Colin Townsend obtained his DPhil at Sussex before taking up teaching positions at Oxford University and the University of East Anglia. In 1989 he moved from the UK to New Zealand, where he was appointed Chair of Zoology at the University of Otago; he is now Director of the Ecology, Conservation and Biodiversity Research Group at Otago. Excerpt. © Reprinted by permission. All rights reserved. Ecological ApplicationsToward a Sustainable World By Colin R. TownsendJohn Wiley & SonsCopyright © 2007 Colin R. TownsendAll right reserved.ISBN: 978-1-4051-3698-3Chapter OneIntroduction - humans, nature and human nature The history of the human species as global caretaker has not been good. As Homo sapiens subspecies exploitabilis we have polluted air, land and water, destroyed large areas of almost all kinds of natural habitat, overexploited living resources, transported organisms around the world with negative consequences for native ecosystems, and driven a multitude of species close to extinction. Our 'evolution' to subspecies sustainabilis needs to involve some significant behavior changes underpinned by ecological knowledge. Chapter contents 1.1 Homo not-so-sapiens? 2 1.1.1 Homo sapiens - just another species? 3 1.1.2 Human population density and technology underlie environmental impact 3 1.2 A biodiversity crisis 4 1.2.1 The scale of the biodiversity problem 6 1.2.2 Biodiversity, ecosystem function and ecosystem services 7 1.2.3 Drivers of biodiversity loss - the extinction vortex 11 1.2.4 Habitat loss - driven from house and home 12 1.2.5 Invaders - unwanted biodiversity 13 1.2.6 Overexploitation - too much of a good thing 14 1.2.7 Habitat degradation - laying waste 17 1.2.8 Global climate change - life in the greenhouse 18 1.3 Toward a sustainable future? 20 1.3.1 Ecological applications - to conserve, restore and sustain biodiversity 22 1.3.2 From an economic perspective - putting a value on nature 28 1.3.3 The sociopolitical dimension 29 Homo not-so-sapiens?Homo sapiens, the name of the most recent in a line of hominids, might well be considered a misnomer. Just how sapient (wise) has Homo sapiens been? We have certainly been clever - inventing an amazing array of tools and technologies from the wheel to the nuclear power station. But how much of the natural world has been disrupted or destroyed during this technological 'progress'? And is our way of life actually sustainable? A crunch question is whether your descendants will be able to enjoy the same opportunities as you. If not, perhaps they will judge their ancestors to have been far from wise. Humans destroy natural ecosystems to make way for urban and industrial development and to establish production ecosystems such as forestry and agriculture. We also exploit the natural world for nonrenewable resources (mining) as well as renewable ones (fisheries and forests). Mining destroys habitat directly, and fishery techniques such as bottom trawling can physically disrupt habitat. The natural ecosystems that remain are also affected by human activities. Our harvesting of species from the wild (whether trees, antelopes or fish) has often led to their decline through overexploitation. Our transport systems allow species from one part of the world to hitch a ride to another where, as 'invaders', their impacts on native biota can be profound. And every human activity, including defecation, transport, industry and agriculture, produces 'pollutants' that can adversely affect the biota locally or globally. You might imagine there would be consensus about what constitutes reasonable behavior in our interactions with the natural world. But people take a variety of standpoints and there are a host of contradictions. Farmers usually consider weeds that reduce the productivity of their crops to be a very bad thing. But conservationists bemoan the farmers' attack on weeds because these species often help fuel the activities of butterflies and birds. The Nile perch (Lates nilotica) was introduced to Africa's Lake Victoria to provide a fishery in an economically depressed region, but it has driven most of the lake's 350 endemic fish species towards extinction (Kaufman, 1992). So gains at our dinner tables can equate to a loss of biological diversity. Then again, our knowledge of plant physiology allows agricultural ecosystems to be managed intensively for maximum food production. But heavy use of fertilizers means that excess plant nutrients, particularly nitrate and phosphate, end up in rivers and lakes. Here ecosystem processes can be severely disrupted, with blooms of microscopic algae shading out waterweeds and, when the algae die and decompose, reducing oxygen and killing animals. And even in the oceans, large areas around river mouths can be so badly impacted that fisheries are lost. The farmers' gain is the fishers' loss. Pesticides, too, are applied to land but find their way to places they were not intended to be. Some pass up food chains and adversely affect local birds of prey. Others move via ocean currents and through marine food chains, damaging predators at the ends of the earth (such as polar bears and the Inuit people of the Arctic). And hundreds of kilometers downwind of large population centers, acid rain (caused by emission of oxides of nitrogen and sulfur from power generation) kills trees and drives lake fish to extinction. Ironically, in other parts of the world a new ecology is imposed in previously fishless lakes because of the introduction of fish favored by anglers. So Homo sapiens has a diversity of views and a wide variety of impacts. But are we really so different from other species? 1.1.1 Homo sapiens - just another species? Feces, urine and dead bodies of animals are sometimes sources of pollution in their environments. Thus, cattle avoid grass near their waste for several weeks, burrow-dwelling animals defecate outside their burrows, sometimes in special latrine sites, and many birds carry away the fecal sacs of their nestlings. Humans are not unique, either, in regarding corpses as pollutants to be removed. The 'undertaker' caste of honeybee, for example, recognizes dead bodies and removes them from the hive. And just like humans, many species make profound physical changes to their habitats. These 'ecological engineers' include beavers that build dams (changing a stream into a pond), prairie dogs that build underground towns and freshwater crayfish that clear sediment from the bed. In each case other species in the community are affected. The impact may be positive (for pond dwellers in the beaver ponds, for species that share the prairie dog town, for insects whose gills are sensitive to clogging by sediment) or negative (stream species, plants displaced by burrowing, insects that feed on sediment). Overexploitation, where individuals of a population are consumed faster than they can replenish themselves, is also a common feature in natural ecosystems. Sometimes overexploitation is subtle, with preferred prey species less common in the presence of their consumers - as compared to their less tasty or harder-to-catch counterparts. But overexploitation may be more dramatically demonstrated when the disappearance of top predators (such as wolves) allows herbivores (such as moose) to multiply to such an extent that the vegetation is virtually destroyed. And the appalling loss of fish species in Lake Victoria after the arrival of the 'invader' Nile perch provides a graphic example of overexploitation by one fish of others. Invaders have always been a fact of nature, when by chance some individuals breach a dispersal barrier such as a mountain range or a stretch of ocean. But some species that migrate or disperse over large distances can carry their own invaders with them - just as humans do along transport routes. Examples include diseases carried by dispersing fruits and seeds and migrating mammals and birds. The animals may also have parasites and small hitchhikers in their fur and feathers. Finally, there are species that, like farmers, increase plant nutrient concentrations in their habitats, and even some that produce 'pesticides'. Leguminous plants have root nodules containing symbiotic bacteria that fix atmospheric nitrogen into a form readily available to plants. The soil in their vicinity, and the water draining into neighboring streams, are both likely to contain higher concentrations of nitrate. And certain plants produce chemicals (allelochemicals) whose function appears to be the inhibition of growth of neighboring plants, giving the producer a competitive advantage. So humans are hardly unique in their ecological impacts. When population density was low, and before the advent of our ability to harness nonfood energy, human populations probably had no greater impact than many other species that shared our habitats. But now the scale of human effects is proportional to our huge numbers and the advanced technologies we employ. 1.1.2 Human population density and technology underlie environmental impact The expanding human population (Figure 1.1) is the primary cause of a wide variety of environmental problems. Someone has calculated that the total mass of humans is now about 100 million tonnes, in comparison to a paltry 10 million tonnes for all wild mammals combined. We are not unique in destroying habitat and contaminating the environment. But we are distinctive in using fossil fuels, water and wind power, and nuclear fission to provide energy for our activities. These technologies have provided the power to transform much of the face of the planet through urbanization, industrial development, mining, and highly intensive agriculture, forestry and fishing. The loss of habitats and the degradation of what remains are responsible for driving a multitude of species to the verge of extinction. Beavers, prairie dogs and crayfish may fundamentally alter the habitats in which they live, but the burgeoning population of Homo sapiens, with attendant technologies, has spread to every continent. The consequences are both intense and widespread, leaving few hiding places for pristine nature to thrive. Many environmental effects are caused locally, although the same patterns are repeated across the globe (pollution by fertilizers and pesticides, the spread of invaders, and so on). In one very important case, however, the scale of the problem is itself global - climate change resulting from an increase in atmospheric carbon dioxide (produced by burning fossil fuels) together with other 'greenhouse' gases. You will discover that this global pollution problem has implications for every other environmental management issue. The remainder of this chapter focuses on the scale of human impacts on biological diversity (and the consequences for human welfare - Section 1.2), as well as the knowledge that needs to be harnessed for a sustainable future (Section 1.3). This will form the backdrop to the remainder of the book where, chapter by chapter and topic by topic, I explore how ecological knowledge can be applied to remedy the problems we have caused. 1.2 A biodiversity crisis It is important to be clear about the meaning of biodiversity, and its relationship to species richness. Species richness is the total number of species present in a defined area. At its simplest, biodiversity is synonymous with species richness - and this is generally how I will use it. Biodiversity, though, can also be viewed at scales smaller (genetic diversity within species) and larger than the species (the variety of ecosystem types present - e.g. streams, lakes, grassy glades, mature forest patches). Human impacts are responsible for driving a multitude of species to such low numbers that much of the world's biodiversity is under threat. In this section I consider just how big this problem is (Section 1.2.1) before discussing the consequences of reduced biodiversity for the way that whole ecosystems function - and for the free 'services' that natural ecosystems provide us (1.2.2). A variety of processes are responsible for species extinctions (1.2.3) and the scale of each of these will be considered in turn: habitat loss (1.2.4), invaders (1.2.5), overexploitation (1.2.6), habitat degradation (1.2.7) and global climate change (1.2.8). 1.2.1 The scale of the biodiversity problem To judge the scale of the problem facing environmental managers it would be useful to know the total number of species that exist, the rate at which these are going extinct and how this rate compares with pre-human times. Not surprisingly, there are considerable uncertainties in our estimates of all these things. For example, only about 1.8 million species have so far been named, but the real number lies between 3 and 30 million. Most biodiversity specialists think it is around 10 million (Figure 1.3). Palaeontologists estimate that species exist, on average, for between 1 and 10 million years. If we accept this assumption, and taking the total number of species on earth to be 10 million, we can predict that each century between 100 (if species last 10 million years) and 1000 species will go extinct (if species last 1 million years). This represents a 'natural' extinction rate of between 0.001% and 0.01% of species per century. The current estimate of extinction of birds and mammals, the groups for which we have the best information, is about 1% per century. In other words, the current rate may be as much as 100 to 1000 times the 'natural' background rate. And when we bear in mind the number of species believed to be under threat (Box 1.1), the future rate of extinction may be more than ten times higher again (Millennium Ecosystem Assessment, 2005a). Estimates of extinction rates are beset with difficulties and most extinctions pass unnoticed. Another way to gauge the problem is to focus on long-term assessments of the population sizes of species that have not yet gone extinct. In the case of British birds it is clear that woodland species and, more particularly, farmland species have been in decline for many years (Figure 1.4a). Worldwide, amphibians (Figure 1.4b) and marine and freshwater vertebrates (Figure 1.4c) also show clear signs of widespread population declines. Consider how instructive it would be to carry out a massive experiment in which a region is allowed to completely fulfill its economic potential while simultaneously documenting the consequences for biodiversity. This decidedly 'unethical' experiment would give us a glimpse of what the world could be like if unlimited population growth and development continue indefinitely everywhere. In fact the 'experiment' has been done and, moreover, in one of the world's biodiversity hotspots in the East Asian tropics. The island of Singapore has experienced exponential population growth, from 150 villagers in the early 1800s to more than four million people as it developed into a prosperous metropolis. During this period 95% of Singapore's forest was lost, initially to make way for crops and more recently for urbanization and industrialization. Many extinctions have been documented since 1800 (Figure 1.5 - green histograms). In addition, species lists from nearby Malaysia can be used to infer the likely pristine biodiversity in Singapore and provide an estimate of the number of extinctions that have gone unrecorded (Figure 1.5 - blue histograms). It seems that the majority of the island's species from a wide range of animal and plant groups are now extinct, an unfortunate consequence of the economic 'success story' of modern Singapore. Of course, Singapore is not unique and a similar exercise would produce an equally uncomfortable result for most of the world's cities and nations. No matter how uncertain the data may be and however imprecise our knowledge of the history of Singapore, or anywhere else in the world, there is no room for complacency - population declines and increased extinction risks need to be confronted. (Continues...) Excerpted from Ecological Applicationsby Colin R. Townsend Copyright © 2007 by Colin R. Townsend. Excerpted by permission. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site. Read less
