Resource partitioning among cape foxes, bat-eared foxes, and black-backed jackals in South Africa

Research Article

Resource Partitioning Among Cape Foxes,Bat-Eared Foxes, and Black-Backed Jackals inSouth Africa

JAN F. KAMLER,1 Wildlife Conservation Research Unit, The Recanati-Kaplan Centre, Department of Zoology, Oxford University, Tubney House,Abingdon Road, Tubney, Abingdon OX13 5QL, United Kingdom

UTE STENKEWITZ,2 Wildlife Conservation Research Unit, The Recanati-Kaplan Centre, Department of Zoology, Oxford University,Tubney House, Abingdon Road, Tubney, Abingdon OX13 5QL, United Kingdom

UNN KLARE, University of Rostock, Weberstrasse 11, 18069 Rostock, Germany

NICOLAS F. JACOBSEN,3 Wildlife Conservation Research Unit, The Recanati-Kaplan Centre, Department of Zoology, Oxford University,Tubney House, Abingdon Road, Tubney, Abingdon OX13 5QL, United Kingdom

DAVID W. MACDONALD, Wildlife Conservation Research Unit, The Recanati-Kaplan Centre, Department of Zoology, Oxford University,Tubney House, Abingdon Road, Tubney, Abingdon OX13 5QL, United Kingdom

ABSTRACT Cape foxes (Vulpes chama) and bat-eared foxes (Otocyon megalotis) are sympatric with black-backed jackals (Canis mesomelas) over much of southern Africa, although competition with and/or predationby jackals may suppress local populations of both fox species. From 2005 to 2008, we captured, radio-collared,and monitored 11 cape foxes, 22 bat-eared foxes, and 15 black-backed jackals on a game ranch in SouthAfrica to investigate their spatial, habitat, temporal, and dietary resource overlap. Mean annual home-rangesizes were 27.7 km2 for cape foxes, 5.0 km2 for bat-eared foxes, and 17.8 km2 for jackal family groups. Homeranges overlapped completely between species, although core areas overlapped less (<45%), with cape foxesand jackals overlapping the least (12%). When active, cape foxes, but not bat-eared foxes, used core areas ofjackal groups less than expected. Additionally, both fox species used jackal core areas less than expected fortheir den sites, suggesting areas outside jackal core areas were used as refuges by foxes. Strong levels of habitatpartitioning were not apparent at the study site or home-range levels, although habitat selection for den sitesdiffered between jackals and cape foxes. Jackals were the most diurnal across seasons, whereas cape foxes werethe most nocturnal. Diets overlapped little (R0 ¼ 0.20–0.34) among the canid species, with bat-eared foxesoverlapping the least with the others. Jackals killed at least 5 collared bat-eared foxes and 1 collared cape fox,indicating potential interference competition, probably for exclusive use of territorial space rather than overshared resources. We conclude that bat-eared foxes coexisted with jackals primarily by their dietaryspecialization and group living. Cape foxes coexisted with jackals by exhibiting high levels of spatial, habitat,temporal, and dietary partitioning. Surprisingly, the fox species exhibited positive associations with eachother. Our results show themechanisms that may allow jackals to suppress fox populations, yet also show howfoxes, in turn, use different mechanisms to coexist with a dominant canid. � 2012 The Wildlife Society.

KEY WORDS bat-eared fox, black-backed jackal, Canis mesomelas, cape fox, interspecific killing, Otocyon megalotis,resource partitioning, South Africa, Vulpes chama.

Throughout most of southern Africa, 3 species of canids arewidespread and sympatric, the cape fox (Vulpes chama, 2–4 kg), bat-eared fox (Otocyon megalotis, 3–5 kg), and black-backed jackal (Canis mesomelas, 6–12 kg; Skinner and

Chimimba 2005). Previous research suggested black-backedjackals may be suppressing local populations of both foxspecies, indicating potential interspecific competition be-tween the jackals and foxes. For example, across 22 sitesin South Africa, predator control measures decreased black-backed jackal numbers, which positively influenced cape foxand bat-eared fox numbers (Blaum et al. 2009). Additionally,in the 1980s cape foxes exhibited range-wide declines innumbers (Ginsberg and Macdonald 1990, Nowak 1999)that coincided with range-wide increases in black-backedjackal numbers (Ginsberg and Macdonald 1990).Interspecific competition can occur as either exploitationor interference (Case and Gilpin 1974), although whether

Received: 3 February 2011; Accepted: 2 December 2011

1E-mail: [email protected] address: Faculty of Life and Environmental Science, School ofEngineering and Natural Sciences, University of Iceland, Askja,Sturlugata 7, 101 Reykjavık, Iceland.3Present address: Department of Recreation, Park, and TourismSciences, Texas A&M University, 2261 TAMU, College Station,TX 77843, USA.

The Journal of Wildlife Management; DOI: 10.1002/jwmg.354

Kamler et al. � Resource Partitioning by Foxes and Jackals 1

either or both occur between jackals and foxes in SouthAfrica is unclear. Anecdotal reports describe black-backedjackals killing cape foxes (Stuart and Stuart 2004) and bat-eared foxes (Schaller 1972, Nel and Maas 2004), althoughit was not clear if killings were due to competition or foodacquisition.Interspecific killing is common among mammalian carni-

vores (Palomares and Caro 1999), and appears to be espe-cially strong within canids, probably because species withinthe same family are constrained by similar ecological needs(Macdonald and Sillero-Zubiri 2004, Donadio and Buskirk2006). Consequently, population suppression or displace-ment of smaller canid species by the next larger canid speciesoften has been reported (Sargeant et al. 1987; Hersteinssonand Macdonald 1992; Peterson 1995; Ralls andWhite 1995;Fedriani et al. 2000; Tannerfeldt et al. 2002; Kamler et al.2003b, c), and may be a common phenomenon among sym-patric canids. To avoid competition and to coexist with largercanids, intraguild-predation theory indicates subordinatespecies could partition resources (Polis et al. 1989). Infact, relatively high levels of resource partitioning havebeen observed among canid species, thus facilitating coexis-tence of different sized species (Major and Sherburne 1987,Thurber and Peterson 1992, Arjo and Pletscher 1999,Fedriani et al. 2000, Nelson et al. 2007). Nevertheless,relatively low levels of resource partitioning also have beenobserved between sympatric canids (Theberge and Wedeles1989,White et al. 1995, Kitchen et al. 1999, Neale and Sacks2001, Carrera et al. 2008, Kozlowski et al. 2008), indicatingresource partitioning may not always be a mechanism forcoexistence among canid species. Clearly, the levels of com-petition, interspecific killing, and resource partitioning varyconsiderably among canid communities, probably becauseof differences in available resources (e.g., prey size anddensity), and interspecific differences in body size and eco-logical niches.Little is known about the interspecific relationships of cape

foxes, bat-eared foxes, and black-backed jackals, as thesespecies have never been studied together. Thus, how the 2fox species coexist with jackals, or how all 3 species partitionspace and other resources among themselves is unknown. Forexample, cape foxes and black-backed jackals may have highdietary overlap, because both species reportedly consumesmall- and medium-sized mammals (Loveridge and Nel2004, Stuart and Stuart 2004). In contrast, bat-eared foxeshave specialized adaptations for consuming insects, primarilytermites (e.g., Hodotermes spp.; Maas and Macdonald 2004),thus they likely have reduced competition with other canidsfor food. That said, cape foxes and black-backed jackals alsoconsume termites and other insects, whereas bat-eared foxescan consume small rodents (Skinner and Chimimba 2005,Klare et al. 2011), thus relatively high dietary overlap poten-tially exists among all 3 canid species. Additionally, compe-tition may occur between bat-eared foxes and other canids forlimited den sites, foraging areas, and optimal habitat. Indeed,because the 2 fox species are similar in body size, potentialcompetition may be greater between them than that betweenthe foxes and jackals (Rosenzweig 1966).

Understanding the level of resource partitioning within thesouthern African canid community will enhance our knowl-edge not only of the ecology and behavior of each species, butalso of the behavioral interactions between them. For exam-ple, information on how all 3 canid species interact couldhelp biologists anticipate changes in canid numbers based onmanagement decisions. Research on this community mightbe particularly useful for understanding canid interactionsbecause the fossil record of these 3 species, and their directancestors, reaches back at least 2.5 million years in southernAfrica (Turner 1990, Walton and Joly 2003, Clark 2005),and genetic data suggests all 3 species were isolated togetherin Africa up to 4–5 million years ago (Wayne et al. 1990,Geffen et al. 1992). Consequently, the mechanisms of coex-istence among these sympatric canids likely have a longevolutionary history. Therefore, we examined resource par-titioning and potential for competition among cape foxes,bat-eared foxes, and black-backed jackals in South Africa bydetermining the spatial, habitat, temporal, and dietary over-lap among species. We also identified mortality factors todetermine the potential for interference competition.

STUDY AREA

We conducted research on Benfontein Game Farm (hereaf-ter, Benfontein; 110 km2; 288530S, 248490E), nearKimberley, South Africa. Benfontein was managed primarilyfor wild ungulate species, including springbok (Antidorcasmarsupialis), blesbok (Damaliscus dorcas), and black wilde-beest (Connochaetes gnou), along with some domestic cattle(Bos taurus). All large (>15 kg) carnivore species were extir-pated from this area prior to 1900 (Skinner and Chimimba2005). In addition to the canids, other carnivore speciespresent included aardwolves (Proteles cristatus), caracals(Caracal caracal), African wild cats (Felis silvestris), black-footed cats (Felis nigripes), small-spotted genets (Genettagenetta), striped polecats (Ictonyx striatus), and at least 5species of Herpestidae. Aside from 1 or 2 annual culls forungulates on Benfontein, there is relatively little humanactivity. No carnivore species was heavily persecuted onBenfontein during the study, although jackals were occa-sionally shot (<3 jackal/yr) during culling operations forungulates. Vegetation on Benfontein contained elementsof 3 major biomes, Savanna, Nama Karoo, and Grassland,although the most dominant was Nama Karoo vegetation(66% of study area). The area had a semi-arid continentalclimate, with a distinct cold and dry period during winter(Jun–Aug) and a hot and rainy period during summer (Dec–Feb), with intermediate rainfall and temperatures duringspring (Sep–Nov) and autumn (Mar–May; Sliwa 1996).The mean (�SD) annual rainfall of nearby KimberlyAirport (1960–2007) was 419 � 134 mm, although the an-nual rainfall for 2006 (497 mm) and 2007 (539 mm) wasabove the long-term mean (South African Weather Service,unpublished data).

2 The Journal of Wildlife Management

METHODS

Capture, Monitoring, and MortalityWe captured cape foxes and bat-eared foxes using wire boxtraps (50 cm � 50 cm � 120 cm) baited with meat scraps.We placed traps along dirt roads and intersections through-out the study site, with>0.5 km separating each trap.We settraps in specific locations for approximately 1 week, thenmoved them so that all areas of the study site were coveredduring the trapping period. Trapping only occurredduring the winter (May–Aug) to avoid capturing juvenilesand pregnant females. We set traps just prior to sunset,checked at sunrise, then left them closed during the day.We fitted captured cape foxes with radio collars (AdvancedTelemetry Systems, Inc., Isanti, MN) weighing 40 g (i.e.,approx. 1% of body mass), whereas we fitted bat-eared foxeswith radio collars weighing 40 g or 60 g (i.e., 1–2% of bodymass). Black-backed jackals do not readily enter cage traps(Fuller et al. 1989), thus we captured this species usingpadded foothold traps (Woodstream Corp., Lititz, PA)set along dirt roads and intersections throughoutBenfontein (Kamler et al. 2008). We set padded footholdtraps with a high pan tension to exclude species smaller thanjackals (Kamler et al. 2008). We fitted captured jackals withradio collars weighing 190 g (i.e., approx. 2% of body mass).All study animals were sexed, weighed to the nearest0.1 kg, and aged as adult (�12 months old) or yearling(9–11 months) according to tooth wear, body size, andreproductive condition. We compared differences in meanadult body mass among species using analysis of variance(ANOVA). We followed the animal care and use guidelinesof the American Society of Mammalogists (Gannon et al.2007) and our research protocol (#0401/05) was approvedby the Department of Tourism, Environment andConservation, Northern Cape Province, Kimberley, SouthAfrica.We located study animals 2–3 times per week primarily

during late afternoon, crepuscular, and nocturnal hours whenmost were active. We radio tracked from a vehicle using anull-peak system consisting of dual 4-element yagi antennas.We also radio tracked on foot using 3-element hand-heldantennas to locate den sites. When locating study animals,observers took �2 readings from known telemetry stations<5 minutes apart. We calculated location estimates usingthe maximum likelihood estimation option in the programLocate II (Pacer, Inc., Truro, Nova Scotia, Canada). Mean(�SE) error of estimated locations was 57.3 (�6.3) m whenusing reference collars (n ¼ 29) placed at known locations0.8–1.5 km from observers (i.e., typical distance when track-ing animals). We assumed locations for individual animals tobe independent for all analyses because only 1 location peranimal was obtained during 6- to 8-hour tracking sessions.Mortality sensors identified when collars were stationary

for >6 hours. We immediately recovered carcasses when amortality signal was detected. We classified causes of mor-tality as predation, human-related, natural, or unknown. Weconcluded foxes died of predation when carcasses had caninepuncture wounds associated with subcutaneous hemorrhag-

ing, indicating the animals were alive when attacked. Weidentified the predator species responsible by examiningfeatures of carcasses (i.e., size and placement of bite marks)and evidence at kill sites (i.e., tracks and pattern of consump-tion; Roberts 1986). We classified causes of mortality asunknown if carcasses were missing or had no visible evidenceof cause of death.

Home Ranges

We determined annual home ranges using the 96% mini-mum convex polygon (MCP) method as calculated by theAnimal Movement extension (Hooge and Eichenlaub 1997)in ArcView 3.2 (Environmental Systems Research Institute,Inc., Redlands, CA). We used 96% MCP because whencompared to other methods (i.e., kernel and harmonicmean) and other percentages, it was shown to be the mostaccurate method for fitting estimated home ranges to actualterritories for coyotes (Canis latrans; Shivik and Gese 2000),thus it would likely work best for other territorial canids aswell. The MCP method is likely more appropriate for terri-torial canids than other methods because home ranges equalterritories (i.e., defended and exclusively used areas) forresident canids (Shivik and Gese 2000), and their territoryboundaries are behaviorally well defined (Gese 2001, Nealeet al. 2007) and rigorously marked (Shivik and Gese 2000).Because black-backed jackals and cape foxes are highly ter-ritorial towards non-group conspecifics (Loveridge and Nel2004; J. F. Kamler, Oxford University, unpublished data), weassumed 96% MCP would best approximate their home-range boundaries. For consistency, we also used 96% MCPfor calculating home ranges of bat-eared foxes, although thisspecies was not as territorial towards conspecifics as the otherspecies. Finally, because MCP is relatively insensitive todispersion of locations within home ranges, it was moreappropriate than kernel and other methods for determiningavailability when analyzing the use of core areas and habitattypes within home ranges (see Habitat Use below for details).We calculated core areas, which are areas of concentrated

use within home ranges (Laundre and Keller 1981, Springer1982), using the 50% MCP method. Core areas were bio-logically relevant for territorial canids on our study sitebecause they encompassed all known natal dens of eachpair or group, and were generally centered within homeranges (i.e., away from boundaries where trespassing wasmore likely). Area-observation curves showed home rangesfor individuals of all species were effectively determined bythe first 30 locations, thus we calculated home ranges andcore areas only for animals with �30 locations and �9months of tracking. If we tracked individuals across multipleyears, then we only used the home range calculated duringthe first year in analyses. For territorial and pack-living Canisspecies, home ranges of individuals accurately reflect those ofits pack (Shivik and Gese 2000), therefore we calculatedhome ranges for family groups of jackals in lieu of individualhome ranges to simplify analyses and comparisons. Thisallowed us to use locations from nearly all radio-collaredjackals, while increasing sample sizes per group. On our studysite, 4–5 adult group members defended a territory, although


they rarely foraged together, so we combined locations of upto 4 radio-collared jackals to calculate group home ranges.We made an exception for radio-collared adult mated pairs,as we only used locations from 1 of the pair in analysisbecause pairs foraged together >70% of the time, thuslocations were not independent. Initial analysis showedhome ranges and core areas of jackal groups remained stablethroughout the study period, despite different individualsbeing monitored in different years within the same group.Therefore, we calculated a single home range and core areafor each jackal group.

DensityWe estimated the pre-whelping density of each canid speciesbased on the number of mated pairs or family groups col-lared, multiplied by the mean number of adult animals pergroup, divided by the total area occupied by collared animals.We calculated a single density estimate from mid-2006 tomid-2007, when we monitored most of the radio-collaredanimals simultaneously, and assumed density to be stablethroughout the study period. Cape foxes were monogamousand territorial, and home ranges of the fox pairs were adja-cent to each other, thus we were confident we collared alladult cape foxes within our trapping area. Bat-eared foxeswere numerous and easily observed on Benfontein.Therefore, we attempted only to collar 1 member of eachgroup, and we focused on monitoring adjacent groups at thecenter of Benfontein. Mean number of adult bat-eared foxesper group was determined by walking in on collared foxes ona monthly or bimonthly basis and counting other adultswithin the group. We noted uncollared groups within thetrapping area and included them in the density estimate. Wedetermined mean number of adult jackals per group byobserving and counting adult jackals at natal dens, and byopportunistically counting uncollared jackals that were reg-ularly observed within core areas of jackal groups. Becauseblack-backed jackal groups are territorial with exclusivecore areas (Loveridge and Macdonald 2001), and all groupswe monitored were adjacent to each other, we were confidentthat we collared all jackal groups within the trapping area.To determine if group sizes of bat-eared foxes influenced

their susceptibility to jackals, we compared mean group sizesof those foxes that died from jackal predation to group sizesof other collared foxes using a t-test.

Spatial RelationshipsWe compared spatial overlap of annual home ranges and coreareas between species. After initial analysis showed completeinterspecific overlap of annual home ranges, we calculatedthe mean percent overlap of individual core areas betweenspecies. We analyzed spatial comparisons only if 1) wemonitored individuals from different species simultaneouslyfor >1 month and 2) we were confident that we radio-collared all individuals or groups from other species thatoccurred within any individual core area. For each studyanimal, we determined percent area overlap with other spe-cies by dividing the overlap area by its total core area.We alsocalculated point overlaps in addition to area overlaps becausethe latter can be misleading as it considers area of the range

covered rather than area used (Kernohan et al. 2001). Percentpoint overlap was determined for each canid by summing thenumber of its locations that fell within the overlap area,divided by the total number of locations within its corearea. For each fox species, we compared point overlapsbetween the other 2 species using Mann–Whitney U-tests.We examined interspecific avoidance of core areas based on

2 types of data: 1) active locations and 2) den-site locations.To determine if foxes avoided other core areas within theirhome ranges while active, we compared number of activelocations within other core areas to that expected (based onpercent of other core areas within individual home ranges)using compositional analysis (Aebischer et al. 1993; seeHabitat Use below for more details about this method).Individual foxes were the sampling unit in this analysis,and we assumed their movements were independent ofeach other.Den sites included 1) burrows that were dug by other

animals, primarily springhares (Pedetes capensis) and aard-varks (Orycteropus afer); and 2) small depressions aboveground, primarily underneath bushes and shrubs and some-times in hollowed-out termite (Trinervitermes trinervoides)mounds (the latter for foxes only). The locations of den siteswere not independent across individuals within each species,because dens were used alternatively, and sometimes simul-taneously, by different individuals of the same species, andthe same individual may have used a particular den on severaldifferent occasions for various periods of time. Therefore, todetermine if foxes avoided other core areas at the study-sitelevel, we grouped all den locations for each fox species, andconsidered the den locations as the independent samplingunits. We compared den sites found within core areas ofother species to that expected using chi-squared goodness-of-fit tests. To calculate expected values, we determined thepercent of other core areas within the entire area occupied byeach fox species, using 100% MCP based on all locationsfrom each species (Kamler et al. 2003a), then multiplied thepercentage by the total number of den sites.

Habitat Use

We had 2 major analyses of habitat selection in our studybased on active locations and den-site locations. For bothanalyses, we generated used and available habitat types usingArcView 3.2. We delineated habitat types using GeographicInformation System (GIS) data provided by the EcologyDivision, De Beers Consolidated Mines, Kimberley,South Africa. Habitat types previously were determinedusing the Braun Blanquet method, and classified into 6categories: pan basin, pan slope, bushveld, savanna, and other(Hauptfleisch 1998). Pan basin (5.1% of Benfontein) oc-curred on an ephemeral lake (i.e., pan) and consisted ofNama-Karoo vegetation, dominated by small shrubs andshort (<30 cm) grasses. Pan slope (60.5%) consisted ofNama-Karoo vegetation surrounding pan basins, whichalso was dominated by small shrubs and short grasses.Bushveld (17.8%) consisted of savanna vegetation, dominat-ed by scattered trees and tall grasses. Pure savanna (11.8%)was dominated by tall grasses mixed with some shrubs. Other


included various habitats with low (<3%) occurrence such aspure grassland and wetland.To determine if the canid species partitioned habitats while

active, we used compositional analysis (Aebischer et al. 1993)to compare habitat use versus available for each species at 2spatial levels: within the study site, and within individualhome ranges. We determined habitat selection of activelocations for all study animals that met the requirementsfor home-range calculations (see above). We assumed therewere no between-year differences in habitat use, especiallygiven that canid densities remained the same during thestudy; thus, we pooled across years. Because jackals andbat-eared foxes foraged in groups, the location of 1 repre-sented the location of several individuals of different sexes,thus we also pooled across sexes for a single analysis of eachspecies. All species had access to all habitat types at the study-site level, based on 100% MCP using all locations of eachspecies. Compositional analysis uses the animal as the sam-pling unit, thus it avoids problems related to 1) samplinglevel; 2) non-independence of proportions; 3) differential useby groups of animals; 4) arbitrary definition of habitat avail-ability; and 5) pseudoreplication (Aebischer et al. 1993). Anassumption of compositional analysis is that animals behaveindependently, which has been used to criticize this method(Manly et al. 2002). Alternative methods using logisticregression have been developed to examine resource selec-tion, primarily resource selection functions (RSF; Manlyet al. 2002). The RSFs can be modeled using various tech-niques such as Akaike’s Information Criterion (AIC; Manlyet al. 2002) and more recently utilization distributions (UD;Millspaugh et al. 2006). However, despite their increasinglywidespread use, approaches that use logistic regressionmay not give correct estimates of resource selection, exceptunder fairly restrictive and usually unconfirmed conditions(Keating and Cherry 2004). Additionally, newer methodssuch as UD have even more drawbacks because the choiceof the UD estimator is sensitive to sample size and user-defined options such as bandwidth and software selection(Millspaugh et al. 2006). Clearly, the theory and appropri-ateness of different resource selection methods is still debat-able (Strickland and McDonald 2006) and no method isuniformly superior (Millspaugh et al. 2006). Consequently,we chose compositional analysis to determine habitat selec-tion for active locations because it appears to be one of themost robust and least controversial methods that is based onthe fewest number of assumptions and user-defined optionsand is less sensitive to sample sizes.The locations of den sites were not independent across

individuals within each species (see Spatial Relationshipsabove for more details). Therefore, to determine if foxesand jackals exhibited habitat partitioning for den sites, wegrouped all den locations for each species, and consideredthe den locations as the independent sampling units. Foreach species, we compared habitat use of den sites versusexpected using chi-squared goodness-of-fit tests. To calcu-late expected values, we determined the percent of differenthabitat types within an availability polygon, using 100%MCP based on all locations of each species (Kamler et al.

2003a), then multiplied the habitat percentages by the totalnumber of den sites. If significance occurred, we usedBonferroni Z-statistics (Byers et al. 1984) to determinewhich habitat types contributed most to lack of fit.

Activity PeriodsWe analyzed activity patterns to determine if the canidspecies exhibited temporal partitioning.We recorded activityfor each study animal while obtaining point locations.When obtaining the last azimuth for triangulation of studyanimals, observers listened for 1 minute and recorded thesignal as active if it had distinct attenuation, or inactive if ithad indistinct or absent attenuation (Kozlowski et al. 2008).We used 3 periods for comparative analyses: day, sunset, andnight. We classified sunset as a 2-hour period, 1 hour beforeand 1 hour after sunset. We classified day as a 6-hour periodpreceding the sunset period and night as a 6-hour periodsucceeding the sunset period. Sample sizes were too low toinclude a sunrise period. We pooled data across years, andcalculated the percent active locations for each study animalduring each period. We used general linear models (GLM)on arcsine-transformed variables (i.e., proportion of activelocations per period), weighted relative to the number oflocations per individual (Hn; n ¼ number of fixes), to eval-uate relationships of activity with species, time period, andindividual (Harrington and Macdonald 2008). Thus, indi-viduals were the sampling unit, and we nested these datawithin species to account for repeated use of the sameindividuals over time. The most relevant interaction termwas species � time, which tested whether the effect oftime was dependent on species. If significance occurred,then we analyzed 2-way interactions between species. Weanalyzed activity data in Minitab 13 (Minitab, Inc., StateCollege, PA).Previous researchers documented significant changes in

bat-eared fox activity between the wet and dry seasons insouthern Africa, primarily due to changes in termite activity(Nel 1990, Nel andMaas 2004). Therefore, we classified datafor all species into 2 broad seasons: wet season (Sep–Feb) anddry season (Mar–Aug). Consequently, we included season inthe initial GLMmodel to determine if there was a significantspecies � season interaction.

Dietary AnalysisWe determined food habits of each species by analysis ofscats. For jackals, we collected scats by seasonally walkingtransects established on Benfontein (for details see Klareet al. 2010). For cape foxes and bat-eared foxes, we collectedtoo few scats along transects, so we made additional collec-tions each season around their den sites.We classified scats tospecies based on size and shape (Chame 2003). We definedseasons as spring (Sep–Nov), summer (Dec–Feb), autumn(Mar–May), and winter (Jun–Aug), to parallel major changesin climate and corresponding changes in food resources. Toobtain adequate sample sizes (37–93 scats/species) for eachseason, we pooled scats across years. Sample sizes of scatswere not adequate for cape foxes in summer; thus, we ex-cluded these from analyses. Following collection, we proc-essed scats in a laboratory to identify prey items (for more


details see Klare et al. 2010). We weighed the dried remainsfrom each scat, and visually estimated volume of each undi-gested food item in the scat to the nearest 5%. We calculatedingested biomass based on the weight of dried remains usingcorrection factors provided by Goszczynski (1974) supple-mented with those from Jedrzejewska and Jedrzejewski(1998). We grouped prey species into the following 10taxonomic–ecological categories: small mammals (<1 kg),hares (Lepus spp.) and springhares, small carnivores, largemammals (i.e., ungulates), squamates, tortoises, birds,arthropods, vegetation, and fruits. We did not includeunidentified mammals in analyses. To test for differencesin the diet composition between species each season, we useda Monte Carlo permutation (using the unimodal modelcanonical correspondence analysis) performed with the com-puter program Canoco 4.5 (Canepuccia et al. 2007). Todetermine degree of dietary overlap between species eachseason, we calculated Horn’s index of overlap (R0; Krebs1989) using biomass of prey categories consumed. Finally, wecalculated Levin’s measure of niche breadth (B; Krebs 1989)for each species using frequency of occurrence of preycategories.Unless otherwise noted, we performed all statistical analy-

ses using the program SPSS 14.0 (SPSS, Inc., Chicago, IL),and deemed differences significant when P � 0.05.

RESULTS

We captured, radio-collared, and monitored 11 cape foxes,22 bat-eared foxes, and 15 black-backed jackals from June2005 to February 2008. The mean (�SE) adult body masswas different (P < 0.001) among cape foxes (2.9 � 0.1 kg,n ¼ 11), bat-eared foxes (3.7 � 0.1 kg, n ¼ 7), and black-backed jackals (9.0 � 0.2 kg, n ¼ 11). Of 3 confirmeddeaths of cape foxes on Benfontein, 1 was from jackalpredation, 1 was from caracal predation, and 1 was natural(den collapsed during heavy rains). Of 7 confirmed deaths ofbat-eared foxes on Benfontein, 5 were from jackal predation,1 was probable jackal predation (i.e., collar was found withteeth marks and within jackal core area), and 1 was unknown(jackal predation was not ruled out). Of 2 confirmed jackaldeaths on Benfontein, 1 was human-related (hunted) and1 was natural (possibly disease). Jackals did not consume2 foxes (1 cape fox, 1 bat-eared fox) they killed, whereas theydid consume (>50% of carcass) the remaining 4 bat-earedfoxes they killed, and presumably the additional bat-earedfox they probably had killed. Mean (�SE) group size ofbat-eared foxes that died from jackal predation (2.54 �0.40 foxes/group, n ¼ 5) was smaller (P ¼ 0.009) thanthat of other collared groups (4.33 � 0.33 foxes/group,n ¼ 14). Estimated pre-whelping densities were 0.49 fox/10 km2 for cape foxes, 10.70 foxes/10 km2 for bat-earedfoxes, and 3.25 jackals/10 km2 for black-backed jackals.We obtained 610 locations on cape foxes, 1,464 locations

on bat-eared foxes, and 1,025 locations on black-backedjackals. Mean (�SE) annual home ranges were 27.68 �1.45 km2 (n ¼ 5) for cape foxes, 4.96 � 0.32 km2 (n ¼16) for bat-eared foxes, and 17.75 � 1.47 km2 (n ¼ 6) forjackal groups. Mean (�SE) core areas were 5.29 � 0.32 km2

for cape foxes, 0.72 � 0.10 km2 for bat-eared foxes, and3.35 � 0.42 km2 for jackal groups. Mean number of jackalsradio-collared per group was 2.33 (range ¼ 1–4). Annualhome ranges overlapped completely among species, althoughcore areas showed more segregation (Fig. 1). For cape foxes,mean point overlap of core areas was 24.3% (range ¼ 20–28%) with bat-eared foxes, and 12.2% (5–20%) with jackals.For bat-eared foxes, mean point overlap of core areas was44.1% (0–100%) with cape foxes, and 36.0% (0–81%) withjackals (Fig. 1). Mean area overlaps gave similar results, andfor cape foxes were 24.4% with bat-eared foxes, and 16.6%with jackals. Mean area overlaps for bat-eared foxeswere 40.7% with cape foxes, and 36.2% with jackals. Forcape foxes, we found greater (P ¼ 0.043) point overlap ofcore areas with bat-eared foxes than with jackals. For bat-eared foxes, point overlap of core areas was similar(P ¼ 0.592) between cape foxes and jackals.Compositional analysis of active locations showed that cape

foxes used jackal core areas within their home ranges lessthan expected (x2

1 ¼ 3:69, P ¼ 0.054), whereas they usedcore areas of bat-eared foxes in proportion to availability(x2

1 ¼ 1:58, P ¼ 0.209). Bat-eared foxes used jackal core

Figure 1. Annual home ranges (A) and core areas (B) of cape foxes (n ¼ 4),bat-eared foxes (n ¼ 11), and black-backed jackal groups (n ¼ 6) monitoredsimultaneously on Benfontein Game Farm (gray outline), South Africa,2006–2007.


areas within their home ranges in proportion to availability(x2

1 ¼ 0:09, P ¼ 0.770), whereas they used core areas of capefoxes more than expected (x2

1 ¼ 3:92, P ¼ 0.047).At the study site level, the den sites (n ¼ 135) of cape foxes

occurred in jackal core areas less than expected (x21 ¼ 34:43,

P < 0.001; Fig. 2), whereas they occurred in core areasof bat-eared foxes more than expected (x2

1 ¼ 21:96,P < 0.001). Similarly, the den sites (n ¼ 225) of bat-earedfoxes occurred in jackal core areas less than expected(x2

1 ¼ 7:44, P ¼ 0.006), whereas they occurred in core areasof cape foxes more than expected (x2

1 ¼ 35:33, P < 0.001).All 3 species showed selection for different habitat types at

the study-site level, and pan slope habitat was ranked highestfor all 3 species (Table 1). Savanna habitat was ranked secondby cape foxes, whereas it was ranked last for jackals. At thehome-range level, habitats of active locations were used inproportion to availability for cape foxes (x2

3 ¼ 2:49,P ¼ 0.477). In contrast, bat-eared foxes and black-backedjackals showed marginal selection for habitat types withintheir home ranges, with pan slope habitat ranking first forboth species (Table 1).Concerning den sites, selection for habitat types was shown

by jackals (x24 ¼ 15:82, P ¼ 0.003), cape foxes (x2

3 ¼ 12:70,P ¼ 0.005), and bat-eared foxes (x2

3 ¼ 26:16, P < 0.001).Jackals located dens in pan slope habitat more than expected,and used savanna less than expected. In contrast, cape foxeslocated dens in savanna more than expected, and used bush-land less than expected. Bat-eared foxes located dens in panslope habitat more than expected, and used bushland lessthan expected.Initial analysis of activity data showed a species � season

interaction (F2,174 ¼ 3.06, P ¼ 0.049); therefore, data wereseparated by seasons for all subsequent analysis. We founddifferences in activity patterns among species in both thewet (F4,63 ¼ 14.37, P < 0.001) and dry (F4,79 ¼ 17.90,P < 0.001) seasons. Activity patterns between cape foxesand jackals differed in both the wet (F2,31 ¼ 25.54,P < 0.001) and dry (F2,41 ¼ 49.05, P < 0.001) seasons,

as cape foxes always were more active than jackals at night,and less active than jackals during the day (Fig. 3). Similarly,activity patterns between bat-eared foxes and jackals differedin both the wet (F2,53 ¼ 19.02, P < 0.001) and dry(F2,66 ¼ 8.46, P ¼ 0.001) seasons, as bat-eared foxes weremore active than jackals at night in the dry season, and lessactive than jackals during the day during both seasons(Fig. 3). Activity patterns between cape foxes and bat-earedfoxes differed in the dry season (F2,51 ¼ 13.81, P < 0.001),but not the wet season (F2,42 ¼ 2.15, P ¼ 0.129; Fig. 3).We collected 312 jackal scats, 133 cape fox scats, and 177

bat-eared fox scats from 2005 to 2007. The Monte Carlopermutation tests showed differences (P < 0.001) in preygroups between species in all seasons (Fig. 4). Jackal dietswere dominated by ungulates, mainly springbok (Antidorcasmarsupialis), which comprised 64.1% (mean ingested bio-mass across seasons) of their diet, followed by hares andspringhares (14.1%), and small mammals (7.9%). Cape foxdiets were dominated by small mammals (70.2%), followedby fruits (11.2%), and hares and springhares (8.8%). Bat-eared fox diets were dominated by fruits (42.6%) followed byarthropods, mainly northern harvester termites (Hodotermesmossambicus), which comprised 36.9% of their diet (Fig. 4).Horn’s index of overlap (R0) showed that mean overlap ofseasonal diets was 0.34 (range ¼ 0.25–0.44) between capefoxes and jackals, 0.26 (0.12–0.46) between cape foxes andbat-eared foxes, and 0.20 (0.10–0.29) between bat-earedfoxes and jackals. Levin’s measure of niche breadth (B) forjackals ranged from 5.4 to 6.2 across seasons, cape foxesranged from 2.6 to 3.3, and bat-eared foxes ranged from1.7 to 2.1. Interestingly, 1 jackal scat contained hair and teethfrom a bat-eared fox, and up to 5 more possibly contained foxremains (i.e., carnivore remains were identified in scats, butthey could not be classified to species; foxes were not ruledout).

DISCUSSION

This study showed both high and low levels of resourcepartitioning among cape foxes, bat-eared foxes, and black-backed jackals, as well as interspecific killing of the foxes byjackals. Cape foxes exhibited high levels of partitioning withjackals for all measured resources, with a strong spatialavoidance of jackal core areas based on both active andden-site locations. Spatial avoidance among canids is a com-mon phenomenon, and has been shown to occur betweenwolves (Canis lupus) and coyotes (Fuller and Keith 1981,Thurber and Peterson 1992), coyotes and red foxes (Vulpesvulpes; Sargeant et al. 1987, Harrison et al. 1989), andcoyotes and swift foxes (V. velox; Kamler et al. 2003c).Thus, we were not surprised that spatial avoidance occurredbetween cape foxes and black-backed jackals. Nevertheless,annual home ranges of cape foxes were significantly largerthan those of jackal groups, the opposite of that predictedfrom body size–home range relationships among carnivores(Gittleman and Harvey 1982). Similarly, densities of capefoxes were far less than those of the other canids, the oppositepredicted from body size–density relationships among car-nivores (Carbone and Gittleman 2002). In previous studies

Figure 2. Den-site locations of cape foxes (black dots, n ¼ 135) comparedto core areas of black-backed jackal groups (gray polygons) monitored onBenfontein Game Farm, South Africa, 2005–2008.


showing spatial avoidance among canids, smaller speciesalways had smaller home ranges, and their home rangeswere placed near the edge, or in between, home ranges oflarger species (Fuller and Keith 1981, Sargeant et al. 1987,Harrison et al. 1989, Thurber and Peterson 1992, Kamleret al. 2003c). In the foregoing relationships, smaller canidsdid not always behaviorally avoid larger canids, but excessivekilling of smaller canids within the core areas of larger canidsoften resulted in the observed spatial segregation (Carbyn1982, Kamler et al. 2003c). In contrast, our study indicatedthat cape foxes actively avoided jackals and that excessiveinterspecific killing did not occur. Therefore, we hypothesizethat the unusually large home ranges and low densities ofcape foxes were due to their avoidance of jackal core areas,which caused the foxes to roam over large areas seekingcompetition refuges. Although not reported among canidsin North America, spatial relationships and densities basedon competition refuges appear common for subordinateAfrican carnivores (Durant 1998, Creel and Creel 2002).For example, cheetahs (Acinonyx jubatus) and African wilddogs (Lycaon pictus) have larger home ranges and lesserdensities than expected from body size, and these 2 speciesactively avoid areas with high activity of lions (Panthera leo)and spotted hyenas (Crocuta crocuta), their dominant com-petitors (Durant 1998, Creel and Creel 2002). Apparently,

Table 1. Results of compositional analysis showing the matrix of means and standard errors of habitat selection at the study-site and home-range levels for capefoxes, bat-eared foxes, and black-backed jackals monitored on Benfontein Game Farm, South Africa, 2005–2008. Under each species, the selection rank ofdifferent habitats is given in parentheses. Note that cape foxes did not show selection (P ¼ 0.477) for habitat types at the home-range level.

Pan basin Pan slope Bushveld Savanna Other

Study-site levelCape fox��

Pan basin (2) �4.426 � 1.823 0.732 � 2.987 �1.817 � 1.748 1.648 � 1.210Pan slope (4) 4.426 � 1.823 5.158 � 1.902 2.609 � 1.514 6.074 � 1.370Bushveld (1) � 0.732 � 2.987 �5.158 � 1.902 �2.548 � 2.858 0.917 � 3.000Savanna (3) 1.817 � 1.748 �2.609 � 1.514 2.548 � 2.858 3.465 � 1.467Other (0) �1.648 � 1.210 �6.074 � 1.370 �0.917 � 3.000 �3.465 � 1.467

Bat-eared fox�

Pan basin (0) �8.345 � 0.283 �2.649 � 1.089 �1.802 � 1.249 �0.715 � 0.419Pan slope (4) 8.345 � 0.283 5.696 � 1.021 6.543 � 1.195 7.630 � 0.283Bushveld (3) 2.649 � 1.089 �5.696 � 1.021 0.847 � 1.151 1.934 � 1.087Savanna (2) 1.802 � 1.249 �6.543 � 1.195 �0.847 � 1.151 1.087 � 1.249Other (1) 0.715 � 0.419 �7.630 � 0.283 �1.934 � 1.087 �1.087 � 1.249

Black-backed jackal�

Pan basin (2) �2.380 � 2.025 �1.169 � 4.028 1.944 � 3.845 0.088 � 1.894Pan slope (4) 2.380 � 2.025 1.211 � 3.420 4.324 � 2.395 2.468 � 2.717Bushveld (3) 1.169 � 4.028 �1.211 � 3.420 3.112 � 2.218 1.257 � 3.054Savanna (0) �1.944 � 3.845 �4.324 � 2.395 �3.112 � 2.218 �1.855 � 3.629Other (1) �0.088 � 1.894 �2.468 � 2.717 �1.257 � 3.054 1.855 � 3.629

Home-range levelBat-eared fox��

Pan slope (2) — 0.140 � 0.108 0.179 � 0.107 —Bushveld (1) — �0.140 � 0.108 0.039 � 0.177 —Savanna (0) — �0.179 � 0.107 �0.039 � 0.177 —

Black-backed jackal��

Pan basin (3) �0.172 � 0.071 0.201 � 0.256 0.196 � 0.169 0.821 � 0.757Pan slope (4) 0.172 � 0.071 0.373 � 3.100 0.368 � 0.222 0.993 � 0.723Bushveld (1) �0.201 � 0.256 �0.373 � 3.100 �0.005 � 0.216 0.620 � 0.835Savanna (2) �0.196 � 0.169 �0.368 � 0.222 0.005 � 0.216 0.625 � 0.816Other (0) �0.821 � 0.757 �0.993 � 0.723 �0.620 � 0.835 �0.625 � 0.816

� P < 0.001.�� P < 0.010.�� P < 0.100.

0

25

50

75

100

Day Sunset Night

Perc

ent (

%) t

ime

activ

e

Wet season

Cape foxes Bat-eared foxes Jackals

0

25

50

75

100

Day Sunset Night

Perc

ent (

%) t

ime

activ

e

Dry season

Figure 3. Percent time active in the wet (Sep–Feb) and dry (Mar–Aug)seasons for cape foxes, bat-eared foxes, and black-backed jackals monitoredon Benfontein Game Farm, South Africa, 2005–2008.


relatively large home ranges of subordinate carnivores occurbecause large parts of their home ranges become unusablewhen dominant carnivores are present (Creel and Creel2002, St-Pierre et al. 2006). We conclude a similar relation-ship occurs between cape foxes and jackals, and that suchactive behavioral avoidance may reflect the long evolutionaryhistory in which these 2 species were sympatric.Cape foxes also exhibited high levels of temporal and

dietary partitioning with jackals. Jackals were the most diur-nal, whereas cape foxes were the most nocturnal, suggestingthat temporal partitioning likely helped cape foxes reduceencounter rates with jackals. More surprising was such lowdietary overlap (R0 ¼ 0.34) between cape foxes and jackals,as several previous studies showed both species to prey mainlyon small- and medium-sized mammals (Loveridge andNel 2004, Stuart and Stuart 2004). Furthermore, otherstudies showed that when interspecific killing occurred be-tween canid species, dietary overlap was relatively high(R0 > 0.72; White et al. 1995, Kitchen et al. 1999, Arjoet al. 2002, Kamler et al. 2007, Murdoch et al. 2010).Although not often reported for black-backed jackals, thisspecies can be a major predator of ungulates, similar to that

found on our study site (Klare et al. 2010). The large herds ofspringbok on Benfontein allowed jackals to focus on this preytype, thus resulting in high dietary partitioning with capefoxes. Niche breadth values also indicated jackals consumed amuch wider variety of foods than cape foxes.We did not find strong differences in habitat selection of

active locations among all 3 canid species at the study-site orhome-range levels, with pan slope habitat being the mostselected habitat type. However, habitat selection for den sitesdiffered between the canid species. Although jackals and bat-eared foxes both had the greatest selection for pan slopehabitat when using den sites, cape foxes had the greatestselection for savanna habitat, which was the habitat leastselected for by jackals. Thus, habitat partitioning of den siteslikely contributed to decrease encounter rates between capefoxes and jackals. Additionally, both fox species used bush-veld less than expected for den sites, possibly because thishabitat made it more difficult for foxes to observe approach-ing jackals. In general, habitat partitioning appears to be anespecially common mechanism of coexistence among canids,as several species of foxes have used this mechanism to avoidlarger canids (Fedriani et al. 2000, Tannerfeldt et al. 2002,Nelson et al. 2007, Thompson and Gese 2007).Bat-eared foxes exhibited relatively low levels of resource

partitioning with jackals, probably because the group forma-tion of bat-eared foxes allowed better protection from jackals.Nevertheless, jackal core areas were avoided when establish-ing their den sites, so bat-eared foxes likely perceived jackalsas predators to their young, as previously reported (Schaller1972, Pauw 2000, Nel and Maas 2004). Similarly, previousresearch showed dens of other fox species often were placedoutside of core areas of larger canids, presumably to avoidcompetition (Voigt and Earle 1983, Sargeant et al. 1987,Kamler et al. 2003c). We observed that when jackals didapproach young bat-eared foxes, adults would form tightgroups to chase away the jackal, similar to that reported forbat-eared foxes from other areas (Malcolm 1986, Pauw 2000,Maas and Macdonald 2004). Nevertheless, jackals killed agreater proportion of bat-eared (23–32% of collared individ-uals) than cape foxes (9%). Although results could have beenan artifact of low sample size, jackals commonly killed bat-eared foxes (e.g., jackals were responsible for 71–100% ofbat-eared fox deaths), despite the group defense of the latter.This was probably because of the relatively high overlap inspace and habitat use between the 2 species, which broughtthem into regular contact. This was in contrast to cape foxesand jackals, which exhibited low overlap in space, habitat,activity, and diet, thus resulting in relatively few opportu-nities for interspecific killing. Thus, although group forma-tion likely allowed bat-eared foxes to forage in more areasthan cape foxes, it was not enough to reduce the relativefrequency of interspecific killing compared to cape foxes.That said, densities of bat-eared foxes were considerablygreater than cape foxes, indicating more interspecific killingdid not suppress populations to the same extent as behavioralavoidance. Also, bat-eared foxes killed by jackals came fromsmaller groups, indicating larger group sizes did offer betterprotection for bat-eared foxes, similar to that reported for

Figure 4. Percent ingested biomass of 5 main food categories for black-backed jackals, cape foxes, and bat-eared foxes on Benfontein Game Farm,South Africa, 2005–2007. The ‘‘�’’ indicates data were not included for capefoxes in summer due to a low sample size.


other group-living carnivore species (Rasa 1986, Caro 1994,Clutton-Brock et al. 1999, Berger and Gese 2007).Bat-eared foxes had activity patterns that were similar to

those of cape foxes in the wet season, whereas in the dryseason they became more diurnal and overlapped more withjackal activity patterns. Previous research showed that activ-ity of bat-eared foxes followed that of their main prey,northern harvester termites (Koop and Velimirov 1982,Nel 1990), which are nocturnal during most of the year,except in the dry season when they becomemore diurnal (Nel1990, Nel and Maas 2004). In our study, bat-eared foxesfollowed this same pattern, so their activity was likely influ-enced most by their prey, rather than by interactions with theother canid species.Bat-eared foxes had low dietary overlap with the other

canids, primarily because of their high consumption of ter-mites and fruits, which also resulted in their low dietary nichebreadth. Because of such low dietary overlap with jackals, wewere unclear as to why jackals commonly killed bat-earedfoxes, because interspecific killing among carnivores usuallyinvolves overlap of resources such as food (Johnson et al.1996, Palomares and Caro 1999, Donadio and Buskirk2006). Similarly, jackals killed a cape fox, despite high re-source partitioning between the species. Because most foxeswere consumed, jackals may have killed foxes as a foodresource. In fact, bat-eared foxes were preyed upon by alllarge carnivore species within their distribution (Kamler andMacdonald 2006), and remains of bat-eared foxes werefound in jackal scats in a previous study (Smithers 1971),indicating jackals in our study may have been killing for foodintake. Nevertheless, fox carcasses sometimes were not con-sumed, suggesting interspecific killing also may have beendue to reasons other than food intake, such as for territorialreasons. Although intraguild predation due to territorialaggression is rarely reported among invertebrates (Poliset al. 1989), it appears to be more common among terrestrialcarnivores. For example, lions and spotted hyenas kill anddisplace each other over territorial disputes (Kruuk 1972,Schaller 1972), thus it may occur among canids as well,regardless of the amount of resource overlap. In fact,black-backed jackals reportedly are more aggressive andbehaviorally dominant than larger jackal species (Estes1991, Kingdon 1997, Loveridge and Macdonald 2002,Macdonald et al. 2004), and their highly structured familygroups are very protective of pups (Kingdon 1997).Consequently, black-backed jackals attack larger predators,such as spotted hyenas, that approach their dens (Estes 1991,Kingdon 1997). Thus, smaller canids might be readily killedby black-backed jackals if they are perceived as threats, real ornot, to jackal young, especially because risk of injury pre-sumably would be low for jackals when killing foxes that areless than half their body size. That all foxes killed by jackals(n ¼ 6), and potentially killed by jackals (n ¼ 2), occurredduring the 6-month period in spring and summer (Sep–Feb)suggests killings were for territorial or protective reasons,because Canis species tend to be most territorial in springwhen pups are born, and later in summer when pups emergefrom dens (Gese 2001). In contrast, interspecific killing

among carnivores, including Canis, during winter tends tobe due to food stress (Palomares and Caro 1999, Kamler andGipson 2004). Furthermore, a recent study of black-backedjackals concluded that this species defends territories not forexclusive use of food resources or den sites, but rather forexclusive space to give birth and raise offspring to indepen-dence (Jenner et al. 2011), indicating territorial aggression byjackals primarily is for protection of young. Interestingly,interspecific killing and population suppression among can-ids for territorial reasons, regardless of amount of resourceoverlap, do not fit the traditional ecological theories ofinterspecific competition. Thus, to best explain the interspe-cific relationships of foxes and jackals in southern Africa,territorial space should be regarded as a limited resource forblack-backed jackals.The 2 fox species did not appear to partition resources,

except food, between themselves, despite being relativelysimilar in size. In fact, we found positive associations be-tween the species that would appear to contradict theoriesabout intraguild competition and resource partitioning, es-pecially among canids (Polis et al. 1989, Hersteinsson andMacdonald 1992, Johnson et al. 1996, Donadio and Buskirk2006). For example, bat-eared foxes had a positive selectionfor cape fox core areas within their home ranges when active.Perhaps more surprising, both fox species had a positiveselection for the other’s core areas when establishing theirden sites. Additionally, we twice observed small groups ofbat-eared foxes foraging <20 m from a cape fox den con-taining pups, yet the adult cape foxes, which were awake andresting 20–30 m away, did not become alert or even payattention to the bat-eared foxes. Apparently, the 2 species didnot view the other as a threat to themselves or their young,which allowed them to be closely associated with each othereven for denning purposes. In fact, both fox species even havebeen reported to simultaneously use the same den (Skinnerand Chimimba 2005). We hypothesize that their close as-sociation on our study site was due to both species avoidingjackal core areas when establishing their den sites, thusforcing both species into the same general areas that func-tioned as refuges. The use of the same areas by foxes did notappear to result from the limited availability of den sites orhabitat, because bat-eared foxes spatially avoided jackal coreareas, even though the latter 2 species preferred the samehabitat (i.e., pan slope) for den sites. Regardless of the reason,our results suggest that dietary partitioning alone can resultin coexistence with little or no interference competitionexhibited between 2 similarly sized canid species. The ap-parent lack of aggression between cape and bat-eared foxes isan exception among canids, because agonistic behavior isusually the rule for sympatric species within this family(Peterson 1995, Macdonald and Sillero-Zubiri 2004,Donadio and Buskirk 2006). Lastly, we are unsure whateffects the lack of large carnivores had on the interactionsof foxes and jackals on our study site. Regardless, largecarnivores are extirpated over most of South Africa(Skinner and Chimimba 2005), thus our results are relevantfor showing the mechanisms of co-existence among foxesand jackals over much of their current distribution, and we


presume relationships among these species would be similarif large carnivores were present.

MANAGEMENT IMPLICATIONS

Populations of black-backed jackals are often heavily con-trolled on private lands in southern Africa (Loveridge andNel 2004). Previous research showed such management ofjackal populations may indirectly affect local numbers of capefoxes and bat-eared foxes (Blaum et al. 2009), although theecological relationships of jackals and foxes were not under-stood. Our results showed the mechanisms by which jackalscould suppress fox populations, yet also showed how, in turn,different fox species coexisted with a dominant canid.Therefore, our results help clarify for biologists andmanagersthe seemingly contradictory nature of jackal and fox relation-ships: that jackals may suppress fox populations despite littleoverlap in resource use, yet all 3 canid species remain sym-patric over large regions. Our results, along with Blaum et al.(2009), suggest that cape fox numbers are strongly influencedby increases or decreases in jackal numbers. Thus, if increas-ing or maintaining cape fox populations becomes a conser-vation objective, then managers will need to consider jackalnumbers in addition to resources such as food and habitat.Finally, we conclude that body size and traditional resourceoverlap may not necessarily be the best predictor of potentialcompetition among sympatric canids, especially if dominantcanids kill subordinate species primarily because of territorialaggression.

ACKNOWLEDGMENTS

We thank De Beers Consolidated Mines for allowing usaccess to their property, and providing support for thisproject. A special thanks goes to S. Cade, P. Gibbs, M.Hauptfleisch, and J. Kruger of De Beers; C. Anderson, T.Anderson, A. Sliwa, and B. Wilson from the McGregorMuseum, Kimberley; and M. Anderson and E. Herrmannfrom the Department of Tourism, Environment andConservation, Kimberley. We also thank L. Mayer and S.Visagie for making traps, Z. Davidson and A. Loveridge forequipment loans, B. Cypher for donation of radio collars, B.Dean, D. Nkosi, T. Keswick, and I. Midoko for help withdata collection, and B. McHugh for help with the GIShabitat map. Funding for J. F. Kamler was provided by aResearch Fellowship from the Wildlife ConservationSociety, New York, and a Marie Curie Fellowship fromthe European Commission, Brussels, Belgium. Additionalsupport was provided by British Airways, and grants toD.W.M. from the Peoples’ Trust for Endangered Species.

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Associate Editor: Kevin McKelvey.


Documents

Resource partitioning among cape foxes, bat-eared foxes, and black-backed jackals in South Africa