What is the influence of climate change on Tanzanian protected areas?

Pangani Longclaw Macronyx aurantiigula is perhaps the best example
of a species extending west, having colonised Serengeti recently.

It's been a long time since I posted anything here - sorry! I have another common birds post in progress, but just keep failing to finish it off. In the mean time I thought I'd talk about one of my own papers that came out a few weeks ago that explores how Tanzanian bird distributions are changing (sorry, it's pay to view, but if you want a copy email me and I'll send it!). This analysis is a fairly major result of my collaboration with the Tanzania Bird Atlas and represents the combined efforts of a very large number of people, volunteers and professionals, who contribute invaluable data to Neil and Liz Baker - I know some of you read this, so firstly, thank you, and secondly, I hope you appreciate seeing how we can use these records to do interesting and (I hope!) useful research.

Indian house crows and invasive aliens

Indian House Crow, not the prettiest... Thanks to Dick Daniels

There are very few birds I don't like to see, but today's common bird is an exception - the Indian House Crow, Corvus splendens. Actually, that's probably slightly untrue, as I have been to India and I was perfectly happy to see the species there. In East Africa, however, this is not a species I'm ever happy to see. Not because there aren't interesting things to say about it, of course, but because it really belongs in India and seems to cause a number of problems elsewhere.

First though, identification is fairly simple: the house crow is a medium-large all black and grey bird, usually found in flocks in towns all along the coast and, in some areas, invading inland too. It is very loud, with a persistent "Carr, Carr, Carr" call that is the constant sound of Dar es Salaam bird life... There are few confusion species in East Africa, the only other common species of crow being the black and white Pied Crow, which often hangs about with the house crow.

Common Birds: the case of the Baglafecht Weaver and missing forests

Male Baglafecht Weaver, Mt Kilimanjaro

 If you live on or near an East African mountain, you're very likely to have Baglafecht Weavers in your garden. Like most of the other true weavers, they're a basic black and yellow colour. The first thing to look at in weavers is usually the colour of the eyes and legs: in Baglafecht weavers you'll always see a yellow eye (easy to see against the surrounding black feathers) and pink legs. Males and females differ slightly: males in the population in northern Tanzania and Kenya have only a black mask on the face, with yellow on the top of the head right down to the (black) beak. Females have an all dark head. In northern Tanzania the back of both sexes is essentially black, with some yellow wing edges, in other areas of Tanzania the back is greenish/grey and not as strongly contrasting. Juveniles of all forms are rather greener and lacking in black, but still have the yellow eye. Like other weavers, they weave their nests from grasses in colonies of 5-15 pairs (not usually in very large groups) and males in the breeding season are pretty noisy with their rather scratchy and squeeky song!

Baglafecht weaver nests aren't the neatest of affairs...

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.”

Climate change and African vertebrates

Last year I spent a very happy evening in Cape Town enjoying some of the local specialities with a colleague and a visiting student. Or at least, that's what I thought - poor Raquel now tells me I was giving her a hard time... Still, good practice for her eventual defence of her thesis I hope. Anyway, she pointed me in the direction of the paper she was writing at the time that's now out and attempts to describe what's going to happen to some 2723 species of African vertebrates as the climate changes over the next several decades. Now, despite climate change being a huge conservation issue and one of my main research interests (and climate/weather being one of my 10 things to talk about), we've not talked much about it here on the blog before, so the chance to discuss what might happen to 2723 species across the continent as a whole is an ideal opportunity to start!

Endemics, or why are some species common?

This Saintpaulia (African Violet), like most others is probably endemic to the Eastern Arc

As you might have guessed, I've been away again. This time I've enjoyed a few days exploring the Amani Nature Reserve in the East Usambara Mountains. It's a fantastic bit (or, really, bits) of forest, perched high above the north coast of Tanzania, and forms a key part of the fames "Eastern Arc" mountains that stretch from northern Tanzania (just catching southern Kenya in the Taita Hills) around and down the coast, cutting back inland through the equally famous Uluguru forests and down to the Udzungwa mountains. And if biodiversity is your thing, then the Eastern Arc has it - forget the savannah, the real wildlife is in these Eastern Arc forests. They form an important part of one of only 34 global biodiversity hotspots (2.3% of the global land surface, but hosting over 50% of all plant species!) identified by Conservation International (NB there are 8 of these hotspots in Africa, the same number as in Europe, Central Asia, North and Central America combined - no wonder I love to be here!). There are at least 96 vertebrate species that are endemic to the Eastern Arc forests - 10 mammal, 19 bird, 29 reptile and 38 amphibian species. A far, far greater degree of uniqueness than you'll find in any savannah. And that brings me to one of my favourite scientific questions - what makes some species common and widespread, and others rare and local? I think we'll leave for now the question of why there should be so many rare species all concentrated into such a small area (why the Eastern Arc is a centre of endemism) and focus on this more general pattern of common and rare species (mostly because it's something I've published on myself and I won't need to look so much up!).

Usambara Pitted Pygmy-chameleons Rhampholeon temporalis are incredibly restricted in range

Most people tend to ask why is such and such a species rare and then struggle to find an answer. Why should these rather cute Usambara Pitted Pygmy-chameleons be completely restricted to the Usambaras, and not hop onto the Pare Mountains just a few kilometers away, or even the forests of Kilimanjaro? No reason at all really - expect they're not there. So recently some people have started asking a slightly different question - why are some species common and widespread? This might seem a trivial piece of semantics, but I don't think it is. In fact, if you look at the areas of occupancies of species in any taxonomic group, you discover that it's not small ranges that are unusual, but large ranges - in other words, rare species are common, and it's commonness that's rare!

This Mt Kilimanjaro Two-horned Chameleon is common in Arusha and clearly related to the Usambara species, but still incredibly local in distribution

Now start looking at the problem this way and you might start wondering where a species starts from in the first place. Let's assume we have an ancestral species that's on the verge of speciation. However we want that new species to split from the ancestral population (by geographical isolation, or together with the other species by, perhaps, chaning breeding season), we're going to start with at least one rather small distribution - perhaps the founders made landfall on some distant island and evolved in isolation into a new species, restricted to this new range. But then along comes an earthquake, and the island is no longer isolated, the species is free to come back to the mainland (where, of course, it's ancestors have also continued a process of evolution and might be rather different by now). Coming back into contact with the descendants of this ancestor the new species can either compete happily and spread in range, or just might not spread at all. It looks like, for most species, they don't bother to spread, just stay nice and localised and rare. But every now and again, one of them makes the grade and becomes common and widespread. What makes this difference isn't yet clear and there's certainly no one simple answer. Rather, it seems likely that to make it big you've got to pass several tests simultaneously - you need to disperse well, breed fast, etc.

The Usambara Bush Viper is so localised and rarely seen that I can't find another photo of a juvenile to be sure of the identification here! This might be some sort of Egg-eater instead.

 On the level of individual species, though, it's still a mystery - why should Rufous-tailed Weavers have such a small range between Serengeti and Tarangire? What's wrong with the savannah that, to me, looks identical just north, south and east of this range that keeps them out? Is it competition? With what? Why can't the evolve just that teeniest bit more to let them spread further? Why is the range changing now (they're recently made it to Kenya)? It seems to be climate, but how and again, what stops that tiny bit of evolution that's needed from happening? Hmmmm. All puzzling questions really, but great to discuss whilst you're looking at some of Tanzania's endemics (especially as many of them, like the rufous-tailed weaver and ashy starline, aren't that inspiring to look at!). And, as ever, if you've got any ideas of your own, feel free to pass them on!

Oh, and do check out the Eastern Arc mountains if you want a truly unique wildlife experience!

Global patterns in forest and savannah species

So I memtioned in my last post how I'd enjoyed taking some of the conference attendees on a little safari on the weekend following the conference. We had a night in Tarangire and then a day in Arusha National Park. Now I'm really an ornithologist, who plays at being a savannah ecologist. I'm not a botanist at all. So driving around with people who really are is always educational, and the number one insight that I got from the weekend was the extraordinary degree to which Bill (who works in Brazillian savannahs) and William (working in African savannahs) could identify a plant - say a Xanthoxylem and William would turn to Bill and ask if they had the same genus in Brazil. To which, almost always, the answer was yes. Even more remarkable (to me) was the fact that on occassions they even had the very same species.

Botanists getting serious, Tarangire June 2011. I think it's a grass.

 Interestingly, whenever there was a genus match between continents, if we were in a savannah, the same genus was always a savannah plant in Brazil, whilst if we were in the forest on Meru, the South American members of that genera are also forest plants. To me as an ornithologist thinking quickly, I can come up with no more than two or three bird genera that are shared between the continents (there are a few Turdus thrushes in both places, Tyto barn owls, etc.), and that's it.

I was brought up as an ecologist understanding that biogeographical (bio - from biology, geographic, from geography of course - biogeography being the study of distributions of species) similarities between continents could usually be explained by a process known as vicariance. This idea essentially explains the distribution of related species by assuming that a common ancestor of the current species lived on a continent that then moved around through the process of continental drift. A typical example might be the distribution of Ratites  - the group of large flightless birds that includes the ostrich. The closest relatives to the ostrich include the emu in Australia, the rhea of South America and the kiwis of New Zealand. Their distribution in these southern continents is explained by their shared ancestor living on the ancient continent of Gondwana, a single continent that eventually broke up (around 200 million years ago) to form the southern continents (plus India and the Arabian peninsular). Each fragment carried a population of this ancient ratites and today we see a distribution of birds across the southern hemisphere.

Ostrich are ratites, a typical Gondwanan group with a distribution explained by vicariance

This explanation of shared ancestry, each population of which floated off on it's own continent it the one that immediately springs to the minds of ecologists of my generation where confronted with similar species across southern continents. But the break-up of Gondwana took place around 200 million years ago - and that's a very long time for evolution to have been acting. Although most ratites are fairly similar and the shared ancestry immediately obvious (though check the kiwis!), they're actually very different and certainly not in the same genus. Now, it's important to remember that, unlike species, genera are not very well defined groups - rather they are a taxonomists attempt to identify common ancestors and group similar species - but whether we group 50 similar species into five genera in one family, or one large and diverse genus within a family is rather more arbitrary than the similar decisions about species (though even there it's actually surprisingly tricky!).  So I already knew that the best predictor of how long ago the common ancestor of any particular genus lived is nothing to do with the variety within the species, but everything to do with the number of taxonomists that work on the group - the more taxonomists, the more genera, the more recent the common ancestor. So my first question was whether the common ancestor of these plant species really lived more than 200 million years ago and are just kept in the same genus because there's such a shortage of taxonomists. And I learnt that whilst my head has been full of other things, I've missed one of the biggest revolutions in biogeography of the last decade.

Meru's forests were full of genera also found in South America (and Australia!) Erica have interesting distributions, but not in the New World.

Now we can use DNA to provide fairly accurate dates on when individual species shared common ancestors, we've been able to see that, contrary to the vicariance ideas I've been brought up with, that imply aces over 200 million years, most of the shared genera across the southern continents seem to be far more recent that Gondwanan in origin, which implies that they must, time and time again, have managed to disperse from continent to continent. Wow! What's more, it seems that more often than not, Africa has been the source of the movement, rather than the recipient. Amazingly (to me at least) even some plant species that are dioecous - i.e. have male and female plants - have amnaged to generate almost global distributions through regular long-distance colonisation events. (Unfortunately plant names have a habit of slipping my mind and I can't remember the one that impressed me most - and my pencil was broken so I couldn't take notes. Rubish, huh?!) That is pretty extraordinary I think! So next time you wonder how a seed disperses from a tree, and how it could ever move more than a few metres, remember that most of these genera have managed to get from one continent to another, probably several times! Surprisingly, though, despite these multiple movements across continents, whenever a plant does make the jump it has never (or nearly never) colonised a different biome - savannah plants have to find themselves a slot in a savannah, forest plants in a forest. Which probably tells us all sorts of interesting things about how plant communities are put together, but that will have to wait for another post...