9 August 2007
Cape Town — Table Mountain may be world-famous for its fynbos, cableway and spectacular landscapes - but in fact it should be just as famous for its invertebrate life, much of which is unique to this mountain.
A 1996 study of the Cape Peninsula found 112 species from the animal kingdom that are endemic (occurring naturally only here). All but one are invertebrates - that is, animals without spinal cords.
Some 97% of all animals on Earth are invertebrates and they include insects, worms, snails, spiders and many marine species.
Most of the 111 invertebrate species occur on Table Mountain itself, Stellenbosch University entomologist and post-graduate student James Pryke told the recent Fynbos Forum.
"These invertebrates have been poorly documented virtually nothing is known about them, and we don't even have seasonal data," he said.
Pryke initiated a research project on the mountain because many of the endemic invertebrates had not been seen for several decades and were believed to have become extinct, such as the Scarce Mountain Copper, Trimenia malagrida malagrida, known only from Lion's Head.
He was particularly interested in how the changing landscape mosaic on the mountain affected the invertebrate biodiversity for example, changes caused by fire, by harvesting pine plantations and clearing invasive alien vegetation.
Some 80 sites across the mountain were intensively sampled using a variety of trapping mechanisms.
"These sites enabled us to make comparisons between vegetation, aspect (landscape), elevation, disturbance levels and the effect of fires.
"We also conducted a Peninsula wide survey of the distribution of conspicuous invertebrates and mapped these distributions to allow further analysis and to identify invertebrate conservation priority areas."
In all, he and research colleagues trapped some 16 000 individuals from 250 invertebrate species, although fires played havoc with some of the research project during one year, four fires destroyed nine of the selected sites.
Apart from finding some species never before recorded on the Peninsula, their preliminary results also threw up some other surprises.
"Amazingly, young unprotected forests which have been quite highly disturbed have the highest invertebrate diversity," said Pryke.
These were areas like Die Hel, above the Constantia Green Belt but outside the Table Mountain National Park. "There are a lot of alien plants in there and it's a bit of a mix.
"Obviously the original forest was cut down and now it's starting to regrow. It's an important area for invertebrates, but it's currently without management, which is quite worrying," he said.
Another surprise was that the cultivated garden area of Kirstenbosch also contained a very diverse invertebrate fauna, of both ground and flying insects.
Two of the species recorded here were unique to Kirstenbosch.
Fynbos sites on the north and west sides of Table Mountain had higher diversities than the other sides.
Invertebrate abundance the actual number of insects was "much higher" in burnt than unburnt areas, but "a lot more" species were recorded in unburnt sites.
There was only "quite low diversity" in pine plantations, with one unique species being found here: the mole cricket. "It's considered a pest in certain fields," Pryke said.
Two ant species were both recorded in "huge" colonies in the burnt areas.
Suggesting a possible sampling bias here, Pryke said: "It's an open question as to whether fires create an ability for ants to colonise areas.
"A large presence of these carnivorous subterranean ants may yet be shown to have some implications for invertebrate biodiversity after fire."
The former chief executive of the SA National Biodiversity Institute, Professor Brian Huntley, raised some eyebrows by suggesting that the removal of all alien pines and gum trees from the Peninsula "might yet prove to be a negative thing in terms of recreation and research".
Because of the "huge difference" between natural fynbos ecosystems and pine plantations, the pines had an educational value for school children, as well as for some scientific research projects like Pryke's, Huntley said.
"This is something I think we must not underplay."
But botanist Julia Wood, chairwoman of the Fynbos Forum and head of the City of Cape Town's nature conservation branch, took issue with him.
"If we are going to experiment, we need to make sure we're not doing it in critically endangered vegetation, for which we have conservation targets," she said.
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