Demographic Theory for an Open Marine Population with Space‐Limited Recruitment

Abstract

We introduce a demographic model for a local population of sessile marine invertebrates that have a pelagic larval phase. The processes in the model are the settling of larvae onto empty space, and the growth and mortality of the settled organisms. The rate of settlement per unit of unoccupied space is assumed to be determined by factors outside of the local system. The model predicts the number of animals of each age in the local system through time. The model is offered in both discrete and continuous—time versions. The principal result is that the growth of the settled organisms is destabilizing. In the model, there is always a state where recruitment balances mortality. However, growth can interfere with recruitment and can destabilize this steady state, provided also that the settlement rate is sufficiently high. The model suggests that two qualitatively distinct pictures of population structure result, depending on the settlement rate. In the high settlement limit, the intertidal landscape is a mosaic of cohorts, punctuated with occasional gaps of vacant substrate. In the low settlement limit, the intertidal landscape has vacant space and organisms of all ages mixed together and spatial variation in abundance is caused by microgeographic variation in settlement and mortality rates.

Larval settlement rate: A leading determinant of structure in an ecological community of the marine intertidal zone

“…Waves of cohorts are observed (14) as patches of free space undergo the cycle of high recruitment, rapid growth, and finally enhanced mortality when free space is nearly exhausted. Glynn (22), in a study ofB.…”

“…A model for the demography and population dynamics of an open population with space-limited recruitment has recently been proposed for marine populations like barnacles (14)(15)(16)(17) This study also confirms a key assumption of the openpopulation demographic model, that settlement to vacant space can be treated as a process in which the rate of settlement in a quadrat is proportional to the fraction of vacant space in it, with a constant of proportionality specific to location and time (including season). Further, this study reveals that disturbance (mortality that removes space-occupying organisms) is a cover-dependent process for barnacles subject to predation by the starfish Pisaster ochraceus and that the cover-independent component of survivorship is independent of age for at least the first 60 weeks of life.…”

Causes of decoupling between larval supply and settlement and consequences for understanding recruitment and population connectivity

“…Researchers have 5 appreciated the role of new recruits in population processes for a long time (e.g., Hjort, 1926;6 Hatton, 1938;Thorson, 1946;Ayers, 1956;Barnes, 1956;Loosanoff, 1964;Yoshioka, 1982). In 7 the 1980's there was increased attention on the role of larval input on rocky shore community 8 dynamics (Roughgarden et al, 1985), baptized "supply-side ecology" by Lewin, (Lewin, 1986;J. 9 Roughgarden, pers.…”

Ecological processes can synchronize marine population dynamics over continental scales

“…This focus is motivated by the lengthy pelagic larval stage commonly found in marine organisms, during which the larvae can be transported over large distances by strong nearshore currents (5). The potential for large-scale transport, along with the difficulties associated with measuring larval dispersal, has prompted many studies to assume either completely closed (no exportation of larvae to other populations) or completely open (no coupling between larval production and recruitment) demography (5, 6, but see refs.…”