Biomedical subjects
Philip S Ward
Publications and source records attributed to Philip S Ward.
The role of opportunity in the unintentional introduction of nonnative ants.
A longstanding goal in the study of biological invasions is to predict why some species are successful invaders, whereas others are not. To understand this process, detailed information is required concerning the pool of species that have the opportunity to become established. Here we develop an extensive database of ant species unintentionally transported to the continental United States and use these data to test how opportunity and species-level ecological attributes affect the probability of establishment. This database includes an amount of information on failed introductions that may be unparalleled for any group of unintentionally introduced insects. We found a high diversity of species (232 species from 394 records), 12% of which have become established in the continental United States. The probability of establishment increased with the number of times a species was transported (propagule pressure) but was also influenced by nesting habit. Ground nesting species were more likely to become established compared with arboreal species. These results highlight the value of developing similar databases for additional groups of organisms transported by humans to obtain quantitative data on the first stages of the invasion process: opportunity and transport.
Energy gradients and the geographic distribution of local ant diversity.
Geographical diversity gradients, even among local communities, can ultimately arise from geographical differences in speciation and extinction rates. We evaluated three models--energy-speciation, energy-abundance, and area--that predict how geographic trends in net diversification rates generate trends in diversity. We sampled 96 litter ant communities from four provinces: Australia, Madagascar, North America, and South America. The energy-speciation hypothesis best predicted ant species richness by accurately predicting the slope of the temperature diversity curve, and accounting for most of the variation in diversity. The communities showed a strong latitudinal gradient in species richness as well as inter-province differences in diversity. The former vanished in the temperature-diversity residuals, suggesting that the latitudinal gradient arises primarily from higher diversification rates in the tropics. However, inter-province differences in diversity persisted in those residuals--South American communities remained more diverse than those in North America and Australia even after the effects of temperature were removed.