Data from: Allee effects may slow the spread of parasites in a coastal marine ecosystem

Allee effects are thought to mediate the dynamics of population
colonization, particularly for invasive species. However, Allee effects
acting on parasites have rarely been considered in the analogous process
of infectious disease establishment and spread. We studied the
colonization of uninfected wild juvenile Pacific salmon populations by
ectoparasitic salmon lice (Lepeophtheirus salmonis) over four years. From
a dataset of 67,896 fish, we observed 88 occurrences of pre-copular pair
formation among 1258 pre-adult female and 611 adult male lice. The
probability of pair formation was dependent on the local abundance of
lice, but this mate limitation is likely offset somewhat by mate-searching
dispersal of males among host fish. A mathematical model of macroparasite
population dynamics that incorporates the empirical results suggests a
high likelihood of a demographic Allee effect, which can cause the
colonizing parasite populations to die out. These results may provide the
first empirical evidence for Allee effects in a macroparasite.
Furthermore, the data give a rare detailed view of Allee effects in
colonization dynamics and suggest that Allee effects may dampen the spread
of parasites in a coastal marine ecosystem.