The population dynamics of Patella vulgata and other limpets
Useful generalisations can be made about limpet populations in much the same way as they can about individual animals. These generalisations can be expressed quantitatively and formed into a framework of population dynamics. In Patella vulgata populations a greater mean size (defined as the 50% accumulative weight size) indicates (i) a faster growth rate, (ii) a larger maximum size, (iii) an increased mortality rate, (iv) decreased mean and maximum life spans, (v) an increased settlement rate, (vi) an earlier and more rapid seasonal maturation of the gonad, (vii) a larger number of eggs produced per female and per unit weight, (viii) a lower radula ratio and a flatter shell at the mean size, than would be found in a population with a smaller mean size. The timing of sexual maturity and of sex change is independent of these correlated features of population dynamics. The correlations were established by the detailed study of four populations at Mount Batten, Plymouth; and verified by experimental alteration of the population structure and a survey of Patella on all types of shore. The range of Patella vulgata in S.W. Britain is limited at the top of the shore principally by desiccation. The penetration of sheltered conditions is determined by interaction between the fucoids and the limpets, On exposed shores, the lower limit is determined by competition between P. vulgata and P. aspera. There is no direct relationship between mean size and population density (expressed as weight per occupied area). P. vulgata is densest at the borders of the fucoid communities on sheltered shores, at the lowest levels on moderately exposed shores, and at the junction with the P. aspera populations on exposed shores. P. vulgata prevents fucoids from establishing communities on many rook surfaces, but where fucoids form dense stands, P. vulgata is not able to settle or feed. Physical factors do not directly limit the range of P. vulgata (except at the top of the shore), although they mediate the competition and interaction which decide the precise boundaries, Inside each P. vulgata population the growth rate 3.8 limited by intraspecific competition for the available food.