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Elegant science can come from ugly things. That's the thought that comes to our minds when we read a new study of nature on how a single invasive species – the black rat Rattus rattus – can have an impact deep not only on the wider sea kingdom scenery that surrounds it.
Elegance stems from the exploitation of fortuitous invasion patterns. The researchers behind the study, led by marine biologist Nick Graham of Lancaster University, examined the Chagos Archipelago, an isolated group of coral atolls in the Indian Ocean. Some of the small islands that make up the archipelago are infested with rats and some are rat-free, result of different types of human habitation in the eighteenth and nineteenth centuries.
Graham and his colleagues found that the difference between the islands is now surprising and need not be contradicted by sophisticated statistical techniques. These islands with rats have something like one or two seabirds per hectare, while those without rats have 1,000 or more in the same area.
On islands without rats, seabirds roam the oceans from far and wide for food, then deposit much of the nitrogen and phosphorus-rich feces on their island of origin. These nutrients are then drawn into the shallow waters of the surrounding coral reef lagoons, where they support a complex food web that ultimately maintains large stocks of fish. The fish then graze the reefs and maintain a healthy balance between the algae and the corals of the island.
Beside the rat-infested islands, however, researchers have shown that fish populations are smaller, grow more slowly, and eat less than half of the algae. These reefs are therefore more likely to be smothered by algae and have less healthy corals.
This general phenomenon is not new. On the Chagos Islands, a few centuries ago, but elsewhere, it can go back thousands of years – humans have been migrating for a long time, taking with them rats and other invaders like pigs, rabbits and cats to cause comparable ecological damage.
The trick here, as the authors have pointed out, has not been to find evidence of the human impact because it is now very ubiquitous, but by finding some examples of something that approaches a natural base – those islands that are still free – that can help gauge the magnitude of this impact.
Accelerated Invasions
Given this history, the history of the Chagos Archipelago does not, technically, part of the Anthropocene – for the current best estimate. The beginning of this putative geological time, still informal, is somewhere in the middle of the twentieth century. But this sheds light on the magnitude – and the likely fallout – of even greater changes associated with more recent human impacts, when the scale and speed of biological invasions continued and even accelerated.
Since the mid-twentieth century, most of the lakes and waterways of North America, for example, have been the scene of a zebra mussel's lightning war , a native crustacean from Asia. The invasive zebra mussels of the London Thames, meanwhile, have seen their ephemeral hold on the river prized by the even more prolific Asian clam that, in the space of a little more than one. decade, has become a dominant species in the river.
San Francisco was once known for hippies with flowers in their hair, but its surrounding bay is also home to less benign visitors, including many of the Amur River clam across the Pacific, and the marine worm (in makes a burrowing mollusk) which, on its arrival, managed to cross many pillars and wooden docks. Meanwhile, on the other side of the world in the East African savannah, there is a plethora of invasive plants, including the "devil weed" and the "weed", which spread rapidly and can annihilating whole harvests
the ecological training effects of these more recent and more numerous examples of the Anthropocene will be more difficult than in the finely worked study of the Chagos Islands of Nick Graham and co. The natural ecological reference level is now even further away, while other effects – from pollution, urbanization, agriculture and climate change – are also intensifying. . In the midst of a tangle of environmental forcing factors, it is increasingly difficult to precisely connect the cause and effect.
It is clear, however, that the Earth system is now on a new trajectory of the Anthropocene. Holocene This new story of rats and reefs highlights how far these changes are likely to be deep.
More information:
Nicholas A. J. Graham et al. Seabirds improve the productivity of coral reefs and function in the absence of invasive rats, Nature (2018). DOI: 10.1038 / s41586-018-0202-3
Elegant science can come from ugly facts. That's the thought that comes to our minds when we read a new study of nature on how a single invasive species – the black rat Rattus rattus – can have an impact deep not only on the wider sea kingdom scenery that surrounds it.
Elegance stems from the exploitation of random invasion patterns. The researchers behind the study, led by marine biologist Nick Graham of Lancaster University, examined the Chagos Archipelago, an isolated group of coral atolls in the Indian Ocean. Some of the small islands that make up the archipelago are infested with rats and some are rat-free, result of different types of human habitation in the eighteenth and nineteenth centuries.
Graham and his colleagues found that the difference between the islands is now surprising and need not be contradicted by sophisticated statistical techniques. These islands with rats have something like one or two seabirds per hectare, while those without rats have 1,000 or more in the same area.
On islands without rats, seabirds travel the oceans from far and wide for food, then deposit much of the nitrogen and phosphorus-rich feces on their island of origin. These nutrients are then drawn into the shallow waters of the surrounding coral reef lagoons, where they support a complex food web that ultimately maintains large stocks of fish. The fish then graze the reefs and maintain a healthy balance between the algae and the corals of the island.
Beside the rat infested islands, however, researchers have shown that fish populations are smaller, grow more slowly, and consume less than half of the algae. These reefs are therefore more likely to be smothered by algae and have less healthy corals.
This general phenomenon is not new. On the Chagos Islands, a few centuries ago, but elsewhere, it can go back thousands of years – humans have been migrating for a long time, taking with them rats and other invaders like pigs, rabbits and cats to cause comparable ecological damage.
The trick here, as the authors have pointed out, has not been to find evidence of the human impact, as it is now very much ubiquitous, but by finding some examples of something approaching a natural basis – those islands that are still free – that can help gauge the magnitude of this impact.
Accelerated Invasions
Given this history, the history of the Chagos Archipelago does not, technically, part of the Anthropocene – for the current best estimate. The beginning of this putative geological time, still informal, is somewhere in the middle of the twentieth century. But this sheds light on the magnitude – and the likely fallout – of even greater changes associated with more recent human impacts, when the scale and speed of biological invasions continued and even accelerated.
Since the mid-twentieth century, most of the lakes and waterways of North America, for example, have been the scene of a zebra mussel's lightning war , a native crustacean from Asia. The invasive zebra mussels of the London Thames, meanwhile, have seen their ephemeral hold on the river prized by the even more prolific Asian clam that, in the space of a little more than one. decade, has become a dominant species in the river.
San Francisco was once known for hippies with flowers in their hair, but its surrounding bay is also home to less benign visitors, including many of the Amur clam on the other side of the Pacific, and the marine worm (actually a burrowing mollusk) which, on its arrival, managed to cross many wooden pillars and docks. Meanwhile, on the other side of the world in the East African savannah, there is a plethora of invasive plants, including the "devil weed" and the "weed", which spread rapidly and can to destroy whole crops. The ecological training effects of these newer and more numerous examples of the Anthropocene will be more difficult than in the finely worked study of the Chagos Islands of Nick Graham et al. The natural ecological reference level is now even further away, while other effects – from pollution, urbanization, agriculture and climate change – are also intensifying. . In the midst of a tangle of environmental forcing factors, it is increasingly difficult to precisely connect the cause and effect.
It is clear, however, that the Earth system is now on a new trajectory of the Anthropocene. Holocene This new story of rats and reefs highlights how far these changes are likely to be deep.
More information:
Nicholas A. J. Graham et al. Seabirds improve the productivity of coral reefs and function in the absence of invasive rats, Nature (2018). DOI: 10.1038 / s41586-018-0202-3
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