Business As Usual Where Does Biodiversity Go From Here

There are «6.7 billion people in the world as we write this, a number that is projected to grow (according to a mid-range forecast) to 9.3 billion by 2050 (Population Reference Bureau, 2007). The continued growth of the human population displaces biodiversity directly, as land is developed to create living room. In one recent example, Venezuelan president Hugo Chavez aims to translocate 100,000 people into a brand new city in El Avila National Park to alleviate overcrowding in Caracas (Forero, 2007). Providing a huge global populace with the resources necessary for survival (much less comfort) also displaces biodiversity. A recent spatially explicit

332 / Paul R. Ehrlich and Robert M. Pringle analysis showed that humanity already appropriates nearly a quarter of global terrestrial net primary productivity, and up to 80% in large regional swaths (Haberl et al., 2007).

Supplying the consumption of the next 2.6 billion people will almost certainly have a greater environmental impact than supplying the last 2.6 billion added since 1975. Our species has already plucked the lowest-hanging resources and converted the richest lands. To maintain the pace, metals will have to be won from ever-poorer ores, and oil, natural gas, and water will need to be obtained from ever-deeper wells and transported farther—all requiring accelerating energy use. So-called ''marginal lands,'' often the last holdouts of biodiversity, are the final frontier, awaiting conversion into more human biomass. Whenever biodiversity preservation poses a threat to human livelihood, comfort, or convenience, the politically expedient choice is usually to liquidate the natural capital. In sum, every increment in the human population accelerates competition with other organisms for Earth's primary production. And, of course, not only do the present poor need more consumption, the present rich also demand it—as certainly will the newcomers. This is all in the face of signs that average per capita consumption is already unsustainable in developed regions (Ehrlich and Goulder, 2007), indicating a stark tradeoff between today's consumption and the basic human rights of future generations.

A major byproduct of human consumption is the toxification of Earth's ecosystems. Human agriculture and fossil-fuel combustion have multiplied the emission and deposition of nitrogen in recent decades, with negative consequences for biodiversity in grasslands (Stevens et al., 2004) and aquatic ecosystems (Carpenter et al., 1998). Widely used herbicides such as atrazine and glyphosphate harm amphibians (Hayes et al., 2002; Relyea, 2005), potentially contributing to global amphibian decline, and the use of antiinflammatory drugs such as diclofenac and ibuprofen to treat livestock in India has ravaged scavenging birds, for which cattle carcasses are a major food source (Oaks et al., 2004; Cuthbert et al., 2007).

Anthropogenic climate change stems from a special case of toxifica-tion: carbon pollution. Many biological impacts of global heating are evident, as animals and plants undergo changes in phenology, distribution, and local abundance (Parmesan, 2006). More alarming, anthropogenic heating has already been directly implicated in several extinctions (Pounds et al., 2006) and seems likely to precipitate others. In the oceans, heating is already reducing the extent and altering the structure of coral reefs via breakdown of the coral-algal symbiosis (Hughes et al., 2003). Moreover, rising CO2 concentrations are lowering oceanic pH, with potentially disastrous consequences for coral reefs and other marine ecosystems (Orr et al., 2005; Hoegh-Guldberg et al., 2007).

Direct exploitation of wildlife species by human beings takes a variety of forms, from subsistence hunting (Brashares et al., 2004) to the harvesting of wild plants and animals for conversion into luxury goods and pets (Root et al., 2006; O'Brien et al., 2003). Large mammals and fish suffer disproportionately from direct human predation. Many of these vertebrates (e.g., apex carnivores, large ungulates, etc.) are strongly interacting species in their native ecosystems (Terborgh et al., 2001; Pringle et al., 2007; Ripple and Beschta, 2007a; Palmer et al., 2008), and overharvesting them may have destabilizing effects on biodiversity and ecological processes such as seed dispersal, nutrient cycling, and even primary production. In oceans, top piscivores suffer disproportionately as fleets fish down the food web (Pauly et al., 1998). Industrialized fisheries have often devastated community biomass of predatory fish within a few decades (Myers and Worm, 2003), with even sharper declines common among the apex predators (Baum and Myers, 2004).

Nonnative species introduced by people into naive ecosystems have occasionally wrought havoc on local biodiversity via predation, competition, and the disruption of co-evolved interactions. Biotic interchange is likely to increase with increasing mobility in an increasingly globalized world; under business as usual, biogeography will be increasingly homogeneous.

A cryptic yet critical threat to biodiversity is the loss of future evolutionary potential. Extinction of genetically distinct populations, decreases in effective population sizes, and homogenization of habitat types are all likely to have negative effects on future biodiversity (Myers and Knoll, 2001; Woodruff, 2001). The positive relationship between speciation rate and habitat area (Losos and Schluter, 2000) indicates that decreases in species geographic ranges will diminish future speciation rates, which in turn will impoverish future diversity (Rosenzweig, 2001). Speciation of large vertebrates, which are highly mobile and require large habitats, may cease entirely (Woodruff, 2001), and biodisparity—the range of morphological and physiological variety on Earth—will decrease as phylogenetically distinct, species-poor branches are pruned from the tree of life (Jablonski, 1995).

Loss of microevolutionary potential will also limit the capacity of populations to adapt to changing environmental conditions, highlighting another important point: The drivers of biodiversity loss will often act synergistically in imperiling populations and species. Habitat loss and fragmentation compound the effects of climate change, as species are unable to track their thermal niches spatially (Travis, 2003). The interactions among logging, fire, and climate change threaten to transform the Amazon rainforest into savanna (Oyama and Nobre, 2003; Terborgh, 2007). Such positive feedbacks seem to be a rule, rather than an excep-

334 / Paul R. Ehrlich and Robert M. Pringle tion, and they make it impossible to generate precise estimates of future biodiversity.

In short, although there are many uncertainties about the trajectories of individual populations and species, we know where biodiversity will go from here in the absence of a rapid, transformative intervention: up in smoke; toward the poles and under water; into crops and livestock; onto the table and into yet more human biomass; into fuel tanks; into furniture, pet stores, and home remedies for impotence; out of the way of more cities and suburbs; into distant memory and history books. As biodiversity recedes, we also lose the stories that go with it and many ways of relating to the world in which we evolved.

We now consider what might happen if humanity changes the way it does business. Ours is not a comprehensive treatment of this issue. The Millennium Ecosystem Assessment (2005a) contains a thorough and colorful summary of the state of biodiversity, and it provides important (and necessarily overarching) recommendations for softening human impact on ecosystems—things like increasing governmental accountability, eliminating environmentally malign subsidies, and reducing greenhouse-gas emissions. However, the breadth and complexity of these objectives, and the considerable political clout required to enact them, can engender the misconception that only governments can determine where biodiversity goes from here. That misconception, in turn, is a recipe for paralysis among concerned individuals. Therefore, we try to focus more narrowly on seven more-or-less concrete sets of actions that individuals or small groups have already set in motion. If implemented more broadly and scaled up dramatically, these actions would collectively enable a different, more appealing fate for biodiversity.

Although each of the following strategies is being used somewhere, none is yet realizing its full potential. Some may not be achievable in all times and places, but none is exclusive of any other. Most of these strategies are familiar to most people in the conservation community; the notion that they are all ''correct'' ways to conserve biodiversity is perhaps less so. Indeed, squabbles over strategy are endemic within the conservation community, perhaps because different strategies are seen as competing for funding and for primacy in the scholarly idea-scape. The alacrity with which international conservation nongovernmental organizations have ''branded'' themselves (Rodriguez et al., 2007) and the sometimes absurdly acrimonious exchanges between conservation academics seem to manifest a widespread ''either-or'' belief that there are absolutely right and wrong ways to protect biodiversity (Wiens, 2007b). Ostrom et al. (2007), in a recent PNAS Special Feature, wrote of the need ''to go beyond relying on abstract cure-all proposals for solving complex problems related to achieving sustainable social-ecological systems.'' By emphasizing a portfolio of partial solutions, we hope to reinforce the idea that maximizing future biodiversity will require a plurality of approaches in creative admixtures that are tailored to local realities. Each place needs a different mixture.

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