Physical and biological factors contributing to changes in the relative importance of recruitment to population dynamics in open populations

Abstract

Changes in population dynamics of open populations are driven by variability in recruitment and post-recruitment processes. The relative importance of these 2 processes varies within and among populations depending on numerous physical and biological variables. We examined variables that determine the correlation between recruitment and population density in 2 populations of intertidal barnacles (Chthamalus spp.). Data were collected over 5 yr at 59 rocky shore sites with various physical and biological characteristics. We tested the influence of recruitment density, recruitment variability, barnacle species, available free space, surface temperature, rugosity, wave intensity, and density of predators on the correlation (Fisher transformed correlation coefficient r z) between recruitment and changes in population coverage. We compared linear models including r z and all possible combinations of physical and biological characteristics measured at each site using Akaike's information criterion (AIC). The effect of each variable deemed important by AIC was determined using partial regression plots. Results showed that the most important variables (and their direction of influence) in determining correlation among recruitment and population density were recruitment density (positive), recruitment variability (positive), rugosity (negative), available free space (positive), and wave intensity (positive). The influence of individual variables and combinations of variables changed spatially and temporally. This study showed that recruitment is an important variable determining the population dynamics in open populations but that post-recruitment factors can also influence the correlation between recruitment and population density. It is also clear that the combination and strength of variables influencing population density change over spatial and temporal scales. © Inter-Research 2010, www.int-res.com.