Essential Nitrogen – Plains of East Africa
On the plains of East Africa, there is an animal that you might think is the least likely to be affected by nitrogen levels in the grassland. Nitrogen, or indeed the lack of it, plays a decisive role in any grassland ecosystems. It’s even intrinsically entwined with the ecology of large predators like these lions. This close, and I’m in no doubt that these animals are at the very top of their food chain. But to find out how essential nitrogen affects predators, I need to start at the bottom of the food chain… And it all begins with the very special plant… One of the great unsung heroes of our planet, grass.
The really great thing about grass is that it’s simple. Compared to other flowering plants, shrubs and trees, it requires minimal protein to build. So it can take all of the nitrogen from its roots and put it not into bulky structures but organise it efficiently, yet simply, to maximise photosynthesis to produce it’s food.
How a Rhinoceros Lives on Sour Grass
Sawgrass leaves have protein at much lower concentrations. But this gives grazing animals a real problem. Impalas are one of Africa’s commonest antelope, a favourite prey of big cats. But their biggest challenge is a much more basic one… How to survive on nothing more than grass.
The key is being very fussy about the sort of grass you eat, because some grass is richer in nitrogen than other grass. This Impala is actually cherry-picking the leaves with the highest concentration of essential nitrogen. Even so she’ll have to work hard to extract it. Just watch her neck closely. any moment now, she’s going to regurgitate a ball of partially digestive grass… And she’ll process it all over again.
It’s called chewing the cud. By digesting grass not once… But twice these animals can extract as much of the essential nitrogen as possible, but it still only works on the very best grass. Antelope, like these Impala, can only survive on a diet of grass which is relatively high in essential nitrogen – grass like this. We call it sweet grass. This long grass, on the other hand, is known as sour grass, because the essential nitrogen in its leaves occurs at even lower concentrations.
But there is an animal here that can change that… A very rare one. This is what I’ve been looking for. The animal that has deposited this dung processes grass through its gut in a very different way than antelope, and I’m sure I can demonstrate that. Here is some antelope poo, and if I take just one of these and break it open here, you can see that what remains is pretty much nothing more than dust.
Where as this, on the other hand, is very different. If I break this one in half… The grass is still very visible. The white rhino. What an animal! The sheer scale. I mean, they’re the closest thing perhaps that we have on the planet to mammalian dinosaurs. And of course, they have a reputation for being pretty feisty, so I’m being very careful and not moving too quickly and keeping my voice down.
In fact, this one is getting a little bit close, so I’m going to stop moving and stop… talking altogether. Their eyesight is poor, so if I’m still, they may not notice me. But they do have a great sense of smell. If the wind changes they could charge.
Absolutely fabulous things. Now, one of these animals has got no horns. It hasn’t lost them in a scrap. They’ve been deliberately removed by the Park Rangers here, as these horns can have a tremendous value.
Rhinos with horns are prized by poachers. The month before I arrived, they killed one in this very park. Cutting off her horn could save her life, and it is hoped that this practice will save the entire species. Losing a species like this would have a drastic impact on the entire grassland ecosystem.
Her huge size allows her to live on grass that antelope just can’t. Her body houses a massive gut, fermentation chamber, so she can make up for the low quality of sour grass by digesting in vast quantities of it. All of which means she produces a lot of dung… Which she drops in a very specific place – a midden. For rhinos, this is important. It’s how they communicate. Rhinos come here from far and wide. By smelling the pile, they can tell who’s around, how they are doing and who is ready to mate. This is sort of faecal Facebook but with added value.
It brings nitrogen-rich-manure from all over the grassland to one place. So the grass growing here becomes increasingly sweeter until, as if by magic, rhinos have created a grazing lawn of sweet grass, perfect for fussy eaters like Impala. Rhinos are ecosystem engineers upon which many other animals depend. That, surely, is their true value. That’s why they’re worth I fear, then. Much more alive than dead.
Right across the world, it’s sweet grass that’s crucial for most grassland grazers… And it’s this quest for sweet grass that drives one of the largest movements of animals on our planet. every year, one and a half million wildebeest migrate 3,000 kilometre, all because of essential nitrogen. And this is when its impact reaches the top of the food chain.
So, what has a lion kill got to do with nitrogen? Well, basically two things. You see, the lines here have identified the richest source of nitrogen available out here in the grassland – large herbivores. You see their bodies are made up of principally proteins, and that protein is where the nitrogen is. Then it’s the sweet grass which dictates where lions like to hunt. King of beasts they may be, but their lives are ruled by nitrogen.
But how would the grassland predator survive if there were no sweet class to hunt in?
External Links
Essential Nitrogen – The Nitrogen Cycle – Vision Learning
