Balance of nature: importance of ecosystems (Introduction)

by David Turell , Tuesday, March 26, 2019, 19:27 (2068 days ago) @ David Turell

They are now carefully studied as food webs:

https://www.quantamagazine.org/with-food-webs-jennifer-dunne-puts-humans-back-into-ecol...

“'Ecologists tend to study ecosystems ostensibly in the absence of humans,” she said. “Of course, humans are everywhere and impact everything.” When ecologists do consider humans, Dunne added, they often treat us as an external factor causing something like climate change. Throughout history, however, we’ve been enmeshed in the planet’s networks of life-forms eating one another.

"Dunne, who is vice president for science at the Santa Fe Institute, arrived at food web research after starting out in plant ecology. By painstakingly cataloging every species in an ecosystem and what it eats, Dunne and her colleagues can quantify an entire food web. In their data visualizations, every species in a food web — from plankton to panthers — is reduced to a little ball, or node, and every feeding interaction becomes a line between them.

"Those nodes don’t have to be alive today. Dunne has worked on several prehistoric food webs, including one represented in the 500-million-year-old Burgess Shale. To figure out feeding relationships among its weird, impossibly old fossil creatures, she and her co-authors looked at fossilized gut contents and bite marks for clues. They found that the structure of the ancient Cambrian explosion’s food web had remarkable similarities to that of food webs today.

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"They arrived at the idea of a new kind of network: not a food web, but a web of use. Their working group, which first came together in early 2017, looks at six populations of preindustrial or nonindustrial humans, cataloging every way that people interacted with the species around them: pelts for clothing, wood for shelter, leaves for medicine and so on. To visualize the results, the researchers map a culture’s five or six most-used species onto a circular plot, along with a “taxonomy of uses.” The result resembles a thickly woven dreamcatcher.

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"Humans are very omnivorous — and because of that, they are not at the top of the food web. Humans are usually kind of in the middle to upper third of the food web for the few systems that I’ve studied. People tend to think humans are at the top. Well, humans are often at the tops of their individual food chains, but because they’re eating everything from plants all the way up to top carnivores, they end up being in the middle of the whole food web.

"Of course, all that’s ignoring parasites and viruses. I have separate work on including parasites in food webs, but that’s a whole different story. But if you ignore parasites and viruses and our microbiome, humans are generally at the top of food chains now. In premodern times, other things would eat us. That’s not so much the case anymore.

"Humans also have short path lines to other species. They have basically two degrees of separation from over 90 percent of the species in the food web, to put it in “Kevin Bacon” terms: Often they’re directly feeding on a quarter to 50 percent of the species, and then almost everything else is connected to those species. So within two links you can get anywhere.

"In the systems I’m looking at right now, humans are super generalists. They feed on many more things than almost all other species.

"In any food web, most animals are fairly specialized in what they eat. Most eat 10 or fewer things. You have a few things that eat more and more. And then out at the very end of the long tail of the distribution is where humans tend to be. In a sense, that is special.

"However, there are always some kinds of generalists in a system. I mean, in the case of the Sanak Aleut nearshore marine food web, there are two super generalists: us and cod. Pretty much anything cod can stuff into their mouth and take a bite of, they do."

Comment: Many systems are described and how many of them are influenced by humans. It is a decisive discussion as to why the bush of life is so important as a food source. And it shows why God knew what He was doing in setting up the diversity so evolution could progress over time with a full energy supply.