Abstract:
Marine species possessing widely dispersing larvae are often considered to have open populations. However, two concepts are covered by the phrase 'open population'. One concept stresses the supply of recruits from outside the local population (genetically open) while the alternative use describes situations where recruitment rate is independent of the local population size (demographically open). These two concepts are not necessarily equivalent. A review of recent literature suggests that there is no consensus on whether a demographic or genetic concept is associated with the use of the phrase 'open population'. The different meanings of open population are never formally acknowledged. Explicit recognition of the different concepts of openness would remove an ambiguity from the literature and may aid communication between disciplines. Processes in natural populations, such as gregarious settlement and homing behaviour, are more clearly described by distinguishing between demographic and genetic degrees of openness. Changes in spatial scale will affect the degree of population openness. However, demographic and genetic aspects of population structure will not necessarily respond in the same ways to changes in scale. This provides further support for the explicit separation of genetic and demographic concepts of openness.
