The R.C. Dening Collection
Introduction to Zambian Butterflies
by R.C. Dening F.R.E.S.
|Zambia is primarily a savanna country with elements of rainforest, afro-alpine
and desert biomes around its borders. In Carcasson's eco-geographic divisions of the
Afrotropical Region, Zambia in general, falls within the Southern Division of the
Sub-region of Open Formations, and in particular within the Zambezi Zone.
borders of the country abut on other zones, considerably increasing its butterfly fauna;
many further species may well be discovered with year-round collecting in these border
areas. Thus at the Victoria Falls, where the Satyrid Mashuna mashuna occurs on the
Zimbabwe side, no confirmed Zambian records are yet available.
Further to the southwest, where only limited recording has occurred, the border lies
close to the Kalahari Zone, altering the species balance in favour of desert and dry bush
conditions. The occurrence seems not unlikely of such species as the pierid Colotis agoye
and Acraea stenobea, the latter mentioned in Carcasson for Zambia, but of which the
present author knows no specimens.
In the east, proximity to the Eastern Zone introduces numerous species such as Charaxes chinteche, Euryphura achlys, and many lycaenids. Here also there is contact with the
Malawi-Nyasa Zone of Carcasson's Highland Forest Division, with the inclusion inter alia
of Papilio jacksoni nyika and Cymothoe
cottrelli. Moreover, within Zambia on the Nyika
Plateau, there is a small area of Tropical Montane Grassland, where the fritillary Issoria smaragdifera and the Small Copper Lycaena
phlaeas occur. Right across the northern border,
in numerous places, elements of Carcasson's Lowland Forest Division (Sylvan Sub-Region)
infiltrate from the Congo Zone. However, with altitudes of around 1,200 metres, these
areas can only be considered lowland forest by contrast with Highland or Montane Forest.
The great African Central Forest Block extends, in many areas unbroken, from the
remaining West African forests through Cameroon and the Congo Republics on the northwest,
Angola in the west, and right across the continent to Rwanda, Burundi, Uganda and Western
Kenya in the east. Across this vast area, thousands of species range, often represented by
subspecies in particular areas.
Thus many areas in the north of Zambia have a surprising riverine rainforest fauna, in
particular northwest Mwinilunga, the Copperbelt, northern Luapula, Lake Mweru and the Lake
Tanganyika southern shores. The likelihood of undiscovered species in these areas remains
high provided the habitats are conserved.
The Influence of Past Climatic Changes
|Over much of
geological time, the climate of Africa has alternated between periods of considerable
aridity, followed by periods of heavy rainfall. This process has continued until
relatively recent times (Adams et al., 1996, The Physical Geography of Africa).
basin levels indicate a wet period between BP (= Before Present) 27,000-21,000 years, when
rainforest may have extended over much of northern Zambia. There was then a period of
aridity during the last northern Ice Age, at its most extreme around the last Glacial
Maximum (BP 18,000). This is believed to have caused mass extinctions over large areas of
the continent, so that the rainforest survived mainly in isolated refugia.
This severe aridity continued until about BP 12,500, when there was a slow return to
humid conditions. Lake Cheshi in Mweru Marsh gives a good indication of the chronology,
its lowest levels having occurred between BP 15,000-13,000, and its highest levels between
BP 8,000-4,000. The latter largely coincides with the Holocene warm period, after which
there was a rapid decline to present lake levels.
It seems likely, therefore, that as recently as 4,000 years ago, there were substantial
areas of rainforest in northern Zambia, which had been re-colonised by numerous butterfly
species from more northerly refugia.
AFRO-ALPINE FOREST BIOMES
fluctuations appear to have occurred in relation to temperature at higher altitudes, as
indicated by the levels of glaciation on East African mountains. These also reached a
maximum in the late Pleistocene, around the northern Glacial Maximum (circa BP 15,000).
Since this was a time of great aridity, the additional ice cover was more likely due to a
temperature decrease rather than to a higher rainfall.
A temperature depression of 5șC
would bring down the main montane forest biomes from 1,500 metres to 700 or even 500
metres. Calculations to date suggest that current montane forest levels have remained
roughly the same for the last 10,000 years, but back at BP 12,000 they extended to 30%
lower altitudes. This could explain the discontinuous distribution of many forest species,
which occur today in the East African coastal regions.
The Satyrid Aphysoneura pigmentaria, which within Zambia is found on the Nyika plateau and the Mafinga
and Makutu Mountains in the northeast, has been shown by Kielland to occur only above
1,500 metres (with one East African exception), even though its foodplant (bamboo) extends
below this altitude (Kielland, 1989). This has resulted in the isolation of eleven
distinct populations, which Kielland has identified as subspecies; some separated by
considerable distances (over 400 km in the case of ssp. vumba). If 12,000 years
ago, the climate which now prevails at 1,500 metres, occurred at 1,000 metres, these
population discontinuities become more readily explicable.
|Relict dunes of
Kalahari sand extend northwards right up the western borders of Zambia, virtually to the
Zambezi/Lualaba watershed. The Cryptosepalum forests, known locally as mavunda,
extending from south of Mwinilunga station to Kabompo and Kaoma, grow on soils with a high
sand fraction; while the Mundwiji Plain, north of the Mwinilunga/Solwezi road, is too
sandy and shallow for the growth of any but dwarf woody plants.
Several phases of dune
activity have been recorded in the late Pleistocene, though satisfactory dating has yet
proved elusive. It would not be surprising if they too coincided with the Northern
Hemisphere Glacial Maximum and the contemporaneous arid period in Central Africa.
In all these sandy areas butterfly re-colonisation, on the return of wetter conditions,
would likely have owed as much to Southern African biomes as to the rainforest biomes
expanding from the north.
TODAY'S SAVANNA BIOMES
classification of biomes is based initially on vegetational characters since:
Vegetation is the entry point of energy into the ecosystem, through the fixation of
(b) It is a reliable indicator of other environmental variables;
(c) It is an indicator of dependent animal species.
However, in many cases butterfly distributions are only loosely related to the
vegetational classifications. Provided foodplants are available and the microclimates are
satisfactory for the species, it may occur in most vegetation types.
Larsen (1991) listed 33 species as having a Pan-African distribution, an additional 73
species as occurring in all African Open Formations, and a further 139 species as being
characteristic of Zambesian Open Formations. However, many of these species are not found
universally within these main categories, but are restricted to particular areas by
microclimatic and other factors.
Adams, M.E., writing on Savanna Environments in the
Physical Geography of Africa (Adams et al., 1996), quotes the following definition
"All tropical and subtropical ecosystems characterised by a continuous
herbaceous cover of C4 grasses that show seasonality related to water, and in which woody
species are significant, but do not form a closed canopy or a continuous cover."
(Frost et al., 1986).
Adams then describes six main types of savanna habitat:
1. Savanna Woodland.
Tall trees over 8 metres and up to 20 metres high; deciduous and semi-deciduous; spaced
at more than the diameter of the canopy; rainfall 600-1500mm per annum. This includes Brachystegia-Julbernardia
(Miombo) woodland, Cryptosepalum forest on the northwest sandy soils, Baikiaea
plurijuga woodlands on deep Kalahari sand, and Colophospermum mopane
woodlands on river basin clay soils in the south.
2. Savanna Parkland
Scattered deciduous trees over 8 metres tall, generally of Acacia, Piliostigma.
Terminalia and Combretum species, growing in grassland; rainfall, 400-800mm
3. Savanna Grassland
Tall, tropical grassland without trees or shade; includes wet and marshy places.
4. Low Tree and Shrub Savanna
Widely spaced, low-growing trees and shrubs, often over 2 metres high, with low-growing
perennial grasses and abundant annuals; rainfall, 350-400mm per annum.
Unstratified tree and shrub communities, e.g. of Acacia, Commiphora and Mopane.
6. Intermediate Vegetation
with a preponderance of, for instance, Burkea, Terminalia and Combretum
Adrian Storrs, on the other hand, in his 'Know your Trees', divides the vegetation of
Zambia as a whole into four main groups: Closed Forest, Open Forest or Woodland, Anthill
Vegetation and Grassland (Storrs, 1979). His Closed Forest classification includes montane
forest, swamp forest and riparian forest, which for butterfly ecology are not a true part
of the savanna biome, and will be discussed separately. His other types of Closed Forest
(Copperbelt Parinari forests, Northern Province Marquesia forests, western Cryptosepalum
forests, and southern Baikiaea forests) coincide only in part with Adams' Savanna
Woodland. While the canopy may often be closed, and the first three genera evergreen, it
seems inappropriate to treat these areas, for butterfly ecology purposes, as Rain Forest
rather than Savanna Woodland.
Storrs' Lake Tanganyika Itigi thicket corresponds to Category 5 above. He classes other
components of Adams' category 1 as Open Forest or Woodland, such as Miombo Woodland, Hill
Miombo, Kalahari Woodland, Mopane Woodland and Lake Basin Chipya. His Munga or Savanna
Woodland, and Kalahari Sand Chipya, would fall into Adams' category 2.
Species and Habitats