Endangered Ecosystems Raymond C Nias, TierraMar Consulting, Sutherland, NSW, Australia r 2013 Elsevier Inc All rights reserved This article is a revision of the previous edition article by Raymond C Nias and John R Mooney, pp 1–15, r 2001, Elsevier Inc Glossary Biodiversity hotspots A region that contains at least 1500 species of vascular plants (40.5% of the world’s total) as endemics and has lost at least 70% of its original habitat Conservation status A classification of species and ecosystems according to their extinction risk; such as vulnerable, endangered, and critically endangered Ecoregion A relatively large area of land or water that contains characteristic, geographically distinct assemblages of natural communities, and species The article outlines recent progress in the development of systematic approaches to the identification of the world’s ecosystems and their conservation status A synopsis is given of how from the mid-1990s through to the present conservation biologists and practitioners have been devising more explicit classifications systems for ecosystem types that has allowed for the identification and mapping of terrestrial, freshwater, and marine ecosystems from the global to local scale Summaries are provided of these studies as well as recent progress in developing a new and more systematic approach to the classification of extinction-risk for ecosystems In addition to overall trends derived from global assessments some examples are provided of globally significant ecosystems considered to be endangered Defining Ecosystems and their Conservation Status In contrast to the situation with threatened species, the definition of an ecosystem as a ‘‘unit of conservation concern’’ has been problematic Difficulties with the identification of distinct ecosystems and what constitutes the extinction of an ecosystem have hampered attempts to develop objective criteria for categorization of ecosystems and their conservation status The definition of an ecosystem as ‘‘a dynamic complex of plant, animal, and microorganism communities and their nonliving environment interacting as a functional unit’’ (Convention on Biological Diversity, http://www.cbd.int/ convention/text/) for example, does not define any specific dimensions or boundaries At the smallest scale there are ecosystems of invertebrates and microbes that exist within a few liters of water or a few kilograms of soil In fact each ecosystem is nested within a larger ecosystem up to the scale of the biosphere which can be considered as a single planetary ecosystem Apart from the question of scale, ecosystems are also dynamic, with many natural changes both in areal extent and composition occurring over time In aquatic ecosystems, for example, the area covered will fluctuate with changing Encyclopedia of Biodiversity, Volume Ecosystem composition The species or functional groups of organisms found within a given ecosystem Ecosystem function The biological and chemical processes that occur within ecosystems such as primary production and nutrient cycling Ecosystem structure The different trophic (feeding) levels within an ecosystem and the interactions between them Extinction risk The likelihood of extinction of a species with specific demographic characteristics and distribution under various threatening processes over time water levels, floods, and tides and entire ecosystems such as ephemeral wetlands may come and go in the space of a few months Terrestrial ecosystems are typically defined by their major vegetation type such as moist broad-leaved (tropical) forest or lowland temperate grasslands, but may also be characterized by unique physical features such as particular geological substrates (e.g., lime-stone-based karst ecosystems) In the marine environment ecosystems may be defined geographically and also by particular attributes of water temperature or chemistry, or by the characteristics of the substrate (e.g., rocky, sandy, or muddy bottoms) Specific plant and animal communities such as seagrass beds, kelp forests, and coral reefs may also form part of the definition of a particular marine ecosystem For individual species, the identification of conservation status as measured by the degree of extinction risk has been widely accepted for decades Species are classified into various categories (such as not at risk, of least concern, vulnerable, endangered, and critically endangered) based on wellestablished criteria that relate to overall population size and trends (Mace et al., 2008) In relation to species the idea of biological extinction is relatively easy to define but for ecosystems made up of multiple species this is far more difficult In a pioneering study of North American ecosystems Noss et al (1995) described ecosystem loss as taking two forms: quantitative loss and qualitative loss Quantitative loss is the decline in areal extent of a discrete ecosystem type (e.g., the conversion of a native prairie grassland into a corn field) while qualitative loss is a change or degradation in the structure, function, or composition of an ecosystem (e.g., the change in species composition of a steppe ecosystem due to overgrazing, or the removal of key predator species in a marine ecosystem though overfishing) Problems arise when the concept of extinction risk is applied to ecosystems and the extent to which the loss of any species from an ecosystem impacts on the overall ecosystem structure and function is still the subject of much uncertainty and research (Duffy, 2003; The´bault et al., 2007) Despite these obvious difficulties there have been http://dx.doi.org/10.1016/B978-0-12-384719-5.00257-4 169