Abstract: Habitat fragmentation, as a result of human activities, is a great threat to biodiversity. Many small populations emerge after habitat fragmentation. Their extinction rate may be accelerated by Allee effect. The Allee effect may also occur during biological invasions, which results to increasing attentions paid to its effect on invasive species. The definition, function and reasons of Allee effect were introduced. It is shown that Allee effect occurs at the beginning of species invasion, which influences the spread speed, spread strategies and even survive of the invasive species in the new habitat. The application of Allee effect to small population management was discussed in relation to preventing biological invasions and protecting rare species.

Key words: conservation biology , small population, biological invasions, Allee effect