onto ecosystem functioning and human well-being. Much remains unknown about 28 this "Anthropocene defaunation"; these knowledge gaps hinder our capacity to 29 predict and limit defaunation impacts. Clearly, however, defaunation is both a 30 pervasive component of the planet's sixth mass extinction, and also a major driver of 31 global ecological change. 32 33In the past 500 years, humans have triggered a wave of extinction, threat, and local 34 population declines that may be comparable in both rate and magnitude to the five 35 previous mass extinctions of Earth's history (1). Similar to other mass extinction events, 36 the effects of this "sixth extinction wave" extend across taxonomic groups, but are also 37 selective, with some taxonomic groups and regions being particularly affected (2). Here, 38we review the patterns and consequences of contemporary anthropogenic impact on 39 terrestrial animals. We aim to portray the scope and nature of declines of both species and 40 abundance of individuals, and examine the consequences of these declines. So profound 41 is this problem, that we have applied the term defaunation to describe it. This recent pulse 42 of animal loss, hereafter referred to as the Anthropocene defaunation, is not only a 43 conspicuous consequence of human impacts on the planet, but also a primary driver of 44 global environmental change in its own right. In comparison, we highlight the profound 45 ecological impacts of the much more limited extinctions, predominantly of larger 46vertebrates, that occurred during the end of the last Ice Age. These extinctions altered 47 ecosystem processes and disturbance regimes at continental scales, triggering cascades of 48 extinction thought to still reverberate today (3, 4). 49The term defaunation, used to denote the loss of both species and populations of 50 wildlife (5), as well as local declines in abundance of individuals, needs to be considered 51 in the same sense as deforestation, a term that is now readily recognized and influential in 52 focusing scientific and general public attention on biodiversity issues (5). However, 53 whilst remote sensing technology provides rigorous quantitative information and 54 compelling images of the magnitude, rapidity and extent of patterns of deforestation, 55 defaunation remains a largely cryptic phenomenon. It can occur even in large protected 56 habitats (6) and, yet, some animal species are able to persist in highly modified habitats, 57 making it difficult to quantify without intensive surveys. 58Analyses of the impacts of global biodiversity loss typically base their 59 conclusions on data derived from species extinctions (1, 7, 8) and typically evaluations of 60 the effects of biodiversity loss draw heavily from small scale manipulations of plants and 61 small sedentary consumers (9). Both of these approaches likely underestimate the full 62 impacts of biodiversity loss. While species extinctions are of great evolutionary 63 significance, declines in the number of individuals in local populations and chan...
Terrestrial mammals are experiencing a massive collapse in their population sizes and geographical ranges around the world, but many of the drivers, patterns and consequences of this decline remain poorly understood. Here we provide an analysis showing that bushmeat hunting for mostly food and medicinal products is driving a global crisis whereby 301 terrestrial mammal species are threatened with extinction. Nearly all of these threatened species occur in developing countries where major coexisting threats include deforestation, agricultural expansion, human encroachment and competition with livestock. The unrelenting decline of mammals suggests many vital ecological and socio-economic services that these species provide will be lost, potentially changing ecosystems irrevocably. We discuss options and current obstacles to achieving effective conservation, alongside consequences of failure to stem such anthropogenic mammalian extirpation. We propose a multi-pronged conservation strategy to help save threatened mammals from immediate extinction and avoid a collapse of food security for hundreds of millions of people.
The modern process of defaunation can be alarmingly obvious or surprisingly cryptic, depending on the scale examined. It is thus important to distinguish three interrelated spatial scales of defaunation. 3.1.1. Global extinction. At a global scale, human-associated extinction of animal life on the planet is profound. Modern rates of vertebrate extinctions have been estimated to be up to 100 times greater than the most conservative background rates of ∼2 vertebrate extinctions per million species per year (Ceballos et al. 2015). Although most of the extinctions to date have been documented in terrestrial ecosystems (e.g., 338 vertebrates since the year 1500) (IUCN 2015), the highest proportion of extinctions has been recorded in freshwater ecosystems (Collen et al. 2014). Marine ecosystems, by comparison, lag much further behind, with only ∼15 marine animal extinctions recorded during this same time period (McCauley et al. 2015b). Regarding invertebrates, information on global extinctions (or defaunation in general) is very limited (Supplemental Figure 1; follow the Supplemental Material link from the Annual Reviews home page at http://www.annualreviews.org), but recent efforts on the levels of threat to species in the International Union for Conservation of Nature (IUCN) Red List (Collen et al. 2012) provide some insights. Of the 3,623 terrestrial invertebrate species assessed on the Red List, 42% are classified as threatened with extinction. Of the 1,306 species of marine invertebrates on the Red List, close to 25% are threatened with extinction. Finally, of the 7,784 species of freshwater invertebrates on the Red List, 34% are listed as threatened, but the Red List includes 131 species classified as extinct. Invertebrates, however, are the least well evaluated faunal groups within the IUCN database, making it challenging to determine precisely the risks faced by data-deficient and unreviewed species (Dirzo et al. 2014, McCauley et al. 2015b).
Control of human infectious disease has been promoted as a valuable ecosystem service arising from the conservation of biodiversity. There are two commonly discussed mechanisms by which biodiversity loss could increase rates of infectious disease in a landscape. First, loss of competitors or predators could facilitate an increase in the abundance of competent reservoir hosts. Second, biodiversity loss could disproportionately affect non-competent, or less competent reservoir hosts, which would otherwise interfere with pathogen transmission to human populations by, for example, wasting the bites of infected vectors. A negative association between biodiversity and disease risk, sometimes called the "dilution effect hypothesis," has been supported for a few disease agents, suggests an exciting win-win outcome for the environment and society, and has become a pervasive topic in the disease ecology literature. Case studies have been assembled to argue that the dilution effect is general across disease agents. Less touted are examples in which elevated biodiversity does not affect or increases infectious disease risk for pathogens of public health concern. In order to assess the likely generality of the dilution effect, we review the association between biodiversity and public health across a broad variety of human disease agents. Overall, we hypothesize that conditions for the dilution effect are unlikely to be met for most important diseases of humans. Biodiversity probably has little net effect on most human infectious diseases but, when it does have an effect, observation and basic logic suggest that biodiversity will be more likely to increase than to decrease infectious disease risk.
Abstract. Large predators are often highly mobile and can traverse and use multiple habitats. We know surprisingly little about how predator mobility determines important processes of ecosystem connectivity. Here we used a variety of data sources drawn from Palmyra Atoll, a remote tropical marine ecosystem where large predators remain in high abundance, to investigate how these animals foster connectivity. Our results indicate that three of Palmyra's most abundant large predators (e.g., two reef sharks and one snapper) use resources from different habitats creating important linkages across ecosystems. Observations of cross-system foraging such as this have important implications for the understanding of ecosystem functioning, the management of large-predator populations, and the design of conservation measures intended to protect whole ecosystems. In the face of widespread declines of large, mobile predators, it is important that resource managers, policy makers, and ecologists work to understand how these predators create connectivity and to determine the impact that their depletions may be having on the integrity of these linkages.
Large mammalian herbivores (LMH) strongly influence plant communities, and these effects can propagate indirectly throughout food webs. Most existing large-scale manipulations of LMH presence/absence consist of a single exclusion treatment, and few are replicated across environmental gradients. Thus, important questions remain about the functional roles of different LMH, and how these roles depend on abiotic context. In September 2008, we constructed a series of 1-ha herbivore-exclusion plots across a 20-km rainfall gradient in central Kenya. Dubbed "UHURU" (Ungulate Herbivory Under Rainfall Uncertainty), this experiment aims to illuminate the ecological effects of three size classes of LMH, and how rainfall regimes shape the direction and magnitude of these effects. UHURU consists of four treatments: total-exclusion (all ungulate herbivores), mesoherbivore-exclusion (LMH >120-cm tall), megaherbivore-exclusion (elephants and giraffes), and unfenced open plots. Each treatment is replicated three times at three locations (“sites”) along the rainfall gradient: low (440 mm/year), intermediate (580 mm/year), and high (640 mm/year). There was limited variation across sites in soil attributes and LMH activity levels. Understory-plant cover was greater in plots without mesoherbivores, but did not respond strongly to the exclusion of megaherbivores, or to the additional exclusion of dik-dik and warthog. Eleven of the thirteen understory plant species that responded significantly to exclusion treatment were more common in exclusion plots than open ones. Significant interactions between site and treatment on plant communities, although uncommon, suggested that differences between treatments may be greater at sites with lower rainfall. Browsers reduced densities of several common overstory species, along with growth rates of the three dominant Acacia species. Small-mammal densities were 2–3 times greater in total-exclusion than in open plots at all sites. Although we expect patterns to become clearer with time, results from 2008–2012 show that the effects of excluding successively smaller-bodied subsets of the LMH community are generally non-additive for a given response variable, and inconsistent across response variables, indicating that the different LMH size classes are not functionally redundant. Several response variables showed significant treatment-by-site interactions, suggesting that the nature of plant-herbivore interactions can vary across restricted spatial scales.
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