Not just mammals but also insects are more productive of food for humans in southern Africa than in Australia
(writing in progress)
Australia is the only vegetated continent lacking any indigenous ungulate, and any herbivore larger than kangaroos.
One possible interpretation is that the Australian vegetation is capable of supporting mammalian herbivores, but herbivorous niches have been emptied by relatively recent extinctions plus isolation from sources of recruitment of new herbivorous taxa. The extinctions took place long before the arrival of Europeans and domestic livestock, but were possibly anthropogenic.
However, herbivorous insects indicate that the Australian environment is relatively unsuitable for herbivores in a fundamental way. The difference between Australia and other continents applies as much to rapidly breeding invertebrates – which are not vulnerable to anthropogenic extinction – as it does to mammals.
This suggests that the difference in herbivory is intrinsic to the quality of Australian plants as food. Caterpillars illustrate the point particularly well.
This is because large-bodied species of emperor moths are widespread in both Australia and southern Africa, yet it is only in Africa that saturniid caterpillars (https://en.wikipedia.org/wiki/Saturniidae) are eaten by indigenous people as a major dietary item. This suggests that caterpillars are more productive in southern Africa than in Australia.
Furthermore, this difference holds good even within plant categories shared between the continents. For example, the genus Syzygium supports a saturniid caterpillar eaten by African people. However, it does not support any analogous caterpillar in Australia.
Large-bodied, edible caterpillars of Saturniidae occur on certain African trees including Colophospermum mopane (https://www.inaturalist.org/taxa/428749-Colophospermum-mopane) and Burkea africana (https://www.inaturalist.org/taxa/340238-Burkea-africana).
It is remarkable that there are no counterparts in Australia, despite the fact that large saturniids do occur on that continent. I can find no record of aboriginal Australians eating saturniid caterpillars. This indicates that there is something more fundamental about the poverty of herbivory in Australia than previously acknowledged.
The insects give us a clue to the real differences, because edible saturniid caterpillars are as different in incidence on the two continents as herbivorous mammals, and there’s no chance that anthropogenic extermination can be to blame.
The saturniid moth Micragone cana, one of about ten saturniid caterpillars on Earth known to be eaten on a considerable scale by indigenous people, eats the foliage of S. cordatum.
Here we have a family of moths shared between the continents. And in the case of this taxon of food-plants, we have not only a family epitomising the Australian flora, but a genus actually shared between Australia and southern Africa: Syzygium.
Syzygium cordatum) is one of few myrtles (https://en.wikipedia.org/wiki/Myrtaceae) that have managed to live beyond fire-free rainforest in Africa. And yet, contrary to all expectations, it is the African syzygium, not the Australian ones, that are food of a saturniid moth so large, prolific and poorly-defended chemically that it is a significant source of food for indigenous humans.
Basquiniana seems to constitute proof, at two levels, of the fallacy of the ‘but they didn’t get here’ and ‘but they were here and people killed them off’ belief.
Firstly, the saturniid family is shared between continents and well-represented in Australia, so there is no biogeographical explanation of an accidental type to explain why it is in Africa and not Australia that this family is food, on a large scale, for humans.
Secondly, the fact that edible saturniids lives on a syzygium in Africa, but not on congeners in Australia, proves that this applies even to within-genus comparisons of food-plants between continents. Even within a genus of myrtles (the plant family most strongly associated with the historical accident that is Australia) the caterpillars are somehow able to be prolific in Africa rather than Australia.
Myrtaceae dominate in Australia, where they provide no caterpillar large enough, common enough, prolific enough, or chemically defenceless enough to constitute food for aboriginal humans. This could easily be seen as a historical accident, and if an ecological explanation is given it is likely to be that myrtles are by their nature poor food for herbivores including insects.
Seen within the context of Australia alone, the lack of edible saturniids here would not seem remarkable at all. However, the error in most people’s assumptions is exposed when we discover that even the few exceptional Myrtaceae that have managed to penetrate savannas in Africa are in fact suitable food for just such kinds of caterpillars: particularly Basquiniana cana. This species eats Syzygium cordatum (https://www.inaturalist.org/taxa/338719-Syzygium-cordatum). This genus of plants is shared with Australia, where - like eucalypts - it hosts no such edible insect.
What this means:
In Africa, even those taxa (e.g. myrtles) usually associated with poor soils and fire are somehow capable of producing noteworthy herbivores (at least insects). Syzygium cordatum is, after all, in the scheme of things a nutrient-poor plant typical of sandy soils and fire-prone savannas.
And this is corroborated by the fact that the two better-known food-plants of edible saturniid caterpillars in southern Africa, namely Colophospermum mopane and Burkea africana, are also regarded as rather poor plants from the point of view of herbivory, being fire-prone, chemically defended, associated with difficult soils (sodic in the case of C. mopane, oligotrophic in the case of B. africana), and shunned by mammalian herbivores - which prefer e.g. acacias.
The bottom line: trees regarded as poor food for mammalian herbivores are capable of supporting edible species of insects in Africa but not in Australia, something that cannot possibly be explained by any accident of history or any anthropogenic extermination. Instead, it’s clear that there’s something in terms of actual resources that causes the intercontinental difference in the success of herbivores, i.e. herbivores across the board regardless of whether they are megaherbivores or just insects.
So, one of the remarkable differences between Australia and southern Africa is that only southern Africa has edible lepidopteran foliage-eating caterpillars, harvested on a large scale for human consumption, on trees belonging to the Caesalpiniaceae such as mopane and Burkea africana.
Interpretation of this intercontinental difference is not a straightforward matter of Australia being nutrient-poorer than southern Africa, because mopane dominates on sodic soils and Burkea (although characteristically African-looking with its flattish crown) is typical of nutrient-poor soils.
What I did point out is that the plants eaten by these caterpillars, viz trees in the Caesalpiniaceae, are poorly represented in Australia. Certain members of the Caesalpiniaceae (e.g. Bauhinia, Erythrophleum) do occur in Australia but no extensive woodland in Australia is dominated by this family and Australia lacks endemic, dominant genera analogous with Brachystegia. The edible caterpillars seem to be associated with this floristic difference.
Here is a parallel case: edible stinkbugs found in Zimbabwe with no analogue in Australia. The species referred to is Encosternum delegorguei (Tessaratomidae, https://www.inaturalist.org/taxa/428764-Encosternum-delegorguei), which sucks the sap mainly of Combretum spp.
My point about this is twofold.
Firstly, just as in the case of lepidopterans, the family of insects involved occurs on both continents, but only in southern Africa does it include abundant, large, edible species harvested as food for humans. The correlation with the big game of Africa is obvious but not yet fully explained. It means that small herbivores do not compensate for the lack of large herbivores in Australia; instead both small and large herbivores are better-represented in southern Africa than in Australia.
Secondly, the food-plants of this edible stinkbug are, in a way, analogous with those of the edible caterpillars. Once again, the family Combretaceae is present in Australia, but the difference is that the genus Combretum, so common in Africa and dominating certain types of woodland, is absent from Australia with no analogue. And once again, there is some ambivalence in the nutrient status of the food plants of the edible insect because Combretum tends to be intermediate in its nutrient status, neither fully eutrophic nor fully oligotrophic.
I think there is a general pattern in this: across the board, invertebrates tend to parallel the big game in being larger/more abundant/more attractive as human food, in southern Africa than in Australia. The same thing applies of course to termites and locusts.
https://en.wikipedia.org/wiki/Tessaratomidae
(writing in progress)
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