1. RH: Lodge and Pretorius • Resource Partitioning in Large Grazing Herbivores
Resource Partitioning and Interspecific Competition amongst Large Grazing
Herbivores
SKYE C. LODGE, Centre for Wildlife Management, University of Pretoria, Private Bag X20
Hatfield, Pretoria, 0028, South Africa
YOLANDA PRETORIUS, Centre for Wildlife Management, University of Pretoria, Private
Bag X20 Hatfield, Pretoria, 0028, South Africa
ABSTRACT Active adaptive management plays a crucial role in the management of Mabula
Game Reserve, Limpopo. By studying resource partitioning between the large grazing
herbivores in the reserve, management practices can be adapted according to what grasses are
selected for most by specific species and how selective those animals are in terms of the
species grazed. The selectivity of the animals determines their niche separation in that grass
species occur in specific geologies and landscapes. Niche separation will help determine
degree of competition between species by looking at where animal species occur and what
other species they overlap with. Multiple factors were taken into consideration when
determining resource partitioning and niche separation such as the size and composition of the
animal group, male to female ratio and animal size. Among these variables, grass species
consumed, height of grass, and soil type were recorded at allocated sites within the reserve to
determine resource partitioning and niche separation amongst large grazing herbivores. Even
though it has been suggested that the size plays an important role in niche separation, the
digestive system of animals plays an equally important role. Data shows that blue wildebeest
(Connochaetes taurinus) and plains zebra (Equus quagga) overlap considerably. While at
2. 2 Lodge and Pretorius
certain sites, dominated by Cynodon dactylon (old settlements), large congregations of
multiple species occur at one time. Sites with Cynodon dactylon are highly selected for in the
late-wet season by most large grazing herbivores due to its high palatability and availability.
The high overlap at old settlements may indicate low quantities of palatable grasses in the
reserve.
KEY WORDS active adaptive management, Mabula Game Reserve, resource partitioning,
niche seperation.
Small fenced reserves and conservation areas are in need of constant monitoring and
management in order to be sustainable. Adaptive management needs to be applied to these
areas in order to accommodate changes in ecological understanding and knowledge, as well as
enabling managers to adapt to unexpected events (van Wilgen and Biggs 2011).This
management approach incorporates research, planning, management and monitoring in
repeated cycles in order to learn what the best ways are to define an achieve objectives
(Pollard and du Toit 2007). Active adaptive management implies that management regimes
need to be flexible and constantly changed as knowledge and understanding of ecological
processes and interactions improve or as environmental conditions or societal values change
(van Wilgen and Biggs 2011).
In order to manage these small properties as best as possible, the history of land-use must
be known. Knowledge of the interaction between land-use, bush encroachment and soil
conditions is important in terms of aiding the understanding of how past land-use in an area
influences sustainable management (Abera and Belachew 2011). Livestock grazing in areas
where settlements used to occur can affect soil nutrient status either through trampling
(directly) or through nutrient recycling via urine and faeces (indirect) (Augustine et al.
2003).Areas where settlements used to be, have increased total nitrogen (N) levels in the soil
3. 3 Lodge and Pretorius
possible due to manure deposition adding nutrients to the soil (Angassa et al. 2012). On the
other hand, pH declines have been seen in soils previously used for crop harvesting (Brady
and Weil 2002). This pH decline may be attributed to the depletion of basic ions such as Mg2+
and Ca2+ as well as increased leaching (Brady and Weil 2002). Agassa et al. (2012) shows that
there is a negative correlation between pH and grass biomass. Vegetation richness and
diversity are heavily influenced by the nutrient status of the soil, which indicates how
important soil management should be in the management of reserves and conservation areas
(Agassa et al. 2012).
In a previous study done on Mabula Game Reserve by Smallwood (2009), herbivore
distributions were looked at in terms of the areas that were preferred and what the vegetation
and soil characteristics in those areas were. Smallwood (2009) and Wydeven and Dahlgren
(1985) emphasized the importance of understanding the habitat requirements of wildlife
species as well as the interaction between species and among species (interspecific and
intraspecific competition) for effective management to occur. Wildlife monitoring in small
reserve like Mabula Game Reserve is very important as it can provide the manager with
knowledge that is crucial for assessing and designing management programs as well as
stocking densities, harvesting rates and vegetation management (Pollock et al. 2002). Mabula
Game Reserve has re-established wildlife into the area as it was previously used for livestock
and grain production (Smallwood 2009). It is therefore important to know how the past land
use may have affected both the soil and vegetation characteristics as this will in turn affect the
distribution of grazing herbivores in the reserve and the sustainable stocking rates that the
reserve can manage in terms of what resources are available.
The aim of this study is to determine what different large grazing herbivores select for in
terms of resources and habitat type. The habitat types are defined by their past land use (old
settlement or old field) or whether it is a drainage line. Grass species composition on each site
4. 4 Lodge and Pretorius
is studied and related to the habitat type as well as the geology to look at differences in
resource composition between sites. At a herbivore level, it has been suggested that variations
in body size are the main contributor to resource partitioning (du Toit and Owen-Smith 1989).
Size variation among large grazing herbivores could lead to the utilisation of different quality
forages in varied quantities. It was found that smaller herbivores consumed forage higher in
quality than larger herbivores who consumed higher quantities of bulkier diets of lower
quality forage (du Toit and Owen-Smith 1989, Kleynhans et al. 2010).
Another herbivore aspect is the relationship between body size and gut capacity. Clauss et
al. (2007) stated that gut capacity increases linearly with body size. This further suggests that
the large quantity of forage eaten by larger herbivores enables then to consume forages of
lower quality (de Iongh et al. 2011). A study in the Kruger National Park on ungulate
assemblage showed a negative correlation between nitrogen content of herbivore faeces and
their body size (Codron et al. 2007). These findings support the notion that differences in
body mass aid niche separation among co-existing herbivores (the Jarman-Bell principle, Bell
1971, Jarman 1974).
Digestive strategies of the herbivore species are also important as it plays a role in resource
partitioning and niche separation. The digestive strategy of a herbivore will impact the quality
of food that the herbivore can eat (Kleyhans et al. 2010). Non-ruminants such as zebra (Equus
quagga) and white rhinoceros (Ceratotherium simum) are less efficient compared to
ruminants in terms of nutrient extraction from forage (Duncan et al. 1990). Non-ruminants
can compensate for this as they have higher passage rates (Duncan et al. 1990). The higher
passage rate allow for more efficient processing of low quality forage for non-ruminants
compared to ruminants of comparable size (Duncan et al. 1990).
5. 5 Lodge and Pretorius
Megaherbivores such as the white rhinoceros are bulk feeders capable of effectively
utilizing poor quality forage, however, protein levels of their diet is relatively high (Owen-
Smith 1988). The deviation from large species consuming diets of lower quality can be
explained by the digestive strategy, intake rate limitations and passage rates (Owen-Smith
1988, Clauss et al. 2007). A relationship between digestive efficiency and mean retention time
(MRT) in the gastrointestinal tract occurs (Kleynhans et al. 2010). This supports the statement
that non-ruminants are more efficient. MRT can vary between species and can be used as a
tool in understanding the factors influencing resource partitioning (Kleynhans et al. 2010).
Digestibility and protein content of grasses vary throughout the year (Kleynhans et al.
2010). These grass characteristics are also negatively correlated with grass height (Kleynhans
et al. 2010). Grasses vary in terms of seasonal patterns of growth and maturation which in
turn affects forage availability and quality (Kleynhans et al. 2010). This could lead to seasonal
differences in resource partitioning and niche separation among herbivores. Herbivores may
move through a reserve to find better resources in the dry season and therefore change their
distribution patterns compared to those seen in the wet season.
Resource partitioning can therefore be influenced by numerous factors such as body size,
grazing composition, digestive strategy and seasonal variation of grass quality and quantity
(Kleynhans et al. 2010). These factors need to be monitored to analyze their effects on
resource partitioning to determine the main driving forces of niche separation.
STUDY AREA
Mabula Game Reserve (MGR) is situated in Limpopo, South Africa, 47 kilometres from
Bela-Bela. The reserve is located in the Waterberg Mountains at 27°54’ S and 24°46’ E.
MGR is divided into two sections. The western section of 8500 hectares was included in the
study. The reserve is surrounded by electrified game proof fencing (Smallwood 2009). The
6. 6 Lodge and Pretorius
public are only permitted to use allocated roads within the reserve to go to and from the
lodges, time-share and whole owner properties. At every other time people must be in a game
vehicle driven by a reserve ranger or personnel that has completed the required test.
Mountainous terrain divided the reserve from north to south into two main geology types,
namely granite and quartzite. The mountainous range covers 12% of the reserve while the
remaining 88% is divided into 67% plains and 21% drainage lines (Bredenkamp and van
Rooyen 1990). The slow weathering of the geology types has resulted in acidic, sandy, loamy
to gravelly soils that have low fertility (Smallwood 2009). The soil fertility is one of the main
reasons why the vegetation in the reserve is low in quality (Smallwood 2009). The soil types
support approximately 122 grass species that are spread throughout the reserve (J. McMillan,
Mabula Game Reserve Ecologist, personal communication).
Mabula Game Reserve occurs in the Savanna Biome, with a unimodal, subtropical savanna
climate (Low and Rebelo 1998). The reserve has an average annual rainfall of 611.3 mm. The
warmest month of the year is January with an average temperature of 23.3 °C (Smallwood
2009). June is the coldest month with a monthly mean maximum temperature of 12.7 °C
(Smallwood 2009).
The land of which is now Mabula Game Reserve was previously used for agricultural
practices and for this reason there are areas spread throughout the reserve that are classified as
old fields. These areas are distinguishable by their clean edges, poor quality grass species and
ridges in the soil from tillage practices. Close to these old fields are areas classified as old
settlements. These old settlements were areas where previously people used to live and keep
their livestock. These areas where then high denuded in terms of vegetation cover due to
trampling by both people and the livestock in the kraals. These sites are distinguished by
7. 7 Lodge and Pretorius
clearings where there is very little tree cover and the ground cover is dominated by couch
grass (Cynodon dactylon).
One of the old fields on the granite geology has been under veld management practices for
the last 10 years (J. McMillan, Mabula Game Reserve Ecologist, personal communication).
Prior to initiation of these practices, the old field was dominated by yellow thatching grass
(Hyperthelia dissoluta). Through the practice of regularly mowing the area once the grass
reaches a certain height, higher quality grasses have begun to grow in between the thatching
grass. The cutting of the grass has also forced the grass to be in a continuous state of growth
thereby making new green growth available all the time. This has encouraged more wildlife,
both in terms of numbers and species, to visit the site especially in the dry season when little
green growth is available.
METHODS
Field studies were conducted in the late-wet and mid-dry season in Mabula Game Reserve.
A total of 27 days was spent doing research in the reserve. The late-wet season observations
were made from 19 March to 22 March and 25 March to 6 April, and the mid-dry season
observations were conducted from 7 July to 16 July. Observations usually started around
07:00 and ended around mid-afternoon with the latest observations being completed at 15:00.
Due to logistical constraints the variations in the time of day during which observations could
be made could not be controlled for leading to a bias in the amount of observations on the part
of the reserve dominated by granite soils.
The reserve was divided into granite (eastern side of the mountainous range) and quartzite
(western side of the mountainous range) geologies. Each geology type was allocated five
sites: two old fields, two old settlements and one drainage line. Each day the sites were
visited. Once at a site, observations were made as to whether wildlife were grazing on the site
8. 8 Lodge and Pretorius
or not. If wildlife were present, the species was identified using binoculars (Steiner SkyHawk
Pro 10x24). Only large herbivore species that are grazers or mixed feeders seen grazing on a
site were recorded. Along with the herbivore species name, the group size, sex ratio, relative
ages of group (adult or juvenile), GPS co-ordinate (Garmin eTrex Vista) of the vehicle upon
herbivore sighting, direction of sighted herbivores (north, south, west, east etc.), approximate
distance from vehicle, date, time, geology type and site name were recorded. After all of the
information is recorded the herbivores are observed in terms of where they were grazing. The
point of grazing was then approached on foot in order to identify the grass specie(s) that were
grazed. Grass blades and stems with edges that were still green (had not turned brown or
started turning brown) were assumed as being eaten by the observed herbivore species.
Animal tracks were also used to verify assumptions.
At the point of grazing a sample of more than 30 grams of the same grass species was
taken using a sickle. The sample was then placed in a paper bag and labelled accordingly. The
height of the identified eaten grass was also recorded using a disc pasture metre. Once the
sample and height reading had been recorded, the disc pasture metre was used to record the
biomass of the surrounding grasses. A radius of 10 metres around the point of grazing was
established and ten random points were then measured and the most dominant grass species
under the disc was identified and recorded.
This exact procedure mentioned above was used for the late-wet season observations. In
the mid-dry season it was difficult to identify grass species as well as the grasses that were
recently grazed. It was therefore decided to omit the steps of identifying the grasses and
taking samples due to the possibility of incorrectly identifying grazed grass and grass species.
Further sampling was done in the form of line transects. Line transects of 50 metres were
done on each site using a 50 metre tape measure. The species at each one meter mark was
9. 9 Lodge and Pretorius
identified and recorded. If the grass was grazed it was recorded accordingly. At one metre
marks where no grass species were found a dot was made during recording meaning that
nothing was found and the grass species identified was observed 10 centimetres past the one
metre mark. If nothing was found at the position 10 centimetres past the metre mark another
dot was made until a grass tuft occurred at a point. Hits were also recorded. This meant that
the grass species occurred directly under mark.
Chemical analysis was done on samples taken from the most frequently eaten grasses.
Some grass species were repeated in order to determine whether differences in nutrient quality
exist between geology types. Each grass species sampled had a respective late-wet season and
mid-dry season sample so that differences in nutrient quality between these seasons could be
analysed. Chemical analysis was done at Nutrilab, University of Pretoria. Chemical analyses
done were dry matter (DM), neutral detergent fibre (NDF), acid detergent fibre (ADF), and
mineral analyses. The mineral analyses included phosphorus (P), calcium (Ca), copper (Cu),
iron (Fe), manganese (Mn), and zinc (Zn). Each grass sample was analysed in duplicate (as
per Nutrilab procedure) to ensure that errors were minimised.
Data analyses
GPS co-ordinates were converted to a format readable by ArcGIS 10.1. ArcMap was used
to create maps of Mabula Game Reserve using GIS layers provided by the reserve. GPS co-
ordinate of observations in both the late-wet and mid-dry seasons were entered into ArcMap
and layers were created for different herbivores to determine changes in site selection
patterns. Tables and figure were then used to represent data in the figures created in ArcGIS
for clarification of information. Tables of grass species consumed per animal species and their
relative frequencies of consumption were also constructed.
RESULTS
10. 10 Lodge and Pretorius
The sites monitored in this study have been labelled accordingly for ease of reference:
Granite: Old field 1 F1G
Old field 2 F2G
Old settlement 1 S1G
Old settlement 2 S2G
Drainage line DG
Quartzite: Old field 1 F1Q
Old field 2 F2Q
Old settlement 1 S1Q
Old settlement 2 S2Q
Drainage line DQ
11. 11 Lodge and Pretorius
Figure 1: Position of sites and their respective abbreviated names in Mabula Game
Reserve. A total of ten sites were observed with five on granite geology and five on quartzite
geology.
Distribution patterns of wet and dry seasons
At each site, animals were observed and the GPS coordinates recorded. This helps
determine changes in distribution. The overall distribution of animals shows differences in
S1GS2G
F1G
F2G
DG
S1Q
S2Q
F1Q
F2Q
DQ
12. 12 Lodge and Pretorius
site selectivity between the late-wet and mid-dry seasons (Figure 2 and Figure 3). A general
movement from granite to quartzite geology was seen in the mid-dry season as well as
significant increases in visits to both F1G and DQ. In the late-wet season, large grazing
herbivores were observed more frequently on S1Q, when compared to observations made in
the mid-dry season, where the frequency of visits to other old settlements remained similar
(S1G, S2G and S2Q). Large grazing herbivores were also more widely spread across the
reserve in the late-wet season. Herbivores did not visit DG frequently in both the late-wet and
mid-dry seasons; however, in comparison, the frequency of observations made at DQ
increased significantly in the mid-dry season. There was a slight increase in observations at
F2G; however, overall very few herbivores were observed grazing at this site. The most
utilised site by all herbivore species was F1G (Figure 2 and Figure 3). On most days there
were more than one species grazing on this site at the same time with an average of 3-4
species being observed at the same time.
13. 13 Lodge and Pretorius
Figure 2: Overall distribution of large grazing herbivores in the late-wet and mid-dry
seasons. The GPS points were plotted onto the Mabula Game Reserve map with the geology
layer to show differences in distribution over the two dominant geology types, granite on the
eastern side of the mountainous ridge and quartzite on the western side of the mountainous
ridge.
14. 14 Lodge and Pretorius
Figure 3: Frequency (number of observations) of visits by large grazing herbivores to sites
compared over the late-wet and mid-dry seasons.
Species specific distribution changes - Some of the herbivore species mentioned in Table 1
were observed on more occasions than others due to their specific habitat preferences. Buffalo
along with roan antelope and blesbok were not observed at all in the late-wet season, on the
allocated sites, with slightly more sightings in the mid-dry season. On the other hand,
waterbuck and nyala were monitored at all in the mid-dry season. Zebra and blue wildebeest
observations remained similar, regarding each species, thereby indicating the possibility of
the two species moving together and therefore being observed at similar frequencies.
0
5
10
15
20
25
30
35
40
45
50
F1G F2G S1G S2G DG F1Q F2Q S1Q S2Q DQ
Frequency
Site
Mid-dry season
Late-wet season
15. 15 Lodge and Pretorius
Table 1: Large herbivore species (common and scientific names) that were monitored on
Mabula Game Reserve and the number of times they were observed grazing in the late-wet
and mid-dry seasons.
Number of observations
Common name Scientific name Late-wet Mid-dry
Blesbok Damaliscus pygargus phillipsi 0 5
Blue wildebeest Connochaetes taurinus 20 18
Buffalo Syncerus caffer 0 4
Eland Tragelaphus oryx 4 5
Gemsbok Oryx gazella 1 7
Impala Aepyceros melampus 11 47
Nyala Tragelaphus angasii 4 0
Red hartebeest Alcelphus buselaphus 7 13
Roan antelope Hippotragus equinus 0 1
Tsessebe Damaliscus lunatus 2 3
White rhinoceros Ceratotherium simum 4 9
Zebra Equus quagga 26 26
Waterbuck Kobus ellipsiprymnus 1 0
In Table 2 and Figure 4, the observations of both blue wildebeest and zebra are shown for
the late-wet and mid-dry seasons to illustrate the similarity in habitat preference. Zebra and
wildebeest were the most observed species, apart from impala, over the duration of the study.
They were found on a various sites in the reserve. Site DQ was only visited once by zebra in
16. 16 Lodge and Pretorius
the late-wet season while blue wildebeest were not found there at all; however, increased
observation of both species were made on site DQ during the mid-dry season. Another site
that was not visited by blue wildebeest in the late-wet and mid-dry seasons was DG while
zebra only grazed at DG once during the mid-dry season. Both the points on the map (Figure
4 and values in Table 2) show that both blue wildebeest and zebra tend to occur on the same
sites.
Table 2: Frequency of blue wildebeest and zebra observations per site in the late-wet and
mid-dry seasons.
Blue wildebeest Zebra
Site Geology Late-wet Mid-dry Late-wet Mid-dry
F1G granite 6 8 11 2
F2G granite - - - 2
S1G granite 5 - 1 1
S2G granite 1 - - 1
DG granite - - - 1
F1Q quartzite 5 2 8 3
F2Q quartzite - - 1 1
S1Q quartzite 3 4 3 5
S2Q quartzite - 1 1 -
DQ quartzite - 3 1 10
Total 20 18 26 26
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Figure 4: GPS coordinates plotted on Mabula Game Reserve map to show the distribution
of zebra and blue wildebeest in both the late-wet and mid-dry seasons.
In terms of white rhinoceros and impala, the distributions are shown in Table 3 and Figure
5. Both herbivores prefer to graze at sites that have more Cynodon dactylon (old settlements,
F1Q, F2Q and DG) in the late-wet season. The sites preferred by these two species in the late-
wet season are S1G (white rhinoceros) and S2G (White rhinoceros and impala). In the mid-
dry season white rhinoceros were seen predominantly on F1G and F2G. Impala observations
significantly increased in the mid-dry season compared to the late-wet season therefore
showing a drastic change in site selection of impala between these two seasons. Impala were
found grazing on nine out of the ten sites, indicating a wider distribution.
18. 18 Lodge and Pretorius
Table 3: Frequency of white rhinoceros and impala observations per site in the late-wet and
mid-dry seasons.
White rhinoceros Impala
Site Geology Late-wet Mid-dry Late-wet Mid-dry
F1G granite - 6 - 7
F2G granite - 1 - 1
S1G granite 4 - 3 11
S2G granite - - 2 2
DG granite - - 2 -
F1Q quartzite - - 1 1
F2Q quartzite - - 1 6
S1Q quartzite - - 1 9
S2Q quartzite - - 1 5
DQ quartzite - 2 - 5
Total 4 9 11 47
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Figure 5: Distribution of white rhinoceros and impala according geology type and site in
Mabula Game Reserve. Distribution is split into late-wet and mid-dry season.
Resource partitioning
Each herbivore species has their own dietary preference and these preferences aid the
division of herbivores into different foraging regimes (bulk grazer, concentrate feeder,
browser and intermediate feeders). Table 4 shows how selective each herbivore species is in
terms of the grass species it was observed grazing and the relative frequency of the number of
times a herbivore chose to eat the same grass species.
Table 4: Grass species selected for by each large grazing herbivore and total number of
times the same grass species was consumed by the same herbivore species in the late-wet
season. Zebra (Z), blue wildebeest (BW), impala (I), red hartebeest (RH), eland (E), gemsbok
(G), nyala (N), white rhinoceros (WR), waterbuck (W) and tsessebe (T) were observed. Grass
species that were not observed as eaten by each herbivore species respectively is marked with
‘-‘.
Herbivore selection frequency
Grass species Z BW I RH E G N WR W T
Aristida adschensionis - - - - - - - - - -
Aristida canescens - - - - - - - - - -
Aristida congesta subsp. barbicollis - - 1 - - - - - - 1
Aristida congesta subsp. congesta 1 - - - - - - - - -
Aristida meridionalis 1 - - - - - - - - -
Aristida stipitata subsp. graciflora 2 - - - - - - - - -
Aristida stipitata subsp. stipitata - - - - - - - - - -
Brachiaria serrata - - - - - - - - - -
Brachiaria nicropitata - - - - - - - - - -
Chloris virgata - - - - - - - - -
Cynodon dactylon 8 14 9 3 3 - 2 4 - 2
Dactyloctenium aegyptium - - - - - - - - - -
Digitaria eriantha - - 1 1 - - - - - -
Digitaria ternata - - - - - - - - - -
Eragrostis biflora - - 1 - - - - - - -
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Eragrostis gummiflua 1 4 - - - - - - - -
Eragrostis heteromera - - - - - - - - - -
Eragrostis lehmanniana - - - - - - - - - -
Eragrostis rigidior - - 1 - - - - - - -
Eragrostis trichophora 2 1 - - - - 1 - - -
Eragrostis viscosa 1 - - - - - - - - -
Heteropogon contortus 3 - 2 - - - - - - -
Hyparrhenia filipendula - - - - - - - - - -
Hyparrhenia hirta 2 - - - - - - - - -
Hyperthelia dissoluta 9 - - 3 - 1 - - - -
Melinis repens 2 2 2 - - 1 - - 1 -
Panicum maximum 2 1 - - - - 1 - 1 -
Perotis patens - - - - - - - - - -
Pogonarthria squarrossa - - - - - - - - - -
Schizachyrium jeffreysii - - - - - - - - - -
Schizachyrium sangineum - - - - - - - - - -
Setaria sphacelata subsp. sphacelata 1 - - - - 1 - - - -
Sporobolus africanus - - - 1 1 - - - - -
Sporobolus ioclados - - - - 1 - - - - -
Tragus berteronianus - - - 1 - - - - - -
Tricholaena monachne - - - - - - - - - -
Trichoneura grandiglumis - - - - - - - - - -
Urocloa mosambiscensis - - - - - - - - - -
Herb - - - - - - - - - -
Total 35 22 17 9 5 3 4 4 2 3
In Table 4, zebra have the widest dietary range consisting of 13 grass species. These
selected grass species range from those of poor quality, such as Hyperthelia dissoluta,
Hyparrhenia hirta and Aristida meridionalis, to those of good and high quality, such as
Cynodon dactylon, Digitaria eriantha and Panicum maximum (van Oudtshoorn 2012). White
rhinoceros are the complete extreme, where in the late-wet season they only consumed
Cynodon dactylon. Tsessebe, nyala, waterbuck, gemsbok and eland were also observed as
having a narrow dietary range; however, they were also only observed a few times. Blue
wildebeest in comparison to zebra, consume the same grass species as zebra; however, they
do not seem to consume the grasses with higher fibre contents, such as Heteropogon
21. 21 Lodge and Pretorius
contortus and Aristida meridionalis. Impala are shown as having a diet consisting of higher
quality grasses.
Chemical analyses
NDF and ADF – Chemical analyses of the samples were done at Nutrilab so that the fibre
fractions could be compared per grass species at each time period to identify if there are any
differences. The ADF and NDF analyses were done using an ANKOM Automated Fiber
Analyzer.
Table 5: NDF and ADF percentages of sampled grass species per site per time period.
Late-wet indicates samples taken in the late-wet season and mid-dry indicates samples taken
in the mid-dry season.
NDF (%) ADF (%)
Grass species Site
Late-wet Mid-dry Late-wet Mid-dry
Hyparrhenia hirta F1G 74,079 77,002 49,794 53,367
Panicum maximum S1Q 69,034 67,172 43,878 43,366
Heteropogon contortus DQ 73.454 71,418 45,767 44,845
Panicum maximum F1G 69,183 69,338 44,372 46,530
Cynodon dactylon S1G 77,118 72,607 44,763 36,659
Melinis repens F1G 74,325 72,997 45,943 44,837
Melinis repens F1Q 75,360 72,441 48,210 46,729
Setaria sphacelata DQ 64,800 69,544 36,514 43,216
Heteropogon contortus F1G 71,333 71,869 46,902 46,671
Hyperthelia dissoluta F1G 74,065 75,879 57,575 51,521
Eragrostis gummiflua F1G 79,753 77,021 48,451 48,132
Cynodon dactylon S2Q 76,219 72,749 38,163 36,549
22. 22 Lodge and Pretorius
Cynodon dactylon S1Q 76,166 68,860 46,823 39,521
Figure 6: Grass species samples analysed per site and their respective NDF (%) in both the
late-wet and mid-dry seasons.
Figure 6 shows that Eragrostis gummiflua taken from site F1G has the highest NDF
percentage for both the late-wet and mid-dry seasons. Cyndon dactylon has the second highest
NDF percentage in the late-wet season regardless of which site the sample was taken from.
Grass species in which the NDF percentage is higher in the mid-dry season than in the late-
wet season are Hyperthelia dissoluta, Hyparrhenia hirta, Panicum maximum (F1G), Setaria
sphacelata, and Heteropogon contortus (F1G). Setaria sphacelata has the lowest NDF
percentage in the late-wet season and Panicum maximum at site S1Q has the lowest NDF
percentage in the mid-dry season.
0
10
20
30
40
50
60
70
80
NDF(%)
Late-wet season
Mid-dry season
23. 23 Lodge and Pretorius
Figure 7: Comparison of % ADF between the late-wet and mid-dry season grass samples
that were analysed.
Hyperthelia dissoluta has the highest ADF percentage in the late-wet season. Hyparrhenia
hirta has the second highest ADF percentage in the late-wet season. Setaria sphacelata has
both the lowest ADF and NDF percentages in the late-wet season. Cynodon dactylon at sites
S1G and S2Q have the lowest ADF percentages in the mid-dry season.
Mineral analyses – Grass species most frequently grazed were tested at Nutrilab. Each
grass species has both a late-wet season and a mid-dry season sample that was analysed so
that differences between these two time periods could be distinguished.
Table 6: Mineral analyses of grass species per site per time period. Ca, P, Cu, Fe, Mn, and
Zn values per sample are illustrated below. D or W after the site name indicates whether the
sample was taken in the mid-dry season (D) or the late-wet season (W).
Grass species Site Ca (%) P (%) Ca:P Cu (dpm) Fe (dpm) Mn (dpm) Zn (dpm)
0
10
20
30
40
50
60
ADF(%)
Late-wet
Mid-dry
25. 25 Lodge and Pretorius
minerals were not of primary concern for this study. However, in most instances Cu, Fe, Mn
and Zn levels were higher in the late-wet season when compared with the same grass in the
mid-dry season.
DISCUSSION
Distribution patterns of wet and dry seasons
The GPS coordinates in Figure 2 and the frequency of observations per site in Figure 3
have identified changes in the general distribution of all large grazing herbivores in Mabula
Game Reserve. The frequency of visits to both F1G and DQ increased significantly from the
late-wet to the mid-dry season (Figure 3). This is thought to be due to the veld management
practices in place on F1G and the higher quality grasses that grow in the drainage lines. The
ecology team on Mabula Game Reserve has been mowing site F1G for the last 10 years,
where as soon as the grass on the site grows beyond a threshold point it is mowed and the cut
grass left on site (J. McMillan, Mabula Game Reserve Ecologist, personal communication).
The cut grass is used as a type of fertiliser where it will contribute to the organic matter
content of the soil as well as protecting the soil surface from excessive solar radiation. This is
all done with the goal of increasing the nutrient quality of the soil in mind as the soil of areas
in Mabula Game Reserve that were once used as fields for crops are very poor in nutrients (J.
McMillan, Mabula Game Reserve Ecologist, personal communication). Agricultural practices
result in the decrease of soil nutrients, if the soil is not sufficiently fertilised and monitored,
due to the high demands of producing monoculture crops and pastures (Angassa et al. 2012).
There is a constant demand for nutrients by plants as once one crop is harvested the next is
reaped and grown and the process continues (Angassa et al. 2012). The veld management
technique on site F1G has been very successful as previously, the site was dominated by
Hyperthelia dissoluta that flourished on sites like this due to low nutrient requirements. The
26. 26 Lodge and Pretorius
constant mowing of the grass on F1G has slowly enabled other more palatable grass species
to grow in between the Hyperthelia dissoluta tufts by reducing the competition between the
grasses, increasing soil nutrient availability from cutting residue, and forcing the grass to be in
a continuous state of growth. Since the grass is forced to be in a continuous state of growth,
there is always green leaf growth (even in the mid-dry season). This is the reason why more
animals are proposed to be visiting this site (F1G) in the mid-dry season. The resource
availability is higher, thereby allowing for more than one species to utilise the site at the same
time and not have to compete with each other.
In terms of the increase of observations at site DQ, it is assumed to be due to the
availability of more palatable grass species in the mid-dry season. The soils in the drainage
lines are generally higher in nutrient content due to water flowing from higher areas through
the drainage line and depositing leached nutrients (Angassa et al. 2012). The higher nutrient
quality soil allows for more palatable species to grow that have higher nutrient requirements
compared to less favourable, fibrous grasses such as Hyperthelia dissolute and Hyparrhenia
hirta. The reason why herbivores visit site DQ more frequently than site DG is not yet fully
understood. Perhaps it could be the effect of the geology type on the grass species growing at
each site and the nutrient composition of each grass species.
The old settlements (S1G, S2G, S1Q and S2Q) are all dominated by Cynodon dactylon
cover and can therefore help identify any of these areas with Mabula Game Reserve. It is
thought that Cynodon dactylon carries the herbivores through winter as in Mabula Game
Reserve the forage quality is low especially during the mid-dry season. This may be the
reason why the number of observations at S1G, S2G and S2Q remained similar between the
late-wet and mid-dry seasons. Observation numbers did not increase as it is proposed that
early in the dry season, these sites are highly utilised before the quality of the Cynodon
dactylon drops below optimal levels (J. McMillan, Mabula Game Reserve Ecologist, personal
27. 27 Lodge and Pretorius
communication). When observations were made during the mid-dry season, there was very
little ground cover at these old settlements thereby supporting the ecologist’s proposal. The
reason for site S1Q observations increasing in the mid-dry season may be due to the sites
position. Close to site S1Q is Kai dam in Mabula Game Reserve and just above it is a small
water source. Apart from the water sources nearby, the site is surrounded by the mountain
ridge that separates the granite and quartzite geologies. This may provide protection to the site
and allow mist in the dry season to linger longer thereby keeping the soil moist. This may
provide more optimal conditions for growth and henceforth result in more resources available
for herbivores.
Species specific distribution changes – Overall 13 different herbivore species were monitored
at the allocated sites; however, some of the species were observed more frequently than others
(Table 1). This may be a result of the sites not being part of their habitat selection at the time
of study. This can explain why there are differences in observation numbers between the late-
wet and mid-dry seasons as the herbivores change their habitat selection according to changes
in environmental conditions as well as resource availability. Some herbivores may even adapt
their foraging strategy according to what is available. Nyala, for example, were not observed
and any of the sites in the mid-dry season as they have a tendency to browse more in the dry
season and all of the sites are dominated by grass cover (Estes 1991).
Table 1 also showed that both blue wildebeest and zebra observation numbers do not vary
to a large degree when comparing late-wet and mid-dry observations between the species.
This indicates the possibility of the two herbivore species occurring at similar sites at the
same time. Table 2 and Figure 4 further shows that blue wildebeest and zebra do occur at
similar sites. In Table 2, it shows that when zebra observations are low so too are blue
wildebeest observations. It does; however, also show a major difference between these two
herbivores in terms of their distribution at sites F1G and DQ where more zebra are observed
28. 28 Lodge and Pretorius
at F1G than wildebeest in the late-wet season. However, a decrease in zebra observations, in
comparison to blue wildebeest, is seen in the mid-dry season. This may be due to zebra
preferring site DQ over F1G as there is a significant increase in the number of zebra
observations in the mid-dry season compared to the late-wet season. There is a similar trend
for the blue wildebeest at site DQ; however, the increase in observations is not as much.
Figure 4 further confirms this notion, as the points show that where one occurs so does the
other.
White rhinoceros and impala are compared with each other in terms of distribution as they
both prefer to graze at sites with Cynodon dactylon in the late-wet season. Even when impala
and white rhinoceros are not seen on old settlement sites, they were found grazing on small
patches of Cynodon dactylon that can be found on other sites (Table 3 and Figure 5). In the
late-wet season there was a high overlap of herbivore species as there was an abundance of
resource (Cynodon dactylon). The Cynodon dactylon flourished after Mabula Game Reserve
received approximately 300 millimetres of rain in the two weeks prior to the initiation of this
study. Since both white rhinoceros and impala are known to graze on shorter, high quality
grasses, it was no surprise that both these species chose to graze at these sites (Kleynhans et
al. 2010). In the mid-dry season, both species showed a wider site selection (Table 3). Impala
observation numbers significantly increased during the mid-dry season. This indicates that
impala changed their selection of sites. This is a similar case to the buffalo, as in the late-wet
season they were not observed on any of the sites and in the mid-dry season they changed
their distribution pattern and this coincided with some of the sites on Mabula Game Reserve.
Resource partitioning
Each herbivore species has grasses that it selects for and these may be similar or different
to herbivore species in the same area. In Table 4, herbivore species were observed as having
29. 29 Lodge and Pretorius
various diets in the late-wet season. Grass species selection by herbivores was not monitored
in the mid-dry season due to the difficulty of identifying grasses and the errors that would be
involved. It can therefore be assumed that resource selection may differ in the mid-dry season
from that which is shown in Table 4. The figures and tables indicating distribution differences
show changes in habitat selection, so it is relatively safe to assume that most herbivores alter
their diet composition in the mid-dry season.
Zebra are non-ruminant grazers and are thought to be are able to cope with a wider variety
of grass quality in their diet due to their digestive strategy (Duncan et al. 1990). This may be
the reason why the zebra on Mabula Game Reserve occur on most sites in the reserve and
have a wide dietary range of grass species. This gives the zebra on Mabula Game Reserve a
competitive advantage over herbivore species such as impala and nyala that are concentrate
feeders, as they have a larger choice of where they can feed and therefore do not have to
overlap with many species in terms of niche separation.
Cynodon dactylon was a highly sought after grass species. Almost all herbivore species
monitored in the late-wet season were observed as eating Cynodon dactylon. This is why such
a high overlap of species could be seen at old settlements, especially S1G. However, in the
mid-dry season lower overlaps between herbivore species was seen possibly due to there
being a shortage of resources at the old settlements and animals began to compete too much
with each other thereby forcing them to graze elsewhere. This notion is supported by Table 3
where the white rhinoceros were observed as moving away from site S1G, and away from
other old settlements, to areas with more available graze, such as site F1G.
The most utilised site by all herbivore species was F1G (Figure 3). This is the site that
has been mowed for a number of years in an attempt to eradicate or reduce the high levels of
Hyperthelia dissoluta and increase the diversity of more palatable grass species on the site.
30. 30 Lodge and Pretorius
The veld management practices have enabled herbivores to graze green growth even in the
mid-dry season. Therefore it makes sense that this site is the most frequently visited among all
the monitored sites. In both the late-wet and mid-dry seasons, there are high overlaps between
herbivore species; however, this was only possible due the high levels of resource availability
thereby reducing competition between species. Reduced levels of competition allow more
species to graze on the same site without forcing each other to move elsewhere in search of
habitats with higher resource abundance.
Chemical analyses
NDF and ADF – Cynodon dactylon grass samples all have higher NDF and ADF
percentages than expected. This may be due to samples consisting only of graze material
being difficult to achieve. Cynodon dactylon is a highly palatable and sought after grass that
grows very low to the ground. It is stoloniferous and therefore when samples were taken a lot
of root material was taken as well. Collecting only leaf material would have made it
extremely difficult to achieve sufficient sample weights for chemical analyses. Hyperthelia
dissoluta and Hyparrhenia hirta are proven to be of poor nutrient quality as they have both
high ADF and NDF percentages and other nutrient in these grasses are therefore highly
diluted.
Mineral analyses – One of the most important mineral ratios is the Ca:P ratio that should
be ideally 2:1 (McRuer and Jones 2009). All of the grass species analysed had a ratio of 2:1
and greater. This may seem to be ideal; however, the problem comes in where the phosphorus
values of all the grasses are extremely low, most of which are below 0,100 %. The P
percentages higher than 0,100 % are of grasses mostly found on old settlements. This may
indicate that previous agricultural practices in these areas may contribute to higher P levels in
the soil and therefore grasses in these areas have higher P levels. All but two of the grass
31. 31 Lodge and Pretorius
samples of the highest P percentages were taken in the late-wet season. This may also indicate
that grasses have higher nutrient quality in the late-wet season than in the mid-dry season. Cu,
Fe, Mn and Zn (dpm) is higher in the late-wet season when compared with the same grass in
the mid-dry season, in most cases. This further proves what Kleynhans et al. (2010) stated that
grass quality decreases in the dry season.
Hyperthelia dissoluta most selected for by zebra is of relatively poor quality in both the
wet and dry seasons. It has a high NDF and ADF percentage in both the late-wet and mid-dry
seasons as well as poor P levels. It has average Ca, Cu, and Zn levels; however, it is
extremely high in Fe in the late-wet season. The Mn levels are also high in both the late-wet
and mid-dry seasons. This indicates that even though Hyperthelia dissoluta is a poor quality
grass it does still have some nutritional benefit. Zebra may be better equipped to cope with
grazing this poorer quality grass than herbivores of the same size due to their digestive
strategy. Zebras are non-ruminants and are able to cope with fibre more efficiently than
ruminants of the same size due to high passage rates (Duncan et al. 1990).
Cynodon dactylon is the most selected for grass in Mabula Game Reserve. Even though
chemical analyses show that it has a high fibre content, it is high in minerals. The Ca:P ratio is
closest to 2:1 at most of the old settlements where the Cynodon dactylon samples were taken
from. These grasses also showed much higher levels of P thereby indicating the benefits that
past land use may have had on the soils in the old settlements. The high mineral content of
these grasses are irrespective of whether they occur on the granite or quartzite geology type.
In the mid-dry season, Cynodon dactylon loses a lot of quality especially in terms of Cu and
Fe. The Ca levels appear to increase in the mid-dry season on both geology types. Since Ca
levels are expressed on a percentage basis it could mean that Ca levels do not increase in the
mid-dry season but merely remain constant; however, since other minerals decrease Ca will
constitute a higher percentage. At site S1G, the P percentage decreases significantly as well as
32. 32 Lodge and Pretorius
Cu, Fe and Zn. This may be the reason why herbivores moved away from this area in the mid-
dry season to the quartzite geology old settlements where the Cynodon dactylon is of better
quality. ADF percentage also increases by more than 10 % at this site in the mid-dry season,
further contributing to why herbivores may have moved to find better quality Cynodon
dactylon.
MANAGEMENT IMPLICATIONS
Mabula Game Reserve is a small fenced reserve and therefore strict management policies
need to be in place to ensure that there are enough resources available for each herbivore
species. Each herbivore species needs to monitored to determine whether they are being
outcompeted or whether they are coping with the conditions within Mabula Game Reserve.
This not only applies to Mabula Game Reserve, but to all small fenced reserves as these are
usually areas with high concentrations of wildlife species. Wildlife in these areas are not able
to migrate, so as a manager, the supply of adequate resources is vital. The only other way of
solving the issue of resource partitioning and niche separation is to reduce wildlife numbers,
which in most small reserves is not an option as that is what the owner wants. Veld
management practices, such as that used on site F1G in Mabula Game Reserve, can greatly
increase the resource availability and quality at a site. However, it must be noted that these
practices are not fast acting. They take a number of years before noticeable results are seen so
it is important to have strict management regimes in place.
ACKNOWLEDGEMENTS
We would like to thank Mabula Game Reserve for allowing us to conduct this study. The
reserve ecologist, Jock McMillan and his ecology team for providing transport in the reserve,
expertise and knowledge. I would like to thank my supervisor, Dr. Yolanda Pretorius, for all
her hard work and dedication to helping me complete my research to the best of my ability.
33. 33 Lodge and Pretorius
Thank you to the Centre for Wildlife Management for providing me with a vehicle to travel
back and forth to Mabula Game Reserve.
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