Download Convergence and divergence in prey of sympatric canids and felids

Blackwell Science, LtdOxford, UKBIJBiological Journal of the Linnean Society0024-4066The Linnean Society of London, 2004? 2004
834
527538
Original Article
DIETS OF SYMPATRIC CANIDS AND FELIDS
O. B. KOK and J. A. J. NEL
Biological Journal of the Linnean Society, 2004, 83, 527–538. With 2 figures
Convergence and divergence in prey of sympatric canids
and felids: opportunism or phylogenetic constraint?
O. B. KOK1 and J. A. J. NEL2*
1
Department of Zoology and Entomology, University of the Free State, PO Box 339, Bloemfontein 9300,
South Africa
2
Department of Zoology, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa
Received 14 April 2003; accepted for publication 2 April 2004
Since the canids and felids diverged in the mid-Eocene or earlier, each family has developed a suite of morphological
and behavioural adaptations for obtaining and consuming prey. We here distinguish between prey taxa captured and
eaten as a result of these phylogenetic adaptations, and those because they are fortuitously encountered, and argue
that such supplementary prey, often opportunistically caught, create a buffer between sympatric, and potentially
competitive, canids and felids and thus enhance coexistence. We base our analysis on dietary data derived from the
stomach contents of four sympatric canid and felid species in the Free State Province, South Africa (canids: Cape fox
Vulpes chama and black-backed jackal Canis mesomelas; felids: African wild cat Felis silvestris lybica and caracal
Caracal caracal), and from results of studies on these species elsewhere in southern Africa. The two canid species
preyed heavily on invertebrates, and thus opportunistically, while the felids (especially the caracal) concentrated on
mammals, prey they are phylogenetically adapted to capture. Only three species of mammalian prey are shared by
the four species. The ratio of opportunistically-to-phylogenetically mediated prey taxa used (the O/P ratio) differ
between the species, with the black-backed jackal having the most opportunistically caught taxa in its diet, and the
caracal the least. As predicted, a comparison of this data with those from dietary studies of the same species carried
out elsewhere indicates that the number of opportunistically obtained prey taxa varies more than those resulting
from phylogenetic adaptations. The largest canid had the widest food spectrum (35 prey taxa) while the smallest felid
had the most restricted one (11 prey taxa). We argue that using the O/P distinction allows a better understanding
of changes in food niche breadth of particular species, especially in xeric areas, and gives a better indication of possible exploitative competition for food by sympatric carnivores than when regarding all prey taxa as actively
pursued. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83, 527–538.
ADDITIONAL KEYWORDS: coexistence – competition – diet – food niche – phylogeny.
INTRODUCTION
The diet of a carnivore reflects both the availability of
its potential prey items, as well as a suite of morphological, behavioural and physiological adaptations
that allow the individual to locate, capture, ingest and
digest a variety of prey taxa. While food availability
varies both spatially and temporally, evolutionary
adaptations are more rigid, but do allow some degree
of plasticity to the predator in obtaining and processing prey not commonly captured.
Carnivore guilds commonly consist of a number of
species differing in size, taxonomic affinities, and mor*Corresponding author. E-mail: [email protected]
phological and behavioural characteristics that help
adapt them for capturing and ingesting a diverse prey
spectrum (e.g. Rosenzweig, 1966; Van Valkenburgh,
1985, 1988; Dayan & Simberloff, 1996). Coexistence of
such sympatric carnivore species can be explained by
both evolutionary divergence (e.g. Van Valkenburgh,
1985, 1989) as well as ecological interactions and
mechanisms (MacArthur & Levins, 1967; Schoener,
1974, 1982). Evolutionary divergence can manifest
itself in, for example, dentition and skull morphology,
and in locomotor adaptations (Van Valkenburgh, 1985,
1989), while ecological mechanisms include the
partitioning of the trophic, spatial and temporal axes
of the niche (Levins, 1968) amongst others. In this
regard differential selection of different prey species
© 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83, 527–538
527
528
O. B. KOK and J. A. J. NEL
(Karanth & Sunquist, 2000), different prey sizes (Gittleman, 1985; Karanth & Sunquist, 2000), different
habitats for foraging (Palomares et al., 1996), different
activity patterns (Fedriani, Palomares & Delibes,
1999; Karanth & Sunquist, 2000), and differential use
of space (Creel & Creel, 1996; Palomares et al., 1996;
Durant, 1998) have been proposed.
During their independent evolutionary history since
the mid-Eocene or earlier, some general family-specific
strategies and adaptations for capturing and consuming prey have evolved in the canids and felids (Ewer,
1973; Van Valkenburgh, 1985), so that today they differ in both morphology and behaviour. Canids are typically long-legged coursers, have retained the original
carnivore dentition of 42 permanent teeth and postcarnassial molars, affording them the ability to evolve
into a diversity of dental and dietary types (Van
Valkenburgh, 1991), and are more opportunistic or
omnivorous (Kleiman & Eisenberg, 1973). Both the
carnassials and postcarnassials afford some crushing
surface (Van Valkenburgh, 1989); retention of the
postcarnassial molars also allows the individual
greater flexibility in its diet, and perhaps the ability to
survive changes in prey availability (Van Valkenburgh, 1991). Felids, on the other hand, typically
remain concealed and ambush and stalk their prey,
using only a short rush or charge (Elliot, Cowan &
Holling, 1977; Kruuk, 1986) followed by a quick killing
bite (Eisenberg, 1981; Skinner & Smithers, 1990).
They kill prey as large or larger than themselves.
Small felids also often pounce on small prey, e.g.
rodents (Kruuk, 1986). Felids have a short rostrum
and have a much reduced dentition of only 30 permanent teeth. There is only one upper molar, but the
molars are the most specialized for a carnivorous life,
with no crushing surfaces on either the carnassials or
postcarnassials (Eisenberg, 1981; Van Valkenburgh,
1989). Felids can therefore be expected to be specialized in their diet as they are consistently hypercarnivores, but although highly specialized have been a
very successful morphotype over evolutionary time
(Van Valkenburgh, 1991). Canids and felids therefore
differ both in their anatomical adaptations for prey
location, capture and killing (Ewer, 1973; Van Valkenburgh, 1985; Biknevicius & Van Valkenburgh, 1996),
and in prey-catching behaviour (e.g. Ewer, 1968).
For most felid species food can also be assigned to
significantly fewer categories than for canids (Kruuk,
1986). This would primarily result from the highly
specialized felid dentition. The degree of specialization
in a particular species can be demonstrated by comparing its diet in different areas, using Kendal’s coefficient of concordance (Siegel, 1956). This measures
the degree of agreement (concordance) between different sets of rank orderings of the same set of parameters, e.g. the diet of a species in different regions.
Previous studies show that felids all have high coefficients of concordance, i.e. they specialize on a
restricted food spectrum, while canids have lower
coefficients (Kruuk, 1986), eat a wider range of food
categories, and are usually termed ‘generalists’ or
‘opportunists’; the two terms are often used interchangeably, and seldom defined. Although the diet of a
felid species can closely correspond in different areas,
suggesting that it is either highly selective of habitats
or highly specialized in hunting techniques, or both
(Kruuk, 1986), between-area differences can and do
occur. In southern Africa this can be ascribed to an
unstable prey base such as major fluctuations in
rodent numbers, or to differences in the availability of
prey species or food categories, as has been found in
the caracal (Smithers, 1971; Avenant & Nel, 1998).
Although primarily carnivorous, smaller felids such as
the black-footed cat Felis nigripes Burchell and the
African wild cat Felis silvestris lybica Forster (we here
follow Bronner et al. (2003) in recognizing F. s. lybica
as a subspecies) also consume a variety of invertebrate
taxa (Avenant, 1993; Sliwa, 1994; Kok, 1996; this
study).
The two canids used in this study are the Cape fox
Vulpes chama (A. Smith) and the black-backed jackal
Canis mesomelas Schreber, and the two felids are the
African wild cat and the caracal Caracal caracal
(Schreber). In southern Africa they are sympatric and
often syntopic over most of their geographical range
(Mills & Hes, 1997). They often share habitats and are
all mostly nocturnal, with black-backed jackal and, to
a lesser extent the caracal, also being partially diurnal
in some areas (Avenant & Nel, 1998; Loveridge &
Macdonald, 2003). All are terrestrial, with the African
wild cat also being partially arboreal, and all are carnivorous with a range of prey items being shared by
two or more species. Examination of the diets of these
species in our study area suggested that the capture
and ingestion of some prey items result from their evolutionary adaptations in morphology, especially dentition, and behaviour as outlined above. Other prey
items again include very small prey taxa such as
invertebrates, which the carnivores are not specifically adapted to capture; the inclusion of these items
in many cases probably resulted from fortuitous
encounters. Such prey are much more variable both
intra- and interspecifically, as well as geographically.
This suggests that the diet of a particular carnivore
should be regarded as consisting of two components:
one resulting from evolutionary adaptations (basic
prey), and the other resulting from chance encounters
(supplementary prey). This helps to explain the coexistence of some sympatric carnivores, because the supplementary component can act as a dietary buffer
between species that are competing for the same basic
prey over and above differences due to evolutionary
© 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83, 527–538
DIETS OF SYMPATRIC CANIDS AND FELIDS
adaptations. We also predict that the supplementary
prey component will tend to vary more between different areas, for a particular predator species or between
species. Low levels of basic prey availability should
therefore result in a higher proportion of supplementary prey, even in specialized hunters such as felids.
While optimization of foraging and feeding plays a
major role in the immediate decision of which prey to
select, evolutionary constraints limit the possibility of
either locating, or of capturing and consuming a particular prey item.
We argue that a more accurate picture of the diet,
and therefore of the food niche, of each predator
species, and consequently of the overlap or separation
in a carnivore guild, can be obtained by separating
these two prey categories. Differences in the ratio of
opportunistically-to-phylogenetically mediated prey
captured (the O/P ratio) could therefore be indicative
of either changes in the basic prey base for a particular species, or of changes in the degree of exploitative
competition between sympatric carnivore species.
Despite the disappearance of large carnivores from
our study area, it is doubtful if those here examined
currently exhibit any competitive release as far as
their prey is concerned. Only the black-backed jackal
that commonly scavenges could be influenced by the
lack of ungulate carcasses due to predation by large
predators. The four predator species investigated here
are still widespread in southern Africa. Results from
this analysis could therefore also be used to compare
the diets of the same species in different parts of their
range, where one or more of the other species may be
absent. This will provide insight into the effect of
decreased competition for food on diet.
The hypothesis that we test is that the supplementary prey category, mostly acquired due to fortuitous
encounters, will vary much more between different
localities for the same predator species, than the basic
prey category, i.e. those prey captured and consumed
because the predator is morphologically and behaviourally adapted to do so. In addition canids, due to
their less specialized dentition and coursing behaviour, would have more supplementary prey taxa
included in their diet than felids, resulting in a lower
Kendal’s coefficient of concordance.
Furthermore we suggest that supplementary prey
acts as a buffer between carnivore species occurring in
sympatry, and could lessen exploitative competition so
as to enhance coexistence.
MATERIAL AND METHODS
To test the above assumptions, we here use two data
sets to determine differences and overlap in the diets
of four sympatric canids and felids. We compare (1) the
stomach contents of the four carnivores from the Free
529
State Province of South Africa, which derives from our
own field research; (2) published results of various relevant studies in southern Africa. Our own data and
those of Smithers (1971) are, however, the only results
that allow comparison of the four species in sympatry,
albeit on different spatial scales. As analyses by different authors vary in resolution, these published
results on prey identity cannot always be directly compared, at least not at the species level. However, comparison at higher taxonomic levels, or using arbitrary
mass categories, is possible.
Stomach contents of 293 black-backed jackals, 76
Cape foxes, 57 caracals and 19 African wild cats were
collected in the Free State in South Africa during all
seasons over a period of 8 years (July 1984–July 1992)
during predator control operations by Oranjejag, a
now defunct predator control organization, and preserved in 70% ethyl alcohol or 10% formaldehyde.
Stomach contents were sorted macroscopically in the
laboratory and dried at 75 ∞C for 48 h in an Inc-O-Mat
drying oven. Food items were identified to the lowest
taxonomic level possible, using a stereoscopic microscope and a reference collection of potential prey. For
all taxa, the frequency of occurrence was calculated as
the proportion of stomachs containing the taxa,
expressed as a percentage of the total number of stomachs analysed.
For a comparison of the diet of the same predators
elsewhere in southern Africa, and for calculating Kendal’s coefficient of variation (Siegel, 1956) published
data were used. These were Grafton (1965); Bothma
(1966a, 1966b, 1971a, 1971b); Smithers (1971); Lynch
(1975); Stuart (1976, 1981); Smithers & Wilson (1979);
Bester (1982); Rowe-Rowe (1983); Bothma, Nel &
Macdonald, (1984); Moolman (1986); Palmer & Fairall
(1988) and Avenant & Nel (1992). The prey categories
used were Arachnida, Insecta, Reptilia, Aves, Artiodactyla, Carnivora, Hyracoidea, Lagomorpha and
Rodentia (all four species), and in addition, for the
Cape fox also the Myriapoda and Macroscelidea. For
an interspecific comparison of the number of food categories, the above categories as well as carrion and
vegetable (fruits) were used.
Most studies report on stomach content analyses,
with a few based on faecal analyses. As the degree of
resolution in the various analyses differs, direct comparison of prey species and other aspects are not
always possible.
For each carnivore species all vertebrate prey was
allocated to the basic category, unless a higher taxon
was captured at < 5% frequency of occurrence (e.g.
Osteichthyes). In xeric parts of South Africa small
mammal population size fluctuates widely over a
number of years and < 5% frequency of occurrence in
the stomachs probably reflects low population numbers of a particular prey species rather than the car-
© 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83, 527–538
530
O. B. KOK and J. A. J. NEL
nivore not being phylogenetically adapted to capture
it. All invertebrate prey were regarded as the supplementary category, unless personal observations on foraging predators indicated otherwise (see below). The
weights of non-vertebrate prey were obtained from
Kok (unpubl. data) and those of mammalian prey from
Lynch (1983) or Skinner & Smithers (1990).
RESULTS
The ratio of males to females in the sample of specimens for each carnivore species from the Free State
did not deviate from parity. Likewise, no gender differences in the dietary composition of the different
predator species could be demonstrated (MANOVA,
P = 0.05). Dietary data for males and females within
each species were therefore combined.
Clear differences in the number of prey taxa consumed by the canids and felids studied emerged, with
more prey taxa represented in the diets of the two
canid species (Tables 1 and 2). These differences are
significant between (P = 0.01) but not within (P = 0.05)
families. In both families the smaller species had a
more restricted diet, but both species of canid fed on a
broader prey spectrum than the largest felid (Table 1,
Fig. 1). Canids also included more invertebrates in
their diet, both as regards the number of taxa and in
comparison to the caracal, also as the percentage of
total occurrence. For the Cape fox the respective values were 10 and 45.5%, respectively; for the blackbacked jackal 14 and 40.0%; for the African wild cat 5
and 45.5%; and for the caracal 3 and 17.65%. Both
canids captured a more representative sample of taxonomic categories and weight class categories as food
(Figs 1, 2). In both families the smaller species took
more invertebrates than the larger ones (notably in
the case of the African wild cat) but only slightly fewer
mammals (Fig. 1). The caracal captured a much
Table 1. Composition of prey in the diet of 76 Cape foxes ( Vulpes chama), 293 black-backed jackals (Canis mesomelas),
19 African wild cats (Felis silvestris lybica) and 57 caracals (Caracal caracal), in the Free State Province, South Africa.
Class totals in bold
V. chama
(2.8 kg)
C. mesomelas
(8.5 kg)
F. s. lybica
(4.5 kg)
C. caracal
(16 kg)
Prey taxon
A
B
C
A
B
C
A
B
C
A
B
C
Invertebrate
Arachnida (total)
Acarina
Araneae
Scorpionida
Solifugae
Crustacea
Diplopoda
Insecta (total)
Blattodea
Coleoptera
Dermaptera
Diptera
Hymenoptera
Isoptera
Lepidoptera
Mecoptera
Orthoptera
Plecoptera
(Unidentified)
1.3
–
–
1.1
0.1
–
–
72.7
–
24.6
0.9
29.8
0.2
1.4
2.9
–
12.8
0.1
–
0.1
–
–
0.1
< 0.1
–
–
6.4
–
2.2
0.1
2.6
< 0.1
0.1
0.3
–
1.1
< 0.1
–
4
–
–
1
3
–
–
37
–
17
3
8
1
4
13
–
16
1
–
3.9
–
0.3
0.6
3.0
0.4
0.5
224.6
0.1
121.7
0.8
13.9
14.3
24.3
4.4
0.3
34.6
–
10.2
0.1
–
< 0.1
< 0.1
< 0.1
< 0.1
< 0.1
2.5
< 0.1
1.4
< 0.1
0.2
0.2
0.3
0.1
< 0.1
0.4
–
0.1
4
–
4
1
1
<1
1
31
<1
21
1
4
4
7
3
<1
7
–
2
0.7
–
–
–
0.7
–
–
6.2
–
4.8
–
–
0.1
0.4
–
–
0.9
–
–
0.2
–
–
–
0.2
–
–
2.1
–
1.7
–
–
<0.1
0.1
–
–
0.3
–
–
5
–
–
–
5
–
–
26
–
16
–
–
5
5
–
–
5
–
–
0.1
0.1
–
–
–
–
–
8.1
–
8.0
–
–
–
0.1
–
–
–
–
–
< 0.1
< 0.1
–
–
–
–
–
0.2
–
0.2
–
–
–
< 0.1
–
–
–
–
–
2
2
–
–
–
–
–
5
–
1.6
–
0.2
–
3
–
–
–
–
–
–
–
16
86
3
3
2
<1
1
10
89
2
–
–
1.5
91.8
0.2
1.5
0.1
< 0.1
< 0.1
2.8
93.2
3.2
–
–
17.2
1037.3
2.7
129.5
5.0
2.1
2.9
246.1
8332.5
287.0
–
284.1
115.8
–
97.6
39.8
–
90
26
17.8
5628.6
21.5
0.3
99.5
0.4
5
97
2
Vertebrate
Osteichthyes
Reptilia (total)
Chelonia
Squamata
Aves (total)
Mammalia (total)
1. Lepus capensis
4
–
–
–
2
–
–
–
–
–
© 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83, 527–538
DIETS OF SYMPATRIC CANIDS AND FELIDS
531
Table 1. Continued
V. chama
(2.8 kg)
C. mesomelas
(8.5 kg)
F. s. lybica
(4.5 kg)
C. caracal
(16 kg)
Prey taxon
A
B
C
A
B
C
A
B
C
A
B
C
2. Hystrix africaeaustralis
Pedetes capensis
Xerus inauris
Aethomys namaquensis
Rhabdomys pumilio
Saccostomus campestris
Tatera spp.
Desmodillus auricularis
(Unidentified)
3. Elephantulus myurus
(Unidentified)
4. Cynictis penicillata
Ictonyx striatus
Suricata suricatta
Otocyon megalotis
Caracal caracal
5. Orycteropus afer
6. Procavia capensis
7. Antidorcas marsupialis
Raphicerus campestris
Redunca fulvorufula
Sylvicapra grimmia
Capra hircus
Ovis aries
(Unidentified)
Mammals unidentified to
order
–
–
5.9
150.1
18.0
–
97.3
–
135.8
2.0
2.0
4.0
–
–
–
–
–
0.7
–
90.0
–
–
–
187.2
6.0
335.6
–
–
0.5
13.3
1.6
–
8.6
–
12.0
0.2
0.2
0.4
–
–
–
–
–
0.1
–
8.0
–
–
–
16.6
0.5
29.7
–
–
4
11
3
–
7
–
18
1
1
1
–
–
–
–
–
1
–
3
–
–
–
5
3
33
92.3
436.1
76.5
440.0
25.0
–
–
–
382.2
–
–
2.5
1.3
234.6
–
66.2
108.5
145.2
912.7
1476.5
–
1016.2
191.1
1786.9
310.7
341.0
1.0
4.9
0.9
4.9
0.3
–
–
–
4.3
–
–
< 0.1
< 0.1
2.6
–
0.7
1.2
1.6
10.2
16.5
–
11.4
2.1
20.0
3.5
3.8
1
6
2
3
1
–
–
–
15
–
–
<1
<1
2
–
1
<1
2
2
12
–
9
2
19
2
9
–
–
–
18.6
21.5
–
57.2
9.1
26.5
–
–
–
–
–
–
–
–
29.5
–
–
–
–
–
–
–
5.9
–
–
–
6.4
7.4
–
19.7
3.1
9.1
–
–
–
–
–
–
–
–
10.1
–
–
–
–
–
–
–
2.0
–
–
–
11
5
–
16
5
21
–
–
–
–
–
–
–
–
5
–
–
–
–
–
–
–
11
–
–
33.0
89.8
–
61.0
–
–
74.8
–
–
97.5
–
–
105.0
–
–
857.0
652.0
6.4
11.9
1054.6
12.3
1864.5
191.3
496.0
–
–
0.6
1.6
–
1.1
–
–
1.3
–
–
1.7
–
–
1.9
–
–
15.2
11.5
0.1
0.2
18.7
0.2
33.0
3.4
8.8
–
–
4
5
–
4
–
–
11
–
–
4
–
–
2
–
–
7
7
2
2
16
2
26
2
11
A, dry mass (g); B, dry mass per cent of total dry mass; C, frequency of occurrence (%) of taxon.
1- 7: Orders Lagomorpha, Rodentia, Macroscelidea, Carnivora, Tubulidentata, Hyracoidea, Artiodactyla.
higher percentage of mammalian taxa than the other
species and was therefore the most carnivorous, concentrating on mammal prey, while the black-backed
jackal was the most omnivorous. The African wild cat
had the most restricted diet, especially as far as the
number (but not percentage) of mammalian prey was
concerned.
When prey are assigned to different weight
classes it is clear that the canids prey more equitably on different-sized prey than the two felids
(Fig. 2). Where the African wild cat captured a preponderance of smaller prey, the black-backed jackal
but especially the caracal favoured large prey, with
the latter species capturing a high percentage of
prey heavier than itself. Clearly, as the size of both
canid and felid species increases, so does the representation of prey larger than the mean body weight
of the predator in its diet (see also Carbone et al.,
1999).
There were also differences in the number and identity of prey that were unique to each species. The
larger species in each family had more unique prey
species than the smaller one, with the black-backed
jackal having the most. Many taxa, mostly mammals,
were shared by the four species (Table 3), but only
three prey species were common to all the carnivores.
Comparisons of the mean percentage occurrence of
the different prey categories from different areas
(Table 4) show that the two canid species consume a
much higher percentage of invertebrates than the two
felids, and in particular insects. While the Cape fox
nearly has equal representation of invertebrates and
rodents in its diet, the African wild cat also consumes
invertebrates, but clearly concentrates on rodents. The
caracal takes nearly equal percentages of artiodactyls
and rodents with the artiodactyls all heavier than
itself, while the black-backed jackal has the most
diverse diet.
© 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83, 527–538
532
O. B. KOK and J. A. J. NEL
Table 2. Number of prey taxa in the diet of four sympatric canid and felid species in the Free State Province, South Africa.
Figures in parentheses indicate percentage occurrence: a single set refer to the total number of prey taxa for the species;
in the case of a double set the first (preslash) refer to the total number of prey taxa, and the second (postslash) to the
particular taxonomic category
Predator
Prey
V. chama
C. mesomelas
F. s. lybica
C. caracal
Total no. of prey taxa in dieta
Invertebrate prey taxa
with < 5% freq. occurr.
Vertebrate prey taxa (n.m)b
with < 5% freq. occur.
Mammal prey taxa
with < 5% freq. occur.
Invertebrate taxa of 1–5 g
Invertebrate taxa of 6–10 g
Vertebrate (n.m) taxa < 50 g
> 50 g
Mammal taxa of < 50 g
51–150 g
151–1000 g
1001–2500 g
2501–5000 g
5001–10 000 g
10 001–15 000 g
15 001–25 000 g
25 001–40 000 g
> 40 000 g
22
10
6
2
1
10
7
7
3
5
8
2
2
2
1
1
1
1
–
–
–
35
14
11
4
3
17
13
10
4
3
18
3
–
4
1
2
1
1
1
1
3
11
5
0
0
0
6
0
3
2
2
4
3
1
–
1
1
–
–
–
–
–
17
3
3
1
0
13
8
3
–
3
14
2
–
2
1
2
1
–
1
2
2
a
b
(45.5)
(26.1/60)
(8.6)
(4.3/50)
(45.5)
(30.4/70)
(30.4)
(13.0)
(21.7)
(34.8)
(8.6/20)
(8.6/20)
(8.6/20)
(4.3/10)
(4.3/10)
(4.3/10)
(4.3/10)
(40.0)
(31.4/78.6)
(11.4)
(8.6/75)
(48.6)
(37.1/76.5)
(28.6)
(11.4)
(8.6)
(51.4)
(8.6/17.7)
(11.4/23.5)
(2.9/5.9)
(5.9/11.8)
(2.9/5.9)
(2.9/5.9)
(2.9/5.9)
(2.9/5.9)
(8.7/17.7)
(45.5)
(54.5)
(27.3)
(18.2)
(18.2)
(36.4)
(27.3/50)
(9.1/16.7)
(9.1/16.7)
(9.1/16.7)
(17.6)
(17.6/100)
(5.9)
(76.5)
(47.1/61.5)
(15.0)
(15.0)
(70.0)
(11.8/15.4)
(11.8/15.4)
(5.9/7.7)
(11.8/15.4)
(5.9/7.7)
(5.9/7.7)
(11.8/15.4)
(11.8/15.4)
Represents lowest taxonomic categories identified, and includes, Class, Order or Species (see Table 1).
n.m, non-mammal.
100
Vulpes chama
Canis mesomelas
Felis s. lybica
Caracal caracal
90
80
Percentage occurrence
70
60
50
40
30
20
10
0
Insects
Arachnids
Reptiles
Birds
Mammals
Prey category
Figure 1. Percentage occurrence of the major prey categories in the diet of four sympatric canid and felid species in the
Free State Province, South Africa.
© 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83, 527–538
DIETS OF SYMPATRIC CANIDS AND FELIDS
533
60
Vulpes chama
Canis mesomelas
Felis s. lybica
Caracal caracal
Percentage occurrence
50
40
30
20
10
0
< 5g
6–50 g
51–150 g
151–1000 g
1001–5000 g
> 5000 g
Mass class
Figure 2. Percentage occurrence of the weight classes of prey, expressed as a percentage of the total percentage of all
classes, in the diet of four sympatric canid and felid species in the Free State Province, South Africa.
Table 3. Prey taxa shared by sympatric canid and felid species in the Free State Province, South Africa
Vulpes chama
Invertebrates
Vertebrates (n.m)a
Vertebrates (mammal)
Canis mesomelas
Invertebrates
Vertebrates (n.m)a
Vertebrates (mammal)
Felis s. lybica
Invertebrates
Vertebrates (n.m)a
Vertebrates (mammal)
a
Canis mesomelas
Felis s. lybica
Caracal caracal
2
7
2
5
8
2 classes
5 orders
none
3 orders
5 species
1
2
1
5
7
2 classes
4 orders
none
3 orders
4 species
1 class
2 orders
1 class
5 orders
10 species
–
–
–
–
–
–
1 class
2 orders
none
3 orders
3 species
classes
orders
classes
orders
species
–
–
–
class
orders
order
orders
species
n.m, non-mammal.
When use of prey categories, as compared to prey
taxa, is compared, the Cape fox included 8.2 (of 11) in
its diet, the black-backed jackal 9.7, the African wild
cat 6.1, and the caracal 7.5. This again indicates that
the two felids have a more restricted diet.
PREY
USE IN DIFFERENT AREAS
Between-species comparisons for most areas were
impossible as in most cases only one species was studied. Exceptions were the Free State, where two previ-
© 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83, 527–538
534
O. B. KOK and J. A. J. NEL
Table 4. Mean percentage occurrence of different prey categories in the diet of sympatric canid and felid species in
southern Africa, as derived from present data and published results. For a list of authors consulted, see Material and
Methods
Predator
Prey category
V. chama
C. mesomelas
F. s. lybica
Invertebrates (total)
Arachnida
Insecta
Vertebrates (total)
Osteichthyes
Amphibia
Reptilia
Aves
Mammalia
Artiodactyla
Carnivora
Hyracoidea
Lagomorpha
Rodentia
54.1
7.4
46.2
?
0
< 0.5
8.7
14.6
44.3
6.6
38.3
?
0.63
< 0.1
4.3
13.9
32.6
9.1
23.4
?
0
1.1
4.6
13.1
5.9
2.9
3.0
?
0
0
1.9
9.9
8.9
< 1.0
< 1.0
6.6
55.6
25.0
1.2
1.2
7.6
34.2
3.0
< 1.0
2.6
8.3
71.7
35.2
3.8
15.0
6.6
32.0
ous studies have been conducted, and Botswana. For
the rest, between-area comparison for a particular
species only could be attempted.
THE CAPE
FOX
VULPES
CHAMA
In all studies arachnids had a low (< 10%), and insects
a fairly high (24–60%) percentage of occurrence,
except for Botswana, with a 35 and 96% occurrence,
respectively. The same applies to reptiles, where the
percentage occurrence varied from 3 to 12%, but was
30% in Botswana. Birds appeared consistently (7–26%
occurrence) in the diet, as did lagomorphs and rodents.
The use of insectivores (elephant shrews) was more
sporadic. Disregarding livestock, predation on artiodactyls was nearly nonexistent.
The appearance of individual insect orders in the
diet varied, much more so than in the case of mammals, for example. However, the degree of occurrence
of particular rodent species depended on the area,
with the largest number of species being recorded in
the diet in Botswana. Kendal’s coefficient of concordance was 0.72 (N = 9), indicating a fairly high degree
of dietary specialization over its range.
for the montane grasslands of the Drakensberg mountains, where several species had a high or unique representation. While insects and arachnids as food
categories were usually well-represented, the occurrence and contribution by the different orders tended
to vary greatly. Kendal’s coefficient of concordance was
0.65 (N = 9), indicating a lower degree of dietary specialization than in the Cape fox.
THE AFRICAN
BLACK-BACKED JACKAL
CANIS
MESOMELAS
Several studies combined arachnids and insects into a
single prey group, making comparisons difficult. However, insects, birds, artiodactyls and rodents always
featured prominently in the diet. Rodent occurrence
tended to show site-specific differences, especially so
WILD CAT
FELIS
SILVESTRIS LYBICA
African wild cats tended to predate consistently on
arachnids and also insects. Birds were common vertebrate prey, as were rodents, while in some areas lagomorphs were also well represented in the diet.
Ignoring small livestock, artiodactyls were virtually
absent from the diet. Considering the large number of
rodent species represented by all studies, this prey
category is the most comprehensive of all. Kendal’s
coefficient of concordance was 0.46 (N = 7), the lowest
of the four species considered here. This indicates a
fairly low level of dietary specialization in southern
Africa.
THE
THE
C. caracal
CARACAL
CARACAL
CARACAL
Fish and amphibians were absent and invertebrates
and reptiles poorly represented in diets from different
areas. A fair number of birds were taken while mammals, especially artiodactyls, hyraxes and rodents
(and in two cases lagomorphs) featured prominently in
the diet. The caracal was the only predator that took
© 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83, 527–538
DIETS OF SYMPATRIC CANIDS AND FELIDS
prey heavier than itself throughout its range. Kendal’s
coefficient of concordance was 0.55 (N = 8), indicating
a medium degree of dietary specialization.
CONVERGENCE
AND DIVERGENCE IN DIETS
Comparison of these results (Tables 1, 3, Fig. 1) with
those of other studies (Table 4 and the references cited
in Material and Methods) shows that convergence and
divergence in diets occur both within, as well as
between, the two families. To some extent this is a factor of the different-sized species being compared as in
both families the smaller species has a more restricted
diet in terms of the number of prey taxa captured than
the larger (Table 1). Based on the percentage occurrence of prey, the smaller species also eats smallersized prey more often (Fig. 2). Both canids fed more
frequently on invertebrates, and also more on nonmammal vertebrates, than the two felids. Conversely,
felids fed more frequently on mammals (Fig. 1), and
more often on larger prey relative to body weight
(Fig. 2). Apart from size, the study area or habitat type
or even the time of study could influence the results.
For example, in our study no birds were recorded in
the diet of the African wild cat, although previous
studies in the Free State (Bester, 1982; Kok, 1996) did
so. Some studies elsewhere also report amphibians,
hyraxes and hares in the diet of this species. Convergence in prey between the two families therefore
results primarily from the mammalian taxa shared,
especially rodents, while divergence is highlighted by
differences in the frequency of use of invertebrates,
and non-mammal vertebrates, excepting birds.
PREY
CAPTURE: OPPORTUNISM VS. PHYLOGENY
Based on prey taxa and percentage occurrence in the
diet (Table 2), the number of opportunistically caught
prey (all invertebrates and non-mammal vertebrates
occurring at a frequency (£ 5%) could be determined.
Comparing these with the number of prey resulting
from phylogenetic adaptations gave an O/P ratio of
0.69/1 for the Cape fox, 0.67/1 for the black-backed
jackal, 0.83/1 for the African wild cat and 0.21/1 for the
caracal. These differences result from the larger number, or proportion, of invertebrate taxa in the diet of
the canids and the African wild cat. Clearly the two
canid species (especially the black-backed jackal) rely
more heavily on fortuitously acquired prey than the
two felid species. Invertebrates are, however, not
always fortuitously acquired: black-backed jackals
actively search for and eat harvester termites
Hodotermes mossambicus (Hagen) (Ferguson, 1980; J.
A. J. Nel, pers. observ.) as well as orthopterans and
coleopterans (J. A. J. Nel, pers. observ.). However, the
general distinction that is made here between prey
535
that are captured opportunistically, and those that are
captured due to evolutionary adaptations, should hold
true.
DISCUSSION
The stomach samples analysed for this study mainly
came from areas where small livestock (sheep and
goats) were available. Therefore to some extent our
data are biased towards the inclusion of these two
types of prey. However, African wild cats have never
yet been recorded as preying on these two prey (Skinner & Smithers, 1990), while Cape foxes can only kill
sheep less than 3 months old, otherwise they can only
be used as carrion (Bester, 1982). The black-backed
jackal and caracal can prey heavily on these livestock,
which to some extent probably replaced wild ungulates lost due to widespread farming practices. However, where dietary composition in areas with and
without small stock were compared, few differences
were evident apart from the addition of livestock as
prey for the caracal (Stuart, 1982; Moolman, 1986;
Avenant, 1993). Elsewhere, the caracal always
included a wide spectrum of mammals in its diet
(Grobler, 1981; Palmer & Fairall, 1988). All studies
point to caracals preying predominantly on mammals,
with the prey range probably reflecting the availability of prey taxa. Even with a mass < 21.5 kg (but being
closer to this transition point of Carbone et al. (1999))
the caracal is unique amongst the species compared
here in feeding mostly on prey ~45% of its mass. In
addition, there is a positive correlation between caracal use of habitat and prey density (Avenant & Nel,
1998). The same applies to the black-backed jackal. All
the published studies (e.g. Bothma, 1966a, 1971a,
1971b; Smithers, 1971; Ferguson, 1980; Rowe-Rowe,
1983) indicate a catholic diet for the jackal, with relative occurrence of prey taxa differing widely between
locations, probably as a response to availability.
Domestic livestock clearly forms an addition to their
normal diet and not a substitute for other items.
Although having a more restricted diet than blackbacked jackal (Bothma, 1966a, 1966b; Skinner &
Smithers, 1990; this study) Cape foxes similarly use
lambs ~3 months old as an additional, and not a substitute, dietary item. Seasonal differences in use,
related to lambing, are clearly apparent here (Bester,
1982).
It should be kept in mind that as a carnivore
matures and increases in mass its diet changes, and
such changes have been documented for growing Cape
fox pups in the Kalahari (Bester, 1982). For example,
Diplopoda are only eaten by young foxes, never by
adults. However, such data are few or nonexistent,
depending on the species, and could not be used in the
present comparison.
© 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83, 527–538
536
O. B. KOK and J. A. J. NEL
Data from our own study, and those from previous
studies in the Free State and elsewhere in southern
Africa support the contention of Kruuk (1986) that
felids include fewer food categories in their diets than
canids, especially if the size of predator is considered.
In general, it also supports the suggestion by Van
Valkenburgh (1989) that felids are highly specialized
for capturing mammalian prey. However, this must be
qualified by noting that the African wild cat captures
nearly equal numbers of invertebrate and vertebrate
prey taxa, albeit that the caracal concentrates heavily
on mammals that are usually as heavy as or heavier
than itself. The two canid species captured a wider
range of taxa, a trend that is especially evident in the
prey of the black-backed jackal, which in our study
took more mammal species than the caracal.
A more realistic appraisal of the diet of a species can
be obtained by comparing results from studies undertaken in different localities, even accepting the difficulties that arise due to different prey categories being
used. In southern Africa, our data and those of others
indicate that the diets of the two canid species differ
less, and have a higher Kendal’s coefficient of concordance, between sites than do the diets of the two felids
species, which have a lower coefficient of concordance.
These results therefore do not support the suggestion
by Kruuk, (1986) that felid diets in different areas are
more similar (suggesting a high degree of selection of
habitats, or very specialized hunting techniques, or
both) than those of canids. A probable explanation for
this discrepancy is that our data derive from studies in
mostly arid-to-semiarid habitats within southern
Africa, where fluctuating and unpredictable rainfall
events influence primary production in the first place,
and through it available biomass in the ascending
trophic levels. This means that the more opportunistic
species, in this case the canids, would always find prey
such as insects or rodents, no matter where they occur,
and that they merely switch between whichever particular species is present. In the case of the phylogenetically more specialized felids, the nonavailability of
a particular prey taxon could force them to be less
selective in southern Africa, which would account for
the lower coefficients of concordance recorded here. In
more temperate habitats, however, food in a particular
category would probably always be available, which
would account for the higher degree of specialization
being reflected in higher Kendal’s coefficients of
concordance. For example, the European wild cat
Felis s. silvestris has a coefficient of 0.67 (Kruuk,
1986) compared with the ecologically fairly similar
Africa wild cat Felis s. lybica that has a coefficient of
0.46 (these results).
As predicted, the fortuitous component of the diet
varies more between different areas than that of the
evolutionarily mediated one. This reduces the Kendal’s
coefficient, which in effect means that canids are more
opportunistic than felids. It can also be argued that
searching techniques per se have an influence on the
capture rate of supplementary prey. Coursers such as
canids would flush many more insects or other invertebrates than felids, which stalk and tend not to be
distracted from their selected prey. Because this opportunistic element depends heavily on the invertebrates
consumed, this allows the creation of a buffer between
the two families as far as prey sharing is concerned.
However, the effect of the size of the predator is always
present, with smaller carnivores feeding more heavily
on invertebrate prey (Carbone et al., 1999). The effect
of this buffer will increase as vertebrate, and especially
bird and mammal prey, decreases. As prey availability
decreases, predators become less selective and their
food spectrum broadens. In southern Africa, and especially the xeric parts, rodent numbers tend to fluctuate
widely. Therefore at low levels of abundance of these
prey, canids can and do switch to a higher invertebrate
component, but even felids can do so (Palmer & Fairall,
1988). This flexibility of canids is also demonstrated by
comparing the geographical distribution of the four
species here compared. In the hyperarid parts of southern Africa, such as the Namib Desert, Cape foxes and
black-backed jackals can exist, but not caracal and
African wild cats (Coetzee, 1969). Where the four species are sympatric, as in our study area and many
other parts of southern Africa, slight differences in
habitat use, activity (only the jackal and to a lesser
extent the caracal are also diurnal) and few shared
mammal prey species would lessen possible competition and mediate coexistence.
We have suggested above that the food niche
(Hutchinson, 1957) of a predator can be better understood if the dichotomy used here is taken into account.
Because food niche breadth is affected by the number
of taxa included in the diet as well as the equitability
of their occurrence, it is obvious that a factor that
heavily influences the number of taxa, as well as
changes in frequency occurrence (dependence on
invertebrates and scarce vertebrates), in the diet plays
a major role in determining food niche breadth. To
combine all prey in a single category obscures the reasons for dietary plasticity.
From the above it will be evident that changes in the
O/P ratio of predators in a given locality should be
expected, and that these are caused by changes in the
availability of specific prey taxa. A decrease in the
availability of prey captured because of phylogenetic
adaptations would tend to increase the reliance of the
predator on opportunistically caught prey, and to
increase the O/P ratio, while an increase in prey such
as rodents would have the opposite effect, because
selection for such a favoured prey would now be
possible.
© 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83, 527–538
DIETS OF SYMPATRIC CANIDS AND FELIDS
In conclusion, we suggest that by assigning prey
taxa to two categories, i.e. those that are caught opportunistically and those that are hunted because of the
evolutionary adaptations of the predator, a better idea
of the prey of carnivores can be obtained. Furthermore, this dichotomy is especially useful when comparing sympatric and potentially competing predator
species. In addition to slight differences in habitat use
and activity rhythms and sharing only a few mammal
prey taxa, such a dichotomy in the prey spectrum
would help explain coexistence of sympatric carnivores that seemingly overlap in their broad prey spectrum. Furthermore, it would also be more meaningful,
and biologically correct, to contrast specialist with
generalist when referring to the range of prey used by
predators. The term opportunist or opportunism
should be therefore confined to those instances where
prey are indeed opportunistically captured after being
fortuitously encountered, i.e. where the search phase
of the prey acquisition sequence is absent.
ACKNOWLEDGEMENTS
We are indebted to J. du P. Bothma, M. J. Somers and
two anonymous referees for many suggestions which
helped to improve this paper. However, we remain
responsible for all errors or omissions.
REFERENCES
Avenant NL. 1993. The caracal, Felis caracal Schreber, 1776,
as predator in the West Coast National Park. MSc Thesis,
Stellenbosch, South Africa: University of Stellenbosch.
Avenant NL, Nel JAJ. 1992. Prey use by four syntopic carnivores in a strandveld ecosystem. South African Journal of
Wildlife Research 27: 86–93.
Avenant NL, Nel JAJ. 1998. Home-range use, activity, and
density of caracal in relation to prey density. African Journal
of Ecology 36: 347–359.
Bester JL. 1982. Die gedragsekologie en bestuur van die silwervos Vulpes chama (A. Smith) met spesiale verwysing na
die Oranje-Vrystaat. MSc Thesis, Pretoria, South Africa:
University of Pretoria.
Biknevicius AR, Van Valkenburgh B. 1996. Design for killing: craniodental adaptations of predators. In: Gittleman JL,
ed. Carnivore behavior, ecology and evolution, Vol. 2. Ithaca:
Comstock Publishing Associates, 393–428.
Bothma J du P. 1966a. Notes on the stomach contents of certain Carnivora (Mammalia) from the Kalahari Gemsbok
Park. Koedoe 9: 37–39.
Bothma J du P. 1966b. Food of the silver fox. Vulpes chama.
Zoologica Africana 2: 205–210.
Bothma J du P. 1971a. Food habits of some Carnivora
(Mammalia) from southern Africa. Annals of the Transvaal
Museum 27: 15–26.
Bothma J du P. 1971b. Food of Canis mesomelas in South
Africa. Zoologica Africana 6: 195–203.
537
Bothma J du P, Nel JAJ, Macdonald A. 1984. Food niche
separation between four sympatric Namib Desert carnivores. Journal of Zoology, London 202: 327–340.
Bronner GN, Hoffmann M, Taylor PJ, Chimimba CT,
Best PB, Matthee CA, Robinson TJ. 2003. A revised systematic checklist of the extant mammals of the southern
African subregion. Durban Museum Novitates 28: 56–106.
Carbone C, Mace GM, Roberts SG, Macdonald DW. 1999.
Energetic constraints on the diet of terrestrial carnivores.
Nature 402: 286–288.
Coetzee CG. 1969. The distribution of mammals in the Namib
Desert and adjoining inland escarpment. Scientific Papers of
the Namib Desert Research Station 40: 23–36.
Creel S, Creel NM. 1996. Limitation of African wild dogs by
competition with larger carnivores. Conservation Biology 10:
526–538.
Dayan T, Simberloff D. 1996. Patterns of size separation in
carnivore communities. In: Gittleman JL, ed. Carnivore
behavior, ecology and evolution, Vol. 2. Ithaca: Comstock
Publishing Associates, 243–266.
Durant SM. 1998. Competition refuges and coexistence: an
example from Serengeti carnivores. Journal of Animal Ecology 67: 370–386.
Eisenberg JF. 1981. The mammalian radiations. London:
The Athlone Press.
Elliot JP, Cowan IM, Hollings CS. 1977. Prey capture in the
African lion. Canadian Journal of Zoology 55: 1811–1828.
Ewer RF. 1968. Ethology of mammals. London: Logos Press.
Ewer RF. 1973. The carnivores. London: Weidenfeld &
Nicholson.
Fedriani JM, Palomares F, Delibes M. 1999. Niche relationships among three sympatric Mediterranean carnivores.
Oecologia 121: 138–148.
Ferguson JWH. 1980. Die ekologie van die rooijakkals Canis
mesomelas Schreber, 1778 met spesiale verwysing na bewegings en sosiale organisasie. MSc Thesis, Pretoria, South
Africa: University of Pretoria.
Gittleman JL. 1985. Carnivore body size: ecological and taxonomical correlates. Oecologia 67: 540–554.
Grafton RN. 1965. Food of the black-backed jackal: a preliminary report. Zoologica Africana 1: 41–53.
Grobler JH. 1981. Feeding behaviour of caracal Felis caracal
Schreber, 1776 in the Mountain Zebra National Park, South
Africa. South African Journal of Zoology 16: 259–262.
Hutchinson GE. 1957. Concluding remarks. Cold Spring
Harbor Symposium on Quantitative Biology 22: 415–427.
Karanth KU, Sunquist ME. 2000. Behavioural correlates of
predation by tiger (Panthera tigris), leopard (Panthera pardus) and dhole (Cuon alpinus) in Nagarahole, India. Journal
of Zoology, London 250: 255–265.
Kleiman DG, Eisenberg JF. 1973. Comparisons of canid and
felid social systems from an evolutionary perspective. Animal Behaviour 21: 637–659.
Kok OB. 1996. Dieetsamestelling van enkele karnivoorsoorte
in die Vrystaat, Suid-Afrika. South African Journal of Science 92: 393–398.
Kruuk H. 1986. Interactions between Felidae and their prey
species: a review. In: Miller SD, Everett DD, eds. Cats of the
© 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83, 527–538
538
O. B. KOK and J. A. J. NEL
world: ecology, conservation and management. Washington
D.C.: National Wildlife Foundation, 353–374.
Levins R. 1968. Evolution in changing environments. Princeton: Princeton University Press.
Loveridge AJ, Macdonald DW. 2003. Niche separation in
sympatric jackals (Canis mesomelas and Canis adustus).
Journal of Zoology, London 259: 143–153.
Lynch CD. 1975. The distribution of mammals in the Orange
Free State, South Africa. Navorsinge van die Nasionale
Museum, Bloemfontein 3: 109–139.
Lynch CD. 1983. The Mammals of the Orange Free State.
Memoirs van die Nasionale Museum, Bloemfontein 18: i–
iv+1–128.
MacArthur RH, Levins R. 1967. The limiting similarity, convergence and divergence of coexisting species. American Naturalist 101: 377–385.
Mills G, Hes L. 1997. The complete book of Southern African
mammals. Cape Town: Struik Winchester.
Moolman LC. 1986. Aspekte van die ekologie en gedrag van
die rooikat Felis caracal Schreber, 1776 in die Bergkwagga
Nasionale Park en op omliggende plase. MSc Thesis, Pretoria, South Africa: University of Pretoria.
Palmer R, Fairall N. 1988. Caracal and African wild cat diet
in the Karoo National Park and the implications thereof for
hyrax. South African Journal of Wildlife Research 18: 30–34.
Palomares F, Ferreras P, Fedriani J, Delibes M. 1996.
Spatial relationships between Iberian lynx and other carnivores in an area of south-western Spain. Journal of Applied
Ecology 33: 5–13.
Rosenzweig ML. 1966. Community structure in sympatric
carnivora. Journal of Mammalogy 47: 602–612.
Rowe-Rowe DT. 1983. Black-backed jackal diet in relation to
food availability in the Natal Drakensberg. South African
Journal of Wildlife Research 13: 17–23.
Schoener TW. 1974. Resource partitioning in ecological communities. Science 185: 27–39.
Schoener TW. 1982. The controversy over interspecific competition. American Scientist 7: 586–595.
Siegel S. 1956. Non-parametric statistics for the behavioural
sciences. New York: McGraw-Hill.
Skinner JD, Smithers RHN. 1990. The mammals of the
southern African subregion. New Edition. Pretoria, South
Africa: University of Pretoria.
Sliwa A. 1994. Diet and feeding behaviour of the black-footed
cat (Felis nigripes Burchell, 1824) in the Kimberley region,
South Africa. Zoologische Garten 64Z: 83–96.
Smithers RHN. 1971. The mammals of Botswana. Museum
Memoir, National Museums of Rhodesia 4: 1–340.
Smithers RHN, Wilson VJ. 1979. Check list and atlas
of the mammals of Zimbabwe Rhodesia. Museum Memoirs, National Museums and Monuments of Rhodesia 9:
1–147.
Stuart CT. 1976. Diet of the black-backed jackal Canis
mesomelas in the Central Namib Desert, South West Africa.
Zoologica Africana 11: 193–205.
Stuart CT. 1981. Notes on the mammalian carnivores of the
Cape Province, South Africa. Bontebok 1: 1–58.
Stuart CT. 1982. Aspects of the biology of the caracal
(Felis caracal Schreber, 1776) in the Cape Province, South
Africa. MSc Thesis, Pietermaritzburg, South Africa: University of Natal.
Van Valkenburgh B. 1985. Locomotor diversity within past
and present guilds of large predatory mammals. Paleobiology 11: 406–428.
Van Valkenburgh B. 1988. Trophic diversity in past and
present guilds of large predatory mammals. Paleobiology 14:
155–173.
Van Valkenburgh B. 1989. Carnivore dental adaptations and
diet: a study of trophic diversity within guilds. In: Gittleman
J, ed. Carnivore behavior, ecology, and evolution. London:
Chapman & Hall, 410–436.
Van Valkenburgh B. 1991. Iterative evolution of hypercarnivory in canids (Mammalia: Carnivora): evolutionary interactions among sympatric predators. Paleobiology 17: 340–
362.
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