David S. Wilcove

QUANTIFYING THREATS TO IMPERILED SPECIES IN THE UNITED STATES

Biologists are nearly unanimous in their belief that humanity is in the process of extirpating a significant portion of the earths spexad cies. The ways in which we are doing so reflect the magnitude and scale of human enterprise. Everything from highway construction to cattle ranchxad ing to leaky bait buckets has been implicated in the demise or endanxad germent of particular species. Acxad cording to Wilson (1992), most of these activities fall into four major categories, which he terms the mindxad less horsemen of the environmental apocalypse: overexploitation, habixad tat destruction, the introduction of non-native (alien) species, and the spread of diseases carried by alien species. To these categories may be added a fifth, pollution, although it can also be considered a form of habitat destruction. Surprisingly, there have been reIaxad tively few analyses of the extent to which each of these factors-much less the more specific deeds encomDavid S. Wilcove is a senior ecologist at the Environmental Defense Fund, Washxad ington, DC 20009. David Rothstein rexad ceived his J.D. in 1997 from Northeastern

Going, going, gone: is animal migration disappearing.

Many of the worlds migratory animals are in decline. This essay explores the unique scientific and political challenges of protecting migratory species while they are still common.

Simple rules guide dragonfly migration

Every year billions of butterflies, dragonflies, moths and other insects migrate across continents, and considerable progress has been made in understanding population-level migratory phenomena. However, little is known about destinations and strategies of individual insects. We attached miniaturized radio transmitters (ca 300u200amg) to the thoraxes of 14 individual dragonflies (common green darners, Anax junius) and followed them during their autumn migration for up to 12 days, using receiver-equipped Cessna airplanes and ground teams. Green darners exhibited distinct stopover and migration days. On average, they migrated every 2.9±0.3 days, and their average net advance was 58±11u200akm in 6.1±0.9 days (11.9±2.8u200akmu200ad−1) in a generally southward direction (186±52°). They migrated exclusively during the daytime, when wind speeds were less than 25u200akmu200ah−1, regardless of wind direction, but only after two nights of successively lower temperatures (decrease of 2.1±0.6u200a°C in minimum temperature). The migratory patterns and apparent decision rules of green darners are strikingly similar to those proposed for songbirds, and may represent a general migration strategy for long-distance migration of organisms with high self-propelled flight speeds.

Persistence of Large Mammal Faunas as Indicators of Global Human Impacts

Abstract Large mammals often play critical roles within ecosystems by affecting either prey populations or the structure and species composition of surrounding vegetation. However, large mammals are highly vulnerable to extirpation by humans and consequently, severe contractions of species ranges result in intact large mammal faunas becoming increasingly rare. We compared historical (AD 1500) range maps of large mammals with their current distributions to determine which areas today retain complete assemblages of large mammals. We estimate that less than 21% of the earths terrestrial surface still contains all of the large (>20 kg) mammals it once held, with the proportion varying between 68% in Australasia to only 1% in Indomalaya. Although the presence of large mammals offers no guarantee of the presence of all smaller animals, their absence represents an ecologically based measurement of human impacts on biodiversity. Given the ecological importance of large mammals and their vulnerability to extinction, better protection and extension of sites containing complete assemblages of large mammals is urgently needed.

The geography of vulnerability: incorporating species geography and human development patterns into conservation planning

Abstract In any country, the geography of species needing protection is central to the development of conservation strategies. In this study we mapped the distribution of restricted-range birds and butterflies not listed as threatened or endangered under the Endangered Species Act in the conterminous United States, as well as measures of projected increases in human population and development. Areas with both restricted-range species and high growth rates were identified as “hot spots of vulnerability”xa0— areas vulnerable to future species loss. These hot spots of vulnerability corresponded to many of the areas currently supporting large numbers of endangered species in the United States. Many of the restricted-range species identified, however, have existing ranges in Mexico and Central and South America. The conservation of these peripheral populations in the United States becomes even more important given that adjacent countries do not have legislation that protects endangered species. The methodology we present here could be used in other countries to identify species and areas of vulnerability before they become endangered.

Grand Challenges in Migration Biology

Abstract Billions of animals migrate each year. To successfully reach their destination, migrants must have evolved an appropriate genetic program and suitable developmental, morphological, physiological, biomechanical, behavioral, and life-history traits. Moreover, they must interact successfully with biotic and abiotic factors in their environment. Migration therefore provides an excellent model system in which to address several of the “grand challenges” in organismal biology. Previous research on migration, however, has often focused on a single aspect of the phenomenon, largely due to methodological, geographical, or financial constraints. Integrative migration biology asks ‘big questions’ such as how, when, where, and why animals migrate, which can be answered by examining the process from multiple ecological and evolutionary perspectives, incorporating multifaceted knowledge from various other scientific disciplines, and using new technologies and modeling approaches, all within the context of an annual cycle. Adopting an integrative research strategy will provide a better understanding of the interactions between biological levels of organization, of what role migrants play in disease transmission, and of how to conserve migrants and the habitats upon which they depend.

Forest fragmentation in the temperate zone and its effects on migratory songbirds

Summary Although much attention has been paid to the impacts of tropical deforestation on populations of Neotropical migrants, fragmentation of breeding habitat may be an equally serious problem for many of these birds. Populations of many migrant songbirds have been declining in recent decades, especially within small woodlots. Censuses from woodlots of different sizes also consistently show that many migrant songbirds are area-sensitive, i.e. they are absent from all but the largest woodlots in a region. In contrast, long-term censuses from large, unfragmented forests show few consistent patterns of decline in Neotropical migrants. Population declines are therefore linked to forest fragmentation because they are most pronounced in small, isolated woodlots. Fragmentation leads to significant increases in nest predation and cowbird Molothrus spp. parasitism, the two most important causes of population declines and area-sensitivity. Predation and nest-parasitism rates are higher in small woodlots and along the edges of larger tracts than in the interior of large tracts. Data from fragmented forests in the American Midwest show that reproductive rates of several forest species are probably well below levels necessary to compensate for adult mortality. Among Wood Thrushes Hylocichla mustelina nesting in central and southern Illinois, for example, 89-100% of nests contain cowbird eggs (average of 2.2-4.6 cowbird eggs/nest) and nest-predation rates range from 50 to 96%. For the Wood Thrush and other forest songbirds, fragmented landscapes may be population sinks with populations sustained by immigration from larger, unfragmented forest tracts. These data emphasize the importance of protecting large, unfragmented forests for breeding habitat. We need far better data on dispersal rates and distances, fecundity and survival rates before we can determine what levels of predation and parasitism migratory birds can tolerate. The effects of silvicultural practices such as clear-cutting and selective logging on migratory songbirds may depend upon the landscape context. Preliminary evidence from a fragmented national forest in the Midwest suggests that selective logging can have relatively little impact on forest songbirds. We tentatively propose that low-volume selective logging be used as an alternative to clear-cutting. Logging roads should be closed and revegetated soon after harvest, and rotation times should be lengthened to permit regeneration of large, old trees.

Strengthening the Use of Science In Achieving the Goals of the Endangered Species Act: An Assessment By the Ecological Society of America

The Ecological Society of America is the nations leading professional society of ecologists representing 7500 ecological researchers in the United States, Canada, Mexico, and 62 other nations. Founded in 1915, ESA seeks to promote the responsible application of ecological principles to the solution of environmental problems through ESA reports, journals, research, and expert testimony to Congress. In March of 1992, then President of the Ecological Society of America, H. Ronald Pulliam, established an Ecological Society of America ad hoc Committee on Endangered Species. The primary charge to this committee, made up of nine distinguished ecologists, was to produce a report addressing the ecological issues relevant to reauthorization of the Endangered Species Act. The Societys goal in this endeavor was to provide legislators with scientifically credible information. The Ecological Society of America has produced other reports focusing on possible ecological consequences of the release of genetically modified organisms, delineation of wetlands, and ecological research priorities. These reports have been favorably received and viewed as credible because of the Ecological Societys reputation and because the reports focused on science in a policy context. The following document is based on an exhaustive effort on the part of the ad hoc Committee that included soliciting comments on earlier drafts from some 30 academic, public, and private agency biologists, open discussions on the topic during annual meetings of the Ecological Society of America, and external review by 20 other biological scientists. It is our hope that this report will prove useful as Congress considers reauthorization of the Endangered Species Act. I For a copy of the report or further information contact: The Ecological Society of America, 2010 Massachusetts Avenue, NW, Suite 400, Washington, DC 20036. Ph: (202) 8338773; Fax: (202) 833-8775.

Oil palm: disinformation enables deforestation

In a recent article in Trends in Ecology and Evolution, Fitzherbert et al. [1] discuss the exponential expansion of oil palm (Elaeis guineensis) agriculture. The article sounds a warning call about the potential impacts of oil palm expansion on tropical forests and biodiversity, particularly in Malaysia and Indonesia; this concern is shared by many environmentalists and concerned scientists [2,3]. However, in spite of efforts by conservationists to curtail deforestation due to oil palm, the global market for palm oil continues to expand.

Threats to Vertebrate Species in China and the United States

Abstract We analyzed the threats to imperiled vertebrate species in China and compared our results with those from a similar study conducted in the United States. Overexploitation is the most pervasive threat to Chinese vertebrates, contributing to the endangerment of 78% of imperiled species, followed by habitat destruction (70%), pollution (20%), alien species (3%), and disease (< 1%). Harvest for food and use in traditional Chinese medicines are the two main forms of overexploitation, while logging is the most pervasive form of habitat destruction. Threats to vertebrate species are strikingly different in the United States, where habitat destruction affects 92% of imperiled vertebrate species, followed by alien species (47%), pollution (46%), overexploitation (27%), and disease (11%). The greater frequency of overexploitation in China stems from Chinas larger, poorer, and more rural population, along with widespread trade in wildlife products. The apparent lower frequency of alien species in China may reflect neglect of this issue by Chinese scientists.