The surprising role death plays in the stability of ecosystems

Ecologists have started to recognise the competition between younger and older generations within the same species, with some startling conclusions about nature’s requirement for mortality

By Laura Spinney

TO THE east of Amsterdam lies a tract of reclaimed marshland, the site of an epic rewilding project called the Oostvaardersplassen. It is sometimes nicknamed the Dutch Serengeti because of the profusion of large herbivores that graze there. But during the bitterly cold winter of 2017-18, deeply shocking images began to emerge. Thousands of deer, cattle and horses lay dead or dying of starvation. Desperate onlookers threw bales of hay over fences in an effort to help – clearly something had gone badly wrong.

Theoretical ecologist André de Roos was neither shocked nor surprised. His research had predicted this disaster years earlier. Without the herbivores’ natural predators, he reported, overpopulation was unavoidable – leading to mass death when food ran out. The cold weather may have accelerated the die-off, but it would have happened anyway. “There were only ever two options: to allow mass starvation or to introduce culling,” says de Roos. One way or another, nature has what he calls a “requirement for mortality”.

This requirement takes centre stage in de Roos’s work. But it is often unrecognised by other ecologists, whose models fail to account for the complexity within any population – in particular, the fact that individuals may vary hugely depending on their stage in life, which can result in intergenerational conflict. As well as highlighting the benefits of death, de Roos’s thinking can explain some of the toughest brain-teasers in ecology. It also suggests novel ways of tackling economically important problems, such as the collapse of fisheries and the impact of noise pollution on marine mammals. …