Wednesday, 28 December 2011

More amazing honeyguide discoveries!

Steel-blue Whydah, Seronera, Dec 2011.
We've featured honeyguides on the blog here before, and I wouldn't normally come back to the same species so soon, but another recent paper (available to all for free here) by Claire Spottiswoode and colleagues has grabbed my attention by demonstrating nicely some of the challenges that generalist brood parasites have to overcome. There are, of course, three groups of brood parasites (birds that lay eggs in the nests of other species to let them raise the young) in East Africa: the well known cuckoos and the less well known honeyguides and whydahs.

Greater Honeyguide, Tarangire, Sep 2011
Now most whydahs are extremely host specific - the Eastern Paradise Whydah will only lay in Green-winged Ptylia nests, whilst Broad-tailed Paradise Whydah nests in Orange-winged Ptylia. Similarly, Straw-tailed Whydah is pretty exclusive to Purple Grenadier, Purple Indigobird is perhaps best identified by listening to snatches of it's host, Jameson's Firefinch, etc. Others are slightly less specific - the Steel Blue Whydah lays in the nests of the very closely related Black-cheeked and Black-faced Waxbills and Pin-tailed will parasitise several waxbill species. Cuckoos and Honeyguides too tend to specialise somewhat, but not completely. And this is where it gets interesting. To some degree is obvious that in a species with a single host there are strong evolutionary pressures on the female to lay eggs of a similar size, colour and marking to that of the single host, a relatively simple problem. But it's less easy if you're trying to match several different species all at once as even closely related species often have differently marked eggs (perhaps as a mechanisim to make brood parasite's lives harder?). And so we find that in some of these groups some interesting evolution has taken place - in Cuckoos we've long known that females will (nearly) always lay their eggs in the nests of the same species as they were fostered in. If such differentiation happened over the long term, one might expect a new species to evolve - one that parasitises one species, another on another (which might well be what happened in the whydahs, or even among the other groups too). But the difference here is that males don't care - they'll mate with any female that looks right and is willing, so the species as a whole remains united, despite female 'races' developing. So then you have to ask whether females from one host lay eggs that differ to those of females from another host, and if so, how can they possibly have evolved such specific genes to colour and pattern the eggs in the face of complete mixing from the males? And this is (part of) the question that Claire and colleagues were interested in.
Male Greater Honeyguide, Tarangire, Sep 2011

They show very nicely that Greater Honeyguides have two main groups of host species - birds that nest in tree holes (African Hoopoe, Green Wood-hoopoe, etc.), and those that nest in earth holes (Little Bee-eater, Striped Kingfisher, etc.). The former have larger and longer eggs, the latter smaller, rounder ones. And so two forms of female greater honeyguides seem to have evolved - one specialising in the tree nesters, one in the ground nesters and as expected the females of each group lay appropriately shaped and sized eggs. So how do they do it? Well, one of the important theories that was developed as long ago as 1933 is based on another fundamental difference between birds and mammals that's important to know. In both mammals and birds the sex of a developing embryo is determined by chromosomes, the DNA containing structures that control inheritance. In mammals, everyone has one 'X' chromosome we inherit from our mothers, but from our fathers we can either inherit another 'X' chromosome (which would make us female), or - like our father - we could inherit a 'Y' chromosome, which would make us male. The 'Y' chromosome is therefore inhereted father to son, to grandson, etc., without ever finding itself in a female, and it's this pattern of inheritance that makes us male or female. Now what differs in birds is that instead of the X and Y combination making us male, it would make a bird female. Male birds have two of the same type of chromosomes, females are the ones with the different pair, and to make this distinction easier we don't use the X and Y terminology, but talk of W and Z chromosomes instead. So, unlike in mammals, it's the females of birds who have a unique chromosome that is passed one through mother to daughter to grand-daughter, without ever passing through a male. So if the information for how to colour your egg is stored on this chromosome, no information about it will ever come from a male. A neat solution to how the species as a whole can be unified by the males, but females can differ (possibly substantially) in the genes they have on their unique chromosome.Hope that's clear...

Now, Claire and her group went one step further and decided to look for differences in a special sort of DNA called mitochondrial DNA that is also only inherited from mother to daughter, and compare the degree of difference between the two groups of tree and ground parasitising females in the mitochondrial DNA with the difference in the DNA in the main part of the cell that comes from both male and females. They expected - and rather neatly demonstrated - that there might be substantial differentiation between the females in mitochondrial DNA, but that the males would mean there's little difference in the main 'nuclear' DNA. And the degree of difference in the mitochondrial DNA between the tree and ground nesters was so much that their ancestors started breeding in these two different way millions of years ago! That's pretty remarkable, and rather different from the more recent splits reported for cuckoos, probably brought on by relatively recent host changes. Why this difference? Well, they speculate that it's thanks to the greater staility of the African climate compared to the Northern one where most of the work on other brood parasites has been undertaken, but I'm not yet convinced - if we could compare similar patterns for a few local cuckoos too, that might be very interesting!

Anyway, all very impressive and a great lesson not only in the complexities of brood parasitism that is fascinating to me, but a bit on sex determination too - a subject we're sure to return to in the future...



Reference:

Spottiswoode, C., Stryjewski, K., Quader, S., Colebrook-Robjent, J., & Sorenson, M. (2011). Ancient host specificity within a single species of brood parasitic bird Proceedings of the National Academy of Sciences, 108 (43), 17738-17742 DOI: 10.1073/pnas.1109630108

Monday, 26 December 2011

TAWIRI conference discussions continued: Ruaha River

Wetlands, like Silale Swamp in Tarangire, are vital for feeding rivers
Returning to the TAWIRI conference back in December that I posted a bit about already, the other talk that set me thinking about economics of conservation was a fascinating talk by Eric Wolanski about ecohydrology. About what, I hear you ask?! Ecohydrology, the study of the interactions between water (hydrology) and ecosystems. Now it occurred to me that we've not done a post specifically about wetlands yet, which is a bit of a major ommission, given their importance in savannah ecosystems. We'll have to rectify that in time, but for now we're going to plunge straight into some important stuff.

Flows in the Mara River have been disrupted by deforestation in the Mau Forest
As we all know, the life-blood of a savannah ecosystem is its permanent water source(s). As we've talked about in our Serengeti Story, the Mara River is the only important permanent water source in the Serengeti Mara ecosystem, and the animals move a long way to get there. Tarangire has the Tarangire River. Ruaha has the Great Ruaha River, etc. What makes these rivers permanent and other rivers in the savannah only seasonal is that they're fed by sources that capture the rain in the wet season and slowly release it during the dry season, whilst sand rivers tend to just be rain fed. The Mara is fed by the Mau Forest in Kenya, Tarangire River by Silale Swamp, and the Great Ruaha by a series of wetlands, including those of the Usangu Flats. Meddle with these 'sponges' and you can get in all sorts of trouble with your permanent water sources.
Birds and other wildlife also love wetlands like Silale! Sep 2011

Eric told a fairly simple story, but a fascinating one none the less (especially when you start doing the sums that I've been looking at). If you have vegetation covering a waterbody, he said, the water loss through evaporation and transpiration (plant breathing) is about 50% of the evaporation you have from open water. Somore water flows from vegetated wetlands into rivers than from ones taht have lost their vegetation through excessive grazing. Which is exactly what had happened during the 1990s and 2000s on the Usangu flats, above Ruaha. Much of the water that flows from Usangu at the end of the wet season is the water that subsequently fills Mtera Dam, so keeping the water flowing - as well as providing a vital resource for the wildlife of Ruaha National Park - is pretty important for electricity generation in Tanzania! Uncontrolled (but illegal) immigration had allowed hundreds of people with an estimated 300,000 cattle to occupy the Usangu Game Reserve (as it was), and the cattle ate all the vegetation over the wetland. As a consequence the evaporation rates increased and less water flowed from Usangu into the Great Ruaha. In 2006 the government decided to evict these people and incorporate the Usangu Game Reserve into Ruaha National Park (in so doing creating the largest National Park in Africa), hoping to restore water flows, though among serious concerns about human rights. And Eric was able to watch the consequences in the flow rates through the Usangu flats and into the Great Ruaha river. Amazingly, this operation alone has resulted in the Ruaha river flowing for an extra month. Now that result is a great success for conservation, but it's not the end of the story by any means and I did some quick back of an envelope calculations of my own that are pretty staggering, but before we go there let me post a few caveats - firstly, I'm not a hydrologist and I'm just reading a few things quickly, I'm not guaranteeing these figures in any way. Also, as I've not always found the exact figures I've tended to err on the side of caution - for example, I've found statements that show dry season flow is unimportant to Mtera water levels (as you'd imagine), but that the dam mostly fills when the Usangu wetlands are flowing full rate at the end of the wet season, but I've not got the relative figures for this so I've assumed that the flow operates continuously - which should underestimate the importance of Usangu. Still, here are some interesting numbers...

Early in 2011 the IMF downgraded it's forecasts for growth in the Tanzanian economy from 7.5% to 6%, due to the costs imposed by TANESCO power cuts (up to 16hrs per day in much of the country!). Tanzanian GDP in 2010 was abour $23 Billion, so the cost to Tanzania of the powercuts, according to the IMF, is $345M. [Interestingly, that GDP is a tiny bit more than George Soros and family have tucked away, is similarly a tiny bit more than the value of the treasure recently discovered in the vaults of an Indian temple and is not even half the annual turnover of GlaxoSmithKlein!] Most of these power cuts were caused by low water levels in dams preventing power generation - Mtera dam (fed by Usangu through the Great Ruaha) feeds two power stations, Mtera and Kidatu, producing between then 284MW of power, which is about 40% of Tanzania's total capacity of 769MW (Thanks TANESCO for these figures). I've not found how many months the stations were going for, but I did discover that for the last few years the Ruaha has flowed for only 9 months, so let's assume it's similar. Now if we assume that 40% of the cost of the blackouts is caused by Mtera not producing (actually, I'm sure it's much higher since it's mainly the Hydro part of the production that's failing, but that's the proportion of overall capacity sourced by Mtera and will give a conservative estimate), those thee months of non-flow each cost the Tanzanian economy $46M. So the government's action to remove cattle, by providing an extra month's flow from Usangu, might well ahve saved about $46M per year. Not a bad investment, I think, even if they had paid the going rate of $150 per cattle the $45M required would have been paid off in one year and as it was many of these cattle moved elsewhere where they caused less damage to sensitive wetland habitats.

Now the final question you'll be asking, I guess, is what about the remaining 3 months of no-flow? How can we get that back? Well Eric and colleagues estimated that if the rice farms that are the other major water user returned only 25% of their water, there's be no problem at all. And I've just done a quick check and found that the estimated cost of completely closing the rice farming industry in this area would cost the national economy 'only' $15.9M per year. If that's what it takes to keep Mtera flowing, it doesn't seem a particularly hard decision for me, and think of the wildlife benefits too!

Anyway, I hope those figures are of some interest - it just goes to show that conservation really can be a 'win, win' option, even when hard decisions need to be made. Let's just hope it doesn't take too long before someone sees sense here - good luck to those people and organisations trying to build awareness of these issues!

Saturday, 24 December 2011

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!


Tuesday, 20 December 2011

The Serengeti Story, part 1: history

So I guess this is the post I've been putting off longest. Not because it's not interesting, but because I know I'm going to forget some crucial component. But I'm just back again from a fantastic trip (thanks to all the guys at Dunia!) and decided it's definitely time to bite the bullet. However, it's going to be a long story, and I'm going to split it in two sections so I don't spend all night here (and so I stand a chance of remembering what I've forgotten before I consider the story told!). If you want more details on any of these things the essential references are the excellent series of very technical books edited by Tony Sinclair and colleagues you can get from Amazon. I've cut and pasted a few of the graphs from 'Serengeti III' into this post, hopefully 'fair use' for education...

I always start telling the Serengeti story with a bit of history, since it helps us understand how scientists have uncovered some of these things. There's no really obvious beginning to the story, but let's start with something we've already discussed on Safari Ecology - the introduction of Rinderpest to Africa in 1887. As we saw in that post, this had a massive impact on wildlife throughout Africa, the disease reaching Cape Town by 1897. The Serengeti migration was decimated, and when it was finally erradicated from the wildebeest population in 1963, there were still only around 250,000 wildebeest (see the plot below).
As you can see, once rinderpest was erradicated the wildebeest population exploded, reaching it's current total of somewhere betwen 1.2 and 1.4 million in about 1977, and this is the huge change that has let us understand so much of what happens in Serengeti.

Now, by now we should all know the 'Big 4' of savannah ecology, so it shouldn't come as a surprise that such a huge change in herbivory had a massive impact on the ecology of Serengeti, perhaps most obviously on the amount of another of the big 4 - fire. The figure below shows very clearly how the rise in numbers of wildebeest reduced the amount of fire in those northern woodland areas (essentially the woods from Seronera north).

This is clearly down to the very simple fact that wildebeest eat grass and grass is what carries fire through the savannah - more wildebeest means less grass which means less fire. And a change in the fire regime, of course, will alter the ecology too. So introduction around 1890 and then erradication of rinderpest in 1963 led to a massive change in both grazing pressure and fire frequency. It's not surprising, therefore, that massive changes occurred in Serengeti during the 1900s, most obviously the change in woodland cover. If you dig through old photos of the Serengeti / Mara area you can find some fantastic images of change. Tony Sinclair did it and came up with this beauty from 1944, that he then returned to in 1983 and took the subsequent photo (I've borrowed them from his talk available online here).
 It's pretty obvious that the woodlands vanished sometime between these two photos were taken and more detailed work suggested a rapid decline in woodland cover from about 1945 to 1980 - just the sort of delay you might expect from the increase in fire around the turn of the 1900th Century, given that fire doesn't kill savannah trees above 2m tall, so any established trees would gradually die of old age some time later.


Interestingly, as a direct consequenc of the decline in trees the national park authorities changed their fire management strategy in the 1970s from late burns at the end of the dry season and in anticipation of the rains, to one of early burns which tend to be cooler and rather less damaging to tree seedlings. At the same time, of course, the wildebeest population was recovering and the fire was declining in frequency as a consequence, so this change was probably less necessary than it seemed at the time (though everyone at TANAPA has since forgotten that the current fire strategy is a relatively new one, of course!). And as you might expect, more recently the trees have returned. Again, Tony Sinclair has some fantastic series of photos of these changes too, this from relatively close to Seronera:


(There's a whole lot more of these sorts of photos available on the web if you search for Tony's various talks.) And so the woodlands returned to Serengeti, as a consequence of the return of wildebeest and subsequent decline of fire. [It's interesting too, that savannahs globally are getting woodier, so there's a chance that this change is also related to global change too, not simply a local Serengeti effect - we might return to this in the future...]

But the story's not quite complete yet, as there's a neat twist at the end involving elephants. During  the 1970s and 1980s there was massive and nearly uncontrolled poaching of elephants throughout Serengeti, ending abruptly with the band on ivory trading in 1989. It's had a massive impact on elephant numbers in Serengeti:

At the same time, however, across the border in Kenya poaching remained under tight control, with no such dramatic change in elephant numbers. Such large herbivores can have a massive impact on the vegetation and the story in Serengeti is a particularly interesting one - Elephants walking across grassy plains often 'weed' out the tree seedlings instead of eathing grass. In woodlands they tend to leave the seedlings and concentrate on adult trees. So if there are lots of elephants it can be rather hard to turn grasslands into woodlands, even if the fire frequency is reduced. The difference between Kenya, where elephant numbers remained high throughout the period, and Tanzania, where they crashed at just the same time the fires declined, is stark. And elephants being rather clever animals, they knew where the border was and they were safe. So here's one last picture of Tony's from northern Serengeti / Mara, where the international border is clearly defined by woodlands.


Amazing to see the impacts of elephants so clearly, but also amazing to see how two different habitats (grassland and woodland) within the savannah biome can be stable under exactly the same environmental conditions - these days elephants are common both sides of the border and yet the woodlands remain in Tanzania, thanks to the different way elephants behave in grasslands from woodlands. So the history lesson ends with an important lesson about how important the initial conditions are to how a savannah looks - to turn a grassland to a woodland you need to reduce fire frequency (which can be done by increasing herbivory), but you also need to at least temporarily exclude elephants. All very complicated...

So, that's the history lesson and the broad overview of some population changes as a whole. The next post will continue the Serengeti Story by, I hope, explaining what we know about the migration and the regional differences across the ecosystem today. Hopefully it won't take so long to create either!

Friday, 9 December 2011

TAWIRI Conference discussions

I've spent most of this week at the Tanzania Wildlife Research Institute (TAWIRI) conference here in Arusha. This is an event that happens every two years and involves a very high proportion of researchers active across Tanzania, so it's always a good place to hear about interesting things going on in these areas. I thought I'd give a few of my highlights today. The two talks that most exicted me were from two different aspects of ecology - one by Dr. Grant Hopcraft on the Serengeti and how climate change might impact wildlife there, the other also related to Serengeti, but this time by Dr. Dennis Rentsch from Frankfurt Zoological Society on the economics of the bushmeat industry. I know both of these folk fairly well, so was able to press them for lots of extra information about both talks, and what I'm going to descibe here represents both their presentations and some of the other stuff we talked about - I hope they don't mind me putting this information out before it's all polished and published!
Wildebeest and zebra migrating through Grumeti Reserves, Feb 2010

Grant knows rather a lot about Serengeti and, in particular, the herbivores of the system. His work has focussed on how nutrition impacts herbivores and his talk fitted well into the overall theme of the conference on climate change, by asking how climate change will affect the nutrient content of the grasses and how this might impact the animals that feed on them. You might think it's crazy to suggest that climate change impacts grass quality (i.e. nutrient content), but actually it can have some pretty profound impacts indeed. Grass growing in high rainfall areas gets very tall very quickly, but also tends to be poor in nutrients - it might be that the grass can only collect the same amount of nutrient from it's roots, but in wet years it grows faster, so there's less nutrient per leaf than in dry years when the plants can't grow as much and pack all the nurients into a smaller volume. So more rain means lower quality grass, but more of it, less rain would mean less, but higher quality grass. In fact, lots of people showed plots of rainfall in Serengeti and demonstrated that the area is getting wetter (though I also suspect there might be shifts in the dry season length which could be even more significant, but no-one really talked about that), so we should be seeing more, lower quality grass. What is the consequence of this? Well, according to Grant, perhaps it means different things for different species, since all the herbivores prefer slightly different combinations of nutrient quality and grass quantity. In particular, hind-gut fermenters like zebra are happy with lots of relatively low quality food, whilst wildebeest are typically selective ruminants and need higher quality grass. Now, Wildebeest in Serengeti are food limited, not predation limited or anything else, so a decline in food quality might be bad for them - but they are, of course, interested in quantity too, particularly during the dry season when any rain is going to provide grazing which is clearly better than no rain at all. So a wetter Serengeti, if it impacts the dry season too, is probably going to mean more food at this crucial dry-season food shortage period, and we can expect that even in a wetter dry season the rain will still be scarce, so the grass will be relatively nutritious. So on the one hand poorer-quality forage during the wet season might be bad news, but more grass in the dry season is certainly going to be good news - which effect wins out isn't yet clear. My money will be on the dry season effects, but we'll wait to see! On the other hand, it seems pretty unambiguously clear that a wetter Serengeti will be good news for zebra, provided again that the dry season remains at least a bit wet too. So more zebra will always be good - though how that will affect everything else is also tricky to forsee. Does more zebra mean better facilitation for the wildebeest? Or might there be more competition? Who knows, as usual, more research needed (and if you want to fund Grant on his next project, do let him know - he's searching for money right now!).

The migration reaches Seronera, Nov 2010. Don't get eaten!
Spot the snare: many animals are poached in Serengeti. Moru Jan 2011
Meanwhile Dennis has been working on bushmeat trade on the western side of Serengeti for many years now. His approach to studying what is, after all, an illegal activity has been to deal not with the hard end in the park of finding and apprehending poachers and trying to get them to tell him how many animals they hunt (they're very unlikely to give an honest answer in such circumstances!). Instead he's focussed mainly on trying to work out how much bushmeat is being consumed in the villages around the Serengeti by asking them about the various protein sources they eat during the week. Although there might still be some resistance to tell the absolute truth in this context, it's likely his numbers are underestimates of the full impact of the harvest (especially as it doesn't include any of the meat that gets exported from the region commercially). Underestimates they might be, but the numbers are still staggering. In the villages surveyed, the average number of meals of wildebeest eaten per family per week was 2.4. Obviously that goes up during the period when the wildebeest are migrating through the particular village, and down when they're far away, but 2.4 meals per week is the average for the villages immediately around Serengeti NP. And knowing the number of households in each village, plus the number of villages Dennis estimates that somewhere between 90,000 and 100,000 wildebeest are harvested (illegally) from Serengeti each year. To put that into context, it's equivelant to a harvest greater than the entire wildebeest population of South Africa each year!

At between 500 and 1500TSh / kg (depending on seasonal availablity), and assuming a conservative 100kg of meat per animal that gives a a total market value of $2.5 - $8.5 Million per year. Compare that to TANAPA income from Serengeti gate fees 10 years ago (the latest I can find online) at about $5.23 Million, and we're talking the same size economy. (Bear in mind that these TANAPA fees are used throughout the national park system to subsidise less well visited parks, so Serengeti NP actually has an opperating budget of only around $2Million per year.) That's a pretty remarkable figure on it's own, but Dennis went on to talk about how consumption is related to price of other meat in the area - if the price of beef goes up, more wildebeest is eaten. Which suggests that it might be possible to reduce the amount of wildebeest eaten, if you bring the price of beef down. Now unfortunately I wasn't quick enough to get all the figures off Dennis's slide to do the calculation here, but I think I'm right in saying that if you want, say to halve the wildebeest harvest, his figures suggest you need to bring the price of beef down by about 3 times as much - so 50% of 50% of 50%, which is an 87.5% reduction in price. That's probably going to be tricky to achieve, unless you fill Serengeti with cattle, which is hardly going to help! So you're rather stuck there. Instead, the only effective solution is to make the wildebeest more expensive - and Dennis suggested you can do that either by giving poachers alternative employment and dry up the supply of meat, or by even more strictly enforcing the regulations within the park. But bear in mind that this is a sustainable harvest - there's no impact of this level of poaching on the wildebeest population overall. The problem is the bycatch - people want to trap common wildebeest, but instead their snares catch resident game sometimes and have had a missive impact. So instead of strictly enforcing current regulations, perhaps TANAPA should be looking at ways to encourage sustainable use and minimse the negative off-take. Perhaps making a few million $$ in the process. What do you think? Should we go this way? Or how should we feed these people?


Thursday, 1 December 2011

Leopard Orchids

Leopard Orchid, Near Tarangire, Nov 2011
I'm just back from 2 weeks in the bush with Ethan and a bunch of other guide trainers and have a stack of photos to sort through (and loads of ideas for new posts, so there might be a flurry of activity on the blog again!). Whilst most of these are going to take a while to ponder and work though, I thought I'd start with a botanical story about the leopard orchid, since we found plants in all stages pre-flower, to ripe fruits and I got a nice set of photos.

Verreaux's Eagle Owl nesting in Leopard Orchid, Tarangire NP, June 2011
Leopard Orchids Ansellia africana are the only species in their genus, and occur widely throughout Africa, always growing as an epiphyte (i.e. growing on another plant, but not taking any nutrients from them - so not a parasite). Just like leopards, they're often seen lying on branches of big leafy trees and the flowers are yellow with brownish spots. They're very pretty, and often taken into cultivation (they're now considered threatened in the wild in South Africa, thanks to this trade), but they're also rather interesting ecologically. Three things particularly interest me: firstly, there's an association with ants - plants secrete nectar (not from the flowers though) that a wide variety of ant species drink. In return for the sugar, the plant gets effective protection from other insects. (Didn't seem to stop these Verreaux's Eagle Owls from using one in Tarangire as a nest site though!)
Leopard Orchid flowers provide no nectar to pollinators, Nov 2011

Next is that strange fact that mature flowers don't produce nectar. Actually, this isn't all that uncommon in orchids - they're well known for their 'deceptive' pollination strategies, a phenomenon noticed and described by Charles Darwin himself, in 1877. Most flowers produce nectar to encourage and reward pollinators, leopard orchids and many other orchid species don't - they rely on scent and appearance alone to persuade pollinators to visit. It turns out that leopard orchids are mainly pollinated by solitary bees, though we don't yet know if the scent the plant produces is similar to that of the pheromones produced by the bees to help them find mates - it certainly is what happens in other orchid species. In these species along comes a male bee expecting to find a female ready to mate, and instead finds a flower - in the case of the bee-orchids the deception even extends to the shape of the flower mimicing that of a female bee too - how cruel! Still, obviously works, as there were plenty of pods on one of the plants we found.
These pods could contain millions of seeds, Nov 2011

Which is where the thrid interesting fact comes in. This time it's general for all orchid species (I think?) - they are wind dispersed and have some of the smallest seeds of any plant - completely lacking any store of food for the new plant. They're so small that in some species each pod can hold over 4,000,000 seeds! I've not found the number for Ansellia, but we can be pretty sure there's lots in there. With so little energy provided, orchid seeds have no chance of germinating unless they can get it from somewhere else - and they all do it by hijacking a fungus. The seed, having settled in a crevase of a tree sits and waits - if a bit of the right fungus grows along the branch looking for something to digest (we call these little bits of fungus mycorrhiza) it infects the orchid, and instead of being digested the orchid grabs the fungus and steals it's nutrients in an act of parastism that enables the seedling to grow. In some species this later turns around and the orchid returns the favour by providing excesses sugar to the fungus (a sort of mutual parasitism if you like, or at least a symbiosis), but increasingly botanists are realising this isn't always the case and many mature plants also maintain this parasitism throughout their lives. So this stage of life is also rather interesting.

Leopard Orchid in Kigelia africana, Near Tarangire, Nov 2011
Happily these orchids still seem very abundant in much of Tanzania (though a quick google search confirms you can easily buy Tanzanian Leopard Orchids from a few suppliers at least, so how long this will last I don't know - I'm not giving you the links so you don't do it!), so you should be able to keep telling these stories for a while at least!

PS If you're here now because you were on the course, great to see you! Join the site, comment, ask questions and pass the address on to your friends too!

Wednesday, 16 November 2011

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.

Sunday, 13 November 2011

Woodpeckers as keystone species


It's been a while since I posted a birdy blog and since I got some nice pictures of a Cardinal Woodpecker at the weekend, I thought I'd use it as an opportunity to talk about woodpeckers in general, since they're surprisingly important in the habitats they occupy. As usual, we'll look to answer the three questions I use to prompt me when seeing wildlife – what is it? What's it doing? And what's it's role in the ecosystem.
Female Nubian Woodpecker, Kisima Ngeda, Aug 2011

So, for identification, woodpeckers are generally fairly easy. In most of northern Tanzania and Kenya, there are four common species of savannah woodpeckers – the commonly seen Nubian, spotted all over; Bearded, the largest and with a black throat and stripy face; the rather small and neat Cardinal, with spots on the back and streaks on the front, and the very colourful Grey. Away from the dry north of Tanzania the Nubian is replaced by a number of other options – Bennett's or Speckle-throated being the obvious ones. There are plenty of other species around, of course, but they're mainly associated with forest and we'll forget about them for now. Woodpeckers in general are rather widespread, obviously similar species occur on every continent except, rather strangely, Australia. They're relatively closely related to barbets and hornbills (note the zygodactyly – two toes forwards, two-toes backwards – they share with the barbets, easily seen in some of these photos). So, that's what they are. Now what do they do?

Male Cardinal Woodpecker, Manyara Ranch, Nov 2011

Normally you'll come across a woodpecker first when you hear it, either calling – Nubians in particular are noisy – or from hearing the 'tap-tap-tap' of their beak on a tree. Calling is often done by pairs, and we can safely assume it serves the dual purpose of strengthening a pair bond and communicating to neighbours that the territory is occupied. The tapping is where it gets more interesting – most of this is exploratory, trying to find hollow bits under the bark where tasty larvae may live, some is more obviously getting at the food once they've found it, and some it again a territorial statement like calling – though this purpose seems to be less common here in Africa than in northern regions. And the most interesting of all is the hard banging they use to excavate nest holes. I'm sure (unless you're Australian!) we've all seen the beautifully neat holes woodpeckers make for their nests, often several holes in a single stem. There's two things that are particularly interesting about this to me – the first is how they do it in the first place. The speed and pressure generated in order to dig into the wood is extraordinary – the deceleration from 6-7m/sec to stationary at impact isequivalent to 1000 times the pull of gravity – the effect on humans would be similar to Usain Bolt running head-first into a brick wall at the end of his 100m sprint. Not pretty, I should think! And the adaptations they have to avoid the problems we'd get from banging out head on a brick wall are also impressive – slightly differentlength upper and lower mandibles, extra thick skull, fluid-filledshock absorbers, unusual size and shape of brain, etc., etc. Quite remarkable really!
Grey Woodpecker, Near Arusha, March 2011

But the second thing about these holes is where they get really interesting. Woodpeckers mostly use theholes they excavate only once, after which the holes are available to anything else that likes to live in holes – birds, bats, other mammals and all. In fact, there's a huge array of animals that live in holes, but can't make them themselves (though some, like barbets, may make adjustments to get the hole right for them). Over time the holes get larger and larger, allowing a whole host of species to find homes. In some northern forests, woodpeckers have disappeared (for anumber of reasons we don't need to go into), and once the holes aregone, so too do all the other species that make use of them. Thus the loss of woodpeckers has much greater impacts on the whole ecology of a woodland than the simple direct effect – the consequences cascade down through other species too. Which is exactly why some people suggest woodpeckers may be seen as keystone species – a single species that holds together a whole load of other species and have disproportionate impacts on the ecosystem. Mighty important things, woodpeckers!
This Brown-breasted Barbet is probably uing an old woodpecker hole, Nr Boma Ng'ombe, March 2011

 

Saturday, 12 November 2011

Phenology – the timing of biological events.


First rains arriving over Manyara Ranch, Nov 2011
This is one of my favourite times to be in the bush, as the rains arrive and the savannah turns green. I love the excitement of the birds as they greet the rain, and the miracle of new grass appearing in just a few days and I probably get as excited by the first thunderstorms as my children! But as we all know, the timing of these events can change year to year. In fact, never more so that recently – one of the first impacts of global climate change that we see here in East Africa. Despite the changing season being such a profound event in the savannah, there's a surprising amount that we don't know about the patterns of seasonal change that we see.

For example, it's obvious that grass growth responds directly to rainfall – or at least to soilmoisture. If the rains are late, the grass stays dry, if the rains are early, it turns green early. But how does it know? To all intents and purposes the grass (or the seed) seems completely dead until something tells it the soil is moist and it's time to start growing again. In this case, actually, it's fairly straightforward – the moisture in the soil is in direct contact with the grass roots (or seed) and as that moisture is absorbed the cell cycles are started up again.
Pre-rains green flush in Brachystigia woodland, Kafue NP, Oct 2011 (pic. H. Frederick)

Other patterns are harder to understand, and the one that fascinates me most is the green flush that we see in miombo woodlands (and on Commiphora and several Combretum species too) before the rains. Not just immediately before the rains either, but some weeks before. How, and why, do they do that?

Let's remember first that savannah woodlands are deciduous (the trees loose their leaves) because during the dry season their leaves would loose too much water to allow the tree to survive. Add water, and there's no problem, so you'll see evergreens in the savannah only in riverine and kopjie habitats. So why, just when water is in shortest supply, do some species 'choose' to use some of their remaining stores of water and put out leaves before the rains come – and not just before, but a long time before? One of the things that we do know that might help us understand this is that once the leaves are out, the plants once again 'switch off' until the rains arrive. They've got leaves out, but they're not photosynthesising and respiration (plants respiretoo, of course) is pretty much dormant too. But then, once the rains do come, they're active within 24hrs. And another clue might come from the fact that we know there's a flush of nutrients (particularlynitrogen) associated with the first rains, that rapidly declines after the first few days of rain. So there's obviously a strong advantage if you can be ready and waiting for the rain – other trees that aren't ready will spend those first few nutrient rich days busy growing leaves and not be able to take advantage of the nutrient flush. So as long as you can minimise the costs of having leaves before the rains come (by essentially shutting down as much as possible), it seems plausible that the benefits could outweigh the costs (and clearly, for some species they do, or they wouldn't survive!). One thing that suggests this idea might be right is the fact that legumes – like Vachellia and Senegalia (I will get you toforget about Acacias!) - don't do it, they respond to soil moisture and, as we know, being legumes hey have no shortage of nitrogen, unlike other savannah species.
More pre-rain greening, Kafue NP (H. Frederick)

But why, then, be so early – why not just wait until the week before the rain before growing leaves and further minimise your costs that way? And here is where we really run out of hard facts and enter the realms of interesting scientific speculation – my guess is that because the date when the rains start is variable, you can't predict it that accurately. If you want to take advantage of that first nutrient flush, you've got to be ready for the earliest possible date the rains might fall – which (like this year) might be several weeks before the rains begin in normal years. I'm far from certain this is right – among other things, it requires that the benefits of being ready for that first flush are extremely strong, such that plants that catch it every year have a meaningful evolutionary advantage over plants that only catch it most years, which is testable but not guaranteed. But it's a good theory to work on for now.

The next part of the story that I'm interested in, of course, is how they do it? How do these plants 'know' when it's October and the rain is coming in a few weeks time? Unlike the grasses that simply detect water, these plants must keep track of the changing date directly. In the north where these processes have been studied in extraordinary detail, plants (andanimals) use changes in day length to keep track of the seasons – in spring and autumn in Aberdeen where I used to live from one day to the next day length could change by as much as five or ten minutes. But I find it hard to conceive that the same process is possible here where day length changes only by two minutes across the entire year – the difference from one day to the next can only be measured in seconds or fractions of seconds, and I find it hard to believe this can actually be the cue. But, amazingly, no-one's studied it so we just don't know.

There are other biological events that depend on precise seasonal timing, of course – like the millions of birds that spend months here until April, then head north to breed, but even here we don't always know the signals that the birds are using and why, for example, so many species seem to have been rather late arriving this year. But this has already been a long enough blog for one day, so that will have to wait for another time...

Thursday, 3 November 2011

Nutrients in the savannah biome

Of all the 'big four' processes that drive the ecology of the savannah, I think I've probably spent least time talking about nutrients. That might be surprising, because in some ways the cycling of nutrients is what helps us define an ecosystem. (Ecosystem is, in fact, a rather poorly defined term, but if there's anything that separates a habitat from an ecosystem, it's the fact that most nutrients and energy are well recycled within an ecosystem, whist habitats, once you ignore solar inputs, often have large in and out flows of nutrients and energy. So an ecosystem, such as Serengeti, can have lots of different habitats. On the other hand, a biome is a globally occuring set of similarly functioning ecosystems - savannah ecosystems around the world form the savannah biome. But let's get back to the point...) Nutrients are, however, extremely importand in shaping savannah habitats, both at large scales, and fine scale.
Termite mound, Mwiba Ranch, August 2011

The large scale patterns of nutrient availablity lead to different vegetation types in different areas, and drive large-scale migrations, both issues we've touched on already in this blog. So today I'm going to concentrate on the smaller-scale processes that act over just a few metres, but still have important roles to play in the ecology of the savannah. Let's start with what might well be the most important nutrient cyclers of the savannah - the termites. On the right is a typical termite mound in the middle of the dry season - note there's lots of uneaten grass in the foreground and background, but on and around the mound itself, there's nothing left but nibbled grass stems. Why? Because the termites have been busy working in the surrounding area to gather up bits of vegetation, and bring them to their mound. By gathering vegetation, then processing it in one spot, they concentrate nutrients at this spot, and the grass growing there is richer and better food than grass growing further away. The termite mounds become a nutrient hotspot, and animals know how nutrient rich their food is. Particularly in the dry season, when they only have dead matter to graze, small differences in nutrient content are very important. And even in the wet season these are preferred foraging areas and are often kept permanently short, as a grazing lawn. Once the process starts, in fact, it becomes self-perpetuating, as regularly grazed grass keeps growing new shoots and new shoots are always tastier (full of nutrients and low in the silica (a natural glass) grasses use as defence against grazing.), prompting more grazing and keeping the grass short, perhaps even spreading beyond the original termite mound as the additional benefits accrue - precicely the definition of a grazing lawn, and a very obvious example of how important the nutrient cycling carried out by termite really is at the large, observable scale we work at.

Impala Midden, Manyara Ranch, Nov 2010


Dikdik midden - what a lot of poo! Manyara Ranch, Nov 2010
The next process that's concentrating nutrients in the savannah is also so obvious that we often miss it - animals that use middens concentrate nutrients over several years in one spot. This nice impala midden shows another feature you often see about middens - again, the grass all around has been grazed to nearly nothing. And for exactly the same reason as before - the nutrient hotspots great lush grass that is heavily grazed, neighbouring grasses are also grazed and the impact spreads out to create a grazing lawn. (In fact, this one has suffered rather from cattle grazing too, but they respond to the same processes as the wildlife.) As you can see, the grazing is much more widespread than simply the focal nutrient spot, but it's quite possible that this midden and the others you can see around are the original cause of the heavy grazing over the whole of this little stretch. Always good things to point out when you're on a walk, especially if there are children about like my two...
Elephant diggings near Gibbs Farm, Dec 2010

See the tusk marks?! Elephant digging - there was also buffalo horn marks!

And for now I'll leave one final special case of nutrient hotspots impacting savannah ecology - the rare locations of mineral deposits utilised by a range of wildlife, but most famously by elephants. In some places, elephants have dug caves over 160m deep into mountainsides in search of nutrients (most famously on Mt Elgon where elephants have dug in search of calcium, sodium and magnesium). Other animals also come from far afield in search of the nutrient rich soil, leaving wide paths through the forest. These photos are from Ngorongoro, behind Gibbs Farm, where elephants are primarily searching for Molybdenum, selenium and cobalt. These micronutrients (nutrients required only in tiny amounts) are important for animal health and animals with deficiencies are generally rather unenergetic and not alert to the dangers of the world. So, rather a useful thing. And, of course, you don't have to head specially out to these caves (though it's worth a walk, and the birding around there is great!) to show this sort of activity to folk - several cuttings ont he main ascent road from Laodare gate to the crater viewpoint show obvious evidence of nocturnal mining by elephants, and the rock here is just as nutrient rich as in the caves at Gibbs.

So, next time your out and about, have a look for signs of nutrient concentrations, and see what's responding to it. And then remember the large-scale variations in nutrients too, that are so important for other processes!