Luke Gibson

Primary forests are irreplaceable for sustaining tropical biodiversity

Human-driven land-use changes increasingly threaten biodiversity, particularly in tropical forests where both species diversity and human pressures on natural environments are high. The rapid conversion of tropical forests for agriculture, timber production and other uses has generated vast, human-dominated landscapes with potentially dire consequences for tropical biodiversity. Today, few truly undisturbed tropical forests exist, whereas those degraded by repeated logging and fires, as well as secondary and plantation forests, are rapidly expanding. Here we provide a global assessment of the impact of disturbance and land conversion on biodiversity in tropical forests using a meta-analysis of 138 studies. We analysed 2,220 pairwise comparisons of biodiversity values in primary forests (with little or no human disturbance) and disturbed forests. We found that biodiversity values were substantially lower in degraded forests, but that this varied considerably by geographic region, taxonomic group, ecological metric and disturbance type. Even after partly accounting for confounding colonization and succession effects due to the composition of surrounding habitats, isolation and time since disturbance, we find that most forms of forest degradation have an overwhelmingly detrimental effect on tropical biodiversity. Our results clearly indicate that when it comes to maintaining tropical biodiversity, there is no substitute for primary forests.

Near-Complete Extinction of Native Small Mammal Fauna 25 Years After Forest Fragmentation

Futile Forest Fragments Most of the planets terrestrial biodiversity is found in tropical forests, but much of this critical habitat now persists as fragmented patches surrounded by agriculture. Smaller forest patches sustain fewer species than larger patches or contiguous forest. However, the numbers of species that will disappear from a forest fragment—and the rate of species loss—remain poorly understood. Gibson et al. (p. 1508) surveyed islands in a reservoir in Thailand to measure the rate of loss of small mammals from small forest fragments. Collapse of the entire native community (up to 12 species) from 16 forest fragments was observed after 25 years of isolation. Thus, small forest fragments hold little value for mammalian biodiversity, and conservation efforts should instead focus on the preservation of large forest expanses. The rapid loss of native mammals from isolated Thai forests suggests that forest fragments cannot maintain biodiversity. Tropical forests continue to be felled and fragmented around the world. A key question is how rapidly species disappear from forest fragments and how quickly humans must restore forest connectivity to minimize extinctions. We surveyed small mammals on forest islands in Chiew Larn Reservoir in Thailand 5 to 7 and 25 to 26 years after isolation and observed the near-total loss of native small mammals within 5 years from <10-hectare (ha) fragments and within 25 years from 10- to 56-ha fragments. Based on our results, we developed an island biogeographic model and estimated mean extinction half-life (50% of resident species disappearing) to be 13.9 years. These catastrophic extinctions were probably partly driven by an invasive rat species; such biotic invasions are becoming increasingly common in human-modified landscapes. Our results are thus particularly relevant to other fragmented forest landscapes and suggest that small fragments are potentially even more vulnerable to biodiversity loss than previously thought.

Conservation successes at micro-, meso- and macroscales

Although large-scale biodiversity declines are ongoing, certain conservation actions have made a positive difference. Rates of extinction and endangerment of vertebrate species, for instance, have probably been reduced via conservation interventions. Such conservation actions operate at different spatial scales. Habitat preservation and endangered species recovery are examples of conservation successes at microscales. Mesoscale conservation includes regional cooperation among neighboring countries that has arrested population declines of endangered species, such as mountain gorillas. At macroscales, public pressure on multinational corporations has sometimes resulted in their abandoning environmentally damaging practices or suppliers with poor environmental records. Overall, conservation projects such as these need more long-term funding and greater political and popular support, and must also include provisions to evaluate and document their outcomes. As we discuss here, a focus on conservation successes achieved at different scales can help to promote these aims and guide future conservation victories.

Possible shift in macaque trophic level following a century of biodiversity loss in Singapore

Biodiversity loss in tropical forests is a major problem in conservation biology, and nowhere is this more dire than in Southeast Asia. Deforestation and the associated loss of species may trigger shifts in habitat and feeding preferences of persisting species. In this study, I compared the habitat use and diet of long-tailed macaque (Macaca fascicularis) populations in Singapore from two time periods: museum specimens originally collected between 1893 and 1944, and living macaques sampled in 2009. I collected hair and used stable carbon and nitrogen isotope analysis to identify temporal changes in dietary source and trophic position, respectively. δ13C ratios were virtually identical, suggesting that macaques foraged in similar habitats during both time periods. However, δ15N ratios decreased considerably over time, suggesting that macaques today feed at a lower trophic level than previously. This decline in trophic level may be because of the disappearance or decline of other species that compete with macaques for fruit. This study highlights the effect of biodiversity loss on persisting species in degraded habitats of Southeast Asia, and improves our understanding of how species will adapt to further human-driven changes in tropical forest habitats.

The role of lethal control in managing the effects of apparent competition on endangered prey species

Abstract Apparent competition is the process by which one prey species may indirectly cause the decline in another species by sustaining a common predator. I argue apparent competition caused Sierra Nevada bighorn sheep (Ovis canadensis californiana) and Channel Island fox (Urocyon littoralis) population declines in the mid-1990s. In the Sierra Nevada, mountain lions (Puma concolor) are believed to have caused bighorns to abandon their winter ranges, thus indirectly contributing to population declines. In the Channel Islands, golden eagle (Aquila chrysaetos) predation is thought to have reduced 3 resident fox populations by over 95%. I argue, in both cases, native predators are the primary cause of the declines. Additionally, I argue these predators are primarily sustained by hyperabundant alternative prey species. In such cases direct management, to include lethal control of predators and hyperabundant alternative prey, may be necessary to restore these endangered bighorn and fox populations.

Biodiversity state and trends in Southeast Asia

Southeast Asia, which encompasses four biodiversity hotspots (Indo-Burma, Sundaland, the Philippines, and Wallacea), is a region of remarkably high biodiversity. Much of the regions flora and fauna is not found elsewhere in the world (endemic). Unfortunately, this region has been experiencing widespread and rapid deforestation and forest degradation over the last few decades, driven primarily by industrial agriculture, such as oil palm development. In this article, the authors discuss the status of key natural ecosystems and taxonomic groups. Additionally, they highlight the major threats to biodiversity as well as the challenges and opportunities for conservation in this region.

Conservation biology : voices from the tropics

Effective long term conservation in the tropics requires the full participation of local people, organizations and governments. The human population of tropical countries is expected to grow by more than 2.5 billion people over the next several decades, with expectations of increased consumption levels growing even more rapidly than population levels; clearly there will be a need for more trained conservationists and biologists. Significant levels of local involvement are essential to conservation success, with the rights of local people fully recognized, protected and fostered by governmental and international assistance. Overarching conservation plans are necessary, but cannot in themselves lead to success.

Homage to an avant-garde conservation leader, Navjot Sodhi

[Abstract] The unconventional Professor Navjot Singh Sodhi of the National University of Singapore died on 12 June 2011 of a particularly aggressive form of lymphoma and associated organ failure. He had been diagnosed only a few weeks before. The shock and suddenness of his loss reverberated through the conservation-biology community at lightning speed, aided by email lists and social media (e.g., a Facebook tribute page was posted within hours of his death). He was only 49 years old and still at the peak of a brilliant scientific career.

Habitats at risk: a step forward, a step back.

THE EFFECT OF ENVIRONMENTAL EXPOSURES ON HUMAN HEALTH IS A GROWING AREA OF concern. The number of new chemicals is increasing exponentially, with approximately 12,000 new substances added daily to the American Chemical Society’s CAS registry (1). Although only a portion of these chemicals are introduced into the environment, data on the hazard posed by even high–production volume (HPV) chemicals (those with a production volume exceeding 1000 tons/year) are available for only a fraction of the HPV chemicals produced or imported into the United States. Currently, the EPA and FDA are charged with safeguarding the health of Americans. This is a daunting task that is hampered by the growing recognition that currently accepted testing paradigms and government review practices are inadequate for chemicals with hormone-like actions. The need for swifter and sounder testing and review procedures cannot be overstated. Recent scientifi c evidence has established direct links between exposures that occur during fetal development and adult disease [e.g., (2, 3)]. Data from the U.S. Centers for Disease Control and Prevention have established clearly that most, if not virtually all Americans, are exposed to contaminants in the environment that cause serious health effects in animal models [e.g., (4, 5)]. Direct links to humans remain uncertain, but there is suffi cient experimental evidence to raise concern. Furthermore, there is growing evidence that some chemicals once thought to be safe and allowed into common and, in some cases, abundant commercial use may not be as benign as previously assumed (4, 5). Although chemical testing and risk assessment have long been the domain of toxicologists, it is clear that the development of improved testing guidelines and better methods of assessing risks posed by common chemicals to which all Americans are exposed requires the expertise of a broad range of scientifi c and clinical disciplines. Collectively, our societies represent approximately 40,000 research scientists and clinicians. The membership of our societies represents leaders in the fi elds of reproductive biology, endocrinology, reproductive medicine, genetics, and developmental biology. As concerned scientists and clinicians, we are writing to offer the expertise of our collective societies. Specifi cally, we offer the expertise of the Boards of Directors for our societies for the purpose of naming appropriate individuals to serve on panels to review and evaluate current programs for effectiveness, to assess the risk of specifi c chemicals through the evaluation of data, and to develop new testing guidelines and protocols. We recognize that the FDA and EPA face challenges on many fronts, and we believe that the vast expertise available through the members of our societies can aid both agencies in achieving their goals. Thus, we ask that you use our scientifi c boards to provide access to leading scientists in diverse fi elds. These experts can help ensure that the most up-to-date scientifi c methodology and scientific understanding are used when devising and refi ning regulatory guidelines, and when reviewing scientifi c data pertinent to risk assessment and risk management decisions.

Land-Use Change Alters Host and Vector Communities and May Elevate Disease Risk

Land-use change has transformed most of the planet. Concurrently, recent outbreaks of various emerging infectious diseases have raised great attention to the health consequences of anthropogenic environmental degradation. Here, we assessed the global impacts of habitat conversion and other land-use changes on community structures of infectious disease hosts and vectors, using a meta-analysis of 37 studies. From 331 pairwise comparisons of disease hosts/vectors in pristine (undisturbed) and disturbed areas, we found a decrease in species diversity but an increase in body size associated with land-use changes, potentially suggesting higher risk of infectious disease transmission in disturbed habitats. Neither host nor vector abundance, however, changed significantly following disturbance. When grouped by subcategories like disturbance type, taxonomic group, pathogen type and region, changes in host/vector community composition varied considerably. Fragmentation and agriculture in particular benefit host and vector communities and therefore might elevate disease risk. Our results indicate that while habitat disturbance could alter disease host/vector communities in ways that exacerbate pathogen prevalence, the relationship is highly context-dependent and influenced by multiple factors.