Revising climate impacts on African vertebrates

A few weeks ago I wrote a piece on climate change and African vertebrates. As I usually do, and especially in this case as Raquel had pointed the paper out to me, I let her know that I'd written something and asked her opinion. After quite a few emails back and forth we confirmed that I'd misunderstood a figure in the paper that I'd thought was the crux of the matter, but it turns out to have been not as useful at all.In light of these discussions, Raquel and colleagues have now produced an addendum to their paper that contains the figure I thought I was looking at and, although I still have some issues with the work, it makes much more sense to me now! In the interests of getting all this information out there, as well as my pointing out the mistakes in the original post and Raquel posting a comment there, I thought her ideas were valuable enough to reprint in full from the comment as a new post, with some more discussion here. So, here's what she has to say:

On cattle in African protected areas

Typical pastoralist scene near Lake Eyasi

Talking about blog topics the other day, a friend asked me about the impact of goats and cattle on wildlife. And then over here someone else started a similar discussion on cattle, which collected a wealth of different ideas, so I thought it would be a good idea to collate all this information for a different audience over here. Increasingly, discussions about cattle come up when people are visiting areas that aren't National Parks - here in Tanzania many people are surprised to see cattle (and their Maasai herders) right in the Ngorongoro crater, as well as around the rest of the NCA. And increasingly (particularly in Kenya where land laws make it much easier, but also here in places like Manyara Ranch) conservancies are being set up where communities set aside land for both wildlife and pastoralist activities. The fact that organisations like the Northern Rangelands Trust are making a real success of this, combined with ongoing concerns about displaced people and human rights issues, has encouraged people to think seriously again about whether the strict 'no people' policy of many national parks in Africa might be relaxed, and recognising this a few years ago the International Conservation Union (IUCN) relaxed their national park category definition to allow management "To take into account the needs of indigenous people and local communities, including subsistence resource use, in so far as these will not adversely affect the primary management objective". So, what are the issues here, and what are the ecological arguments? In this post I'm going to deal with cattle, and leave the goats and sheep for a future occasion.

Why do savanna trees have flat tops?

Umbrella Thorn, Serengeti: An icon of the savanna?

From sunsets behind a silhouetted acacia (properly Vachellia), to photos of rolling grasslands studded with isolated trees, a savanna landscape is immediately identifiable thanks to the flat-topped tree. But why is this? Why do so many Vachellia and other savanna trees have such a distinctive structure that they have become a virtual icon of the African savanna?

It's an interesting question that was given some answers in a nice paper by Sally Archibald and William Bond who studied one species called the Sweet Thorn (Vachellia karroo) that, rather like some of our Vachellia species in East Africa exhibits a range of different growth forms in different habitats. In the semi-desert of the Karroo, it grows as a medium-sized ball of thorns, whereas in the savanna it has a fairly typical medium-tall  flat-topped acacia look to it and in a forest it's a tall, thin tree. These differences are meditated mainly by genetic differences within the species, but equally could be caused in other species by a variable response to the environment - it's not really important to this discussion and, in fact, much of our discussion could focus on different species if we wanted. As always when we're thinking about what makes the savanna species, we'd be well advised to start with the savanna big four: nutrients, water availability, fire and herbivory.Now, the first two processes have impacts in all biomes, whereas it's the second two that are most distinctive about savanna and where we'll start our discussion.

Ecology for safari guides

This blog was set up originally to be a resource for safari guides around east Africa, and I hope it still fills that purpose. (We're coming up to 100 posts soon, so that might be a suitable moment to see how well we're doing...) Over the last couple of weeks we've been talking with a bunch of folk about forming a society for Interpretive Guides which could develop and maintain a qualification for guides in Tanzania - at the moment there's nothing widely recognised in the industry. With the assistance of the PAMS foundation, we're collecting syllabuses and guiding standards from around Africa and trying to develop something that may be seen as defining 'best practice' for guides in the region. As part of this process I've been putting together the things that I consider guides should know about ecology, and I thought it might be interesting to post the rough ideas I've got here for comments. There's much more that will go into the syllabus of course, this is just going to help contribute to the ecology module we're putting together, there's got to be lots more natural history modules in the course, covering mammals, birds, reptiles, plants and all the rest. And there's also likely to be as much about guiding ethics, psychology of groups, etiquette, etc., as well as the hard skills like proper driving, first aid  and (if you're walking) firearms. So don't worry about those bits just now, I'm just doing the ecology bits.

Why is snake venom so toxic?

Puff-adders probably cause more human snake-bites than any other African
snake, but are rarely fatal. This is a juvenile, but don't think it's harmless.

After discovering all the amazing things about pedarin and the 'Nairobi Eye' last week, it set me thinking again about why so much wildlife is so incredibly toxic. Think about it - a little beetle small enough to crawl over you without you noticing at all, is more than toxic enough to kill a grown man - indeed, several. A snake like a black mamba can give a bite that's sufficient in toxicity and volume to kill an adult elephant. Many natural venoms aren't simply one chemical, but a mixture of nasty toxins with a whole range of activities - why go to the trouble of evolving a whole suite of nasty chemicals, when one is usually enough to kill most things? Why should it be so toxic? What's the purpose?

Distribution of Ethiopian Bush-crow and the nature of explanations

Yesterday I was sent a link to a press release from the excellent BirdLife International (read it here). It's talking about some research by an international team to try and explain the remarkably restricted range of the Ethiopian Bush-crow (cute picture here, since I've never actually been there to take my own), and in it, Paul Donald the lead author makes some interesting comments:

“The mystery surrounding this bird and its odd behaviour has stumped scientists for decades – many have looked and failed to find an answer.  But the reason they failed, we now believe, is that they were looking for a barrier invisible to the human eye, like a glass wall. Inside the ‘climate bubble’, where the average temperature is less than 20°C, the bush-crow is almost everywhere.  Outside, where the average temperature hits 20°C or more, there are no bush-crows at all.  A cool bird, that appears to like staying that way.”

The reason this species is so completely trapped inside its little bubble is as yet unknown, but it seems likely that it is physically limited by temperature – either the adults, or more likely its chicks, simply cannot survive outside the bubble, even though there are thousands of square miles of identical habitat all around.

BirdLife International’s Dr Nigel Collar is co-author of the study. He added “Whatever the reason this bird is confined to a bubble, alarm bells are now ringing loudly.  The storm of climate change threatens to swamp the bush-crow’s little climatic lifeboat – and once it’s gone, it’s gone for good.”

How do Kopjes form?

It's a question I regularly get asked by guides and also one that seems to bring a lot of google-searching visitors to the site, but I've not actually posted much of an answer yet although we have covered it briefly here, so here goes...

Cross-section through a kopje in the process of formation
from smooth, uninterrupted landscape at the top to
typical kopje at bottom, following millions upon
millions of years of erosion.

We start by remembering that Africa is old - most of the surface rocks are pretty ancient (and consequently washed clean of most nutrients - an issue we've talked about repeatedly). During these millenia, mountains have been formed and then worn down to small hills, whilst the valleys, plains lakes and seas have been buried in the sands and gravels of this erosion process. Over time and with immense pressure these sands and muds too have sometimes been 'recycled' into sandstones and mudstones in someplaces. It's not just been static though: later volcanic events sometimes push magma (un-errupted lava) through the layers of rock towards the surface where it cooled and formed an intrusion of new rock within a mass of older layers. (As shown in the diagram!)