11.   Ecologists generally define an alien species as one that people inadvertently or deliberately carried to its new location.

12.   Even if alien species cause extinctions, the extinction phase will eventually end and new species may then begin to evolve, he explained.

13.   Gwilym Jones, a biologist at Northeastern University in Boston, argues that using alien species to fight aliens is dangerous.

14.   In the March issue of the journal Evolutionary Ecology Research, Rosenzweig, the editor, challenges the prevailing view that invasive alien species reduces biodiversity.

15.   Just as scientists seem to gain control of one invader, a new alien species appears.

16.   Sawgrass and other native plants already face an invasion of alien species, including hydrilla, Brazilian pepper and the water-guzzling melaleuca.

17.   The oratory surrounding political conventions sometimes leaves the impression of a citizenry divided into alien species.

18.   The starling, Sternus vulgaris, is an alien species much despised by birdwatchers for killing and taking over the nests of domestic songbirds.

19.   The vast majority of alien species arrive with human help.

20.   This may explain why marketers tend to adopt an anthropological tone, implying that women are an alien species, mystifying yet tractable if approached correctly.