Juan J. Armesto

Bio: Juan J. Armesto is an academic researcher from Pontifical Catholic University of Chile. The author has contributed to research in topics: Rainforest & Temperate rainforest. The author has an hindex of 55, co-authored 249 publications receiving 18382 citations. Previous affiliations of Juan J. Armesto include Spanish National Research Council & Rutgers University.

Global biodiversity scenarios for the year 2100.

Abstract: Scenarios of changes in biodiversity for the year 2100 can now be developed based on scenarios of changes in atmospheric carbon dioxide, climate, vegetation, and land use and the known sensitivity of biodiversity to these changes. This study identified a ranking of the importance of drivers of change, a ranking of the biomes with respect to expected changes, and the major sources of uncertainties. For terrestrial ecosystems, land-use change probably will have the largest effect, followed by climate change, nitrogen deposition, biotic exchange, and elevated carbon dioxide concentration. For freshwater ecosystems, biotic exchange is much more important. Mediterranean climate and grassland ecosystems likely will experience the greatest proportional change in biodiversity because of the substantial influence of all drivers of biodiversity change. Northern temperate ecosystems are estimated to experience the least biodiversity change because major land-use change has already occurred. Plausible changes in biodiversity in other biomes depend on interactions among the causes of biodiversity change. These interactions represent one of the largest uncertainties in projections of future biodiversity change.

Patterns of Nutrient Loss from Unpolluted, Old‐Growth Temperate Forests: Evaluation of Biogeochemical Theory

Abstract: Atmospheric pollution and other human activities have altered natural ele- ment cycles over large regions of the world. Much current understanding of nutrient dy- namics in temperate region ecosystems has been derived from such biogeochemically altered areas. While it is increasingly difficult to find regions of temperate forest that can be classified as free from human influences, studies of unpolluted and undisturbed areas can (1) provide important "baseline" information about natural patterns of element cycling, against which disturbed cycles can be compared; (2) provide insights into the biogeochem- ical conditions that acted as evolutionary and selective constraints on biotic communities before the advent of regional-scale human impacts; and (3) provide an opportunity to evaluate the general nature of biogeochemical theories that have been developed in areas subject to strong human influences. We here report on patterns of hydrologic nutrient loss from old-growth temperate forest ecosystems in southern Chile based on chemical analyses of small streams draining 31 watersheds. These forests have not been subject to air pollution inputs and have remained floristically stable throughout the Holocene. For major elements our results support pre- dictions from current biogeochemical theory (the "nutrient retention hypothesis") that net biotic retention of elements should be minimal in old-growth forest ecosystems. Despite the dilute nature of watershed streams, the overall patterns of loss of most elements could be explained almost exclusively by atmospheric inputs of marine aerosols. In contrast, patterns of nitrogen loss were more complex than predicted by current conceptual models. Hydrologic N losses occurred nearly exclusively (95% of total N) as dissolved organic forms of nitrogen (DON), rather than as the inorganic forms NO3- (0.2% of total N) and NH4+ (4.8% of total N). The strong dominance of organic over inorganic losses of N indicates that losses of N from old-growth forest ecosystems are not exclusively subject to traditional mechanisms of direct biotic control (i.e., mineralization supply or biotic uptake), but are also subject to indirect biotic control associated with the long-term ac- cumulation, humification, and leaching of soil organic N during ecosystem succession. The view of unpolluted old-growth forests as "leaky" vs. "non-leaky" with respect to N depends on whether ecosystem budgets or models consider dissolved organic, as well as inorganic, forms of N. High- and mid-elevation forests in our study area showed the lowest efflux concentrations of N as NO3- reported from any old-growth temperate forest ecosystem (0.10 vs. 0.30 pg/L, respectively). Comparisons against other old-growth forests, subject to varying levels of N deposition, indicated that levels of NO3- and the relative abundance of NO3- vs. NH4+ in Northern Hemisphere forests may be strongly influenced by atmospheric N inputs. Our analyses suggest that patterns of N cycling, as well as evolutionary selective pressures on plant and microbial species, may have changed as a function of regional-scale increases in atmospheric N deposition to European and North American temperate forests. We hypothesize that, because they inherently are more poor than aggrading forests at retaining added nutrients, old-growth forest ecosystems are particularly sensitive indicators of N deposition.

Models, mechanisms and pathways of succession

Abstract: The study of succession has been hampered by the lack of a general theory. This is illustrated by confusion over basic concepts and inadequacy of certain models. This review clarifies the basic ideas of pathway, mechanism, and model in succession. Second, in order to prevent inappropriate narrowness in successional studies, we analyze the mechanistic adequacy of the most widely cited models of succession, those of Connell and Slatyer. This analysis shows that models involving a single pathway or a dominant mechanism cannot be treated as alternative, testable hypotheses. Our review shows much more mechanistic richness than allowed by these widely cited models of succession. Classification of the mechanisms of specific replacement, called for by existing models, is problematic and less valuable than the search for the actual mechanisms of particular seres. For example, the “tolerance” mechanism of succession has at least two contrasting meanings and is unlikely to be disentangled from the “inhibition” mechanism in field experiments. However, the understanding of particular species replacements through experiment and knowledge of the conditions of a particular sere and species life histories is a reasonable and desirable goal. Finally, we suggest the need for a broad mechanistic concept of succession. Thus, based on classical causes of succession that have survived recent scrutiny, we erect a framework of successional mechanisms. This framework aims at comprehensiveness, and specific mechanisms are nested within more general causes. As a result of its breadth and hierarchical structure, the framework performs two important functions: First, it provides a context for studies at specific sites and, second, is a scheme for formulating general and testable hypotheses. The review of specific successional mechanisms and the general mechanistic framework can together guide future work on succession, and may foment the development of a broad theory.

The ecological concept of disturbance and its expression at various hierarchical levels

Abstract: Current definitions of disturbance are intuitive, narrow, and only implicitly based on system structure. This is because the concepts are based on experience at particular levels of organization or on systems whose structure is well known. The definitions are thus inadequate for the development of a general theory of ecological disturbance. A universally applicable definition would 1) identify the object disturbed; 2) distinguish between change in the object that is disturbance versus change that is not; and 3) distinguish between direct and indirect consequences of disturbance. To meet these requirements, we formally link the hierarchical organization of ecological objects and the concept of disturbance. Any persistent ecological object will have a minimal structure, or system of lower level entities that permit its persistence. Disturbance is a change in the minimal structure of an object caused by a factor external to the level of interest. Using these definitions, disturbance can be unequivocally identified and associated with various specific ecological levels of organization. Because of the dependence of the concept of disturbance on recognizing the minimal structure of ecological systems, application of the concept will advance as refined models of the hierarchical structure of ecological systems are elaborated.

Community studies in pollination ecology in the high temperate andes of central chile. i. pollination mechanisms and altitudinal variation

Abstract: Pollination mechanisms and pollinators are reported for a total of 137 species (75% of the non-abiotically pollinated flora) as they occur at three altitudinal levels (subandean scrub: 2,200-2,600 m; cushion-plant zone: 2,700-3,100 m; subnival feldfield: 3,200-3,600 m) in the Andean (alpine) zone on the Cord6n del Cepo (33?17'S) in central Chile as part of community oriented research in reproductive biology in the high temperate Andes of South America. Only around 4% of the species studied failed to be visited by potential pollinators. Hymenopterans (principally bees) are important pollinators of 50% of the biotically pollinated flora, butterflies of 24% and flies of 46%. Other vectors include beetles, moths, and hummingbirds. An estimated 17% of the flora is anemophilous. Bee species-richness, specialist feeding, and melittophily reach maxima in the subandean scrub; thereafter, bees diminish rapidly in number, with bees pollinating only 13% of the subnival flora as contrasted with 68% of the subandean flora. Although fly and butterfly species-richness also decline with increasing altitude, the proportions of species pollinated by these vectors actually increases. High-altitude populations of melittophilous species with broad altitudinal ranges are invariably serviced by fewer bee species as compared with lower populations. The rich bee fauna at the lower end of the Andean zone in central Chile appears to have resulted from upward colonization from that of the subtending lowland Mediterranean sclerophyllous woodland vegetation. Altitudinal variation in pollination spectra is discussed in relation to contrasting life history characteristics and different modes of thermoregulation in the insect groups involved. RECENT STUDIES on the energetics of foraging (e.g., Heinrich, 1974), nectar and pollen con'Received for publication 22 September 1980; revision accepted 4 December 1980. 2 Departamento de Biologia, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago, Chile. 3Department of Botany, Boston University, Boston, Massachusetts, USA. Many students, but especially Paulina Uslar and Michaelangelo Trevalli, are thanked for their collaboration with field work. Hymenopterans were identified by Dr. H. Toro, Depto. de Zoologia, Universidad Catolica, Valparaiso, lepidopterans by Dr. J. Herrera, Fac. de Ciencias, U. de Chile, Santiago and dipterans by Dr. M. Etcheverry, Fac. de Ciencias, U. de Chile, Dr. Raul Cortes, Universidad del Norte, and Dr. Jorge Artigas, Secci6n de Entomologia, Depto. de Zoologia, Universidad de Concepci6n, all in Chile and without whose collaboration this research would have been impossible. We are especially grateful to SDCACI, U. de Chile for providing a special travel grant to R. Primack and to Dr. P. H. Raven, Missouri Botanical Garden, who provided much unavailable literature, and with whom many useful discussions were held during the writing of this paper. The Club Deportivo, Universidad de Chile provided logistic support and Hoteles Portillo granted permission to circulate on high Andean access routes, for which we are most appreciative. This research was supported by Grant No. B388/803 to M.T.K.A. by SDCACI, Universidad de Chile and forms part of MAB-6 (UNESCO/UNEP 1105-77-01). stituents (e.g., Baker and Baker, 1979) and relationships with flowering phenology (e.g., Stiles, 1978; Whelan and Burbidge, 1980) have added new dimensions to research in pollination biology. The implications of these studies, nevertheless, have yet to be thoroughly explored at a community level, and as Faegri and van der Pijl (1979) recently stated in reviewing progress in pollination ecology, "until now the evolution of community pollination spectra has only been touched on." In high-mountain plant communities above timberline, opportunities for growth are restricted to the spring and summer months, and, in temperate regions, prevented during the remainder of the year by low temperatures and associated snow cover. Flowering as a consequence must be limited to a relatively short period of the year, which tends to decrease in length as the upper vegetational limit is approached. Increased low-temperature stress with altitude also affects the distribution and abundance of insects (Mani, 1962). Thus predictably, plant-pollinator relationships might change both quantitatively and qualitatively with altitude. From the work of early naturalists (e.g., Muller, 1880), and more recently that

A safe operating space for humanity

Abstract: Identifying and quantifying planetary boundaries that must not be transgressed could help prevent human activities from causing unacceptable environmental change, argue Johan Rockstrom and colleagues.

Extinction risk from climate change

Abstract: Climate change over the past approximately 30 years has produced numerous shifts in the distributions and abundances of species and has been implicated in one species-level extinction. Using projections of species' distributions for future climate scenarios, we assess extinction risks for sample regions that cover some 20% of the Earth's terrestrial surface. Exploring three approaches in which the estimated probability of extinction shows a power-law relationship with geographical range size, we predict, on the basis of mid-range climate-warming scenarios for 2050, that 15-37% of species in our sample of regions and taxa will be 'committed to extinction'. When the average of the three methods and two dispersal scenarios is taken, minimal climate-warming scenarios produce lower projections of species committed to extinction ( approximately 18%) than mid-range ( approximately 24%) and maximum-change ( approximately 35%) scenarios. These estimates show the importance of rapid implementation of technologies to decrease greenhouse gas emissions and strategies for carbon sequestration.

Effects of biodiversity on ecosystem functioning: a consensus of current knowledge

Abstract: Humans are altering the composition of biological communities through a variety of activities that increase rates of species invasions and species extinctions, at all scales, from local to global. These changes in components of the Earth's biodiversity cause concern for ethical and aesthetic reasons, but they also have a strong potential to alter ecosystem properties and the goods and services they provide to humanity. Ecological experiments, observations, and theoretical developments show that ecosystem properties depend greatly on biodiversity in terms of the functional characteristics of organisms present in the ecosystem and the distribution and abundance of those organisms over space and time. Species effects act in concert with the effects of climate, resource availability, and disturbance regimes in influencing ecosystem properties. Human activities can modify all of the above factors; here we focus on modification of these biotic controls. The scientific community has come to a broad consensus on many aspects of the re- lationship between biodiversity and ecosystem functioning, including many points relevant to management of ecosystems. Further progress will require integration of knowledge about biotic and abiotic controls on ecosystem properties, how ecological communities are struc- tured, and the forces driving species extinctions and invasions. To strengthen links to policy and management, we also need to integrate our ecological knowledge with understanding of the social and economic constraints of potential management practices. Understanding this complexity, while taking strong steps to minimize current losses of species, is necessary for responsible management of Earth's ecosystems and the diverse biota they contain.

Freshwater biodiversity: importance, threats, status and conservation challenges

Abstract: Freshwater biodiversity is the over-riding conservation priority during the International Decade for Action - 'Water for Life' - 2005 to 2015. Fresh water makes up only 0.01% of the World's water and approximately 0.8% of the Earth's surface, yet this tiny fraction of global water supports at least 100000 species out of approximately 1.8 million - almost 6% of all described species. Inland waters and freshwater biodiversity constitute a valuable natural resource, in economic, cultural, aesthetic, scientific and educational terms. Their conservation and management are critical to the interests of all humans, nations and governments. Yet this precious heritage is in crisis. Fresh waters are experiencing declines in biodiversity far greater than those in the most affected terrestrial ecosystems, and if trends in human demands for water remain unaltered and species losses continue at current rates, the opportunity to conserve much of the remaining biodiversity in fresh water will vanish before the 'Water for Life' decade ends in 2015. Why is this so, and what is being done about it? This article explores the special features of freshwater habitats and the biodiversity they support that makes them especially vulnerable to human activities. We document threats to global freshwater biodiversity under five headings: overexploitation; water pollution; flow modification; destruction or degradation of habitat; and invasion by exotic species. Their combined and interacting influences have resulted in population declines and range reduction of freshwater biodiversity worldwide. Conservation of biodiversity is complicated by the landscape position of rivers and wetlands as 'receivers' of land-use effluents, and the problems posed by endemism and thus non-substitutability. In addition, in many parts of the world, fresh water is subject to severe competition among multiple human stakeholders. Protection of freshwater biodiversity is perhaps the ultimate conservation challenge because it is influenced by the upstream drainage network, the surrounding land, the riparian zone, and - in the case of migrating aquatic fauna - downstream reaches. Such prerequisites are hardly ever met. Immediate action is needed where opportunities exist to set aside intact lake and river ecosystems within large protected areas. For most of the global land surface, trade-offs between conservation of freshwater biodiversity and human use of ecosystem goods and services are necessary. We advocate continuing attempts to check species loss but, in many situations, urge adoption of a compromise position of management for biodiversity conservation, ecosystem functioning and resilience, and human livelihoods in order to provide a viable long-term basis for freshwater conservation. Recognition of this need will require adoption of a new paradigm for biodiversity protection and freshwater ecosystem management - one that has been appropriately termed 'reconciliation ecology'.