Introduction
In today’s day and age, National Parks not
only preserve natural heritage for future
generations, but must also be able to sustain
themselves financially, simply if it doesn’t
pay it doesn’t stay. This attitude has
resulted in a great deal of attention being
directed at the more ‘crowd pulling’
friendly facets of fauna and flora, good examples
being elephants and lions.
Other elements are sadly neglected due to
financial constraints and through no fault of
themselves.
During the course of this study attempts were
made to obtain an official permit to collect
inside the Pilanesberg National Park,
unfortunately to no avail, hence this is an
informal study. Because of access restrictions
due to the introduction of dangerous animals, in
particular, lion into the park, areas displaying
prime habitat remained unexplored, resulting in
biased sampling. Using historical biographic data
it is possible to some degree of accuracy to
predict scorpion fauna for a particular region.
Taking specific species requirements it is
possible to further refine this prediction to an
even finer degree of accuracy.
Few arthropod fauna have enjoyed more attention
than scorpions. The Southern African scorpion
fauna have enjoyed more attention than most other
parts of the world (Hewitt 1918, 1925; Lamoral
and Reynders 1975, Lamoral 1979, Lawrence 1955).
Several taxonomic reports characterised the
substrate on which particular species are found
(Lamoral 1979; Williams 1980). In conjunction
with such reports, known species habitat
requirements, climatic data and the topographical
and geological of the Pilanesberg National Park,
it was possible to predict scorpion diversity to
a fine degree.
Collection records from Southern
African Museums and some overseas museums and
personal records were consulted and general
distributions noted. Physical collection of
specimens was sparse and concentrated at specific
areas, commonly already disturbed due to
development. It was noted that more
Opistophthalmus species were collected from
disturbed areas than any other species, although
this reflects upon their pioneering dispersal
abilities rather than their tolerance to a
disturbed habitat or vague habitat requirements.
The Friends of the Pilanesberg Society operate
within the parks under to Authority of the North
West Parks department, Pilanesberg National Park,
Borokalalo National Park and more recently,
Madikwe. Much of the work involves development of
areas for future public access. Records have been
kept from April 1991, pertaining to scorpion
distributions. Due to the introduction of lions
into the Pilanesberg National Park limitation
imposed upon FOP resulted in biased sampling
methods in direct relation to Friends Of
Pilannesberg Society’s (FOPS) activities
were incurred. Activities were generally
restricted to areas of public access with few
exceptions, for example picnic sites, view
points, Geological sites, Potokwane and Tambooti
Camps, Ecological Educational Zone. Moreover,
these areas have, in most cases been disturbed to
a lesser or greater degree by development. It is
unclear whether this has any effect upon scorpion
distributions. Most specimens were collected by
overturning rocks and surface debris during the
day. Some specimens were dug out of their
burrows. No nocturnal collecting was conducted
employing ultraviolet lights. Previous records
were sparse. No formal study was conducted upon
the arachnid fauna of the park. Other areas
exhibiting favourable habitats are unexplored due
to access limitations, the Northern area in
particular remained excluded from sampling.
Collection records from the Spider Club of
Southern Africa members were noted.
Evolutionary influences of Scorpion distributions
in the Pilanesberg National Park
As members of populations, individual organisms
are part of societies or communities that, over
time evolve to suit the environmental fields in
which they are engulfed, providing that these
fields stay constant long enough for adaptation
to occur. An individual species can live only
within a certain tolerance of environmental
factors - the effect of too much or too little of
any one factor may inhibit growth or even prove
fatal. (Huggett 1995)
Many physical factors influence the spatial
distribution of scorpions, including temperature,
precipitation, soil or rock characteristics,
stone or litter cover and environmental
physiognomy (Polis 1994). Scorpion distribution
also seems to be influenced by edaphic factors
(Sam Martin 1961; Smith 1966; Lamoral 1978; 1979;
Bradley and Brody 1984; Polis and McCormick
1986). Temperature and precipitation are probably
the most important determinant of general
geographic range (MacArthur 1972; Kock 1977,
1981; Newlands 1978).
For instance, the type and texture of soil or
substrate is crucial to animals that seek refuge
in burrows, and those that have modes of
locomotion best suited to relatively smooth
surfaces. Burrowing species, may be confined to a
particular kind of soil (Huggett 1995). In
particular scorpions that burrow in soft soils
tend to be restricted to a smaller ranges of soil
hardness than those burrowing in harder soils(
Huggett 1995). Scorpions, like other
poikilotherms, exhibit a limited temperature
range within which, optimal field activity is
maximised (Shulov and Levy 1978; Polis 1980) For
example O. latimanus has a preferred thermal zone
of 32° C to 38° C (Polis 1994). Hadogenes
troglodytes exhibit a skatotaxic affinity to
black foyite formations although their
distribution within the park is not exclusively
determined by it. The Pilanesberg National Park
receives on average 650mm of rain annually,
although the actual annual rainfall fluctuates
greatly between 200mm and 1400mm annually. The
genus Parabuthus exhibit a relation to the 600mm
isohyte (Newlands 1978), and as a general rule
are not found in areas receiving more than 600mm
annual rainfall. Areas of complex geomorphology
contain a higher scorpion density than the
surrounding plains (Prendini 1996), however even
though the Pilanesberg rise less than 700m above
the surrounding plains, they do have a profound
effect upon climatic conditions, probably
regulating the exclusion of Parabuthus sp. due to
rainfall. The distribution of P. transvaalicus in
Southern Zimbabwe indicates that they occur at an
altitude less than 1000m above sea level.
Scorpions are not distributed randomly within a
habitat, rather particular species are normally
associated with specific microhabitats (Polis
1970). Several taxonomic reports characterised
the substrate on which particular species are
found (Lamoral 1979; Williams 1980). In
particular soil hardness and texture determine to
distribution of Opistophthalmus sp. in Southern
Africa. Lamoral found that each species is
restricted to soils within a particular range of
hardness rather than a particular soil type.
Scorpion response to soil hardness is so defined
that as burrows descend they actually track
changes in hardness and stay within a preferred
range. This pattern is most likely explained by
the highly specialised morphological and
behavioural adaptations that characterise
psammophilic and lithiphilic scorpions. Such
ecomorphotypical adaptations facilitate burrowing
and locomotion on sand or rock but make these
animals inefficient in or on foreign mediums
(Polis 1994). The strongly recurved tarsus of
Hadogenes sp. enable them to locomote inverted on
smooth rocks, their elongated and laterally
compressed body and appendages lend themselves
towards a trogofilic existence. Indeed, these
scorpions are so restricted to distinct rocky
outcrops and mountains that even narrow valleys
between populations create an insurmountable
barrier that prohibits gene flow. (Newlands 1985)
Uroplectes planimanus, a semi-psammophilic
scorpion shares this affinity but not in such an
exacting manner. U. flaviviridis prefer sandy
areas displaying typical psammophilous
adaptations for life on sand i.e. sand combs on
the tarsus. Uroplectes carinatus demonstrate a
very wide habitat tolerance, making them
generalists in their habitat selection.
It is unclear whether vegetation influences
scorpion distributions. Studies of
scorpion-vegetation associations in North America
(Gertsch and Alfred 1965; Williams 1970; Polis
and McCormick, unpl. data) suggest that most are
generalists living in several vegetative zones.
Pseudolychas pegleri are distributed in the
moister eastern part of the subcontinent. They
exhibit a close affection to vegetated zones,
this may be due to the high humidity found within
vegetated areas in comparison to sparsely
vegetated areas. Scorpions such as Hadogenes sp.
and Opistophthalmus sp. are protected from
desiccation in different ways. Opistophthalmus
sp. shelter in burrows, in this way temperature
and humidity of the burrow can be regulated, the
deeper the burrow the cooler the ambient
temperature inside the burrow. Hadogenes sp.
shelter under rocks, where the water content of
the soil under a rock is considerable higher than
that of the soil surrounding a rock.
The extra water found under rocks
is the result of one or more of three processes.
Firstly, while rain is falling, water flows over
the stones and accumulates in the soil matrix
between and under the stone. Secondly,
evaporation loss is reduced by the stone layer
with prevents capillary rise to the soil surface.
Thirdly, at sunset, falling temperatures promote
condensation in the hollow spaces between the
stones.
Animal species are adapted to conditions in their
local environments. Many animal species adapt to
gradual geographic changes in climate. Such
adaptation is often expressed in the phenotype as
a measurable change in size, colour, or other
trait. The gradation of form along a climatic
gradient is called a cline (Huxely 1942). Clines
result from local populations developing
tolerance to local conditions, including climate,
through the process of natural selection. Such
local populations constitute an ecological race.
Ecological races may display either gradual or
abrupt change along an environmental gradient,
and these racial gradients are called ecoclimes.
Clinal factors, notably temperature and moisture,
might be designated climoclines (Hugget 1995).
For example, Hadogenes troglodytes display
intraspecific colour variants. Populations within
the Pilanesberg National Park exhibit a uniform
charcoal-black coloration. Populations elsewhere
exhibit colour variation effecting their
appendages, the largest specimens inhabiting the
Northern parts of their range, notably the
Soutpansberg Mountains.
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