Saturday, 29 October 2011

Echos of extinction...

Black Rhino browsing (?!) Ngorongoro Crater, Feb 2011
Driving around places like Tarangire I often find myself wondering what impact the loss of black rhinos have had on the ecosystem. Sadly, these days there's nowhere in Tanzania with a significant rhino population (though you've got a good chance of seeing them in the Crater still) and it's easy to forget just how common they were, not so very long ago - more than 700 in Serengeti alone in 1974. Friends of mine (rather older than me!) talk of driving from the Tarangire gate to Silale and seeing over 20 rhino in a drive, and being areas they'd avoid walking in because the rhino densities were just too high to make it safe. They're big animals, at about 1500kg for a bull, and they eat a lot of food. Such large populations of a large mammal crashing about in the bush like a tank must have had massive impacts on the landscape - but there's nowhere we can go now to see what an East African savannah with a decent rhino population looks like.
Close enough to this Black Rhino! Kruger NP May 2011

Black rhino may have been important dispersers of Sausage tree seeds.
Fallen Kigelia africana flowers are a valuable food source for many species

We can speculate that perhaps some of the large, thick patches of bush of a single age now found in central Tarangire might well have been more open and varied habitats when there were rhinos there - but we really can't say for certain, because no-one's been monitoring the changes and we've nowhere to cross-check against anyway. There is one species that might, in time, show some changes - that essential savannah tree, the Sausage Tree Kigelia africana. Ever wondered what disperses Kigelia seeds? Not much eats them - baboons do when they're desperate, insects have a go and elephants will when pressed, but did you know they're a favourite of Black Rhino, and considered important seed dispersers for this species? In fact, Kigelia seeds don't germinate unless they've been eaten by something like a rhino, so mayube much of the pattern we see currently in this species related to ghosts of past rhino distribution? Who knows.

Interestingly, following the recovery of rhino populations in South Africa before the latest spate of poaching, we did discover that White Rhino are massively important in shaping landscapes - as massive grazers they create grazing lawns that are then colonised by a large number of other grazers and, impresively, but some rather rare grassland bird species that specialise on these grazing lawns. Before rhino number built up to their current levels, this sort of lawn was rather rare, and the increase in rhino has greately increased the variability of the landscape of Kruger and Hluhluwe-iUmfolozi parks, with important benefits for the populations of other species - this species, if not necessarily a keystone species, is certainly an 'ecosystem engineer'. (Why Tanzania and Kenya - despite what many will tell you - have never formed part of the range of the critically endangered Northern White Rhino is a mystery to me - so much grass here, they'd surely love it (and when not being poached they do rather well in Kenya, it seems).) Maybe they were driven to extinction by our ancestors long before modern times?
Southern White Rhino trying hard to make a grazing lawn, Kruger NP, May 2011

Anyway, all interesting things to think about when you're lucky enough to come acros a rhino, or even if just enjoying the shade of a sausage tree. Let's hope the current spate of poaching can be controlled and the increases seen earlier will continue again. (That's twice in a week I've blogged about one of the big five. Shock! Must find smaller fare for next time...)

No comments:

Post a comment