Food habits and resource partitioning between grey and culpeo foxes in
southeastern Argentine Patagonia
SONIA C. ZAPATA1, ALEJANDRO TRAVAINI1, MIGUEL DELIBES,2 &
ROLANDO MARTÍNEZ-PECK1
1
Universidad Nacional de la Patagonia Austral, Puerto Deseado, Santa Cruz, Argentina, and 2Estación Biológica de Doñana
(CSIC), Sevilla, Spain
Abstract
We studied the annual and seasonal food habits of sympatric grey fox (Lycalopex griseus) and culpeo fox (Lycalopex culpaeus)
in a protected area, in southeastern Argentine Patagonia, to test the hypothesis that both foxes partition prey. Grey foxes
consumed a larger proportion of rodents than culpeos (66.1% versus 37. % of occurrences in feces, respectively), and
culpeos consumed a larger proportion of the introduced European hare (Lepus europaeus) (32.8% versus 7.1%, respectively).
Additionally, arthropods made up a significant portion of the diet of the grey fox, and occurred in the 95.5% of the analyzed
feces. Despite the great differences in size of culpeo and grey foxes, the former being significantly larger, both species
consumed the same type of prey, and no significant differences in the mean weight of vertebrate prey were detected in their
diets. Culpeo and grey foxes diets differed during spring – summer with low values of mean diet overlap (31%). But in
autumn – winter, when prey diversity is lower in Patagonia, diet was more similar and diet overlap (73%) increased. An
exploratory analysis of habitat use by culpeo and grey foxes suggested that both species utilize habitat in a similar way. Our
data agree with generalizations about competitive interactions between the large and the small canid in an assemblage.
Although both foxes can potentially consume the same type of prey, through interference the larger culpeo would exclude the
smaller grey fox from habitats with high-quality prey, resulting in prey partitioning. The possibility that both foxes partition
habitat at a finer scale in our study area should be explored.
Keywords: Lycalopex griseus, L. culpaeus, diet, resource partitioning, Patagonia, Argentina
Introduction
The small grey fox (Lycalopex griseus) is found in
central Chile and in Argentina along the Andes, from
at least Salta province south to Rı́o Negro province
and then across the whole country south to Tierra
del Fuego (Redford & Eisenberg 1992; Novaro
1997). The culpeo fox (Lycalopex culpaeus), the
largest Neotropical canid after the maned wolf
(Chrysocyon brachyurus), ranges from northern Ecuador to southern Chile and Argentina, along the
foothills of the Andes, including Tierra del Fuego,
and throughout the Patagonian steppe of Argentina
(Redford & Eisenberg 1992; Novaro 1997). However, their distributions do not completely overlap
and few cases of sympatry were reported in Chile and
in Argentina (see Jimé nez et al. 1996 and references
therein). Nevertheless, in central-eastern Santa Cruz
province, southern Argentine Patagonia, both species co-occur (Travaini et al. 2000, 2001). Early
accounts indicated that culpeo foxes were found only
along the Andean Cordillera and its foothills during
the early 1900s (Prichard, 1902 in Novaro 1997), but
at present they extend their range to the coast of
Patagonia south to 438S (Novaro 1997). The
increase in the culpeo range may be related to the
introduction of European hares (Lepus europaeus)
and sheep (Ovis aries) in the early 1900s (Crespo &
De Carlo 1963; Griguera & Rapopport 1983).
In their generalization of competitive interactions
between the largest and the smallest canid in an
assemblage, Johnson et al. (1996) argued that
Correspondence: S. C. Zapata, Centro de Investigaciones de Puerto Deseado, Universidad Nacional de la Patagonia Austral, Unidad Acadé mica de Caleta
Olivia, Av. Lotufo s/n. 9050- Puerto Deseado, Santa Cruz, Argentina. Fax: + 54 297 4870511. E-mail: titinazapata@yahoo.com.ar
although the mechanisms for partitioning resources
are complex, where little diet overlap occurs the two
canids usually overlap spatially, and may or may not
use different habitats. But when food habits are more
similar between the two canid species, then interference competition is common, and the larger
species tends to be distributed wherever there are
sufficient food resources to meet its energy requirements and there are no other limiting factors. The
smaller species in this scenario tends to occupy
adjacent areas offering lower amounts of food
resources, and thus often appears to be selecting
different types of habitats or food.
Sympatry in culpeo and grey foxes has been studied
in central and southern Chile (Fuentes & Jaksic 1979;
Jaksic et al. 1980, 1983; Johnson & Franklin 1994a,
1994b; Jiménez et al. 1996). According to Johnson
et al. (1996), although both foxes can potentially
consume the same type of prey, through interference
the larger culpeo excludes the smaller grey fox from
habitats with high-quality prey, where the introduced
European hare is abundant, resulting in differences in
feeding habits and habitats used.
We studied the annual and seasonal food habits of
sympatric grey and culpeo foxes in a protected area,
the Monumento Natural Bosques Petrificados National Park (MNBP), southeastern Argentine
Patagonia, to test the hypothesis that both foxes
coexist by partitioning prey. According to Johnson
and Franklin (1994a) and Jimé nez et al. (1996) we
expect that although the two species are able to
consume the same type of prey, culpeo fox will
consume more energetically rewarding foods. We
also present an exploratory analysis of habitat use of
culpeo and grey foxes.
Materials and methods
Study area
We searched for feces of culpeo and grey foxes in
MNBP (47839.887’S; 67859.729’W), a protected
area covering about 60 000 ha belonging to the
Departamento Deseado, Santa Cruz province, Patagonia, in southern Argentina. Annual rainfall ranged
between 100 and 300 mm. Summer temperatures
averaged 178C, and winters were comparatively
mild. Most of the country was covered by tussock
grasses and low, dome shaped, spindly shrubs
(Soriano 1983), with cover ranging from less than
10% in the most arid areas to 4 60% (Ares et al.
1990; Bertiller & Bisigato 1998).
Diet analysis
We collected a total of 316 feces of culpeo during
spring – summer (September 1999 to March 2000,
n = 166) and autumn – winter (May to August
2000, n = 150) and a total of 203 feces of grey
foxes (n = 127 in spring-summer and n = 76 in
autumn[-winter) by walking secondary roads. In
our study area, culpeo foxes are significantly
heavier and larger than grey foxes. The mean
weight for culpeos is 8.03 kg and mean total length
1228.8 mm (n = 11), while for grey foxes these
values are 2.6 kg and 867.6 mm (n = 17), respectively. Their feces are easily distinguished because
those from culpeos are at least twice as large as
those of grey foxes (diameter: x = 23.5 mm + 2.04 SD,
n = 13, vs. x = 12.3 mm+ 2.29 SD, n = 20) and
because of the particular pattern of scat deposition
for each species. Feces of culpeos were found spread
on bare soil in the roads and those of the grey foxes
beside shrubs. Only fresh fecal samples were
collected and care was taken to avoid collection of
more than one scat that could have been from the
same individual in a couple of days. We discarded
feces that could not be attributed to either species.
Feces were air-dried, their components separated by
hand and identified using a reference collection
(birds, small mammals) and a key to small mammals
skulls (Pearson 1995). Mammal hairs were identified
from medulla types and scale patterns following the
methodology of Brunner and Coman (1974) and the
keys of Chehé bar and Martin (1989). Birds were
classified into large birds ( 4 1000 g), e.g. the lesser
rhea (Pterocnemia pennata), and the upland goose
(Chloephaga picta), medium-sized birds (200 –
1000 g), e.g. the elegant crested-tinamou (Eudromia
elegans) and small birds ( 5 200 g) were all passerine
birds. Reptiles were discriminated to the genus level.
Scorpions, coleopterans and their larvae were
grouped as arthropods. We present results as
frequency of occurrence in feces of each vertebrate,
arthropod prey and fruits. We tested for seasonal
differences in prey items for each fox species.
Occurrences of food items were grouped into nine
classes: small rodents, large rodents, edentates,
lagomorphs, other mammals, carrion (prey items
too large to have been killed by the foxes), birds/
reptiles, arthropods and fruits. Then these categories
were compared by season through a contingencytable analysis (G-test, Sokal & Rohlf 1981). We
tested for interspecific differences in occurrence of
vertebrate prey items in feces by chi-square analysis
and then partitioning of chi-square contingency
tables were made after Siegel and Castellan (1988).
For this purpose, vertebrate prey items were grouped
into five categories: rodents, edentates, lagomorphs,
carrion and birds plus reptiles. To describe and
compare the diets of both foxes we also used the
parameters proposed by Jaksic et al. (1986): (1)
geometric mean weight of vertebrate prey based on
weight values of small mammals obtained from
Pearson (1995), Redford and Eisenberg (1992) and
for edentates, lagomorphs, carnivores, birds and
reptiles obtained by us in the field. We did not
include the guanaco (Lama guanicoe) because we
considered it to be scavenged. (2) We calculated
Colwell and Futuyma’s (1971) standardized form
(Bsta) of Levins’ index (B) to measure food-niche
breadth (Levins, 1968), an index of diet diversity:
Bsta = (Bobs - Bmin)/(Bmax - Bmin), where Bobs is the
observed niche breadth, Bmin = 1, is the minimum
niche breadth, and Bmax is the maximum possible niche breadth (the number of taxa taken).
Bobs is = 1/S pi2, where pi is the relative occurrence of
prey taxon i in the diet. The Bsta allows comparison
of diets with different numbers of prey categories
and ranges from 0 to 1 (i.e. from narrow to broad
food niche). We measured food niche breadth
for each species of fox at the finest level of taxonomic resolution of prey categories. (3) Overlap in
food niche, a measure of dietary similarity, was
determined using Pianka’s (1963) index, where
o = S pij pik /(S pij2 S pik 2) 1/2. This index ranges from
0 to 1 (i.e. from dissimilarity to complete similarity).
Analysis of habitat use
Habitat use data were derived by combining the data
taken from Travaini et al. (2001), of the numbers of
visits of the two fox species to bait stations, and
environmental data taken at each station. Bait
stations were established in two areas of the Monumento Natural Bosques Petrificados: El Cuadro
(September 1999) and Cerro Horquetas (April
2000). At each area, we established 9 – 10 transects,
each with six bait stations spaced 0.5 km apart, and
transects were at least 1 km apart. On the first day, we
established the stations on alternate sides of secondary unpaved roads. On the three following mornings,
we checked the stations and identified tracks of
station visitors (see Travaini et al. 2001 for details).
We included in this approach only the stations visited
by foxes (n = 32). No station included the visit of
individuals of the two species simultaneously. To
describe habitat characteristics within a radius of
200 m around each bait station we estimated the
proportion of coverage (in %) by the following classes
of vegetation and other features: (1) low cover:
vegetation less than 20 cm high; (2) medium cover:
vegetation between 20 cm and 2 m high; (3) high
cover: vegetation more than 2 m high; (4) bare soil:
without any plant cover; (5) free water: flooded land;
(6) aspect class: presence of herbaceous steppe, shrub
steppe, or bare soil; (7) road: type of road, path
between ranches or little used path; (8) topography:
small lake border, ravines, slopes, or pampas.
Then, to explore the relationship between the
presence of a fox species and the range of environ-
mental variables described above, a GLM model was
fitted with the program GLIM (Baker 1987).
Because the response variable was presence or
absence of a fox species we considered that error
would follow a binomial distribution and used a logit
link (Crawly 1993). We started by fitting a null
model so that the significance of the variables could
be assessed by comparing the changes in the
deviance from the null model to the model with
the variable fitted (Crawly 1993). The changes in the
deviance were compared with chi-square statistics.
Results
Seasonal differences in diets of Culpeo and Grey foxes
Mammals were the main prey items in the diet of
Lycalopex culpaeus in MNBP, and among these, at
least six species of rodents were very important in
the diet, chiefly lesser cavies (Microcavia australis)
(Table I). Introduced European hares (Lepus europaeus) were also important in culpeo diet. Mammals
like the pichi (Zaedyus pichiy) and the guanaco
(Lama guanicoe) were moderately frequent in the
feces and other carnivores were only occasionally
consumed (Table I). Birds were present in 10.7%
of the feces (Table I). Fruits of both native (Berberis
buxifolia, Schinus molle) and introduced (apple,
quince, prune) species were found in the feces
while lizards and arthropods were poorly represented (Table I).
Foods items recorded in feces of Lycalopex griseus
included 11 species of mammals, birds, reptiles,
arthropods and fruits (Table I). Arthropods and
mammals, mainly rodents, were the most frequent
items in grey fox diet. Among the rodents, the lesser
cavy (M. australis), Akodon spp, Maguellan’s tuco
(Ctenomys magellanicus) and unidentified rodents
were the most frequent (Table I). Other mammals
(edentates, lagomorphs, carnivores and carrion) as
well as birds, reptiles and fruits, were poorly
represented in grey fox feces (Table I).
The standardized food niche breadth
values
calculated for culpeo diet during spring – summer
and autumn – winter were very similar (0.27 versus
0.24, respectively). Nevertheless, birds, arthropods
and fruits were more frequently consumed during
spring – summer (Table I). Consequently, there were
qualitative seasonal differences in the culpeo diet (Gtest, G = 21.5, df = 8, p 5 0.01). Though culpeos
consumed mammals in similar proportions in the two
periods studied (Table I), the geometric mean weight
of vertebrate prey was higher during autumn – winter
probably due to the greater consumption of European
hares during these seasons (Table I).
Significant seasonal differences in prey composition were detected in grey fox diet (G-test, G = 22.3,
Table I. Annual and seasonal diets of culpeo (Lycalopex culpaeus) and grey foxes (Lycalopex griseus) in Monumento Natural Bosques
Petrificados (MNBP) expressed as the frequency of occurrence (%) of vertebrates, arthropods and fruits found in the feces. Spring –
summer: September to March; autumn – winter: May to August. Bold numbers = broad taxonomic groups.
Culpeo fox
Prey items
Spring –
summer
Autumn –
winter
Mammals
84.4
Edentates
6.5
Chaetophractus villosus
0.5
Zaedyus pichiy
6.0
Rodents
40.2
Akodon spp
8.5
Eligmodontia typus
1.01
Phyllotis darwinii
0.5
Reithrodon auritus
3.5
Microcavia australis
19.6
Ctenomys magellanicus
2.5
Unknown rodent
4.5
Lagomorphs
32.1
(Lepus europaeus)
Carnivores
1.5
Galictis cuja
–
Conepatus humboldtii
1.5
Felis catus
–
Carrion
4.0
(Lama guanicoe)
Birds
12.0
(Pterocnemia pennata, and Chloephaga picta)
6.0
Eudromia elegans
2.5
Passerine birds
3.5
Bird eggs
2.0
Reptiles
1.5
(Liolaemus spp.)
ARTHROPODS
12.0
FRUITS
36.7
GARBAGE
1.2
Number of feces
166
Food niche breadth1
0.27
Food niche breadth1 (mean + standard error)
0.25 + 0.09
Geometric mean weight of vertebrate prey (g)
472.5
Grey fox
Annual
Spring –
summer
Autumn –
winter
86.5
7.3
0.3
7.0
37.7
5.5
0.9
0.3
3.0
20.8
1.8
5.2
32.8
92.7
10.0
–
10.0
71.8
25.4
5.4
–
2.7
19.0
8.1
10.9
3.6
89.0
12.3
–
12.3
57.5
9.5
4.1
1.3
–
20.5
9.5
12.3
12.3
91.2
10.9
–
10.9
66.1
19.1
4.9
0.5
1.6
19.6
8.7
11.4
7.1
2.4
0.8
0.8
0.8
7.3
1.8
0.3
1.2
0.3
6.7
1.8
–
1.8
–
5.4
1.3
1.3
–
–
5.4
1.6
0.5
1.0
–
5.4
9.0
2.4
4.9
1.6
0.8
0.8
10.7
4.6
3.3
2.7
1.5
1.2
3.6
–
0.9
2.7
–
3.6
10.9
–
1.3
9.5
–
–
6.5
–
1.0
5.4
–
2.1
89.3
9.02
–
9.0
35.2
0.8
0.8
–
2.4
23.7
0.8
6.5
35.2
2.6
10.6
2.0
150
0.24
7.6
24.3
1.5
316
717.1
100
1.5
–
127
0.5
0.58 + 0.15
104.6
57.8
–
–
76
0.66
Annual
95.5
0.9
–
203
257.7
1
Colwell and Futuyma (1971) standardized food niche breadth.
df = 6, p 5 0.01), with an increase in lagomorphs and
birds during the cold season, and a decrease in the
consumption of rodents
and arthropods. Both
standardized food niche breadth and geometric
mean weight of vertebrate prey were higher during
autumn – winter (Table I).
Interspecific differences in the diet of Culpeo and Grey
foxes
Although the vertebrate prey types eaten by both
culpeo and grey foxes were the same, diets were
significantly
different
(w2 = 108.04,
df = 4,
p 5 0.001). Partitioning the degrees of freedom of
the chi-square table revealed that grey foxes consumed higher proportions of rodents (w2 = 4.6,
df = 1, p 5 0.05) and arthropods but lower propor-
tions of European hares (w2 = 21.4, df = 1, p 5 0.01)
and fruits (w2 = 633.12, df = 1, p 5 0.001).
Grey foxes had higher seasonal indices of standardized food-niche breadths than culpeo foxes for both
seasons and annual mean (these values are in Table
I). Although we did not find significant differences in
the mean weight of vertebrate prey taken by the two
species (Kruskal – Wallis, H = 1.15, p = 0.76) the
geometric mean weight was lower for grey foxes
(Table I). Diet overlap between culpeo and grey
foxes were low during spring – summer (0.31) and
high during autumn – winter (0.73).
Habitat use
The exploratory analysis of habitat use by culpeo
and grey foxes showed that none of the eight
Table II. GLM model to explore the relationship between the
presence of grey and culpeo foxes and eight environmental
variables using binomial erros and logit link. None of the variables
analyzed resulted significant enough to explain the presence of any
of the two species.
Variables
Low vegetation coverage (%)
Medium vegetation coverage (%)
High vegetation coverage (%)
Bare soil (%)
Free water (%)
Aspect class
Road
Topography
Reduction Reduction
in deviance
in df
1.627
0.187
2.858
3.358
1.285
4.22
2.489
2.376
1
1
1
1
1
2
2
3
P
ns
ns
ns
ns
ns
ns
ns
ns
Null model: deviance = 38.024, df = 31. Significance of each
environmental variable was assessed by fitting to the null model
and computing the changes in the deviance. Differences in
deviance were compared with chi-square statistics, the degrees of
freedom are shown in the table.
environmental variables analyzed significantly explained the presence of either species (Table II),
suggesting that both foxes utilize the habitat in a
similar way in Bosques Petrificados.
Discussion
Feeding ecology of culpeo and grey foxes
Our data on the diet of culpeo and grey foxes agree
with the general pattern summarized in Medel and
Jaksic (1988) and characterize them as opportunistic
predators. However, they can be locally selective for
certain prey as in southern Chile where European
hares were the main item for both culpeo and grey
foxes (Johnson & Franklin 1994a). In our study area
foxes still fed mainly on native prey as do all the other
carnivore species of the assemblage (Zapata et al.
2002), whereas in northwestern Argentinean Patagonia, culpeos nowadays rely primarily on hares and
grey foxes on carrion of introduced ungulates
(mainly Ovis aries) (Novaro et al. 2000). In our
study area and its surroundings, as in most parts of
Santa Cruz province, sheep ranging was abandoned
about 15 years ago (Travaini et al. 2000), allowing
wildlife to restore their numbers and inter-specific
interactions to a status similar to that before
European settlement.
During spring and summer, arthropods were a
significant portion in the diet of grey foxes, and fruits
in that of culpeos. As in northwestern Argentine
Patagonia (Zapata et al. 1998), this study also
revealed an increased consumption of arthropods
by grey foxes during the reproductive season
(November – January) and this finding sustains earlier conclusions that adult foxes eat the smaller and
less rewarding prey on the spot and feed their cubs
with the relatively bulkier items that can be carried
away. This opportunistic way of exploiting resources
is consistent with the central place foraging theory
(CPF, Orians & Pearson 1979). Frugivory by grey
foxes was reported in Patagonia (Zapata et al. 1998),
but in Bosques Petrificados only culpeos feed on
fruits. This is in contrast to other studies that
reported increasing dietary overlap between canid
when fruits were available, for example red foxes
(Vulpes vulpes) and coyotes (Canis latrans) (Major &
Sherburne 1987), north American grey foxes (Urocyon cinereoargenteus) and coyotes (Neale & Sakcs
2001), and maned wolves (Chrysocyon brachyurus)
and crab-eating foxes (Cerdocyon thous) (Juarez &
Marinho-Filho 2002).
Food partitioning
As expected, grey and culpeo foxes consumed the
same type of prey, and no significant differences in
the size of vertebrate prey species were detected.
Nevertheless, they differed in the proportions of
vertebrate prey in different size classes. The same
pattern was reported for sympatric foxes at Aucó, in
Central Chile (Jimé nez et al. 1996): European hares
were more abundant than rodents in the diet of
culpeo foxes and rodents in grey fox diets. Nevertheless, in Torres del Paine, southern Chile, the
European hare was the most common vertebrate in
both foxes diets, but culpeo ate higher proportions of
these lagomorphs than grey foxes (Johnson &
Franklin 1994a). This may be related to the higher
abundance of European hares in Torres del Paine
than in Aucó (Jimé nez et al. 1996). Rodents
occurred in a similar proportion in both foxes diet
and carrion was important in the diet of the grey fox
(Johnson & Franklin 1994a).
Culpeo and grey fox diets were different in
Bosques Petrificados during spring – summer with
low value of mean diet overlap (31%), but in
autumn – winter diets of the foxes became more
similar and an increase in mean diet overlap (73%)
between them was observed. Like in northern
latitudes (Litvaitis 1992), prey diversity is limited in
winter in Patagonia (Terborgh 1992), which can lead
to an increase in dietary overlap between sympatric
predators. Arjo et al. (2002) stated that carnivore
species can coexist with high overlap if diversity is
greater in one species’ diet (White et al. 1995), if
prey are partitioned by size (Rosenzweigg 1966) or
differential use (Mills 1984), or if prey are abundant.
Although mean diet overlap is high in winter in
Bosques Petrificados, coexistence of both foxes can
be explained by the diversity of their diets, which was
different, and by the standardized food niche breadth
that was higher in grey foxes diet. Finally, because
they partition prey by size, although both foxes prey
upon rodents and lagomorphs (the most rewarding
prey) in a similar way, they eat different proportions
of these vertebrate prey. Accordingly, the hypothesis
that both foxes coexist by partitioning prey would be
valid in Bosques Petrificados.
Habitat partitioning
We did not find significant differences in habitat use
by both foxes in Bosques Petrificados, possibly due
to our small sample size. On the other hand, our
study area is more homogeneous than those studied
in Chile and we must test whether the foxes partition
habitats at a finer scale in Bosques Petrificados than
in other places. A previous study in Bosques
Petrificados (Travaini et al. 2001) showed that only
one fox species (i.e. grey or culpeo fox) visited bait
stations during the first night after they were
established. No station was visited simultaneously
by both fox species suggesting avoidance and
probably habitat partitioning at a finer scale.
Acknowledgments
We thank C. Zoratti, F. Escobar, P. Collavino, G.
Aguilera and G. Soria for all their help during field
work and C. Chehebar and the Administración de
Parques Nacionales for authorizing us to work inside
the protected area. Funds were provided by the
Universidad Nacional de la Patagonia Austral (P.I.
29/B013, 29/B050), the Secretarı́a de Agricultura,
Ganaderı́a y Pesca de la Nació n (SAGPyA Nos. 613/
96, 716/97 and 925/97) and the Consejo Agrario
Provincial. Javier Bustamante helped SCZ with the
GLM model and Pablo Ferreras, Hubert Hendrichs
and two anonymous reviewers substantially improved a previous version of this manuscript.
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