Why are some species naturally rare whilst others are common? Do rare species make any difference in the larger scheme? These questions have puzzled biologists for centuries. Truth be told, even today, scientists have uncovered just a few pieces within this complex puzzle as we discover in Eric Dinerstein's The Kingdom of Rarities [Island Press, 2014; Guardian Bookshop; Amazon UK; Amazon US/kindle US]. In this engaging and informative narrative, the reader accompanies the World Wildlife Fund's chief scientist on his lifelong journey to visit some of the world's rarest species and remotest places. Along the way, Dinerstein discusses contributions from a variety of disparate scientific fields that shed light onto why some species are rare whilst others are not.
Dinerstein begins by retelling the story that captured my attention like no other at the time, that amazing story of Bruce Beehler's expedition to the Foja Mountains of western New Guinea. This remote region was noteworthy because no one -- not even the local tribespeople -- had ever set foot there. The purpose of this expedition was to survey all species that could be found in this pristine place but Beehler also had a personal objective: to rediscover several "lost" species of rare birds. Specifically, Beehler hoped to discover the home of the golden-fronted bowerbird, a bird so rare that it was known only from four dusty old museum skins purchased from locals in the mid-1800s. These tribesmen reportedly obtained the skins somewhere in western New Guinea.
Soon after Beehler and his colleagues arrived, it became obvious that nestled within the Foja Mountains' rugged and forbidding terrain was the topographical isolation necessary for new species to evolve and adapt to restricted niches. Although the spectacular golden-fronted bowerbird was incredibly rare overall, they were quite common here. But other rare birds were also locally common, including the mysterious six-wired bird of paradise and a new-to-science honeyeater that was voiceless, a most peculiar trait for a songbird.
This points to the fundamental question: what is rarity? We can all agree that those species comprised of just a few individuals inhabiting small ranges are rare, as for the golden-fronted bowerbird and other residents of the Foja Mountains, but what about species that are locally uncommon but widespread? Are they rare, too? This is precisely the situation for thinly-distributed "apex predators", such as the New World's puma and jaguar. In the case of these big cats, each species occurs within a vast range and occupies a wide variety of habitats, ranging from montane forest to desert and even tundra (in the case of the puma). Both puma and jaguar are sparsely distributed throughout the rain forests of Central and South America, where their natural histories and their interactions are poorly known.
Many scientists maintain that the food pyramid adequately explains the scarcity of large predators since it takes a lot of herbivores to support just a few predators -- particularly the largest "apex" predators perched at the top of the food pyramid. This hypothesis is consistent with the argument presented in Paul Colinvaux's book, Why Big Fierce Animals Are Rare.
But how do pumas and jaguars live side by side in the Amazon rain forest? Despite these two big cats' overlapping ranges, their similar habits and shared prey preferences are some of the reasons they carefully avoid each other -- effectively making each species even more scarce. But the explanations are more complicated and subtle than this since, for example, jaguars show clear sex-based habitat preferences: adult female jaguars reside along rivers and on flood plains whereas males, which are nearly twice their size, live higher up and farther from rivers. Why would they do this? The evolutionary and ecological rationales for these distinctive behaviours are not known at this time.
Overall, wide-ranging but thin distribution patterns make intuitive sense for large predators, but what might you conclude if you learned that scarlet macaws, which range widely, are also locally scarce? Additionally, what might you think if you learned that bald-faced saki monkeys are so rare that most primatologists have never seen them in the wild? Further, even particular tree species, such as mahogany, are so scarce that only one individual can be found in every few hectares or less. Why would certain tree species have a population distribution pattern that resembles that of an apex predator?
According to biologist Deborah Rabinowitz, there are three reasons why species are rare. In addition to the two already mentioned, there's a third, more complicated, reason; extreme loyalty to a particular habitat. Basically, this is the situation faced by America's most imperiled bird, the Kirtland's warbler. These colourful songbirds breed only in fire-prone small-stature jack pine groves in northeastern North America. Yet when these trees are made available through land management practices, this still isn't enough; even the soil and undergrowth must be just right for this ground-nesting species to prosper.
Unfortunately for Kirtland's warblers, after the appropriate habitat had been restored, these diminutive birds were confronted by a second threat: invasion of brown-headed cowbirds. Originally known as "buffalo birds", cowbirds are nomadic nest parasites whose entire life history evolved around following enormous herds of bison that roamed the American West, scaring up clouds of delicious edible insects. After human settlers substituted herds of domestic cattle for the newly-exterminated bison, cowbirds survived because they managed to transfer their allegiance to a new partner. Where ever cattle went, cowbirds followed.
This is how Kirtland's warblers met cowbirds. Having never experienced nest parasites before, the evolutionarily naive warbler ended up fostering hoards of cowbird chicks. Soon, almost no Kirtland's warbler parents were raising their own young. Only after the US Fish and Wildlife Service launched a program to daily capture and euthanise the thousands of cowbirds that popped up inside Kirtland's warbler breeding habitat did this species began to recover. But how long must Kirtland's warbler be managed so intensively? some people ask. Forever, perhaps?
But this simple question has universal ramifications: there are other, more famous, examples of extreme habitat specialists, including some of the world's most iconic and beloved animals; giant pandas and polar bears, northern spotted owls and penguins.
Dinerstein then moves on to consider other critically important questions: are all rare species on the verge of extinction? Have all species that are currently rare always been historically rare? Which common species are likely to become rare in the future? What sort of impact do rare species have upon their habitats and indeed, upon the overall function of larger ecosystems?
I actually read this book as a hardcover almost one year ago, but other projects prevented me from writing my review then. (And for this, I apologise.) But this personable travelogue was such an intellectual delight that I just had to tell you about it so when I learned this title had recently been republished as a paperback, I seized the opportunity to remedy my oversight. Rereading this book was a pleasure -- if anything, it was even better the second time through. The writing is compelling and at times, poetic, the stories, captivating, and the scientific data, illuminating and well-chosen.
In this engaging and thought-provoking chronicle, we tag along with the author as he shares the story of his lifelong quest to appreciate rarity in all its facets. His search takes us on a personal guided tour through the world's four major tropical rain forests -- the Amazon and Congo basins, Southeast Asia and (my favourite place) New Guinea. We sit next to him before crackling campfires when he joins fellow scientists and listen as they explain their life's work to understand the many nuanced reasons that make some species rare. Dinerstein examines decades of research in both mammals and birds and, in contrast to so many books I've read, he frequently discusses findings for plants, too. Passionate but never polemic, Dinerstein deftly weaves together findings from many disparate fields of research, along with the urgent necessity to conserve these rare species.
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Eric Dinerstein earned his PhD from the University of Washington and did postdoctoral work in Nepal with the Smithsonian Institution. He has published over one hundred scientific papers and nine books, including The Return of the Unicorns: The Natural History and Conservation of the Greater One-Horned Rhinoceros and Tigerland and Other Unintended Destinations. In 2007, Tigerland won the American Association for the Advancement of Science's award for science writing, the AAAS/Subaru SB&F Prize for Excellence in Science Books. Dinerstein is Chief of Conservation Science and Vice-President for Research at World Wildlife Fund. He resides in Washington DC.
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Disclaimer: GrrlScientist has no known connection to the book's author. Outside of receiving a free review copy of this book, no compensation was received by either GrrlScientist or the Guardian for this review. All images appear here by courtesy of the publisher.
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