A-NO, n = 80; LO, n = 57; MO, n = 12). The selection of par-ticular pairwise comparisons depended on available DNA samplesand the quality of the DNA fingerprints. An average relatednessvalue (Reeve et al. 1992) was computed for each of the 4 catego-ries of home-range overlap.

Protocols used for DNA isolation and preparation of DNA fin-gerprints have been described in detail in Schenk (1994). Non-radioactive detection of DNA fragments was performed throughhybridization with alkaline phosphatase labelled oligonucleotides(Molecular Biosystems SNAP®) analogous to Jeffreys’ 33.6multilocus probes (Jeffreys et al. 1985a, 1985b) and detection witha chemiluminescent system (Tropix Southern Light).

DNA fingerprint analysisDNA fingerprints of matriarchs and each female within a puta-

tive matriarch group were structured so that they were comparedwithin 4 lanes of each other on a single gel. Pairwise comparisonsof bears with different degrees of home-range overlap were ana-lyzed regardless of lane position on a gel, but were limited to com-parisons within a gel. Autoradiograms were visually scored usingacetate overlays. The center of each band occurring between 1.4and 25 kilobases (kb) was marked. A match was declared when2 bands had similar electrophoretic mobility (±0.5 mm) and thesameapproximate intensity (following Westneat 1990). When1 band wasless than half the intensity of another band thathad the same electrophoretic mobility, or if it was obscured bya nearbyband, it was omitted from the total band count. Bandsthat had a population-wide frequency greater than 50% were omit-ted from the analysis in order to obtain an accurate estimate of re-latedness (Reeve et al. 1992). Band-sharing coefficients (S) werecalculated as 2NAB/(NA+ NB), whereNA andNB represent the totalband counts for individuals A and B andNAB represents the totalnumber of shared bands (Wetton et al. 1987; Lynch 1990). Thevalue ofS varies from 0 (no bands shared) to 1 (all bands shared).Relatedness was estimated using the formula described by Reeve etal. (1992), so that average relatedness (r) is calculated asS– b/1 – b,where S represents the average band-sharing coefficient within agroup andb represents the average band-sharing coefficient amongpresumably unrelated individuals. The value ofb was estimated us-ing male–female and male–male comparisons. It was calculated tobe 0.282 (n = 60). Relatedness of the known mother–offspring andsibling samples was estimated to examine the validity of using anaverage relatedness estimate. Based on an average band-sharingcoefficient of 0.677 (n = 12), average relatedness was estimated tobe 0.550, which is within the range expected for first-order rela-tionships.

Significance for all statistical tests was set at the 0.05α level.Averages are reported with standard deviations unless otherwisespecified.

Radio-trackingThe distance between estimated and actual collar loca-

tions from the telemetry accuracy test was 343 ± 245 m (n =87). There were no significant differences in bearing stan-dard deviation as calculated by Locate II (Pacer 1990) be-

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Schenk et al. 1513



tween the two types of receivers used (t34 = –0.525,p = 0.6),among observers (F[7.76] = 1.152, p = 0.34) or across thestudy area, therefore an overall standard deviation was cal-culated (6.95; Schenk 1994) and used for all radiolocationestimations. Based on the average error distance, the maxi-mum acceptable confidence ellipse used to eliminate inaccu-rate locations was calculated as 0.4 km2 (π r2; White andGarrott 1990).

During 1991, 40 female bears were radio-tracked. Over2500 locations were obtained, 1800 of which met the accep-tance criteria and were considered to be within the homeranges. Thirty-three bears had sample sizes of 30 or more lo-cations (49.6 ± 15.6) and were used in the home-range anal-ysis (Worton 1987). Home-range size, based on kernelestimation using the low-overlap contour, was 14.3 ±4.2 km2. Extensive home-range overlap among adult femaleswas observed in this population. A female had low overlapwith 6.4 ± 3.2 (range 1–15) females and moderate overlapwith 1.5 ± 1.0 (range 0–4) females.

DNA fingerprint analysisA sample of a DNA fingerprint hybridized and detected

with chemiluminescence detection methods is illustrated in

Fig. 1. The number of bands detected per fingerprint was30.9 ± 4.7 (n = 83). After common bands were omitted,15.1 ± 2.9 (n = 83) remained. A number of pairwise compar-isons were replicated on different gels. This permitted deter-mination of the degree of variability in band-sharingcoefficients between gels. From 126 replicates, the differ-ence in band-sharing coefficients was 0.062 ± 0.045.

Band-sharing coefficients between the 3 chosen matriarchswere determined to be 0.323 (matriarch 1 (M1) – matriarch2 (M2)), 0.417 (M1 – matriarch 3 (M3)), and 0.412 (M2–M3). These values are lower than the average band-sharingcoefficient of 0.677 determined for known first-order rela-tionships in this population. Therefore, the relationships be-tween the matriarchs themselves are unlikely to influenceother comparisons.

DNA fingerprint analysis of the 3 matriarchs and their re-spective groups revealed that the matriarchs were not consis-tently most closely related to neighbouring individuals(Table 1). Unexpectedly, M3 was related most closely togroup 2.

A detailed analysis using the 4 different categories ofhome-range overlap also showed no obvious relationship be-tween spatial proximity and degree of genetic relatednessamong females (Table 2). Negative relatedness values werereported in some categories, which are most likely due tosmall sample sizes and values that closely correspond tothose of presumably unrelated individuals within this popu-lation.

During the course of the DNA fingerprint analysis, severalpairs consistently revealed high band-sharing coefficients,above the average relatedness values observed amongknown kin relationships. However, no consistent relationshipbetween age, degree of home-range overlap, or relatednesscould be determined. Figure 2 and Table 3 illustrate exam-ples of the overall pattern of home-range overlap, which isclearly not the direct result of the social relationships amongadult females.

Figure 3 examines the spatial relationship between aknown mother–daughter pair for the first 3 years of inde-pendence. During the first 2 years the daughter showedmoderate home-range overlap with her mother. By the thirdyear they had only low home-range overlap. It appears thattheir home ranges are moving apart.

Black bear populations display a great deal of variation intheir spatial organization. Their behaviour is reported to

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1514 Can. J. Zool. Vol. 76, 1998

Fig. 1. Sample DNA fingerprints of 7 adult female black bears.Bear numbers are indicated along the bottom (“S” is seal DNA).Bands that were found to have a population-wide frequency of50% or more are indicated on the right-hand side (=) andmolecular weight markers (kb) are indicated along the left-handside.

M1 M2 M3

S r S r S r

Group 1 (8) 0.328 0.064 0.414 0.184 0.386 0.146Group 2 (11) 0.335 0.074 0.459 0.247 0.509 0.317Group 3 (8) 0.294 0.018 0.368 0.121 0.335 0.074

Table 1. Average band-sharing coefficients (S) and averagerelatedness estimates (r) for DNA fingerprint comparisonsbetween the 3 oldest female bears (matriarchs), M1, M2, andM3, and females within each matriarch group (groups 1, 2, and3; numbers in parentheses are the sample size for each group).



range from extensive home-range overlap (e.g., LeCount1980; Reynolds and Beecham 1980; Powell 1987) tointrasexual territoriality (e.g., Pelchat and Ruff 1986; Rogers1987; McCutchen 1990). It would be expected that territorialbehaviour would be the optimal spacing mechanism for fe-male black bears, since reproduction is strongly dependenton nutritional status and food is usually limited (e.g.,Bunnell and Tait 1981; Kolenosky 1990). Previous studieshave suggested that low-productivity areas, such as the bo-real forest, promote territorial behaviour (e.g., Powell 1987).However, the CCGP population, located in the boreal forest,exhibits extensive home-range overlap.

The most commonly documented spacing pattern forblack bears has been varying degrees of home-range overlap(e.g., Amstrup and Beecham 1976; Horner and Powell1990). It has been suggested that this may reflect a patternof intraspecific relationships (e.g., Jonkel and Cowan 1971;Lindzey and Meslow 1977). This supposition stems from thewidespread pattern of minimal dispersal by female blackbears away from the natal area during the first few years ofindependence (Reynolds and Beecham 1980; Elowe andDodge 1989; Clevenger and Pelton 1990; Schwartz andFranzmann 1992). In Alaska, Schwartz and Franzmann(1992) documented one instance of long-distance femaledispersal from a sample of 30 females. The individual thatmoved died that year. In the same study, 18 of 21 males dis-persed to non-adjacent areas. Similarly, in a study by Eloweand Dodge (1989), 1 of 13 females dispersed 15 km by age2, whereas males dispersed over distances ranging from 30to 200 km by the same age.

Minimal female dispersal and a system of overlappinghome ranges could result from mothers tolerating theirdaughters (Waser and Jones 1983). Tolerance of kin within afemale’s home range may evolve if there was guaranteedrecognition (Waser and Jones 1983) and increased inclusivefitness for tolerant mothers. Data on solitary as well as gre-garious mammals suggest that individuals do not behaveequally towards all conspecifics, but make distinctions basedon relatedness (Waser and Jones 1983). Among black bears,recognition among family members beyond the age of inde-pendence has been suggested (e.g., Rogers 1987; Clevenger

and Pelton 1990; Schwartz and Franzmann 1992). However,even if there were no means of recognition, natural selectionmay still favour increased tolerance among a class of indi-viduals if the probability of its neighbours being close kin ishigh (Waser and Jones 1983).

Detailed life histories of selected individuals were com-piled from birth through to adulthood in a 16-year study inMinnesota (Rogers 1987). All subadult females (n = 22)were philopatric at age 2, whereas 65% of the males had dis-persed by that age and all males dispersed by age 4 (n = 20).Mothers tolerated female offspring within and on the periph-ery of their territories and realigned their areas to allow theirfemale offspring to establish nearby (Rogers 1987).

A maternal-lineage structuring of the population, as sug-gested by Rogers (1987), was not evident in the CCGP pop-ulation. There was no pattern of intraspecific relationshipsamong adult females despite the extensive degree of home-range overlap displayed. The average relatedness betweenmatriarch groups was not different from the average amonggroups, indicating that home-range overlap was not re-stricted to closely related females. In the absence of an abil-ity to recognize close relatives beyond the age ofindependence, a strategy of tolerating neighbouring youngerfemales is likely to lead to invasion by unrelated cheaters,especially where resident females occupy prime habitat. Thismight explain the pattern of extensive home-range overlapamong distantly related females observed in the CCGP pop-ulation. However, there is no evidence that black bears innorthern Ontario are less likely to recognize female off-spring than black bears in Minnesota, so this explanation ofthe difference between the two populations does not seemtenable.

There are several possible reasons for the differences be-tween the results of Rogers’ (1987) study and the currentwork. Genetic analyses may be somewhat confounded bythe promiscuous mating pattern of black bears. The elevatedlevels of band-sharing among individuals likely result frombreeding among kin promoted by a longer life expectancyand a high density of bears in this protected population(Schenk and Kovacs 1996). Littermates may have differentfathers and neighbouring litters may have the same father

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NA-NO A-NO LO MO

Blot No. S n r S n r S n r S n r

1 0.358 13 0.107 0.352 38 0.098 0.420 12 0.193 0.376 3 0.1322 0.328 4 0.065 0.337 26 0.077 0.364 21 0.114 0.286 4 0.0063 0.389 2 0.149 0.259 4 –0.032 0.359 4 0.1084 0.402 3 0.167 0.348 19 0.093 0.358 19 0.106 0.413 4 0.1835 0.296 1 0.021 0.216 9 –0.092 0.366 15 0.118 0.285 3 0.0056 0.195 2 –0.120 0.314 13 0.046 0.340 11 0.081 0.322 2 0.057Average

acrossblots*

0.274 21 0.065±0.043 0.274 80 0.032±0.032 0.308 57 0.120±0.016 0.297 12 0.095±0.035

Note: NA-NO, non-adjacent, non-overlapping ranges; A-NO, adjacent, non-overlapping rages; LO, low degree of range overlap; MO, moderate degreeof range overlap.

*Overall band-sharing averages (w) for each category were calculated using average coefficient values for samples replicated on different blots. Geneticrelatedness (mean ± standard error from between-gel variation in relatedness estimates) for each category was estimated across all blots (w – b/1 – b;Reeve et al. 1992).

Table 2. Average band-sharing coefficients (S), sample sizes (n), and average relatedness estimates (r) for comparisons made betweenbears with different home-range spatial relationships.



(Schenk and Kovacs 1995). Therefore, paternal DNA adds asomewhat unpredictable amount of variance to relatednesscomparisons in this species.

Additionally, because home-range information in thisstudy is largely limited to adult females (age 8.3 ± 3.3 years,range 4–19 years;n = 42), there is a possibility that natalphilopatry may have been more prevalent than the data sug-gest. Subadult females may show a philopatric pattern in theCCGP (Fig. 3). It is possible that by sexual maturity, daugh-ters have moved sufficient distances in establishing theirown home ranges that they no longer overlap with theirmother. However, despite confounding factors such as theage of females and half-sister situations, it would be ex-

pected that occurrences of above-average relatedness wouldstill be reflected if natal philopatry was a primary factor in-fluencing the degree of home-range overlap.

There may be a real difference between the population un-der study here and Rogers’ (1987) population in Minnesota.A possible explanation for the lack of a discernible correla-tion between relatedness and spatial proximity in the CCGPmay be occasional but marked female dispersals. Occur-rences of high levels of relatedness among pairs of femalesthat were spatially separated suggest that such events occurin this population with some frequency. For example, the

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Bear1 Bear2 Age1 Age2 Overlap* S

1 2 9 6 NA-NO 0.444

2 3 6 10 NA-NO 0.444

3 4 10 10 NA-NO 0.546

4 5 10 14 NA-NO 0.412

1 6 9 8 A-NO 0.513

3 6 10 8 A-NO 0.559

4 6 10 8 A-NO 0.611

4 8 10 12 A-NO 0.588

5 6 14 8 A-NO 0.417

5 8 14 12 A-NO 0.606

6 7 8 20 A-NO 0.408

1 3 9 10 LO 0.319

3 7 10 20 LO 0.467

3 8 10 12 LO 0.444

6 8 8 12 LO 0.405

1 7 9 20 MO 0.582

1 8 9 12 MO 0.430

2 5 6 14 MO 0.397

6 9 8 6 MO 0.210

7 8 20 12 MO 0.334

*NA-NO, non-adjacent, non-overlapping ranges; A-NO, adjacent, non-overlapping ranges; LO, low degree of range overlap; MO, moderatedegree of range overlap.

Table 3. Band-sharing coefficients (S), home range overlapcategory, and ages for available pairwise comparisons of femalesdepicted in Figs. 2a and 2b.

Fig. 2. Spatial relationships among a sample of 9 female blackbears illustrating home-range sizes (using 5% of maximumdensity contour; low degree of overlap) (a), and core areas(using 50% of maximum density contour; moderate degree ofoverlap) (b). Numbers in circles and different stippling weightsrepresent different bears. Number on thex and y axes are UTMcoordinates (km).



high degree of relatedness between matriarch 3 and group 2suggests that this female dispersed away from an area occu-pied by relatives. Cases of adult female dispersal or immi-gration into a population have been documented in otherblack bear populations (e.g., Lindzey et al. 1983; Rogers1987; Kolenosky 1990).

It has been suggested that social intolerance and dispersalare responses to high levels of competition for food andspace among bears (Stokes 1970; Beecham 1980; Garshelisand Pelton 1981). These factors may be relevant for theCCGP population. Localized movement into the preservemay be promoted by the threat of nearby hunting. Densitiesin the preserve are high and individuals typically occupysmall home ranges. This may result in increased demandsbeing placed on the environment (Young and Ruff 1982;Nagy and Haroldson 1990). The system of overlappinghome ranges may be a response to the high densities ob-served in the CCGP. Adult females in this populationoccasionally occupy overlapping areas of their ranges simul-taneously. Avoidance behaviour may take place passivelybecause of patchy resource distribution in small areas or itmay be an active social response that limits neighbouring in-dividuals to core areas (Lindzey and Meslow 1977; Seamanand Powell 1990). The population substructures observed byRogers (1987) may occur only under certain density re-gimes.

The results of this study suggest that the degree of home-range overlap among black bears is not a consequence of aphilopatric tendency. It is likely that a combination of inter-related factors, such as high population density and the pat-tern of food distribution, contributes to the observed spatialorganization. In the past, the impact of philopatry on the so-cial organization of a population could only be assessed vialong-term (e.g., Hoogland 1982) or manipulative studies ofgenetic relatedness (e.g., Kawata 1987). The conclusionsreached in this study were made possible, in a greatly re-duced time frame, through the application of molecular tech-niques. Broader use of these techniques will allow us todetermine the prevalence of matriarchal assemblages inblack bears experiencing different resource regimes or, moregenerally, to evaluate the influence of relatedness on the dis-tribution and social organization of populations.

We thank G.B. Kolenosky for his support during thisstudy. We also thank the many field crew members who as-sisted with radio-tracking, D. Joachim for tooth aging, andD. Craughwell for helpful comments on initial drafts of themanuscript. This work was supported by the Ontario Minis-try of Natural Resources, a Natural Sciences and Engi-neering Research Council of Canada (NSERC) postgraduatescholarship to A.S., and NSERC research grants to K.M.K.

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Fig. 3. Home-range spatial relationship between a knownmother-daughter pair over a 3-year period. The mother’s homerange is represented by a solid line and the stippled area is thecore of her range. The daughter’s home range is represented bya broken line and the hatched area is the core of her range.Numbers on thex and y axes are UTM coordinates (km).



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