Messages from Islands: A Global Biodiversity Tour

By Ilkka Hanski

From a small island in the Baltic Sea to the large tropical islands of Borneo and Madagascar, Messages from Islands is a global tour of these natural, water-bound laboratories. In this career-spanning work, Ilkka Hanski draws upon the many islands on which he performed fieldwork to convey key themes in ecology. By exploring the islands’ biodiversity as an introduction to general issues, Hanski helps us to learn how species and communities interact in fragmented landscapes, how evolution generates biodiversity, and how this biodiversity is maintained over time.

Beginning each chapter on a particular island, Hanski dives into reflections on his own field studies before going on to pursue a variety of ecological questions, including: What is the biodiversity crisis? What are extinction thresholds and extinction debts? What can the biodiversity hypothesis tell us about rapidly increasing allergies, asthma, and other chronic inflammatory disorders? The world’s largest island, Greenland, for instance, is the starting point for a journey into the benefits that humankind acquires from biodiversity, including the staggering biodiversity of microbes in the ecosystems that are closest to us—the ecosystems in our guts, in our respiratory tracts, and under our skin. Conceptually oriented but grounded in an adventurous personal narrative, Messages from Islands is a landmark work that lifts the natural mysteries of islands from the sea, bringing to light the thrilling complexities and connections of ecosystems worldwide.

• Language: English
• Publisher: University of Chicago Press
• Release date: Dec 14, 2016
• ISBN: 9780226406589

Book preview

Messages from Islands

Messages from Islands

A Global Biodiversity Tour

Ilkka Hanski

The University of Chicago Press

Chicago and London

The University of Chicago Press, Chicago 60637

The University of Chicago Press, Ltd., London

© 2016 by The University of Chicago

All rights reserved. Published 2016.

Printed in the United States of America

25 24 23 22 21 20 19 18 17 16    1 2 3 4 5

ISBN-13: 978-0-226-40630-5 (cloth)

ISBN-13: 978-0-226-40644-2 (paper)

ISBN-13: 978-0-226-40658-9 (e-book)

DOI: 10.7208/chicago/9780226406589.001.0001

Library of Congress Cataloging-in-Publication Data

Names: Hanski, Ilkka, author.

Title: Messages from islands: a global biodiversity tour / Ilkka Hanski.

Description: Chicago: The University of Chicago Press, 2016. | Includes bibliographical references and index.

Identifiers: LCCN 2016019373 | ISBN 9780226406305 (cloth : alk. paper) | ISBN 9780226406442 (pbk.) | ISBN 9780226406589 (e-book)

Subjects: LCSH: Biodiversity. | Island ecology.

Classification: LCC QH541.15.B56 H364 2016 | DDC 577.5/2—dc23 LC record available at https://lccn.loc.gov/2016019373

This paper meets the requirements of ANSI/NISO Z39.48-1992 (Permanence of Paper).

To Eeva and Natalie,

a chronicle of what your life partner and grandfather has done

Contents

Preface

1  Biodiversity: Species and Where They Live

2  How Is Biodiversity Generated?

3  Changing Biodiversity

4  Species on the Move

5  Habitat Loss and Fragmentation

6  Why Is Biodiversity Important?

Epilogue

References

Index

Preface

Biodiversity, and life in general, is the defining feature of our planet. Small children are fascinated by biodiversity, but sadly that interest often wanes because we grown-ups and our educational systems fail to nurture it, and fail to build bridges between children’s instinctive attraction to animals and plants and sound understanding of the ecological and evolutionary processes that keep the world running. Not all children lose their early curiosity about biodiversity, however; their interest may mature and lead to a profession in ecology and evolutionary biology. That is what happened to me. I remember one early incident that played an especially big role. I spent all my school holidays in the country, at my grandmother’s place, which I value in hindsight as a huge privilege. At the age of eight, I took up collecting butterflies and moths, following the example of a few older boys. For the others this interest lasted a year or two, but mine never stopped. One reason that I stayed interested was a butterfly that I collected in 1964. The butterfly, a dusky meadow brown (Hyponephele lycaon), had gone extinct in Finland around 1936. My specimen must have been a vagrant from somewhere southeast of Finland. I was surprised and delighted to have captured such an unusual species; my father thought that I should let others know about it, and so I attended my first meeting of the local entomological club. The news about my butterfly was conveyed to Esko Suomalainen at the University of Helsinki, a population geneticist who is still remembered for his work on chromosome evolution in Lepidoptera (butterflies and moths). Suomalainen published a paper in 1958 on the extinction of the dusky meadow brown from Finland, in which he discussed the role of inbreeding in the disappearance of the last small populations. His thinking was ahead of his time; research on the effect of inbreeding on extinction became a hot topic only in the 1970s. He sent me a reprint of his publication, which I could not read as it was written in German, but you can imagine the effect on an eleven-year-old boy of receiving his letter and a copy of his scientific paper. Collecting that butterfly and receiving that reprint made it practically certain that I would become a biologist.

Research on biodiversity, and reading and finding out more about it, has a dark side that most other fields of research do not. Biodiversity is declining rapidly both locally and globally, because the human impact on the planet has reached such a level that many researchers describe our time as a new geological epoch, the Anthropocene. The world is changing so rapidly that an individual observer can record very substantial changes in his or her lifetime. I have been struck by dramatic changes in the composition of a bird community on a small island in the Gulf of Finland during forty-six years, changes in the elevational distribution of dung beetles on a mountain slope in Borneo during thirty-five years, and a sudden shift in the lemming dynamics in Greenland at the turn of the century, apparently due to climate warming. Changes can be represented by numbers in tables and graphs, but the human mind is such that only what we have seen with our own eyes, heard with our own ears, and touched with our own fingers seems real. A cool summer makes people doubt climate change. At the same time, the human perception of time is so inadequate that unless you make an effort, you can miss the change. You become used to the altered environment so quickly that you do not realize that the world is changing at all. Researchers who are concerned about the loss of biodiversity and speak out about it are occasionally accused of partisanship. (Oddly enough, medical doctors who are concerned about public health are unlikely to be accused of partisanship.)

Many discoveries about biodiversity and the ecological and evolutionary processes shaping it have been made on islands. Isolation and distinctness of islands have influenced the populations and communities inhabiting them, and these features have also affected researchers. Island populations are well-delimited targets for research; the island environment is often different enough to impose new selection pressures; the size of island populations is related to island area; and the exchange of genes and individuals with other populations is affected by island isolation—all features that facilitate research. It is probable that the short visit that Charles Darwin made to the Galápagos Islands in September 1835, toward the end of his five-year voyage around the world, and the birds that he collected there helped him take the mental leap to the idea of natural selection. The equilibrium theory of island biogeography composed by Robert MacArthur and Edward O. Wilson was not based on any particular island, but on islands in general, and the result was a paradigm change in biogeography and ecology. Closer to home, my predecessor in the chair of ecology in the University of Helsinki, Olli Järvinen, biogeographer and conservation biologist, thought that Finnish population biologists are especially fortunate because of the huge number of islands in the Baltic Sea and in the many large lakes in Finland. Each of the six chapters in this book is launched with a short narrative of my personal experiences and, in most cases, research done on six islands, from a tiny islet in the Gulf of Finland to Borneo, Madagascar, and Greenland.

The six islands featured in this book.

The purpose of this book is not to describe the global distribution of biodiversity. There is no shortage of wonderful field guides, especially on birds, but also on many other groups of animals and plants. Leafing through the maps of species’ geographical ranges helps one understand the big picture of biodiversity around the planet. Naturally, the best way to become familiar with biodiversity locally is to take your field guides to the field. Neither does this book catalogue changes in the state of biodiversity, which is well done in many books, reports, and websites. My purpose is to present an overview of what biodiversity is, how it has evolved in the course of evolution, and how it changes at present; how we humans shape biodiversity by unintentionally helping other species expand their distributions and by converting their habitats; and why biodiversity is important, why we must protect it. These are big topics on which there is a vast literature. My goal is not to summarize all that knowledge, but rather to present it from the perspective of one working scientist. I hope that short stories of how research has been done will convey a glimpse of the excitement of doing research on biodiversity.

There are many friends and colleagues whom I wish to thank for providing illustrations, material, and advice and for comments on particular sections of the text: Robert Angus, Tony Barnosky, Paulo Borges, Stan Boutin, Jukka Corander, Maria Dornelas, Steve Ellner, Mikael Fortelius, Marcos Baez Fumero, Eeva Furman, Nanna Fyhrquist, Olivier Gilg, Peter Grant, Tari Haahtela, Jorma Keskitalo, Ilpo Kojola, Janne Kotiaho, Bill Laurance, Marko Mutanen, Otso Ovaskainen, Camille Parmesan, Stuart Pimm, Juha Pöyry, Tomas Roslin, Marjo Saastamoinen, Ilik Saccheri, Dan Simberloff, Benoît Sittler, Olli Tahvonen, Chris Thomas, David Tilman, Tuuli Toivonen, Heidi Viljanen, and Chris Wheat. Juha Markola drew the illustrations that appear at the beginning of each chapter. Sami Ojanen, Jenni Hämäläinen, and Joann Hoy helped in many ways during the preparation of the manuscript, and Christie Henry and Gina Wadas from the University of Chicago Press assisted me greatly in turning the manuscript into this volume. I thank them all. Words are not sufficient to thank my wife, Eeva, and my children, Katri, Matti, and Eveliina, for supporting me during this difficult time after an exceptionally lucky life.

1

Biodiversity

Species and Where They Live

Expedition to Borneo

The airplane landed at the Bandar Seri Begawan airport in Brunei, on the north coast of Borneo, on March 22, 1978. I could hardly believe it. I had never been in the tropics, and now in Borneo, of all places! For the young ecologist this was a dream come true. I could have run after the first butterfly crossing the runway, but instead I had to walk with my expedition companions through passport control and customs. The rules and regulations may have changed since 1978, but in that year any male traveler entering the state of Brunei was expected to possess a feature that I lacked—short hair. To their credit, the authorities offered me two options, either to have an instant hair cut or an instant departure from the country. I could have agreed to the former, but there was no need for it—a driver was waiting to take us from the airport across the border to the town of Miri in Sarawak, Malaysia, where the length of my hair was my own problem. From Miri we continued in a big fast boat along the Baram River to Marudi, where we boarded, a day later, a narrow longboat and spent ten more hours traveling up Baram and its tributary Tutoh, toward the mountain range that gradually took shape in the distance. Our destination was Gunung Mulu, a region of virgin forests on steep mountain slopes, 100 kilometers from the coast. The area was inhabited by nomadic Penan people in 1978 (figure 1.1). Today, the remaining Penans are settled, or have been settled, in a few villages. Gunung Mulu is a national park and a UNESCO World Heritage Site, famous for its caves, bats, and karst formations in the limestone mountains surrounding Gunung Mulu itself, a peak of sandstone towering above sea level.

Fig. 1.1 Penan people lived in small family groups, constantly moving from one place to another without any permanent dwellings.

One reason for the exceptional biological diversity in the Gunung Mulu National Park is exceptional geological and topographical diversity. Indeed, an important facet of biodiversity is diversity of habitats and ecosystems, which set the living conditions for all the creatures inhabiting them, from microbes to plants and animals. For animals, plants and their communities are a big part of the living conditions. Cause and effect also work the other way around, especially when we consider long spans of time, as animals, plants, fungi, and microbes influence the way habitats and ecosystems change. The current atmosphere, especially the high concentration of oxygen (21% by volume), is the result of photosynthesis, started by cyanobacteria more than 2 billion years ago. Similarly, though less spectacularly, habitats and ecosystems were engineered by the ancestors of the species that now occupy them, which themselves keep the processes going. Our own species is the supreme engineer of the physical conditions on the planet, often, alas, to the detriment of many other species, which lose their prime habitat while our species converts it to something else, for instance, tropical forests to oil-palm plantations.

Ecologists routinely use the terms habitat and ecosystem, but what do we actually mean by them? Habitat is the physical and biological conditions that can support, in principle, viable populations of a species. The conditions include the right kind of soil, the range of tolerable temperature and precipitation, food resources, and natural enemies. Different species tend to differ in their resource requirements and other needs; hence species differ in their habitats, at least in the fine details. In Gunung Mulu, as I was to discover, the limestone mountain Gunung Api and the sandstone mountain Gunung Mulu, though only kilometers apart, have very different kinds of plants and animals, most likely because the rocks and the soils are different. The forested slopes on the limestone and sandstone mountains represent different ecosystems, entities that consist of the physical environment as well as the community of all the organisms living in the area, plus all the interactions that take place between the species and their environment—a very complex system.

Today, the word ecosystem is used by mobile-phone and other companies, which argue about whose ecosystem is most advanced and complete. Hijacking the term ecosystem for such usage may reflect an appreciation for the workings of real ecosystems, but I would prefer CEOs to use more imagination and other vocabulary. Talking about ecosystems around companies may lead people to think that real ecosystems are there only for the benefit of humans, and to value some ecosystems above others. People may start thinking that we should make natural ecosystems work better, and that manipulation of real ecosystems is not only possible but also desirable, comparable to companies arranging deals with their contractors. In reality, natural ecosystems have not been designed for any purpose, and tinkering with their components to enhance their performance (from a human perspective) is apt to lead to unexpected consequences. I return to these issues in later chapters, but for now I’ll just say that the task of predicting the dynamics of complex ecosystems with thousands of interacting species that may even evolve new features in response to our manipulation is simply beyond the capacity of today’s ecologists, and probably also beyond the capacity of tomorrow’s ecologists.

In 1978 I was a member of the Royal Geographical Society Expedition from London to Gunung Mulu. During 15 months, more than 100 researchers spent time in Gunung Mulu, studying the habitats and their animal and plant inhabitants, or the biodiversity of Gunung Mulu, as we would say today. I became aware of Gunung Mulu in a pub in Oxford, where I overheard someone chatting about the upcoming expedition. I had started my doctoral studies in the autumn of 1976, supported by a fellowship from the Queen’s College, which I had been awarded in the third year of my undergraduate studies in Helsinki. I joined the Animal Ecology Research Group (AERG) without knowing anybody there, and without knowing what I would end up doing. There were no e-mails and no websites in those days, of course—not even personal computers. The only computer at the Department of Zoology was a big machine that filled one small room. In the morning, and whenever some unexpected error had occurred, one Richard Dawkins entered the room and fed a big reel of paper tape to the guts of the machine to make it behave.

After my arrival at Oxford, I talked to John Phillipson, the director of AERG, about possible doctoral projects. Phillipson was a pioneer in the measurement of the energetic content of animal populations, part of the broader effort to characterize the flow of energy and matter through populations and ecosystems. AERG and John Phillipson had replaced the Bureau of Animal Population and Charles Elton in the late 1960s. Elton is widely and properly credited for establishing the field of population ecology, and he was one reason that this young Finnish student wanted to go to Oxford. Elton had long been retired when I arrived, but he came to the office every now and then, and I had a chance to talk to him on a few occasions. Phillipson proposed that I start working on some old samples of soil mites that he had accumulated in a project that was part of the International Biological Program, a global initiative to kick-start ecosystem ecology in the 1960s. I panicked, but luckily rescue was at hand, by Malcolm Coe, a lecturer who had moved from Kenya to Oxford in the 1960s. Malcolm had worked on dung beetles, organisms that were familiar to me from my undergraduate studies in Finland and much preferable to soil mites. The decision was made that I would start work on the community of dung beetles in Wytham Woods near Oxford. This pleasing decision made me feel that I was following in the steps of Charles Elton, who pioneered much of population and community ecology through his long-term studies in Wytham Woods. Going to Gunung Mulu for two months in the spring of 1978 would be a distraction, but Malcolm understood that he could do little to stop me. Besides, I explained, very little was known about the ecology of dung beetles in tropical forests, I could produce some interesting results, and in any case I would be back in late spring to start fieldwork in Wytham Woods.

The first days in the expedition base camp, a longhouse by the Tutoh River, surrounded by floodplain forest, were memorable (figure 1.2). On the way from England to Sarawak, my more experienced companions had explained in some detail the conditions that we should expect, with a particular emphasis on parasites and diseases—and leeches, with which the forests were teeming. There was plenty of time to mull over these matters, especially as we missed our flight at the Royal Air Force Brize Norton station, north of Oxford. The Royal Air Force had agreed to take expedition members to Hong Kong in their weekly flights operated for their personnel. We had checked our bags in time and had then gone to have a cup of tea with a buddy’s aunt, who happened to live near the airport. We were careful to return in time, but that was our time; we did not realize that the Royal Air Force operated on GMT, one hour ahead of everyone else’s time. It was embarrassing to go back to the department in Oxford for another week, having just recovered from the farewell party the night before, but all these mishaps only increased my enthusiasm. Parasites and diseases were soon forgotten when I finally reached the jungle. And the leeches, yes, they were abundant in places, but you get used to them, just like you get used to mosquitoes in Finland.

Fig. 1.2 Researchers at the expedition base camp in Gunung Mulu, Sarawak, in the spring of 1978. (Photo courtesy of Nigel de N. Winser.)

The first days in the forest showed that the student of dung beetles has an enormous advantage. Tropical forests harbor incredible numbers of insects, but researchers have to do an enormous amount of work to find out exactly how many there are. Yves Basset and no less than 101 colleagues spent nearly 25,000 trap days sampling a mere 0.5 hectare of tropical forest in Panama, using the full assortment of traps and sampling methods. The result: 6,144 species of insects in a sample of 129,494 individuals (Basset et al. 2012). In contrast, I was working on my own, helped by two young local men, and I had less than two months for my sampling. Nonetheless, at the end of my study in Gunung Mulu, I could be rather confident that I had sampled a large fraction of all the dung beetle species that could be found there. This is how it was done. Take a small plastic cup and dig it into the ground so that the top is level with the ground; pour a little water into the cup; add a drop of liquid detergent to remove surface tension; take a piece of fish, wrap it in mesh, and hang it from a stick above the trap; leave it in the forest for two days and nights; and return to collect all the beetles that were attracted to the bait and fell into the trap. A single trap is not enough, of course, but it took us only half a day to set up 100 traps. I repeated trapping in many places in Gunung Mulu. Trapping for more than a few days at a particular site would have increased the numbers of beetles caught in the cups, but after the first few days, the species were mostly the same that had already been caught, which shows that dung beetles are easily attracted to traps. So the trick is, instead of crawling through the forest in search of them, letting them come to you! Using fish as a bait was also convenient. Most tropical forest dung beetles are attracted to any kind of decomposing animal matter, probably because severe competition for resources would make a high degree of specialization a real handicap. (I will say more below about the coexistence of many species in spite of their competition for shared resources.)

Dung beetles’ appetite for dung and carrion may seem—how should I put it?—a less exciting spectacle than the spring migration of birds or the mating behavior of bears. But nobody can deny the significance of these little creatures for ecosystems, for cycling of nutrients, improving soils through their tunneling activities, and controlling populations of dung-breeding pestiferous flies. The numbers speak for themselves. In South Africa, 700 to 1,500 beetles colonized fresh cattle-dung pats in twenty-four hours (Bernon 1981), and 7,000 beetles representing no less than 120 species were counted from a single pile of elephant dung (Scholtz et al. 2009). I am happy to report that the record goes to my PhD supervisor, Malcolm Coe, who documented the incredible number of 16,000 dung beetles attracted to 1.5 liters of elephant dung in two hours in East Africa (J. M. Anderson and Coe 1974)—after which there was nothing more to observe about that pile of dung. And it is not only eccentric researchers who know the importance of dung beetles. Many Australians do as well. There are no elephants, buffalo, antelopes, or other favorites of dung beetles in Australia, where the vast majority of native dung beetles have evolved to use the pellets of marsupials, the native dung producers. Today, Australia has some 30 million cattle and 100 million sheep, which produce, as a rough estimate, more than 1 million tons of dung every day. And what happens to that dung? The native dung beetles are ill prepared to do much; they are small-bodied and mostly occur in forests. They just cannot cope with the millions and millions of cattle-dung pats, a resource that their ancestors never encountered during their evolutionary history over tens of millions of years. In this situation, researchers initiated in the 1960s an extensive program to introduce dung beetles to Australia, apparently to good effect (more about this in chapter 4).

My own fascination for dung beetles does not stem from their role in removing dung pats from pastures or in cycling nutrients, nor for any other reason that dung beetles might be considered useful to humans. I find dung beetles attractive because of biodiversity. I do not know many other communities of sizable animals that can be so easily attracted to a single spot in large numbers: hundreds or even thousands of beetles of different sizes and shapes, often of brilliant metallic colors. Admittedly, an even greater diversity of insects can be seen at night, especially in the tropics, in places where bright light has lured moths, beetles, stick insects, and others to the wall of a building or, even better, to a white bed sheet that you have hung out for the purpose. Without exception, people who see for the first time this congregation of literally hundreds of different kinds of insects—small and large, bright and dark, slow and fast—are surprised and fascinated. A knowledgeable entomologist can identify many species to the family level, but otherwise the species remain anonymous; not much is known about their biology. They arrive from the dark jungle as messengers of its riches. The assemblage of insects that is attracted to light in one place is just a small sample of the vast numbers of species in the forest—one would need to spend years sampling to see even a fraction of all the species. Dung beetles are different: their biology is well known, and they can be effectively attracted by bait, so that intensive sampling during a single week yields practically all the species that are present at a study site.

As a researcher, I find dung beetles attractive because it is possible to address many fundamental questions about the ecology of populations and communities, and of biodiversity, by studying them. The number of beetles is often so huge that the resource is depleted in a short time. In other words, many species compete for the resource. So why doesn’t one or a few species replace the others? How can so many species coexist in spite of severe competition? I knew from lectures, textbooks, and scientific papers where the answers might lie. Tropical forest dung beetles use decomposing animal matter as their food resource, both dung and carcasses, but there is nonetheless room for specialization. Perhaps different forest types would have different species, though if they do, that would raise new questions as to why. I was in Gunung Mulu because I wanted to find out which species occurred in the lowlands and which species at higher elevations, and at exactly which elevations. Which species were attracted to the fish bait, and which species came only to primate dung (guess which primate), or some other type of dung? Which species were active in the day, and which species flew only at night? In brief, I was interested in describing the biodiversity of dung beetles in Gunung Mulu and how the different species differ in their habitat use, in resource requirements, and in any other way that I might find. This would go some way toward explaining how they could coexist in Gunung Mulu, though I realized that such a description would not suffice to predict why there were just so many species, not fewer, not more. My fellow expedition members were working on similar questions with their own favored groups of plants and animals. I will recount below what I discovered about dung beetles, and what others have found about the numbers of beetles and other insects in tropical forests. Studies on tropical forest beetles are instructive about biodiversity on Earth, because beetles make up a disproportionate fraction, roughly a quarter, of all the scientifically described species of animals and plants, and because there are many more species in tropical forests than in any other ecosystem. J. B. S. Haldane, a leading evolutionary biologist of his time (he died in 1964), famously replied to a clergyman who asked what could be inferred about the mind of the Creator from the works of his creation: An inordinate fondness for beetles.

How Many Million Species?

My work in Gunung Mulu made a small contribution toward answering a very basic question about biodiversity: How many species of animals, plants, and fungi exist on our planet? It may surprise many readers that the answer is not well known; all we have are rough estimates. Before examining what researchers have found out, let us ask another seemingly simple question: What is a species? Here is another surprise: biologists have not been able to come up with a clear-cut definition of species. The reason is not incompetence