You and I and termites have a lot in common. For one thing, we are all dependent on microbes to stay alive (though few microbes depend on us).
A Natural History of the Future, by Rob Dunn, Basic Books, November 2021
Besides, humans and termites, along with every other multi-celled living creature, belong to just one small branch on the evolutionary tree of life. All of us multi-celled types together – be we plants, insects, fish, birds or apes – are barely a rounding error in the catalogue of life, in which the overwhelming majority of varieties of life are bacterial.
These perspective-correcting points loom large in Rob Dunn’s A Natural History of the Future (Basic Books). If it were merely a compendium of curiosities the book would still make a really good read, given Dunn’s ability to highlight recent work by dozens of other researchers combined with his gift for clear exposition. But in his discussion of key laws of ecology Dunn has a practical purpose in mind: he wants to give us a better chance at surviving this new age of instability which we call the anthropocene.
In spite of all our clever technologies, he argues, human life is and always will be limited by basic principals of ecology. These laws of ecology are particularly important as we leave a millennia-long period of relative climate stability and begin to cope with the climate chaos we have created.
Climate change sometimes recedes into the background in A Natural History of the Future … for a few pages. Dunn takes us billions of years back into evolutionary history, and he spends much of the book reviewing events of recent decades, but his aim is to elucidate our near future. And in the near future no challenges loom quite so large as climate change.
In the big picture, think small
At the outset Dunn helps us understand the scope of our ignorance. When Western scientists such as Linnæus started to classify species, they focused mostly on species which were relatively large, beautiful, or directly useful to us. These scientists also tended to work in northern Europe, an area with very little biological diversity relative to much of the world.
By the second half of the twentieth century this limited world view was being challenged from within academic science. Once they paid close attention, ecologists realized that species of insects vastly outnumber all the species of larger animals. As Terry Erwin wrote in 1982, “there might be 30 million tropical arthropod species.”
Other scientists were exploring the bewildering variety of fungi. Still others, aided by new techniques in genetics, got a glimpse of the staggering diversity of bacteria. A study published in the National Academy of Sciences in 2016 “estimated that there might be a trillion kinds of bacteria on Earth.”
Dunn summarizes the perspective shift in these words:
“By the time I was a graduate student, Erwin’s estimate had led scientists to imagine that most species were insects. For a while, it seemed as though fungi might be the big story. Now it seems as though, to a first approximation, every species on Earth is a bacterial species.” (A Natural History of the Future, page 28)
‘A Novel Representation of the Tree of Life’ (from Nature, 11 April 2016), shows the predominance of bacteria in the tree of life. Dunn includes a simplified version of the same graphic, and he writes: “All species with cells with nuclei are part of the Eukaryotes, represented in the lower right-hand section of the tree. … The Opisthokonta, one small part of the Eukaryote branch, is the branch that includes animals and fungi. Animals, if we zero in, are just one slender branch of the Opisthokonta. … [V]ertebrates do not get a special branch on the tree. The vertebrates are a small bud. The mammals are a cell in that bud. Humanity is, to continue the metaphor, something less than a cell.” (Graphic by Laura A. Hug, Brett J. Baker, Karthik Anantharaman, Christopher T. Brown, Alexander J. Probst, Cindy J. Castelle, Cristina N. Butterfield, Alex W. Hernsdorf, Yuki Amano, Kotaro Ise, Yohey Suzuki, Natasha Dudek, David A. Relman, Kari M. Finstad, Ronald Amundson, Brian C. Thomas and Jillian F. Banfield; via Wikimedia Commons.)
For good or ill, our smaller companions on earth have always played large roles in natural history. Termites, for example, were just another type of cockroach until they acquired the gut microbes that allow them to digest wood. We humans “are probably dependent on more species than any other species ever to exist” – including, to mention just a few, all the insects that pollinate all the plants we eat, and all the gut microbes that help us to digest that food.
While we can’t hope to fully understand or even name all the varieties of life, we can, Dunn says, understand basic rules that influence how new species evolve, how existing species go extinct, and how species interact with each other and with their changing ecosystems. If we respect those rules we lessen the chances that we will threaten our own chances of survival any further.
Islands and corridors
The book covers too many subjects to adequately summarize in one review, but consider two simple concepts. A discussion of island ecosystems highlights the principle that bigger islands tend to have more species. It is equally true that ecosystems with greater diversity of species are more stable through time.
“Islands” can refer to bodies of land surrounding by water – but also to isolated specific habitats surrounded by very different ecosystems. One effect of our own rapidly climbing population and the explosive growth of urban habitats, Dunn explains, is the fragmentation of many ecosystem into an array of tiny islands – small areas of forest or plots of prairie – surrounded by cities or monoculture farms. These fragments – islands – are often too small to support a diverse number of species, and too widely separated from similar fragments for species to move between the islands. The result is that these islands are all highly vulnerable to significant or rapid change – including the change we are now enforcing by our rapid release of greenhouse gases.
The ecology of corridors is attracting wide interest, because it is readily evident that many species will need to move to survive. In some places and for some species, corridors that we carefully preserve or recreate may help plants and animals move along with the warming climate.
Corridor biology can also have unintended and unwanted consequences, Dunn points out. Not only are we building megacities, but these megacities are sometimes merging. In the nearly unbroken urban area from Washington DC to New York City,
“We have already created a corridor, a perfect and immense corridor, but it is not a corridor for rare butterflies, jaguars, and plants. It is, instead, a corridor for urban species, species able to move along roads and live amid buildings, species that live not in green spaces but in gray ones.” (page 72)
A corridor, in other words, for pigeons, Norway rats, and less-beloved species including some of the parasites that plague people in warmer cities, and which will move north with ease as the climate heats up.
Diversity and stability
The global market economy has pumped hundreds of billions of tonnes of carbon dioxide into the atmosphere, and it has appropriated most of the world’s arable land for monocultures of a small number of staple crops. Taken singly each of these transformations would have destructive effects – but in tandem they put us in a real heap of trouble:
“We have built a food system that thrives when variability is minimized. But … we have also altered Earth’s climate in such a way as to make it much more variable and unpredictable.” (page 150)
The diversity-stability law implies that “Regions with a greater diversity of crops have the potential to have more stable crop yield from year to year and hence less risk of crop shortages” (page 11). Dunn cites analysis by Delphine Renard, who compared nationwide yields from 91 countries, for 176 crop species, over a 50-year period. The yields were summed in terms of calories, so that agricultural yields from corn to potatoes to peaches could be compared in a common unit of measurement. The result: Countries with high crop diversity experienced 25 percent overall yield declines an average of once in 125 years. Countries with the lowest crop diversity experienced 25 percent declines an average of once in eight years.
The coming century will be more challenging than the past century, Dunn says. It would be easier, though still difficult, if we could expect steadily rising temperatures in every area. That is not, of course, how climate change is working. Instead, the general heating trend will be punctuated at unpredictable intervals by damaging cold spells. Dry areas are likely to get dryer, but with occasional damaging downpours, while wet areas get wetter but experience occasional droughts.
Considering climate physics and ecological principles together, then, it is essential that we begin the re-diversification of agriculture.
Other topics that Dunn covers include the dangers in indiscriminate use of biocidal chemicals – be they antibacterial hand creams routinely applied, antibiotics routinely added to animal feed, or herbicides sprayed on nearly every major crop field in whole countries. He discusses why some types of avian intelligence will help birds cope with climate change, while other kinds of birds will be at a terrible disadvantage. He explains that in spite of our advanced technologies, the dense concentrations of humans occupy the same geographic areas today that we tended to favor 6,000 years ago; this is a subject I hope to return to in a coming blog post.
The final chapter focuses once again on bacteria. We humans will die off some day, Dunn says, because no species last forever. If we mess up in spectacular fashion, millions of other multi-celled species will go extinct along with us – mammals, birds, fish, insects, trees and flowers. But uncounted millions of unicellular species – teeming masses of bacteria that thrive in scalding heat, concentrated acids, or intense radiation – will survive any calamities we are able to bring on.
A Natural History of the Future is a big book in its scope and in the degree of detail. Throughout, Dunn makes things clear for non-specialist readers. Highly recommended.
Photo at top of page: A Mastotermes darwiniensis worker termite. The giant northern termite is a large endemic species which lives in colonies in trees and logs in the tropical areas of Australia. Photo courtesy of Commonwealth Scientific and Industrial Research Organisation (CSIRO), via Wikimedia Commons.