How to protect lions?

Lions: just big kitties really!

There have been a couple of lion stories in the news in the last week or two, and enough interest in them that I felt compelled to write something. First there was a paper by Craig Packer and many coauthors about lion populations in Africa, their current declines, and the possible role of fencing in protecting them. Then, shortly after, there was a letter in the New York Times by Tanzania's own Director of Wildlife, asking the US government not to list the lion as endangered, as lion hunting is crucial to their conservation in Tanzania.

Ground Pangolins and Convergent Evolution

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On a recent safari I was fortunate to get my first ever sighting of a Ground Pangolin. This animal is quite fascinating.

1.     What is it?

Kakakuona (Swahili) is a mammal that belongs to its own Order called Pholidota. It is a monophyletic order which means there is only one family Manidae.

2.     What is it doing?

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:

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?

Exercise like a lion!

Wildebeest wrestling - the ultimate fitness regime? Selous GR, June 2010.

I came across a paper this last week - I can't remember how, because it's certainly not my usual reading material (though my wife has just pointed out a report on the BBC today) - but it suggested an answer to one of the things that puzzle me about lions. Like most cats, lions like to sleep. A lot, in fact - they're perfectly content sleeping for 21hrs a day, so it's no wonder tourists don't normally see them doing very much. As a consequence, I think lions are rather boring: I'd rather be birding. Still, on the occasions when I've got visitors staying who need to see lions I do go and look at them, sleeping away, and I wonder. How is it that a lion, sleeping 21hrs per day, can still be so fit and healthy? On the rare occasions when they do shift themselves, wild lions are certainly lean, mean killing machines. But how do they remain in such good condition, when they sleep nearly all the time, and even when hunting tend to walk as slowly as possible, or sit motionless in ambush?

Tarangire wildebeest migration

Tarangire wildebeest on the move, Sep 2011.

Following the ATBC / SCB conference in June I mentioned a talk by Thomas Morrison on the movements of the wildebeest in Tarangire. The Tarangire migrations is, of course, tiny in comparison to the better known Serengeti migration and involves a different race of wildebeest (C. t. mearnsi in Serengeti, C. t. albojubatus in Tarangire) , but it's just as interesting to understand, and Tom and his supervisor Doug have recently published some work describing the movement that was covered in the conference talk. Until fairly recently, Tarangire was home to a large wildebeest population, though only around 6000 remain today. It's still one of my favourite places to visit though... These animals move into Tarangire in the main dry season (arriving in June) and then move out to one of two main areas for the wet season either east onto the Simanjiro plains, or north-west towards lake Natron. As with the Serengeti migration, these wet season movements are onto grasslands growing on recent volacanic soils with high nutrient content and just what is needed during late pregnancy, then when lactating after calving in February. One of the mysteries, however, is whether the population that moves to Simanjiro is the same as that moving to Natron - do the animals go one direction one year, and the other the next? And as those moving to Natron pass close to another population in Manyara, do those Manyara animals also join the movement? It's important to know the answers to these questions if we're to try and protect the animals, given that they spend around six months of the year outside the National Park system.

Why is the African Savanna so full of thorns?

Giraffe lick leaves between thorns. Note how obvious the white thorns are.

Spinescence. Now there's a word! It simply means having spines and one of the first things many visitors to the African savannah notice is that everything is covered in thorns. Or, in other words, Africa is spinescent. It's not a wise idea to brush past a bush when you're walking, and you certainly want to keep arms and legs inside a car through narrow tracks. These are thorns that puncture heavy-duty car tyres, let alone delicate skin. But why is the savanna so much thornier than many of the places visitors come from? Or even than other biomes within Africa, such as the forests?

This post I've just written as a guest blog over at "Nothing in Biology Makes Sense". I'm incuding it here too, but do go and check that blog out if you're interested in evolution! You can read the rest here, so skip to the story there if you want...

How the zebra got his stripes?

 Most animals in the savanna come in one shade of brown or another, except for zebra. Zebra, as everyone knows, are stripey. Black with white stripes, at that; or are they white with black stripes? Anyway, why they're stripey has puzzled many people for a very long time: even Wallace and Darwin debated whether zebra stripes make them conspicuous or not! For stripes to have evolved there must be some evolutionary advantage, but what, exactly is it? There are a huge number of theories out there (many reviewed here), from the rather obvious to the some more ingenious ideas too:

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!

How to survive the Serengeti: predation, food and body size

Serengeti Lions eat a diversity of mammal species.

Another paper describing one of my favourite talks from the TAWIRI conference back in December has just been published, this time in the Journal of Animal Ecology (available to some here). Grant Hopcraft and colleagues are interested in why different grazing animals use different parts of Serengeti in different ways when they all eat grass. Why, for example, do you usually find buffalo around riverine areas, whereas gazelles tend to be on the open plains? At some level it's obvious that where you find an animal is the place that it survives best and there are two aspects to survival that most ecologists would agree are crucially important: where will you eat? And where will you be eaten? Although both buffalo and gazelles eat grass, and both are eaten by large cats, it's quite possible that grazers of different size will be affected differently by these same two processes. And that's what Grant and colleagues set out to test.

Life spans of tropical birds

Admirng a White-browed Scrub Robin!

Pangani Longclaws are very impressive up close

This morning I took my children with me to go out and do some bird ringing (banding, if you're from the US or Australia!) with some friends just out of town. As is often the case when I'm ringing, I get asked lots of questions about why we ring birds, today's best was why we keep catching immature birds? There are lots of answers to this question and some of them focus on the fact that young birds are just less careful and are generally more stupid than their parents - but this bias aside it is a really good question and had me thinking again about the differences between bird lifestyles here in Africa, and those in higher latitude areas like Europe and North America. It just happened that the question came up after we'd caught two migrant birds (from Europe) and a very new baby White-browed Scrub Robin - all birds hatched within the last year. What I said at the time (and now I can look back over all the birds we caught this morning it's even clearer) was that whilst we often catch more immature than adult migrants, that's not true for the resident African birds we were catching. In fact, we only caught about 25 birds this morning, and only three of them were migrants (we were hoping for more, but this year has been surprisingly poor so far down here, the talk of all the local birds at the moment, as conditions seem good to us!), but all the migrants were young, whilst of the remaining resident African birds, only three were immature. This sample alone, of course, is of limited use: as a scientist I'd want much larger sample sizes - and I'd also want to know it wasn't just a seasonal thing - many of our local birds are only just begining to breed, so there simply aren't many babies around yet. But put our results together with many others, and start to look at the data gathered in more detail and it is indeed clear that African birds do things rather differently to their higher latitude counterparts - as described in a nice paper by Wiersma et al "Tropical birds have a slow pace of life" (get it free here!). Not unlike a lot of people living here either!

Lovebirds can live up to 20 years - they can also bite hard, so be careful extracting!

The Serengeti Story 2: the great migration

Lion admiring the massed migration on the plains, near Naabi, Dec 2011

The second part of the Serengeti Story is the tale of the great migration, the defining heart of the Serengeti Ecosystem. At the broadest level, this is an easy enough  thing to understand - thre are two very important environmental gradients across the ecosystem and the wildebeest (and zebra and eland and gazelles, etc.) are trying to maximise their access to important resources. So, let's start with the two important gradients: rainfall and nutrients, the remaining two of the big four we didn't cover in the first part of the story.

Average Serengeti Rainfall, adapted from here

Starting with rainfall, the broad pattern is for lots of rain in the north and west, and (much) less in the south and east. Perhaps more important still is the seasonal difference in rainfall patterns - most rain falls during the wet season, of course, and the wet season rainfall shows a similar pattern to the overall pattern. But dry season rainfall is the key - the far north and the far west have an average of 400mm of rain even during the dry season, and what's more that's fairly reliable rainfall - the rest of the ecosystem is either compeltely dry, or only ocassionally it by a shower every few years. There's also only one permanent river in the ecosystem - the Mara river in the north. So dry season rainfall means there's green grass to eat, and the Mara river means there's water to drink during the dry season in the far north - an obvious reason for migrant animals to be on the Kenyan / Tanzanian border during the dry season. (In fact the animals move around quite a lot at this time, following local patterns of rainfall and often crossing and recrossing the Mara river throughout their time up there.

A small crossing of the Mara: local movements, not migration, Sept 2011

As the rains become more widespread in November the animals quickly move south, heading away from the woodlands to the short grass plains of the Serengeti NP / Ngorongoro CA border. Why? Well, this is where the other important gradient comes into play, that of nutrients. And this is best understood by looking at the geology of the Serengeti ecosystem in the figure below. Orange areas are 540 - 1500 Million years old, grey areas are recent (within 65 Million years - most only 3 Million years old), Pink areas are over 2500 Million years old and tan coloured bits are also relative recent alluvial (flood) bits, derived from earlier shorelines of Lake Victoria.

Geology of Serengeti, detail from Ordanance Survey map, Saggerson 1961

Broadly speaking there are three geological areas in Serengeti - the southern areas with very recent soils formed on top of the ash deposits from the crater highlands (which form a hard pan that plants can't get their roots through, and only having shallow soil - as illustrated in this picture below froma cutting just east of Naabi gate), the western areas and the north-eastern areas. The north eastern areas are characterised by rocks formed over 2500 Million years ago, whilst the western areas have some more recent deposits from the rivers and different shores of lake Victroia. Unsurprisingly, the nutrients from the ancient rocks in the north have long-since washed away, leaving the north in particular extremely nutrient poor, whilst the short grass plains of the south are very, very rich. Particularly in phosphorus and calcium, both particularly important nutrients for pregnant and lactating wildebeest. The recent soils of the west are rich too, but mainly in Nitrogen, important, but not especially when pregnant. So here, immediately is a massive pull for animals away from those wet, but nutrient poor northern woodlands, down to the dry but nutrient rich grasslands of the south. Obviously they can only get here when it's wet, so timing their breeding to the rainy season on teh short grass plains is a great idea. What's more, predation down here is much lower too, as the hard pan and low rainfall prevents trees and lions have a much tougher time hunting away from the rivers and woodlands, which is great for baby animals.

Soak-away near Naabi showing the hard pan that limits tree growth, but makes grass very fertile

So, now we've got the important data we need for understanding the broad-scale movements of the migration. During the dry season, you've got to be near the Mara, in the far north. Once the rains come you want to move as fast as possible down to the nutrient rich grasslands of the south, where it's wise to give birth. But then once the rains stop, the bad news is that even though the grass stays green for a while, the standing water at Masek and Ndutu is so rich in nutrients that it's actually toxic - so even though the food is still there and still good you've got to start moving off as soon as the rain stops. But instead of heading straight back up the the north, it makes sense to move west, where there's still relatively rich grazing and water remains in the Grumeti and Mbalageti rivers. So come late May the migration moves away from the short grass of the south and heads into the Western Corridor, staying as long as the grass remains before gradually filtering north again as the good grazing is eaten in the west. (That date has got later in recent years, as there's now a lot more grass left in the Grumeti Reserves, thanks to a policy of burning only after the migration has been through - which explains why those northern camps have had some tough starts to the season in recent years!)

Movements of individual wildebeest caught near Seronera (blue circle) from here

And so you have the broad pattern - a triangular migration in a clockwise direction, covering between 500 and 1000kms, and one of the most amazing wildlife sights anywhere on earth. But, as always, the broad scale picture isn't all there is to it. Individual animals take some remarkably different routes around the ecosystem, as some data from gps collared indivudals shows - all these animals were caught near Seronera at the same time, but all have done different things - the dark blue one is particularly interesting, and none of these animals came down the eastern side of the NP at all. Why not? No-one knows - maybe simply because they were all passing Seronera instead. More recent work in the Masai Mara has made even more exciting discoveries, with animals I'd have assumed previously to be local migrants into and out of the Mara showing some extraordinary movements, even joining the main Serengeti migration in some years, but not others - look at these maps from here (they're updated very regularly, as the animals are still out there!)

The first of these spent a year in Kenya, migrating from wet season home in the west to the east and back, but then joined the main Serengeti migration this year and is somewhere in the NCAA today, whilst the other left Kenya last year and headed off to Loliondo for the wet season, before returning this year to wet season home in the north east! What made these animals change their routes from one year to the next? It will be fascinating to try and find out as more data on the movements of individual animals become available. Clearly, understanding the broad scale pattern is only a tiny fraction of the question as a whole and we've lots more to learn.

Anyway, I hope that's a pretty good introduction to some of the Serengeti Story. It's far from static, and there's still lots more to learn, so we're bound to return to the issue in subsequent posts, but I hope this is a good start at least. Meantime, Happy Christmas!

What can we learn from mutants?

Elephants with one tusk are common, but not mutants. Tarangire NP, Aug 2011

One of the joys of working in the bush is that there's always something new to see, and every now and again we come across something very, very odd. Some times we see the disfiguring effects of a disease or accident – one tusked elephants are particularly common. But occasionally we find evidence of a much more fundamental accident – a genetic mutation. One of the commonest is albanism, or partial albanism (more properly called leucisism – technically, you can't have a partial albino). True albinos are very rare in nature and occur when all the genes that control colour are, somehow, switched off (even those involved in eye-colour). I don't know if this baboon is a true albino, as I couldn't see the eyes, but I wouldn't be too surprised if he was. (I'll find out one day I'm sure – he lives in Arusha NP and I first saw him as a tiny baby over a year ago. One day he'll come close enough to see!) More often you'll see animals that lack colour in just some parts of their body, or sometimes lack all the pigments of one type – lacking melanin (which gives the black colours) is relatively common, and often results in sandy looking creatures, as the orange and yellow pigments are still present. Still rarer than colour mutations are the really strange mutants you sometimes see, like the buffalo below – something completely mad has happened here!

Albino Baboon, Arusha NP, Aug 2011

Entertaining as it is to see such strange creatures, I think there's quite a lot we can learn from these animals. Look, for example, at this buffalo, and compare it with the normal animal in the same herd – it's not doing very well! That's not surprising – with horns like that I find it very hard to believe it can graze properly – more likely ir can only nibble the tallest grass everyone else leaves, or is forced to browse, which can hardly be good for a buffalo. As for the baboon, well, he seems healthy enough – but I was still rather surprised to see him still going strong now aged one year – there are so many crowned eagles, leopards and martial eagles around Arusha National Park, and he sticks out from the crowd so much I expected him to be the first to go. He's been lucky so far... Which gives us our first lesson - most mutations are bad for the health, which explains why we don't see many more mutants when we're out and about.

Mutant buffalo (probably cow), Tarangire NP, Sep 2011

Much more normal buffalo, same herd!

So what about evolution, I hear you ask? Evolution is works because mutations are passed on from one generation to the next, yet lesson one is that mutations are bad for the health! What's going on there? Now, whilst that is definitely true for big and obvious mutations (in fact, most of the really big mutations that occur are probably automatically aborted - miscarried - in the womb before birth), it doesn't mean there aren't lots of mutations happening that we don't obviously see. In fact, for every human it's estimated that there are NNN unique mutations we have that have occurred in the genes we inherited for our parents: we don't have perfect copies of our parents DNA at all. Happily, most of the mutations have no or very little impact – which is why we don't see them – but the good news is that a few might have small benefits. And so this is lesson two, that evolution normally happens in very, very small stages – the accumulation of lots of tiny little beneficial mutations that we generally never see. That's not to say that we can't see evolution in action with the mutations we do see – in fact, the elimination of 'bad' mutations from the population is just as much a part of the evolutionary process as the incremental development of new changes. So simply by looking at this skinny buffalo, we see natural selection working – whilst the animal might still be alive (and obviously has survived a number of years), I don't think it's in any condition to pass its genes on to the next generation. So that could be my third and final lesson that we can learn from these mutant animals – that natural selection results not only in the accumulation of beneficial traits, but also in the elimination of sub-optimal genes too. That might not sound so important right away, but maybe in time we'll look at why it does matter, particularly when animal populations are reduced and individuals start to breed with their own relatives.

And finally, let's just remember that accidents – like the one-tusked elephant – are completely different from mutations. The effect of an accident will never be passed on to future generations because it's got nothing to do with genes (though the propensity to have accidents, of course, might do!). Only mutations in the DNA will be passed on to future generations, if the animal concerned survives to breed.

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...)

The landscape of fear

Serengeti Landscape of Fear - where would you feed? On the green by the river where predators hide? In the bare bits on the plain with no grass left but a good view? Or risk the woodlands somewhere in between?

Lions are often in thickets (N. Serengeti)

But sometimes on kopjes... S. Serengeti

where you might also find a cheetah! N. Serengeti

It might sound like the sort of novel you's find abandoned at a camp by passing visitors, but understanding what ecologists mean by the 'landscape of fear' - how predators have impacts on the ecology of a savannah that go well beyond their direct predation events - is such an important concept that I'm going to break my usual rule of not talking about the big five! Actually, understanding the concept is simple - it's about looking at a landscape and working out where you'd be (most) scared to be walking. Long grass? Yup, scary. Thick riverine vegetation? Not for me! Nich bushy kopjie? I'll give it a miss, thanks. You get the idea - any place you might think about looking for predators whilst on a game drive, is going to be a scary place for herbivores too. And it's not simply a function of the numbers of predators that are present, but how efficiently they might be able to hunt within that habitat - I'd be much happier walking a short grass plain with a high density of lions than I would walking through some tangled thickets with a much lower density of lions. (Obviously I'm also a bit warier of buffalo and elephant than most herbivores have to be, but if you've done a few walking safaris you'll have the idea anyway.)

So what? These patterns are so obvious, we don't really think about them, or think they have an important part to play in very much - but we'd be wrong. In places where top predators have been removed, we rapidly see changes in the behaviour of herbivores and, soon after, we'll see changes in vegetation. Perhaps nowhere more famously than in Yellowstone National Park in the US (described here) - when wolves were eliminated elk and bison were released from their major predator and the populations changed - they didn't change in numbers very much, becausee like Serengeti's wildebeest and zebras (and, of coruse, elephants and the rest of the mega-herbivore group) they're limited by bottom-up processes of food availability, not top-down processes like predation. But they changed in behaviour, spending much less time looking around for predators and not moving around very far from their favoured willow patches. Which mean that after 50 years of no wolf predation, those patches of willows were in a bad way - it looked possible this form of riverine vegetation would vanish forever. Until 1994, when wolves were reintroduced. Within a matter of months the female elk and bison were spending significanty more time looking around, avoided open areas and only stayed in one place for a little period before moving on. And, in time, the riverine areas started to regenerate. We'd witnessed a 'trophic cascade' - removal of a top predator had had a massive impact on vegetation and landscape, the impacts 'cascading' down from top predator through the herbivore to the basal layer.

Leopards like riverine too, C. Serengeti

And lions often hunt by rivers and small ridges, Tarangire

These Fringe-eared Oryx have spotted something from their vantage in the Tarangie plains

The same processes are in operation on our east african savannahs all the time. Lions are far, far more efficient predators in areas where they can conceal themselves (in bushes, around kopjies, along even small river lines and shelves) than in the open - and as we know they plan their hunts accordingly. Similarly, leopards are best looked for around kopjies and riverine forests, where they're both able to avoid lions and can hunt sucessfully. Even cheetahs are often around kopjies to get a good view. So these are scary places for animals and, as we've seen so often before, if you start altering grazing pressure (one of the big 4 processes in the savannah), you'll see a change in the vegetation - riverine forests get a headstart if there's a big predator population living in them, scaring all the wildlife out! There's even the possibility that this processes becomes a positive feedback - as bush increases, so does predation success, making bushes even scarier, leaving fewer herbivores to keep the bushes back, meaning the bushes spread further, etc. And on the other hand, grazers like to graze areas where they have a good view - short grass - but if there are enough of them, their very grazing ensures the grass stays short, reinforcing the benefits.

Of course, things are complex for a herbivore - you can't simply decide never to forage in a wooded area because you might get eaten, because maybe half-way through the dry season you'll have eaten all the grass on the plains, and all that's left is in those scary woods. So you can either starve to a certain death in the plains, or head into the woods and risk predation, but at least stand a chance of avoiding starvation. Animals must constantly be assessing and weighing up the costs and benefits of foraging in high reward (grass under legumes like Vachellia is often of higher nutrient content than elsewhere) but risky areas, versus the safer but less beneficial areas on the plains. Not only will seasons make these decisions change, but so too will the details vary during the day - it's far more important to be in the plains at night than it is during the day, resulting in a evening movement of animals out of woods and onto plains - woodland edges are a great place to be at sunset!

Tarangire Wildebeest treck from the woodlands to the plains every evening

Spotting predators on Serengeti's short-grass plains is easy - no fear here!

Anyway, once you've got the idea of trophic cascades and the landscape of fear, you'll start seeing how it works all the time, and I hope I've given you enough here to start thinking about at least. (You'll get a much more in-depth and very readable discussion of tropic cascades and the landscape of fear in this nice article here.)

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!

The roles of elephants...

Elephants, Tarangire NP, Aug 2011

As you've probably guessed, I've been away again, so thanks to Ethan for sharing his discoveries whilst I was away. I'm sure we'll come back to the migration again soon (especially as I'm hoping to be in the thick of it again this weekend!), it's such a fascinating subject. Meanwhile, part of my travels took us to Tarangire where the elephants can never fail to impress, so in a rare forray into the world of the 'big 5', here's a post about elephants... The Tarangire elephants are a population fast recovering from the poaching of the 1980s (though I'm sure some still goes on at times) - in 1960 there were only 440 animals in the park, by the last full census I can find numbers for in 1996 there were 2000. Many of these early arrivals migrated into the park from outside to escape the even heavier poaching in peripheral areas and have since become resident (or semi-resident) within the boundaries.  But since 1993 the closely monitored population in the north of the park has continued to increase at about 7% per year (pretty close to the maximum theoretically possible, given gestation rates, etc.), which is rolled out over the whole park to 2011 would give about 5500 animals. A not unreasonable estimate I'm told. As the park has an area of aroud 2850km2, that gives a density of nearly 2 animals per square kilometer. Compare that to the densities during periods of regular culling in Kruger NP of around 0.4 animals in the same area, and you can see the extremely high densities present in Tarangire.

Eles love to wallow - digging waterholes as they do and removing up to 1 m3 of soil a time.

In actual fact estimating densities of any animal is trickier than you might imagine - they're certainly not unifrom across the landscape, with local concentrations in certain areas, or in different seasons. So it's fairly hard to make direct comparisons of densities across different National Parks, but it's pretty clear that Tarangire is certainly among the top two or three elephant parks in Africa. So the question I'm innevitably asked, is what is the impact of these elephants on the landscape? Weighing in at around 3000kg and eating as much as 200kg of food per day, elephants can have a massive impact on the landscape - add to that the fact they're pretty good a toppling tasty looking trees (generally across the quieter tracks I like to frequent, it seems!) and there's a lot going on. In some corners of Africa it is certain that they've had massive impacts on vegetation - creating rather unsightly bare areas around permanent waterholes and rivers. However, whilst tourists might not like these places, increases in elephants are often associated with similar increases in buffalo and impala, and the biological impacts are not all negative. It's also difficult to discuss issues of elephant density from a well informed basis as we don't actually have any real idea about the starting conditions before massive hunting for ivory - most of Africa's elephants were hunted out alongside the slave trade in the 1800s, so even in the high density areas of today we really don't know how this compares to densities of even only 200 years ago, nor do we know what the environment looked like particularly well back then.

Tarangire Elephants deep in the swamp keep the water open. Aug 2011

In Tarangire, however, the elephant population increase has occurred at the same time as the density of trees in the park has increased (for reasons we might ponder in a later post), and whilst they certainly leave their mark on the baobabs, there's little evidence of major vegetation changes as a consequence of incredibly heavy elephant browsing. So, for now I'm going to skip discussions of potentially negative impacts of elephants and will illustrate just one of their particularly beneficial aspects that was plainly on view in Tarangire - their role in keeping waterholes open.

Open water created ideal habitat for water birds: Silale Swamp, Tarangire

From the picnic site I counted more than 380 elephants enjoying the Silale swamps - they were there for food and water, of course. But in the process, they keep the edges of this swamp free from vegetation. Elsewhere along the river their rolling and wallowing  was keeping pools of water open much more than would be possible without them (each animal can walk off from a mud bath with up to 1m3 of mud attached, a volume that takes me a serious effort to move!) - indeed, elephants are capable of digging in sand rivers to access the water (and at times salt) well over 1m below ground. So they create waterholes and maintain open, vegetation free areas in swamps (a role often also played by hippos, but not in Tarangire). They're also great fun to watch splashing in the water, and as well as explaining how fussy they are about the cleanliness of the water they like, it's also worth talking about how their activities benifit all the other animals around that need water too. They are certainly worth of the name 'eco-system engineer' as well as that of a 'keystone species'.

When you're tired of elephants you'd better stop guiding... Tarangire May 2011

Why Are There So Many Wildebeest Compared to Other Animals in The Serengeti?

Herds crossing into Kenya.

Having been on safari for the last couple months, I’m unworthy of being called a co-author of this blog considering the wonderful posts that Colin has been writing. In my travels I have been to the Serengeti ecosystem four times in the last few months, three times in Serengeti and once in Maasai Mara and of course we have followed the spectacular herds of wildebeest.

When you’re driving through hundreds of thousands of wildebeest, or watching tens of thousands plunge into the Mara river because the grass is greener on the other side, its hard to wonder why there are so many of them. Why not zebra, topi, kongoni, impala, dikdik or one of the other antelopes?

So, I thought I would explore this topic and discovered this wonderful paper online, which you can download if you want to read a more scientific explanation. (Click here )

Part of Colin’s themes has been that there are things that shape or influence the environment, and that the environment then shapes the species in it. It’s a two-way interaction that steers what happens. E.g. When there is predation on plants they evolve defense mechanisms like thorns or chemicals.

So, what is it about the Serengeti that promotes these massive herds of wildebeest?

The simple answer:

Climate and soils.

The Serengeti ecosystem extends between two geologically significant features:

In the east, are the rift valley volcanoes that blew volcanic ash over the eastern part of the Serengeti, starting millions of years ago. These became the extremely fertile short grass plains between Maswa and Piyaya.

The short grass plains of Piyaya- the volcanoes in the distance.

In the west, Lake Victoria gives the north-western Serengeti a much higher rainfall (1200mm) than south-eastern Serengeti (500mm), especially when everywhere else is dry.  

Put these two factors together and you have high quality grazing every month of the year. In the wet months of the year (Feb, March, April), the soils in the short grass plains make the grass particularly excellent grazing with extra dose of calcium and phosphorous - perfect if you are a wildebeest trying to make milk for your calf. In the dry season- well, you migrate to where its raining and you find green grass which is much more nutritious than dry grass. (Wildebeest need 30% more energy, 5 times as much calcium, 3 times more phosphorous and 2 times as much sodium when they are lactating than pregnant and the short grass plains are perfect.)

A newborn wildebeest in Piyaya. It stands within 20 minutes
 to suckle. The milk is a high-cost to the mother but she
survives because of the minerals in the grass.

So, now we understand that the whole 25,000km2 Serengeti ecosystem always has nutritious grass (and drinking water) somewhere at all times of the year. The next question we have to investigate is- why wildebeest? Why not zebra, topi, kongoni, eland etc. etc?

The simple answer:

                   Wildebeest are special.

As you might know, wildebeest belong to a tribe of antelopes called the Alcelaphines. This means they are fairly closely related and if you want to know how close, well, they are about 4 million–year-old cousins. All of them are ruminants, which means they have a four-chambered stomach that they use to digest cellulose. Rumination is a very efficient way of extracting nutrients from plants but each species will have it’s own efficiency and Coke’s hartebeest are actually the most efficient of the three species. So why isn’t it Coke’s hartebeest?

Topi in the long less nutritious grass on the Lamai wedge

We can start by looking at the mouth structure of these animals and realizing that wildebeest actually have a mouth that is perfect for eating grass that is 3cm high, which is when the grass has the highest levels of protein.

The next thing they do is chose the parts of the grass that are also more nutritious- the leaves and fresh shoots. Coke’s hartebeest and topi eat more stems and leaf sheaths than wildebeest, zebra survive on almost only stems. But there’s a lot more grass stems than grass leaves so you would rather expect zebra populations to be in the millions but they aren’t- what is actually happening, is that zebras suffer very high losses of young, so predators keep zebra numbers down.

Now, you might ask, why aren’t wildebeest populations kept low by predators?

Answer: Synchronized reproduction and rumination.

80% of wildebeest calves are born in 3 weeks in February= 250,000 wildebeest calves= 500 per hour. It is an amazing sight. In scientific terms: extreme synchronous breeding outstrips predator’s ability to limit wildebeest recruitment.

Calves are most vulnerable when they are very young but they reach a certain age when they become equally vulnerable as the other wildebeest. There is a limit to how many calves predators can take per day, so by all having their babies at the same time, more calves have the chance to live past the age where they are vulnerable. Topi and hartebeest do not have as synchronized breeding as wildebeest.

Zebra on the extra nutritious short grass plains.

As we mentioned before, wildebeest are ruminants. They spend about 8hrs a day grazing so they have 16hrs a day to look for predators. Zebra on the other hand, spend 15hrs a day grazing so they only have 9hrs to look for predators. This is because they are hind-gut fermentators. This is obviously simplified.

Now, we’ve established the benefit of synchronized breeding but there are other advantages to being a wildebeest. Serengeti’s short grass plains are the best place for the females to get the nutrients they need to lactate, but they are also a great place to spot predators, which also helps to reduce the number of calves killed before they are out of the vulnerable stage.

Finally, calves are born precocial with a very strong imprinting instinct. The mother and calf learn to recognize each other immediately by smell and the calf stands as soon as it can and then stays as close to its mother as possible. The calf then also tends to run on the hidden side of the female so that predators have a harder time seeing them. The effect= reducing predation.

Wildebeest calve's coats change color to look like their
mothers at 2 months. Predation drops drastically.

There are other minor influences and for more details download the paper, but to try to sum it up in a sentence: The Serengeti’s unique climate and soils provide the perfect conditions to allow wildebeest to live in such large migratory herds because of wildebeest’s unique biology.