National Academies Press: OpenBook

In the Light of Evolution: Volume II: Biodiversity and Extinction (2008)

Chapter: Part I: Contemporary Patterns and Processes in Animals

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Suggested Citation:"Part I: Contemporary Patterns and Processes in Animals." National Academy of Sciences. 2008. In the Light of Evolution: Volume II: Biodiversity and Extinction. Washington, DC: The National Academies Press. doi: 10.17226/12501.
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Page 1
Suggested Citation:"Part I: Contemporary Patterns and Processes in Animals." National Academy of Sciences. 2008. In the Light of Evolution: Volume II: Biodiversity and Extinction. Washington, DC: The National Academies Press. doi: 10.17226/12501.
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Page 2
Suggested Citation:"Part I: Contemporary Patterns and Processes in Animals." National Academy of Sciences. 2008. In the Light of Evolution: Volume II: Biodiversity and Extinction. Washington, DC: The National Academies Press. doi: 10.17226/12501.
×
Page 3
Suggested Citation:"Part I: Contemporary Patterns and Processes in Animals." National Academy of Sciences. 2008. In the Light of Evolution: Volume II: Biodiversity and Extinction. Washington, DC: The National Academies Press. doi: 10.17226/12501.
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Page 4

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  Part I CONTEMPORARY PATTERNS AND PROCESSES IN ANIMALS T here is no doubt that humans are the root cause of most ecosys- tem stresses and biotic extinctions in the modern world. Negative human pressures on biodiversity occur via pollution, introductions of alien species, overexploitation, landscape transformations, and other factors. Like the asteroid impact 65 million years ago, human impacts extend to many kinds of terrestrial, aquatic, and marine organisms. The chapters in Part I illustrate some of the challenges of quantifying the mag- nitude of extant biodiversity and deciphering extinction rates and patterns in a diverse but representative selection of contemporary animal taxa. Oceans cover three-quarters of the Earth’s surface, and their inhabit- ants might seem at first thought to be somewhat buffered (compared to terrestrial and freshwater species) against anthropogenic disturbance. However, in Chapter 1, Jeremy Jackson compiles evidence from four major marine realms—estuaries and coastal areas, continental shelves, open ocean pelagic zone, and coral reefs—that marine ecosystems are under extreme duress from the oft-synergistic effects of habitat destruc- tion, overfishing, introduced species, warming and acidification, toxins, and nutrient runoff. One common result has been the degradation of biodiverse marine ecosystems with complex food webs capped by an abundance of top-echelon predators into simplified biotic communities increasingly dominated by smaller animals, algae, and microbes. Among the many ramifications have been the economic collapse of numerous marine fisheries and massive degradation of coral reefs that formerly rivaled tropical rainforests in terms of spatial coverage and biotic richness. 

  /  Part I The data paint a disturbing picture about current and projected ecological states for the world’s oceans. In Chapter 2, David Wake and Vance Vredenburg describe a similarly gloomy scenario for the global status of amphibians. Of the approximately 6,300 extant species of frogs, salamanders, and caecilians, at least one-third are currently threatened with extinction, and many more are likely to become so in the near future. A dramatic worldwide decline in amphibian populations was first noticed in the late 1980s. Several ecological factors including habitat degradation and climatic changes probably are involved, but so too is an unanticipated, recently uncovered threat: an emerging virulent disease (chytridiomycosis) caused by a pathogenic fungus. The source of this fungus and its mode of spread are poorly understood, but the disease (perhaps in synergy with other ecological factors) has devas- tated amphibian populations in such distant sites as the Americas and tropical Australia. Whatever the proximate and ultimate causes of the ongoing amphibian extinctions, the trend is especially disturbing because amphibians otherwise have been quintessential evolutionary survivors that managed to persist across several earlier mass extinction events in the Earth’s history. Biodiverse coral reefs are among the most threatened ecological sys- tems on Earth. About 70% of coral reefs globally have either been degraded beyond recognition in recent years (20%), are in imminent danger of col- lapse (24%), or are under longer term threat of demise (26%) (Wilkinson, 2004). In Chapter 3, Marjorie Reaka and colleagues survey reef-dwelling stomatopods (a large group of marine crustaceans) as a model taxon to assess global hotspots of extant biodiversity, endemism, and extinction risk, the intent being to identify evolutionary sources and sinks of stomato- pod diversity, infer driving mechanisms, and provide an additional focus for conservation and management efforts on coral reefs. Stomatopod spe- cies diversity (like that of several other reef-dwelling marine taxa) is high- est in the Indo-Australian Archipelago, gradually declines eastward across the central Pacific, and shows a secondary peak of species richness in the southwestern Indian Ocean. From these and other data (related to body size, ecology, and spatial pattern of endemism), the authors explain how a “merry-go-round” evolutionary model might account for the differential dynamics of species origin and extinction in different ocean regions. Extinctions in the ongoing biodiversity crisis apply not only to free- living organisms but also to their parasites. In Chapter 4, Andy Dobson and colleagues address the possible magnitude of this problem by review- ing estimates of the total number of parasitic species on Earth (with special reference to helminthes that parasitize vertebrate animals) and the fraction of extant biodiversity that is parasitic. The authors conclude that about 10–15% of parasitic helminthes (Trematoda, Cestoda, Acanthocephala,

Contemporary Patterns and Processes in Animals  /   Nematoda) are at risk of extinction by virtue of being dependent on threat- ened or endangered species of vertebrate host. They also conclude that parasite species diversity does not map linearly onto host species diversity, and that approximately three-quarters of all links in food webs involve a parasitic species. These findings provide a sobering reminder that the current extinction pulse is affecting many kinds of organisms (not just the conspicuous megafauna), and that extinction processes could therefore have many unforeseen ramifications for ecosystem operations.

Next: 1 Ecological Extinction and Evolution in the Brave New Ocean--JEREMY B. C. JACKSON »
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The current extinction crisis is of human making, and any favorable resolution of that biodiversity crisis--among the most dire in the 4-billion-year history of Earth--will have to be initiated by mankind. Little time remains for the public, corporations, and governments to awaken to the magnitude of what is at stake. This book aims to assist that critical educational mission, synthesizing recent scientific information and ideas about threats to biodiversity in the past, present, and projected future.

This is the second volume from the In the Light of Evolution series, based on a series of Arthur M. Sackler colloquia, and designed to promote the evolutionary sciences. Each installment explores evolutionary perspectives on a particular biological topic that is scientifically intriguing but also has special relevance to contemporary societal issues or challenges. Individually and collectively, the ILE series aims to interpret phenomena in various areas of biology through the lens of evolution, address some of the most intellectually engaging as well as pragmatically important societal issues of our times, and foster a greater appreciation of evolutionary biology as a consolidating foundation for the life sciences.

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