Balance of nature: entire Earth ecosystems mapped (Introduction)

by David Turell , Thursday, October 20, 2022, 20:58 (555 days ago) @ David Turell

Life and death within systems adds another layer of complexity:

https://www.newscientist.com/article/mg25634090-500-the-surprising-role-death-plays-in-...

"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. Perhaps it is time we took it seriously.

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“'The biggest source of variation is that individuals go through a life cycle,” he says. Between a fertilised egg and an adult, an individual’s weight might increase as much as a billion times, depending on the organism. That requires resources. In most species, maturation isn’t dependent on age but on resources. Reproduction is also resource-dependent, and only a lucky few pull it off. Just 1 per cent of butterflies’ eggs become butterflies, for example. Juveniles and adults have different predation risks too. Essentially, they occupy different ecologies, but the field’s classical models take no account of that. The question de Roos asked himself nearly 30 years ago was: would it change our understanding of ecosystem dynamics if they did?

"The answer from his first forays into research was yes. Ever since, he has pursued a “life history” approach, building developmental stage into his ecological models. This means that he accounts for how the available resources affect a population’s structure – the ratio of developing juveniles to reproductive adults, say – as well as how the population’s changing structure affects those resources. “He closes the loop,” says Sebastian Diehl at Umeå University, Sweden, one of de Roos’s former collaborators.

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"Not everyone is entirely convinced by the emphasis on life history, though. Theoretical ecologist Peter Abrams at the University of Toronto, Canada, says that is just one of many factors that classical ecology overlooks. In 2005, he and Hiroyuki Matsuda at Yokohama National University in Japan coined the term “hydra effect”, after the many-headed serpent of Greek myth that sprouted two heads for each one Hercules sliced off, to describe any situation in which a higher death rate causes a species’ population to rise. Their description of the phenomenon doesn’t take life stage into account, and although Abrams agrees that life history might shape some systems, he suspects it is irrelevant in others. The toxic algal blooms that clog certain lakes each summer, for example, are best understood not in terms of life history, but in terms of the interactions of the microbial culprits with other microbes.

"But de Roos does have a handful of loyal supporters, including Diehl. “The problems that we deal with in ecology are typically hard, and that means the predictive power of models is often limited,” he says. Ecology is complex, making it hard to untangle the various processes and come to simple conclusions. It can be frustrating, Diehl adds. “But if we don’t develop [life history] theory further, we may be looking for the wrong things in our data.'”

Comment: the article is filled with many examples of the issues. They are complex and at times the conclusions are counterintuitive. Adequately feeding our huge and expanding population is risky if not handled by first understanding the rules of ecosystems. dhw's complaint about 'humans and food' underscores his lack of appreciation of the attendant problem with meddling before learning of the issues.