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...


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!

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