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Landscape ecology

Why did the wildebeest cross the road? Watch Dr. Colin Beale explain how we can find out.
Why did the wildebeest cross the road? It might sound like the start of a somewhat tired joke, but to an ecologist this question is the entry point to fascinating science. Is it because there are fewer predators on the other side? Or is the grass greener? And if so, why? How could we tell the difference anyway? We could test the first hypothesis by designing a predator survey and testing whether there more on one side than the other.
Of course, this wouldn’t be enough: we’d need to see if wildebeest know and respond to predator density as expected. Maybe we’d set up an experiment where in some places we played lion calls, spread lion droppings and sprayed lion urine about, and in others we did the same with herbivore signs. With GPS collars to track the wildebeest we could see if they moved away from areas with apparently high predator densities. We could even measure stress hormones in the wildebeest droppings, predicting that animals would be more stressed
where we’ve increased the apparent predation risk: ecologists are the jack-of-all-trades of biologists, using techniques from counts, through molecular biology to high-tech GPS collars to test theories. Testing the ‘greener grass’ hypothesis could involve
similarly varied methods: we could combine satellite images showing greeness with collar locations to test whether animals move towards greener areas. We’d probably find that in the dry season, when there’s little green about, animals do this, but in the wet season everywhere’s green, so movements must be explained some other way. We’d want to think about why they do this anyway - is green grass more nutritious? Again we could use chemistry to test this. In fact, wildebeest are great at identifying nutrient-rich grasses, even when there’s no difference in greenness. Indeed, wildebeest will walk 100s of kilometres to find calcium rich grass when they’re pregnant, which begs the question why don’t they stay there the all the time ?
In some areas like Serengeti, variation in rainfall and nutrients combine to favour migrations of grazing animals, pulled towards nutrient-rich areas in the wet season, but pushed away again when the rain ends. Such seasonal movements aren’t possible for territorial predators, so predator numbers are limited by food
availability when the migration isn’t around: when the migration returns predation has no impact on the population. Such huge numbers of animals have a profound impact on the ecosystem, from the transport of nutrients, to eating tons of vegetation and altering fire regimes. Studying the interplay between biotic and abiotic processes helps ecologists explain the behaviour of individuals, the growth of populations, the diversity of communities and even the services that ecosystems provide humans. What could be more exciting than ecology?

Ecologists use a diverse range of techniques to understand the processes driving the movement of, and interactions between, organisms in ecosystems. Here we look at an African ecosystem to learn more.

In this video we think about how predators and prey interact with their wider environment at a landscape scale, and the impacts this can have. We also consider some of the techniques that we can use to understand the processes occurring in our ecosystems.

Here are some questions to consider while you’re watching the video. We’d be happy to hear your views in the comments after you’ve watched the video.

  • So why did the wildebeest cross the road?!

  • Just how much poo (and associated nutrients) do 1.4 million wildebeest produce each day and what would the impact be on the ecosystem?

  • 15,000 years ago the UK had herds of mammoths and woolly rhino, large numbers of deer of various species and a complete set of large carnivores. How might the extinction of these animals affect the ecology of the UK today?

You can read more about African ecology in Colin’s blog.

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