Species Selection: Theory and Data

From the Arctic to South Africa - one finds them everywhere: Ants. Making up nearly 15% of the entire terrestrial animal biomass, ants are impressive not only in quantitative terms, they also fascinate by their highly organized and complex social system. Their caste system, the division of labor, the origin of altruistic behavior and the complex forms of chemical communication makes them the most interesting group of social organisms and the main subject for sociobiologists. Not least is their ecological importance: Ants are the premier soil turners, channelers of energy and dominatrices of the insect fauna. TOC:The importance of ants.- Classification and origins.- The colony life cycle.- Altruism and the origin of the worker caste.- Colony odor and kin recognition.- Queen numbers and domination.- Communication.- Caste and division of labor.- Social homeostasis and flexibility.- Foraging and territorial strategies.- The organization of species communities.- Symbioses among ant species.- Symbioses with other animals.- Interaction with plants.- The specialized predators.- The army ants.- The fungus growers.- The harvesters.- The weaver ants.- Collecting and culturing ants.- Glossary.- Bibliography.- Index.

The taxonomic challenge posed by cryptic species (two or more distinct species classified as a single species) has been recognized for nearly 300 years, but the advent of relatively inexpensive and rapid DNA sequencing has given biologists a new tool for detecting and differentiating morphologically similar species. Here, we synthesize the literature on cryptic and sibling species and discuss trends in their discovery. However, a lack of systematic studies leaves many questions open, such as whether cryptic species are more common in particular habitats, latitudes or taxonomic groups. The discovery of cryptic species is likely to be non-random with regard to taxon and biome and, hence, could have profound implications for evolutionary theory, biogeography and conservation planning.

A latitudinal gradient in biodiversity has existed since before the time of the dinosaurs, yet how and why this gradient arose remains unresolved. Here we review two major hypotheses for the origin of the latitudinal diversity gradient. The time and area hypothesis holds that tropical climates are older and historically larger, allowing more opportunity for diversification. This hypothesis is supported by observations that temperate taxa are often younger than, and nested within, tropical taxa, and that diversity is positively correlated with the age and area of geographical regions. The diversification rate hypothesis holds that tropical regions diversify faster due to higher rates of speciation (caused by increased opportunities for the evolution of reproductive isolation, or faster molecular evolution, or the increased importance of biotic interactions), or due to lower extinction rates. There is phylogenetic evidence for higher rates of diversification in tropical clades, and palaeontological data demonstrate higher rates of origination for tropical taxa, but mixed evidence for latitudinal differences in extinction rates. Studies of latitudinal variation in incipient speciation also suggest faster speciation in the tropics. Distinguishing the roles of history, speciation and extinction in the origin of the latitudinal gradient represents a major challenge to future research.