RESUMO
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.
Assuntos
Ecossistema , Agricultura , Animais , Atmosfera , Dióxido de Carbono , Clima , Água Doce , Modelos Biológicos , NitrogênioRESUMO
Despite the extrame aridity of the coastal Atacama Desert in northern Chile, sparse communities of leaf succulent shrubs and small cacti are regularly present. While most shrub species have small succulent leaves and accumulate high concentrations of salts in their tissues, the variable rooting patterns and mixed dominance of CAM and C3 species indicates a significant divergence in adaptive strategies. All dominant shrubs are readily surviving extended drought, but some species are much better able than others to maintain active growth and flowering. Regular flowering may not be a prerequisite for shrub population maintenance since large piles of viable seeds are present under the canopies of many species.
RESUMO
In the Atacama Desert of northern Chile, cacti of the genus Copiapoa occur in extensive, relatively dense, monospecific stands. The spatial distribution patterns within several stands of Copiapoa cinerea v. columna-alba were analyzed for evidence of competitive interactions among individuals. There was no indication that competition was affecting stand density. Mean annual precipitation is only 25 mm/yr, but estimates of maximum possible water use within a stand were much lower. It was shown that the time between rainstorms is long compared to the water storage capacity of the plant stems, especially in the case of small individuals. We conclude that population densities in Copiapoa are limited by the difficulty of establishment, not by competition.