How many species are there on Earth?

Tropical Deforestation and Habitat Fragmentation in the Amazon: Satellite Data from 1978 to 1988

Landsat satellite imagery covering the entire forested portion of the Brazilian Amazon Basin was used to measure, for 1978 and 1988, deforestation, fragmented forest, defined as areas less than 100 square kilometers surrounded by deforestation, and edge effects of 1 kilometer into forest from adjacent areas of deforestation. Tropical deforestation increased from 78,000 square kilometers in 1978 to 230,000 square kilometers in 1988 while tropical forest habitat, severely affected with respect to biological diversity, increased from 208,000 to 588,000 square kilometers. Although this rate of deforestation is lower than previous estimates, the effect on biological diversity is greater.

Counting dinosaurs: how many kinds were there?

Dinosaurs figure prominently in discussions of mass extinctions and evolutionary metrics, but their usefulness is hampered by archaic taxonomy, imprecise biostratigraphy, and imperfect preservation that bias our understanding of dinosaur diversity. A critical evaluation shows that of 540 genera and 800 species of dinosaurs proposed since 1824, 285 genera and 336 species are probably valid. Nearly half of all genera are based on a single specimen, and complete skulls and skeletons are known for only 20% of all dinosaurs. Dinosaurs are known from every continent. Countries with the greatest known diversity of dinosaurs are (in descending order) the United States, Mongolia, China, Canada, England, and Argentina; the greatest future increases may be expected from Argentina and China. Nearly half of all dinosaur genera are of latest Cretaceous age (Campanian or Maastrichtian). Estimates of the average duration of a dinosaur genus range from 5 million to 10.5 million years, with the most likely value about 7.7 million years. Dinosaurs evolved as rapidly as Cenozoic mammals. Global dinosaur diversity during the Campanian and Maastrichtian is estimated at 100 genera per stage, using a logistic model to estimate future discoveries. A model of increasing diversity and a bottleneck model compensate for the biasis in the preserved fossil record. The number of dinosaurs that have ever lived is estimated at 900-1200 genera. The fossil record of dinosaurs is presently about 25% complete. Dinosaurs disappeared in the Maastrichtian near the peak of their historic diversity.

[Ecotoxicology exemplified by an analysis of the chemical spill into the caused Rhine by Sandoz in Basel]

A fire at a chemical manufacturing plant at Schweizerhalle (near Basel) in November 1986 and the subsequent release of toxic agrochemicals into the Rhine river is taken as a basis to discuss some problems and needs in ecotoxicological research. Especially serious is the lack of knowledge about chronic effects of mixtures of chemicals to individuals and whole ecosystems. There is an urgent need for generally applicable principles and concepts. A discussion of the relationship between toxic effects to fish, exposure time, and concentration provides some hints about the direction towards which research should proceed. Finally, eight theses pertaining to ecotoxicology summarize what can be learned from the analysis of a chemical spill.

The stability of ecosystems

Stability criteria and phase boundaries for complex ecosystems are obtained and contrasted with previously studied scenarios. The stability of such systems is determined by the behaviour of the largest eigenvalue of matrices governing the response of the system to small perturbations. As a result we show that ecosystems with unstructured cooperative interactions between arbitary species can be less stable than had been previously determined. We also examine hierarchical ecologies, and demonstrate their increased stability under certain conditions.

Macroecology: The Division of Food and Space Among Species on Continents

Analyses of statistical distributions of body mass, population density, and size and shape of geographic range offer insights into the empirical patterns and causal mechanisms that characterize the allocation of food and space among the diverse species in continental biotas. These analyses also provide evidence of the processes that couple ecological phenomena that occur on disparate spatial and temporal scales-from the activities of individual organisms within local populations to the dynamics of continent-wide speciation, colonization, and extinction events.