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The World Wildlife Fund for Nature (the “WWF”) released a report this fall (October 2018) that analyzed the 2014 populations of 17,000 vertebrate animal species around the world. This report (the “WWF Living Planet Index”) noted that 4,000 of these vertebrate species showed population declines of 60% or more since 1970. The causes of any species’ decline are complex, but, according the report’s authors, the overwhelming factor that led to the loss of so many animals was the human destruction or degradation of their natural habitats for agricultural purposes, resource acquisition or industrial development. The most serious declines were observed in Central and South America and in the islands of the Caribbean where wild, vertebrate populations showed a nearly 90% reduction in their numbers of individuals.
The report notes that freshwater vertebrates were particularly hard hit by the consequences of human activity. Further, the authors predict that by 2050 the amount of land area on Earth that is unoccupied by people and unaffected by human activity will fall from the present day’s 25% to just 10%. There will be little room for species that are unable to tolerate the presence of humans and the consequences of human activities.
Vertebrates (mammals, birds, reptiles, amphibians and fish) are the organisms most people recognize as being “animals.” Vertebrates, though, make up a tiny fraction of the numbers of species and total numbers of individuals found in the Kingdom Animalia. There are, by conservative estimates, 1.5 million living animal species on Earth. Of these just a bit over 66,000 are vertebrates (about 4% of the total!). The remaining 96% of animal species are lumped together into an imprecise classification called the “invertebrates.”
Many of these invertebrates include some of my favorite creatures: earthworms, polychaete worms, clams, oysters, crabs, spiders and mites! But, if we want to find the “poster organisms” for this invertebrate group, the logical animals are the ones that make up 70% of the group’s known species (over 1,000,000 identified to date!). These are, of course, the insects, the most successful group of animals that has ever existed on our planet! Sadly, it turns out that insects are even faring worse than the vertebrates in dealing with the changing features of our “Anthropocene” world!
As I reported this past summer (Signs of Summer 5, July 5, 2018) insect populations declined 76% over the past few decades in the natural preserves around Krefield, Germany. The causes of this decline were all human related: habitat destruction, pollution, pesticide use, etc. As I wrote in the Signs of Summer post, the relationship between insects and humans is complicated. Many people initially respond or react to the word “insect” with the image of household vermin, a biting/stinging nuisance, a disease transmitting vector, or a crop/garden destroying pest. This emotional reaction might then give way (or in many cases it might not!) to the recognition of all of the “good” that insects do (pollination, decomposition and functioning as a broad base for many important food chains). One third of the food we consume require insect pollinators. That service alone has been assigned a $500 billion a year value, and the monetary calculations for all of the wild plants that are pollinated and all of the food chains fed by insects would probably dwarf that human-food value estimate.
An example that might help to illustrate the importance of insects in decomposition can be found in the history of the European colonization of Australia. The cattle industry in Australia nearly came to an end because native insects were specialized to break down the very fibrous feces of marsupial grazers and could not decompose the dense, wet piles of feces produced by introduced cattle. Dung piles accumulated in the fields and around watering holes driving the cattle away from grass and water. Dung beetles had to be imported in order to clear the fields so that the cattle would freely graze and drink. Dung beetles in the United States, by the way, thankfully a group of native species, are estimated to benefit cattle ranchers to the tune of $380 million a year!
Insects are worth many hundreds of billions of dollars to the world’s economy and make the Earth both productive and inhabitable for all of the other living organisms on it! It turns out, however, that the Krefield, Germany observations are just the beginning of worldwide observations of an ongoing insect apocalypse (see B. Jarvis’ article in the November 27, 2018 issue of the New York Times).
In the United States, monarch butterflies have decline 90% in past twenty years (see Signs of Summer 8 (2018) and Signs of Summer 15 (2016)), and the rusty patched bumblebee has declined by 87%. In Great Britain 30 to 60% of the native insect species have significantly reduced ranges, and in California a 46 year butterfly census has shown declines in many species and local extinction of many others. Around the world honey bee hives are being decimated by Colony Collapse Disorder (see Signs of Fall 7, Signs of Fall 8 and Signs of Fall 11 (2018)), and an article published in Science in 2014 that analyzed insect data from a wide range of published papers concluded that insect populations in these long term studies have declined by 45%.
These declines in insect populations then have reverberations that echo through their ecosystems. In France a number insectivorous bird species that live in farmlands have had precipitous declines in numbers over the past few decades. Partridges were down 80%, nightingales were down 50% and turtledoves were down 80%. Initial analysis of these data indicated that habitat loss or the increased use of agricultural chemicals were the most likely direct causes of dwindling populations of birds. Later considerations, though, refined these conclusions and indicated that, in fact, these primary causes reduced insect numbers and that these birds then declined due to the lack of food.
In the Puerto Rican rain forest as part of a 40 year study of insectivorous lizards, total biomass of insects was regularly collected. In the 1970’s standard insect monitoring methods at specific spots in the rain forest generated 473 mg of insect biomass per collection. Now using these same collection methods at these same sites only 8 mg of insect biomass is collected. The surrounding rain forest seems pristine and undamaged, but its vital insect community is eroding away possibly toward some calamitous, ecological tipping point. The cause in these protected Puerto Rican rain forests is thought to be the rising temperatures due to climate change. The average temperatures in these sites have increased two degrees C over the four decades of the study and extreme heat waves have become more frequent!
Imagine the bleak, post-insect- apocalyptic world that would inevitably follow this massive die off of insects. E. O. Wilson in his 2006 book The Creation: An Appeal to Save Life on Earth does just that:
“The human species survives, able to fall back on wind pollinated grains and marine fishing. But amid widespread starvation during the first decade, human population plunges to a small fraction of their former level. The wars for control of the dwindling resources, the suffering, and the tumultuous decline to dark age barbarism would be unprecedented in human history. Clinging to survival in a devastated world, and trapped in an ecological dark age, the survivors would offer prayers for the return of weeds and bugs.”
Wilson feels that a better name for the Anthropocene (“the age of humans”) is the Eremocene (“the age of loneliness”). It would be the ultimate dystopia!