If the past few months has shown us anything at all, it is how interconnected everything is in our globalised world. An animal-human interaction on one side of the planet can quickly spread to become a global phenomena. For this post, I thought I’d draw together some other examples of just how odd and bound together things can get on our crazy, complex little marble.
Otters, urchins and the Steller’s sea cow.
When you hear the term “keystone species” maybe you think of Yellowstone wolves and rivers, or of otters, sea urchins and kelp. The otter story is much better supported by evidence, and in many ways is the bread-and-butter tale of ecology. It goes something like this:
Fur hunters decimate otter populations. Urchins, whose populations are normally kept in check by otters, explode in number and proceed to munch-up kelp forests. In turn, this destroys the underwater jungles that form the habitat of countless species.
This chain of events has become something of a go-to cautionary tale, a warning klaxon for what can happen if you mess with a species that plays a disproportionate role in forging an entire ecosystem. What I only found out recently is that this hunter-otter-kelp-forest sequence might have actually been behind the extinction of massive herbivores, like the bumbling Steller’s sea cows around the Commander Islands, previously thought to have just been the victim of human appetite.
Guns, elephants and lianas.
Recent work has highlighted that whilst the strange corkscrewing, climbing vines that make rainforests mental might be getting more and more common around the world, proliferating in a changing climate, in areas of the Congo Basin, they seem to be in decline. The reason? Well it might have something to do with years of warfare and its effects on trunked tramplers. Many lianas species rely on open, light conditions to grow. Exactly the sort left in the wake of a stomping elephant. Fewer elephants = fewer gaps = fewer lianas, it seems.
Civil war, waterbuck and mimosa
Sticking with warfare, the near-eradication of large vertebrates in Gorongosa national park, Mozambique, during the civil war (1977-92) did something good for an invasive shrub, Mimosa pigra, one of the 100 worst invasive plants in the world. It turns out that an environment left ungrazed was just right for this tough shrub to thrive and stifle the natural regeneration of an entire savanna ecosystem. Fortunately in this case, all it takes is a bit of a helping hand (or nibble) from some reintroduced megafauna to bring Mimosa back down to pre-war levels.
Anchovies, tortillas and vanilla
In 1972, an El Niño drought caused a collapse in the Peruvian anchovy fishery. Bad for people, but probably not so bad for forests, right? Wrong. Back then anchovies were a mainstay for feeding livestock, so farmers turned to soybean feedstock instead, driving substantial forest loss in Brazil. Other odd market ricochets happened when a boom in biofuels in the US made tortillas pricier in Mexico. Because maize usually directed towards stomachs was instead being used to make fuel, the cost spike led to tortilla turmoil. Similar volatile boom-and-bust price cycles are currently threatening the livelihoods of Malagasy vanilla growers.
A song of ice and fire
When you think of melting glaciers, chances are what comes to mind are images of chunks of ice sliding into the sea in the Arctic. But there are glaciers in the tropics too, in the steep spots of South America, Africa and Indonesia. These glaciers provide water for millions of people but they too are melting, often at even faster rates than at higher latitudes. And it appears that land-use change doesn’t help the situation much. Emissions of black carbon from fires in the Amazon blacken the ice of Zonga Glacier in the far-off Bolivian high Andes, speeding up the melting process many hundreds of kilometres away
Rain, crops and lessons from the Lagoon of Mummies
Climate change will increasingly cause ‘shudders in the system’, driving secondary knock-on effects that we might not expect. It already has. Changes in the variability of the rainfall have have led to a 9% increase in crop expansion in developing countries over the past two decades, especially in those places lacking irrigation infrastructure. It appears that less frequent rainfall causes drops in farm yields, meaning that during arid times farmers have to spread out over a larger area to compensate, taking out forests in the process.
Perhaps it’s a pattern we might expect based on evidence from the iconic archaeological setting of Laguna de los Condores in the Peruvian Central Andes. You might know this area as the “Lagoon of Mummies,”–home of an old civilization that used to practise cliff-side tomb burials. In a fascinating example of how climate change, croplands and forests might interact in a changing world, recent research on fossilized pollen and lake sediments in this deep, forested valley reveals a stark and repeating pattern. During times of drought, cloud forests would parch out and farmers would move upslope to clear these areas and grow maize. (The peak of forest clearance happened in the dry periods starting around 800 AD, around the time the Vikings were invading Britain). But as wetter periods returned, these maize fields were abandoned and forest regrew, with pulses of forest loss and regrowth closely tracking the onset of drought and wetter conditions over the last 2100 years.
So there you have it. We live in a world of odd connections, where events thousands of kilometres away, or just next door, can cause system changes with broad, cascading consequences. The world is a huge game of Jenga. It’s up to us to make sure we don’t tip it too far.
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