Effets Allee Démographiques

Résumé du livre

A component Allee effect (cAE) describes reduced individual fitness at a reduced population size and can manifest as reduced population growth at reduced population size - a demographic Allee effect (dAE). Assuming no taxonomic or publication bias, I reviewed the Allee effect literature, using the intuitive mate-finding Allee effect mechanism as an example, and found that cAE are common in natural populations but rarely manifest as dAE. There are myriad reasons for this including benefits accrued from reduced intraspecific competition. However, since so many of todays populations are declining and threatened, I predicted a higher incidence of dAE. An analysis of 1198 natural populations failed to support this prediction and detected a dAE in less than 1 in 92 populations. Nevertheless, the analysis had a poor power to detect dAE and that variability would prevent their detection. We used a simulation study to show that detecting dAE in highly variable time series is likely to be challenging. Subsequently, we borrowed from existing time series analysis methods to develop a statistical procedure to better detect dAE in highly variable time series, and illustrated its advantage using real datasets. We then applied the new statistical procedure to large datasets collected for nine species of UK social bats and revealed a dAE in 4 of 9 bat species. This reaffirmed our confidence in the new statistical procedure and calls into question the paucity of dAE observed in other social species.