What's to like about rats?!

Yesterday we talked about vultures, and now a fascinating new publication by Jonathan Kingdon and colleagues working in UK, Kenya and the US has inspired me to write about another often despised group, the rat! In fact, I'm not going to be general, but just going to highlight some of their fascinating findings regarding the Crested Rat Lophiomys imhausi. This is a species of the arid and semi-arid habitats of NE Africa, just making it into some of the driest areas of northern Tanzania and the drier parts of Kenya (interestingly IUCN don't think it's in Tanzania - anyone know differently? I've never seen it here but there are lots of unsourced references I can find like here). They're a rather large, slow moving rat with distinctive black and white crest and strange-looking hairs - I've no pictures myself, but there's a nice one here. You might see them every now and again on night drives, shuffling along a little like a small porcupine. That sort of slow, unconcerned attitude is pretty unusual in small fluffy creatures that everything wants to eat, and the black and white colourings are often a warning to other animals that's they're something to be afraid of. But what defence can a rat possibly have?

Well the new research has found that these rats chew on the bark of Acokanthera schimperi and smear the chewed bark and saliva on that crest, transferring the poison there, and possibly modifying it slightly in the process to make it even more potent. Any animal taking a bite gets a mouthful of poison and either dies very fast, or gets ill enough to remember not to take another bite of this species! The posions (actually, there are several, but it seems as though the rat is only using one) in Acokanthera schimperi is capable causing a heart attack by greately increasing the force of the heart-beats. In fact, it's the same poison that used to be used by the Waliangulu of Tsavo for elephant hunting. In a neat extra adaptation, the rat's fur along this crest contains special absorbant holes for soaking up the poison rather like a sponge. The paper reports that normally the animals cover the special fur with longer normal, grey fur to protect it from light rain and sun, which could mean that they're not immediately showing their warning colours and may get bitten - but they also show several adaptations that suggest they can survive a hefty bite, with thickened skull and other bones - hopefully meaning that when the predator gets a mouthful of poison, any damage it causes to the rat is minimal.

The big question, of course, is how do the rats do it? Why doesn't chewing the bark kill them, the same way it woudl kill an elephant? And the new paper has nothing concrete to say about this (though does suggest that the large salivary glands might have something to do with it). It's interesting though - because if we can understand how the rats prevent heart-attack induced by this poison, we might have a whole new set of tools available to us to treat heart conditions (we already use the poison itself in some medical treatments).

So who said that rats were dirty and uninteresting?! This one at least has a nice series of tricks up it's fur. The question you might then have, of course, if if they're so very toxic and don't need tow orry aout predators very much, why aren't we over-run with the beasts? And it's a good question - they'r emostly vegeterian in the wild, but can certainly tuck into mean when it's available, so there shouldn't be too much food limitation either. But there must be something more to this, as they are restricted to arid areas and the tree is much more widespread, so there's obviously something else specialised going on we don't know about yet - any thoughts?!

African Vultures

Adult White-backed Vulture in flight - note white under-wing coverts.

So, it's time to return to the savannah I think, and although I've not been out for a while now, I've spent some of the day thinking about vultures, having been reviewing a paper on their distributions. So I thought it would be a good opportunity to think about these overlooked, but rather important birds.

White-headed Vulture, Tarangire, July 2010

Mixed Vultures, white-backed, Ruppell's and Lappet-faced, Manyara Ranch Jan 2011

Let's start by looking at the vultures we get here in East Africa and working out how to identify them. Some, like the above white-headed vulture are always easy - that profile is obvious even in babies. Same goes for the biggest of our East African species, the Lappet-faced, to the right.

But how about the other two common species - Ruppell's Griffon Vulture, and African White-backed? These aren't always so easy. Adults are OK - Ruppell's have pale ends to their feathers, resulting in a scaly look whilst adult white-backed have, well, white backs... But the immatures and (particularly) juveniles are not so easy at times, and if their white-back isn't showing, how do you know? First, you need to decide if it's an adult or not. Look again at the mixed fulture flock on the right here - the second bird from the front has a clear white ruff around the neck - the first bird has a brown one. That's a very good hint that your second bird is an adult. Similarly, look at the birds in the back row and you'll see another white ruff on the bird immediately left of the back-row Lappet. This bird also has a huge pale horn-coloured beak and scales - a typical adult Ruppell's, whilst the second from the front is uniformly pale and has a rather thiner and pointier dark, beak - a typical adult white-backed. So, all is well and good with the adults now you can age them (see the other adult white-backed there?), but what about the juveniles?

White-backed and Ruppell's Vultures squabbling, Manyara Ranch, Jan 2011

This is harder - the Ruppell's only get the scales and pale bill as they get older, but the bill shape is the same. So start by looking at the two adults at the back of the earlier picture to get a handle on bill-shape, and then look at the squabbling birds on the left. The two having a go at each other are obviously Ruppell's (neither is a juvenile, though the bird on the left still has the dark bill and brown ruff so it's obviously immature) and the bird looking right at the front is clearly a White-backed - much thinner beak.

The birds are a little better behaved in the picture below, and you should be able to start getting you eye into those beak differences which are all you've really got (bar size) on the real juveniles. And, of course, if you're in southern Tanzania you're not likely to find Ruppell's at all, though they do wander from time to time. Which means, I'm afraid, that flight identification of juveniles is really, really tricky - I don't think it's possible to be certain all the time.

Feeding Vultures, Ruppell's Griffon and White-backed

The other vulture you're likely to see in Tanzania is the Hooded Vulture, and I can't seem to find any of my own pictures here, but there are plenty of good ones online, and it's not hard to identify - small, thin beak, pink head, etc. And, when I first came to east Africa, you also used to see Egyptian Vultures all the time (again, the adults are easy to identify, black and white plumage with a bright yellow face, though immatures are possibly confusable with Hooded - check the length/shape of the tail (shortish and square = hooded, long and diamond shaped = Egyptian) and the colour of the face (pink = hooded, black or yellow for Egyptian)), but sadly no more - an immature seen in Serengeti and reported to the Tanzania bird atlas recently is the first sign of breeding in the region for a while. Why not, you ask? I have no idea - probably the biggests mystery decline at the moment, so if you've any ideas let us know!

Right, ID sorted, what's to like about vultures? Most people see them as pretty disgusting scavengers, with no redeeming features. But in fact they're very useful - not only do their early morning movements give you a good idea of where the lions might have made a kill, but imagine what happens when you get rid of them. They're incredibly efficient scavengers, known to be more efficient than their mammalian competitors - the flock pictures from Manyara Ranch Conservancy in January were feeding on a wildebeest killed by lions and within 30 minutes had finished the remaining half of the carcas, leaving just bones and a few tatters of skin. Not bad! So, take them away, and their competitors - the jackals, hyaenas and feral dogs will take over, being freed from these highly efficient birds. In fact, this is exactly what has happened in India, where poisoning by Diclofenac killed off nearly all the vultures in just 10 years, with a massive increase in rabies and anthrax too suggested to be caused by the decline of vultures and subsequent increase in mammalian scavengers and uneaten carrion. Not nice, huh? We should be glad of vultures and ensure we reverse African declines too...

How they achieve this efficiency has long been known - foraging vultures keep an eye on each other, and once they find a carcass different species (in general) tackle different bits. Typically the smaller species - white-headed and hooded are the first to arrive at a carcass and they might have a peck at the eyes and other soft parts, but they're not strong enough to rip through the thick skin, so have to attract the attention of larger species. For the thickest skinned carcasses, only the Lappet-faced can cut through, though White-backed and Ruppell's can tackle many. Generally, once the carcass is opened, White-backed and Ruppell's take all the nice soft meat. White-headed and Lappet-faced then come back in and will take all the tough bits - skin and tendons in particular. Finally, the scraps are cleaned up by hooded and Egyptian, with their fine beaks for cleaning around joints, etc. All very efficient, and obviously strongly avoured by evolution because new world vultures (which we now think again are probably raptors, btw), asian vultures and even extinct vulture populations from long ago all seem to have the same three groups.

White-backed Vulture in Baobab, Tarangire, Oct 2009

So, much to be interested in vultures really. And they do make for wonderful sunset shots to leave you with!

Coastal Habitats

Common Sandpiper on mangrove creek

So, in what's probably going to be the last coastal blog until I get back to the beach again, I thought I'd give a first introduction to some of the interesting coastal habitats. (Note the logical progression - off stuff in the sea, interesting things on the shore, and now interesting things on the land but near the sea. Anyone would think I had it planned!) So, let's start by thinking about what's down by most beaches. And in East Africa you don't have to spend long before realising it's basically a mixture of coconut plantations and sisal estates, with a bit of cashew thrown in for good measure. So you won't be surprised to learn that the northern coastal regions have some of the highest population densities in Tanzania (here), though to be fair most of the plantations were originally started by colonial Germans and Brits some time ago. So the remaining native habitat fragments are in a rather bad way, and can be hard to find. They are worth seeking out, though, as ther are some special things living in them.

For the purpose of this post, I think I'm going to focus on the two of the most interesting coastal habitats: coastal forest and mangroves. Coastal forest has obvious functional similarities to forests elsewhere in Africa, though the species composition can be pretty different. Mangroves, on the other hand, have no inland analogues, so let's start there.

Mangroves still do grow on open coasts here north of Pangani

If you've not seen them, mangroves are starkly different to any other habitat. They're mainly tropical in distribution (there are some in the Australian temperate zone, and a few on the East Coast of the US, but these are the exception that prove the rule), and once upon a time would have occured on any tidal zone (ie, on land covered by the high tide, but exposed at low tide) with a minimal degree of shelter from the full force of the sea - they used to cover over 3/4 of tropical tidal areas. At one time, that included even rather isolated islands like Maziwe, but now you'll rarely find them on the beach front themselves, but mostly limited to tidal creeks. And you'll know when you find one, because you'll be walking through the coconut plantation and suddenly hit a dense, dark and glossy thicket growing like a wall out of the bar mud or sand (sometimes even rock) substrate.

Mangrove edge in cocnut plantation, Ushongo Beach July 2011

If you can make your way through the mangroves, you'll see some interesting sights. Down on the ground the most obvious things are the arial roots - sometimes poking up like fingers, other species rely on multiple branches from the stem. These have a wonderful scientific name - pneumatophores - and their purpose is simply to allow the plants absorb air. But they also form a unique and busy microhabitat of their own - a mini-forest that traps passing mud and can harbour much richer muds than surrounding areas as well as providing lots of nice little places to hide from predators. Consequently, the root systems of mangroves are home to lots of life - there's always crabs to see, and in areas nearer to low tide limit there are often air breathing fish called mudskippers, which are kind of neat and perhaps remind us of our distant ancestry... What's more, these root systems are often extremely important nurseries for the young of reef fish important in many local fisheries.

Aren't those roots odd! Mangrove pneumatophores, Ushongo Beach

These pneumatophores aren't the only interesting adaptations of mangroves though - not only do the have to survive in water-logged soil, but it's very salty too (and in areas where shallow seawater sits around in the hot sun the concentrations of salt can be extremely high) and most plants can't tolerate salt. Mangroves have a number of adaptations to help, of which the most obvious is the glossy, thick leaf itself which reduces water-loss. But more fundamental are adaptations to the root that we can't see that simply filter the salt out of the water - by the time water arrives in the root, 82 - 97% of the salt has been filtered out. Given how difficult we find it to extract frest from salt water mechanically in desalinisation plants, that is a remarkable adaptation! And then what salt does get into the plant can be collected and excreted through the leaves, giving them a silvery appearance at times.

These roots also  absorb air in another mangrove species, Ushongo Beach

In such harsh environments, it's going to be particularly tricky for seedlings to thrive, so mangrove species have another neat adaptation up their leaves - they're (mostly) viviparous. What? Live-bearing plants?! Yes indeed, most mangrove species don't immediately drop their fruits, but retain them on the plant whilst the seedlings develop to a stage where they can photsynthetise themselves - some seedlings growing entirely inside thr fruit, others growing through and out. Then, when they're ready, the plant drops them either like a dart into the mud below them, or into water to float the seas until washed up in some suitable substrate, when the young plant is ready to go. Which explains why many mangrove species have extremely large distributions, dispersing on cross-oceanic currents.

Mangrove fruits germinating on the plant and ready to fall.

So, that's the structure of the mangrove, and it's obvious that this sort of harsh environment is going to be home to species of plants that are survivors - all their obvious competitors are eliminated by the environment itself. And just as the roots are home to lots of little beasties, the trees themselves are home to a pretty good selection fo birds and animals too. The really special bird to look out for in this area is Mangrove Kingfisher, but the mangroves can often be full of mixed species flocks of starlings (mainly Black-breasted), barbets and greenbuls, etc. Some great birding to be had if you can see into the thickets!


So, all in all, mangroves are wierd but great coastal habitats. And it's a shame there aren't more of them, because they are fantastically useful to us too, not least through their very impressive abilities to mitigate against the impacts of tsunamis.


Hmmm. Well, seems like this is probably a long enough post for now anyway, so coastal forests can wait for another time. Ecologically, they're rather similar to other forest types anyway, even if the species they hold are sometimes very different!

On the shore

As I mentioned in the last post from the beach, there's both a huge density and diversity of invertebrates (mostly Annelid worms and molluscs) in the sand and mud. So much so, in fact, that the intertial mud and sand is a huge feeding resource for wading birds. I was once told that if you extract all the worms and molluscs that birds like to feed on from a sample of estuarine mud 1m square and 10cm deep, you'd have a food sample with a total energetic content of around about 1.5 Mars bars. Now, I've had a quick search online for the primary literature that back this statement up, and I wasn't too surprised to discover that althere the cubic metre equivalent is easily found on a google search (you get many answers from 13 mars bars per cubic metre, to 20, with most around about 14 or 15) none of them pointed me to the primary literature at all. And I can't do so either. But I did find papers like this and this that, once you do the sums, suggest it's not a bad approximation. And it's a nice thing to help people understand just how rich an environment this is - everyone knows what will happen to them if they eat to many Mars bars, and there's lots more than 1 square metre in most estuaries! What's more, the rate of productivity is prolific too, so even as it gets eaten, the resource is being continuously replenished. And, of course, the mud isn't the only place with massive densities of invertebrates either - if there's seaweed left to decompose on the beach it harbous massive densities of arthropods, another favoured food resource.

Spot the white-fronted sandplover on it's nest...

White-fronted sandplover nest - two eggs here.

Unsurprising, therefore, that many birds choose to forage in these rich habitats. Some of them, like the White-fronted Sandplover I found nesting at Ushongo (can you spot it on the nest?! This seems to be the first breeding record for the northern coast of Tanzania) are resident. But most of them are migrants fron the north and now, in mid July, most of them are busy finishing off their breeding season. Not all, though - a few first year birds will hang around in Africa all year, waiting to breed for another year, and already those adults who failed in their breeding attempt have come back. In the next few weeks more and more will pour south - and they don't just look for coastal estuaries either, the soft mud around many shallow lakes are similarly rich feeding areas so even if you're only passing the odd soda lake in the traditional safari areas you'll be able to see many of these birds as they start to return in ever bigger numbers. In fact, places like Lake Manyara will soon be home to truly spectacular gatherings of wading birds from the north - well over 1 million little stint are there in most years, and even more at times (up to 3 million have been estimated by Neil Baker of the Tanzanian bird atlas project).

Turnstones, curlew sandpipers and sanderling

Curlew sandpipers and turnstone

So, let's have a little look at some of these migrants that I saw last week - if only to illustrate some of the amazing migrations these birds are capable of. In the pictures above there's a mixed group feeding on invertebrates in rotting seaweed. Most of them - the ones with the orange legs and beaks - are (ruddy) turnstones. These birds, if they migrated this year, will have attemtped to breed right on the tundra beside the Arctic ocean - check here for a map. That's an extraordinary movement - and amazingly, these birds can easily live for 30 or so years, doing these phenomenenal migrations each year. (They also have a remarkably wide diet, with a memorable series of papers reporting ever increasingly bizarre food items from soap and other rubbish, to dead whales, until the editor finally stopped the correspondence when the title reached "Turnstones feeding on human corpse". Nice.). Anyway... You'll alsoalso see (at the right of the top picture, and several in the lower picture) lots of grey waders with rather longer beaks. These are Curlew Sandpipers, and have a similar breeding distribution in the Arctic (but only the Russian Arctic, not North America). These are clearly birds that didn't migrate this year, as the breeding adults at this time are a beautiful rusty red colour and we'll start seeing them soon. Long, decurved beak, long black legs and a white stripe above the eye help identify this species. And if you look carefully on the top picture you can spot one other grey bird running up the sand bank, a bit stockier looking, with a shorter beak - this is a sanderling, and when not breeding in the Arctic is a typical bird of sandy beaches around the world.

Greater sandplover and turnstones

Standing still among the rushing turnstones in this picture is a non-breeding Greater Sandplover, a species with a rather different migration route - this time breeding in the areas around the Caspian Sea in central Asia - not anywhere near as far as the other two, and obviously closely related to the other plovers we see around here, which a much shorter beak and big looking head. We also saw a few lesser sandplovers, which are extremely similar, but tend to have smaller beaks, small heads and shorter, blacker legs (you can see this is a bit greenish on this bird).

There were plenty of others around too, but I didn't get any good pictures I'm afraid. It's always worth checking through the wading bird flocks, though, as anything might turn up - many species show amazingly long migrations and occassionally extreme vagrants turn up among the flocks of commoner species. All very nice.

Vachellia tortilis, or why there are no Acacias in Africa

I'd promised to write about marine things this week, but here's an interruption that can't be ignored as I read today that there really aren't any Acacia in Africa. (Bad news for the Acacia Rat and Acacia Tit, etc!) What's that, you say? Well, you may (or may not) have heard that for the last few years there's been some discussion among plant taxonomists about the correct taxonomy and names for the genus Acacia. And what seems to be the final final word on the matter was decided on Monday at a meeting of the International Botanical Congress over in Australia – the result? Africa no longer has any Acacia.

Vachellia tortilis will always make good sunsets, whatever you call them!

Now, this is going to cause some confusion (especially to poor ornithologists like myself), and it probably helps to understand a little about where these scientific names come from in the first place. Let's say you find an odd little plant, look around a lot and can't find anything like it. After quite a lot of asking the experts you conclude you've got a new species, so you need to give it a name. Now, ever since Carl Linnaeus back in 1735, scientific names have had two parts – one genus, one species. You can add extras designating sub-species if you like, but when you see a scientific name the important parts are the genus (always capitalised) and the species (never capitalised, even if named after a person). The aim of the name you chose is to tell you something about the plant and the first thing you have to do is identify the genus. Does your plant have any obvious relatives? If so, I'm afraid you're not free to chose the full name – you'll have to name your species with the same genus, though you can chose the species name (btw, it's generally considered bad form to name it after yourself, sorry. You could name it for a friend though – or get them to name it for you, if you feel particularly narcissistic). So in a scientific name, the genus should tell us about evolutionary relationships. And if our understanding of the evolutionary relationship changes then, bad news, the name will have to change too. Which is what has happened with the genus Acacia. In fact, we touched on the issue yesterday, when I wrote about sponges not being monophyletic, but we didn't take that discussion very far.

Still, what's happened to Acacia? Well, the genus was first described back in 1754 (lots of these details from here, but it's behind a paywall I'm afraid) and until the recent changes referred to some 1300ish species, of which 960ish live in Australia, where they're known as wattles. It's long been noticed that within this large genus, there are some specific sub-groups (called subgenera) that are more closely related to one another - like those Australian wattles (two of which made it to Madagascar, btw) - but that's OK as long as the genus refers to all the relatives. The problem came when studies started showing that some of these sub-groups were more closely related to other members of the Mimosoidae subfamily, than to other members of the genus Acacia, which is what means the group is no longer monophyletic. Now, it's easiest to explain this with a little diagram, I think. So, here's what we used to think Acacia relationships were:

 You can see how all three groupings (subgenera) within the genus Acacia are grouped together, and all the Acacias are separate from the other members of the Subfamily Mimosoideae. That's good - it's a monophyletic group and everyone could have Acacias. (You know a few of the members of tribe Ingeae, btw - this is where Albizia are found.

Now, however, recent DNA evidence has shown a different pattern (it's not quite certain which pattern, so I've given an illustrative diagram from one paper):

Now this shows the problem - no matter how you twist and turn the branches, Acacia subgenus Phyllodineae comes out as more closely related to members of the Ingeae than other two groups of Acacia. As the genus therefore describes multiple branches of the tree, but not all the descendents, we know it's polyphyletic, and we're going to have to change some names. We could, of course, resolve the problem by naming all the plants within the tribe Ingeae as members of Acacia too - then the name would only refer to one group and would again be monophyletic. But imagine the chaos that would cause - suddely all the (obviously different) Albizia and their diverse relatives within the entire tribe, would have to become Acacia. No, it's much simpler to split the Acacia genus into several different genera, each of which are monophyletic. And because Australia has by far the most species in the old genus, they've got the Acacia name for their wattles, leaving the rest of the world to find some other names.

In fact, there are some names out there that look set to be standard. Many of our well known Acacia species look set to become Vachellia, whilst others will become Senegalia. Which become which, I've not sorted out yet. But, but I do know what was Acacia mellifera will be Senegalia, whilst A. tortilis will become Vachellia, and for many species it's fairly obvious which of these two are more similar, suggesting likely names - bushy, multi-stemmed versions look set to become Senegalia, big trees follow tortilis into Vachellia. The good news, of course, is that there's no reason to change the common names - we can still have Whistling-thorn Acacias if we want, even if their scientific name becomes Vachellia drepanolobium. Unless, of course, someone decides common names should change too, something I find much harder to understand (and I still see Crowned Plovers, even if they are Vanellus) - in which case there really will be trouble for the poor Acacia Rats...

Update: You can find a (nearly) complete list of the new species names here.

Marine life

I've been at the beach for the last week (hence silence on the blog!) having fun with family and friends. Despite the fact I grey up about as far away from the sea as is possible in the UK (which, I admit, isn't really that far...), I love beaches and sealife. It's a lot further to the sea from most of the safari circuit than where I used to live, but many visitors to East Africa will combine a safari with a beach trip, so you might find youself down there from time to time. And if you don't, I thoroughly recommend it for a fun trip some time. Tourists don't usually think of the beach as a place where wildlife happens, but actually marine and coastal habitats are completely fascinating and I thougth I'd make use of the pictures I took down there to give a few hints about what you might talk about if you do find yourself on the long drive to the beach. So today I'm going to start with what I think is most amazing about sea life - it's extraordinary diversity and plain weirdness.

This mollusc has an unusual foot - and you can see its eyes too!

Now, you have probably been told that after kingdom, the main division of all life is the phylum (in fact, if you were told this, it wasn't quite right - botanists refer to plant divisions, leaving phyla to zoologists - that's the  plural, btw, it's from the Greek phylon meaning race or stock). And the Animal kingdom is divided into around 40 phyla (12 divisions for plants). Being such a basic division of animal life, animals in different phyla can be expected to be remarkably different - insects belong to the phylum Arthropoda, and it's fairly clear they different to us humans, being representatives of the phylum Cordata. Similarly, snails belong to Mollusca and are pretty different to earth worms, belonging to Annelida. You get the idea - these divisions are pretty fundamental. Now, of the 40 phyla out there, I wonder how many you could name? (I don't think I'd do too well either, to be honest...) But what I do know is that whilst there are no extant Onychophora (velvet worms) living in the oceans, all the other phyla are found there but only 10 are found on land (if we exclude internal parasites of other species). So three-quarters of the most fundamental of divisions of the animal kingdom are entirely aquatic, most of them restricted to marine environments. Which, of course, means life is pretty different in the sea. Why this should be is obvious, of course - the original animals that formed the ancestors of modern phyla lived a very, very long time ago (during a period known as the Cambrian explosion, about 500-580 Million year ago) when there was only life in the sea (there's a nice time line of life here).

Tide-line discoveries from Ushongo beach, July 2011

Cuttlefish shell, also a mollusc

Why does this interest me? Well, when you go to the beach you have a chance of finding some of those rather more bizarre life-forms that never made it onto land. The above picture shows a few of the more obvious things we found on the beach. As everyone knows, there are lots of mollusc shells (phylum Mollusca) - but look at the major divisions within this phylum too - only gastropods, the snail type, have made it onto land, but the sea is full of bivalves and other classes we never see too. In fact, nearly a quarter of all classified marine species are molluscs and there's every reason to believe that some of them (octopus - the're also molluscs and belong to the same group as cuttlefish in the picture beside) have evolved remarkable intelligence, capable of solving problems and allowing them to practice deception.

Note crab carapace, top right, sponge top left and corals.

Hermit crabs have almost made the terrestrial transition but still return to sea to breed

Then you'll see a crab exoskeleton. Crabs are members of the Arthropoda, just like insects and spiders, and some of them have taken to the land - though they must return to water to lay eggs. The subphylum they belong to Crustacea does have truly terrestrial representatives - the woodlice are an example - but most are still aquatic creatures and there's another example here too in the goose barnacles near the back in the middle. Look further and you'll start seeing som true aquatic specials. There's a couple of sorts of coral there, belonging to phylum Cnidaria which also includes the sea anemones and jelly fish. These, in the form of hydra, make it to fresh water, but no cnidarian with their usually soft bodies have made it onto land. And there's also a cnidarian look-alike in the sponge belonging to Porifera. Actually, this phylum probably includes animals from more than one group and excludes some of the descendents of the original sponge (all the rest of the animal kingdom, in fact!), so we'd call if polyphyletic and expect taxonomists to break it into other groups when they understand the relationships better. Poriferans are an extraordinary group of animals that, when I was doing my first degree, everyone was excited to think might be a whole different kingdom (or even several kingdoms). Now this seems less likely, but it seems very likely that all the rest of animal life did evolve from a sponge, rather a long time ago.

Note sea-urchin top centre and goose barnacles bottom right

What else is there? Ah, a sea urchin, belonging to phylum Echinodermata. Here, at last, we find a purely marine phylum - starfish, sea urchins, sea cucumbers and crinoids are all here, and none of them has even moved up the rivers. They all have five-sided symmetry as adults (or there abouts), but as larvae they start life, as us, with bilateral symmetry. Very odd, but very important in some places, as grazing by these species can completely alter the ecology of a coral reef or sea-weed forest.

Casts from some annelid worm (I expect) in roots of a mangrove

Annelid tentacle trails radiate from the animals home in the centre

A few other things didn't make it into the group photo, but are interesting too - the vast numbers of 'worms' of one sort or another (mostly Annelida, but maybe one or two other phyla are around too, I've certainly found others before on these beaches). They're responsible for these casts and the strange patterns around this hole - at high tide the inhabitant stick lots of tentacles out of the hole to filter food back to the mouth at the top of the hole. And these worms and other invertebrates can occur at fantasic densities, providing masses and masses of food in the intertidal zone, for lots of nice birds and beasts. Those will have to wait for another time now, though, whilst we remain amazed by the extraordinarily diverse numbers of ways marine organisims seem to have evolved to survive. Remarkably, I'll leave you with the surprising thought that despite this huge diversity of live-forms, there are far more species of animals on land. In fact, far, far more. And most of them are beetles, phylum Arthropoda. Why should it be that such extraordinary diversity has evolved on the land and not in the sea, where evolution has been going on for an awful lot longer? Odd...

Connecting forests and savannahs

Pre-montane forest - note the high diversity of tree species, Lake Duluti, July 2011

In my last post I said I's intended to talk about the connections between forests and savannahs, but got distracted by pretty birds. So I thought I'd do it now instead, becuase it's still an interesting topic. Once upon a time, a surprisingly recently time ago, there were rather more forests in East Africa than there are today: even in the relatively well-wooded Eastern Arc mountains, it seems like nearly 80% of the prehistoric forests have been lost. And they were an important part of the landscape - both in their own right (harbouring massive biodiversity with hundreds of plant, vertebrate and invertebrate groups endemic to the Eastern Arc), but also through the role they play for many savannah animals.

Montane forest in Arusha NP is kept open by grazing and browsing - that's a C3 grss understory. June 2011

We've already seen that forest and savannah can both occupy areas where the rainfall is over 1000mm per year, and that fire seems to be the key factor determining which actually wins out. We've seen how riverine forest is a forest habitat within the savannah biome, and we probably also know that thickets are fairly similar too. But true forests are different, and we don't usually think of them as connected to the savannah at all. Yes, forests are different - they're not dominated by C4 grasses (though they can still have some pretty thick understory of C3 grass) as we've seen defines the savannah biome, but I think this distinction is unfortunate as they are connected, at times vitally so.

Forest C3 grass species - short, round leaves are typical. Duluti July 2011

Yes, it really is a grass!

For example, the loss of forest in the Mau escarpment that feeds the Mara river is believed to be responsible for the altered hydrology of the Mara river within the Serengeti-Mara ecosystem - less forest means less water is soaked up by the landscape, so more flows down the river in the wet season and less remains to flow during the dry season. More directly, East African forests provide homes for many of the species more typically associated with savannahs. You might not visit Arusha NP to see the elephants or buffalo, but they're there. And what's more, those elephants move - they go down the Ngara Nanyuki river and down onto the savannahs of West Kilimanjaro. Where, of course, they must meet elephants that have done the same from the forests of Kilimanjaro and those that have come out of Amboseli. The same seasonal movements of elephants into and out of forests is a regular pattern, whereever such movements remain possible. Typically, savannah elephants will move into the moister forest habitats during the dry season when food becomes scarcer and poorer quality on the savannahs. But elephants aren't the only animals making this movement - in other areas where the savannahs are moister than around West Kili, buffalo and several other species make the movements too, though it's usually a shorter-distance movement and less seasonal.

Buffalo (and other forest mammals...) Arusha NP, December 2009

We all know of the regular movements and migrations of many ungulates. This is usually driven in part by the need for dry-season forage (we'll have to post more about migrations later). But what's interesting even about the well-known Serengeti migration, if that's its variable both in route taken, and timing. And the key driver is food and water availability - if there's food and water around, the animals stay longer, if they see/smell rain somewhere else, they shift their routes to exploit it. This is a very sensible response to living in a highly variable environemnt, and it seems that many savannah animals are similarly flexible when they need to be, even if they don't show large-scale and well-known migrations. So the forest and thickets of the northern Mara can be heaving with wildlife during droughts, and provide an important buffer for animal populations when conditions get really harsh. Indeed, the loss of forest in Amboseli is believed to be one of the key changes that meant the drought there in 2009/10 had such a serious impact. It seems that many animals have their regular dry-season refugia (often wetlands like Silale in Tarangire) but if these dry up in a really bad drought, they'll move to the nearest forest and tough it out there. But if the forest patches have disappeared - particularly the lower-elevation forests - or are now separated by fences, then the animals can't do this ocassional movement and there's going to be trouble. So although true forests aren't usually considered part of the savannah biome, they certainly have a role to play in a well-functioning ecosystem. And what's more, they're a great change from the savannahs for visitors to East Africa, so don't avoid them just because you won't find lions there!