A challenge of biblical proportions
Amsterdam, September 7th, 2017
If you could be another species for a while, which would you choose?
I would choose the... wait for it... I have an incubation period of about a week. After I hatch, I increase my weight two thousand-fold in a two-week feeding frenzy, followed by a fortnight in emerald colored sheets. As an adult, I have a wingspan of ten centimeters and weigh less than a gram. I can fly up to fifty kilometers per hour and six hundred in a day, taking part in a multi-generational migration. I’m among the select group of species that has been to space. My wings are bright orange with black stripes and some white dots. Yes, my friends also call me tiger. Have you guessed it by now? My choice would be the Monarch butterfly.1 How wonderful it must feel to emerge from one’s pupa and spread one’s wings for the first time, fluttering through the sky. Dancing like birds of paradise, carpe diem like a mayfly, taking it easy like a sloth, or even having a bat day, there still is plenty to choose from. Before I proceed with more serious matters, during the last years of finishing these letters I felt most like the sand mandala artist of the ocean: the Japanese puffer fish.
Source: BBC (2014)
I’m writing to you because we are losing species at an alarming rate. For example, our amphibian friends have witnessed ten members of their class going extinct over the last thirty years, including the fairy-tale-like golden toad.2 Gone, forever.3 The loss of ten species may not sound like much, but extinctions are rather rare events during ‘nature as usual’. With roughly six thousand recorded amphibian species, one would expect about one extinction every hundred sixty to sixteen hundred years; in other words, the recent amphibian extinctions were sixty to six hundred times the natural rate.4
Survival of the fittest you may say, but the group of endangered species is not limited to slow and colorful toads. Many powerful, fast, and smart species have suffered significant population reductions during the last century; take for example the blue whale population that is “depleted by at least 70%, and possibly as much as 90%”, the tiger “population of mature individuals may be fewer than 2,500 ”, or the orangutan “decline of over 80% over the last 75 years” on Sumatra and “well over 50% during the last 60 years” on Borneo.5 The World Wildlife Fund (WWF) reports that global wildlife populations had declined to half of its 1970 levels by 2012.6 The same report shows that wildlife in freshwater and marine habitats had declined by about three quarters and third, respectively, so we may need to think outside the ark for solutions.
There are good chances that Edward O. Wilson would have answered my opening question by choosing to be an ant. Judging from his production and his influence over our understanding of the ant, he probably had the work ethic of one already. His Theory of Island Biogeography, joint work with Robert H. MacArthur, has been even more influential than his work on ants and earned him the nickname of being Darwin’s ‘natural heir’.7 MacArthur and Wilson (1967) propose that the species richness of an island is related to its size and distance from the mainland. According to the theory, an increase in an island’s isolation decreases the odds that species arrive by migration and an increase in its size allows it to sustain more species.8
Wilson went through quite extremes to find evidence that supported their theory: Together with Daniel Simberloff, he turned six small mangrove islands in the Florida Bay lifeless by fumigating them. They monitored the variety of species that re-colonized these islands for a year, and in line with the theory, the islands most distant from the continent remained least species rich.9 Since, their theory has been extended to describe species richness for other types of ‘islands’ as well, such as oases, mountain tops, or fragmented habitats due to human influence. Consistent with the species richness increases with 'island' size part of the theory, Figure 1.1 shows that the number of extinctions is decreasing with the size of national parks in the US. Not only has the theory of island biogeography been largely supported by data, it also has practical implications for the conservation of nature; for instance, wildlife corridors may aid conservation by creating larger connected habitats.10
Figure 1.1: Relationship between park area and natural extinctions since the establishment of 14 US national parks.
Source: Newmark (1987)
The theory of island biogeography may help to provide a peek into the future as well. Pimm and Raven (2000) used the proposed area-species relationship to simulate the loss of species due the ongoing decrease and fragmentation of habitats in the coming century. The estimates for the current extinction rates by Pimm and Raven range between 500 and 2,500 extinctions per million species*years, depending on the scenario.11 Under their ‘business as usual’ scenario, the rate peaks at 5,000 by the middle of the century. “Applying the species–area relationship to the individual hotspots gives the prediction that 18% of all their species will eventually become extinct if all of the remaining habitats within hotspots were quickly protected.”12
If the current patterns of human destruction continue unchanged, according to Wilson, “half the species of plants and animals on Earth could be gone or at least fated for early extinction by the end of the century”.13 Wilson is not alone with this grim outlook, others have already claimed that we may find ourselves at the start of the sixth mass extinction event.14 Earth lost at least 70% of its species during each of the previous five mass extinctions. I request your help to halt this worrisome trend of extinction. I have tried to appeal to your heart, let me also appeal to your reason for as to why it is important to preserve biodiversity.
Biodiversity makes ecosystems more efficient: “… as a general rule, reductions in the number of genes, species and functional groups of organisms reduce the efficiency by which whole communities capture biologically essential resources (nutrients, water, light, prey), and convert those resources into biomass.”15 and more stable: “Ecosystems that depend on a few or single species for critical functions are vulnerable to disturbances, such as disease, and at a greater risk of tipping into undesired states.”16 Moreover, “… in recent years, a consistent picture has emerged—biodiversity loss tends to increase pathogen transmission and disease incidence.”17 Finally, preserving biodiversity gives the next generation a larger set of nature’s solutions, which is likely to spark more innovation.18
During the coming months, I intend to send you more information about the likely causes of the current surge in extinctions and share what I can find about proposed solutions. I hope that my readings and travels may prove beneficial to you at some point. Sure, I am aware that I leave you with a challenge of biblical proportions, but your help may just be the flapping wing of a butterfly that we need to turn this tide of extinction.
“The great challenge of the twenty-first century is to raise people everywhere to a decent standard of living while preserving as much of the rest of life as possible.”
Edward O. Wilson (2006, p.17)
1. On November 30th of 2009 the first Monarch butterfly emerged from its pupa in space. The first animals in space were fruit flies, followed by monkeys, mice and dogs. The list of animals and plants in space was more extensive than I thought, albeit all were send or brought by humans.
2. The Redlist includes 32 extinct amphibian species. While the moment of extinction is often hard to pinpoint, some are likely to have occurred well before the last thirst years (e.g., the Gunther's Streamlined Frog that has not been observed the past hundred years). The nine other extinctions that were recorded in the last thirty years are: Atelopus vogli, Quito Stubfoot Toad, Longnose Harlequin Frog, McCranie's Robber Frog, Heredia Robber Frog, Las Vegas Leopard Frog, Southern Gastric Brooding Frog, Eungella Gastric-brooding Frog, Mount Glorious Torrent Frog.
3. There are several projects that aim to revive extinct species, either through selective breeding (e.g. Quagga project), through cloning (e.g. Pyrenean Ibex), or genetic engineering (e.g. Woolly Mammoth revival project). Proponents of such ‘de-extinction’ projects argue that the revived species could fulfill important services to the ecosystem (e.g. grazing by Mammoths may help to transform tundra into more productive grassland). Opponents warn us that de-extinction projects may divert resources away from conservation projects and remind us that revived species are likely to behave differently from their genetically identical extinct counterparts (e.g. due to being raised by another species).
4. The scientific community has adopted the term background extinction rate to describe extinctions during these nature as usual periods. The background extinction rate is commonly thought to be between 0.1 to 1 extinction per million species*years (where species*years is short notation for species times years). I have taken the estimate for the background extinction rate from Rockström et al. (2009). It considers extinctions outside of earlier mass extinction events (e.g., meteor impact). The uncertainty about the background extinction rate of one order of magnitude is due to the use of fossil data, which limits the number of species that are be included, as well as uncertainty about the total of number species. One extinction per million species*years means that for a million species we expect one extinction per year, and species have an expected lifetime of a million years.
5. Quoted from the IUCN website, see Reilly et al. (2008), Goodrich et al. (2015), Singleton, Wich, and Griffiths (2008), and Ancrenaz et al. (2008), respectively. I was least precise about the tiger population, the estimate referred to the most populous subspecies, the Bengal tiger. Of the remaining five subspecies there are less than 1.500 mature individuals combined, and three subspecies have already gone extinct, see Arkive.
6. To be more precise, WWF estimates a decline of 48 percent to 66 percent, based on the assessment of 14,152 populations, including 3,706 species (WWF, 2016). For the subsamples living in freshwater and marine habitats, the declines were 68 to 89 percent and 20 to 48 percent, respectively.
8. The theory refers to ceteris paribus increases in isolation or size. Ceteris paribus is a latin phrase often used by economists, which means ‘keeping all other factors constant’. Obviously, there are more factors that determine the species richness on an island; for example, its climate. However, the theory holds that, given a certain climate, an increase in isolation decreases species richness.
9. See Simberloff and Wilson (1969).
10. That said, the success of wildlife corridors is context dependent; for example, the corridors could harm biodiversity by introducing alien species in case the islands were not previously connected, or the corridors could facilitate the spread of diseases.
11. See Pimm and Raven (2000, Box 1).
12. Pimm and Raven (2000, p 844). See Myers et al. (2000) and Figure 4.1 for the biodiversity hotspots; these hotspots collectively hold a disproportionate share of Earths terrestrial biodiversity (30-50%) on a relatively small area of land (1.4%).
13. Quoted from Wilson (2006, p. 16).
14. For example, Leakey and Lewin (1995), Wake and Vredenburg (2008) and Barnosky et al. (2011).
15. See Cardinale et al. (2012, p.60-61) for the quote and references therein for evidence that biodiversity enhances the efficiency and the stability of ecosystems.
16. Rockström et al. (2009, p.474).
17. Keesing et al. (2010, p. 647).
18. You may not feel as excited about protecting poisonous spiders, snakes or jellyfish, yet their venom may give improvements in medicine, for example in pain relief. An example of novel use comes from Stellar Biotechnologies Inc., which cultivates and protects a sea snail that produces a protein used in immunotherapy. Other innovations come from biomimicry – the imitation of nature’s solutions to human problems – e.g., termite hills inspired ventilation systems or butterfly wing inspired water-repellent surfaces.