COMPENSATORY IMMIGRATION FROM PROTECTED AREAS

DETERMINANTS OF THE MAGNITUDE OF COMPENSATORY IMMIGRATION

    I provided replicated evidence for compensatory immigration from protected areas to my experimentally fished areas. Immigration can increase total yield of “harvesters” if fished areas are attractive (i.e. higher habitat quality in the fished area) and where there is a large supply of potential migrants in protected areas. Interestingly, functional connectivity did not affect immigration for these species at that scale (but see Turgeon et al. 2010). We also provided evidence that immigration can negatively impact the metapopulation by severely depleting adjacent protected areas (Turgeon & Kramer 2012).

• Immigration of individuals from adjacent areas can substantially compensate for localized mortality (panel a), even in species considered to have very low mobility and therefore not expected to show strong compensatory immigration following localized mortality.
• By estimating the size of the population that could immigrate into the depleted area, we have provided one
  of the first documentations of the effect of compensatory immigration on adjacent source populations (panel b). Of these potential migrants, an average of 35% and a maximum of 61% of the S. diencaeus emigrated, indicating a potentially very large effect of localized mortality on adjacent source populations (Turgeon & Kramer 2012).

Complex NON-LINEAR patterns of density-dependent immigration

   I also investigated how a broad range of densities affected the rate of immigration. In 5 of 7 sites, immigration increased to a peak and then decreased as density decreased, showing a complex pattern of density dependence. In the other 2 sites, immigration did not change consistently with density.

This is the first experimental evidence for a hump-shaped relationship between density and immigration. It also suggests that patterns of density dependence can vary over relatively small spatial scales (i.e. among sites; Turgeon & Kramer 2016).