Population regulation by post-settlement mortality in two temperate reef fishes

Abstract

Input of individuals dispersing into open populations can be highly variable, yet the consequences of such variation for subsequent population densities are not well understood. I explored the influence of variable input ("supply") on subsequent densities of juveniles and adults in open local populations of two temperate reef fishes, the bluebanded goby (Lythrypnus dalli) and the blackeye goby (Coryphopterus nicholsii). Variable recruitment was simulated by stocking a natural range of densities of young fishes on replicate patch reefs. Density and mortality of the stocked cohorts were followed over time, until the fishes reached maturity. Over the first day of the experiments, mortality of both species was significantly density-dependent; however, there was still a very strong relationship between density on day 1 and density on day 0 (i.e., simulated recruitment was still an excellent predictor of population density). At this point in the study, the main effects of density-dependent mortality were to reduce mean densities and variation about the mean. Over the period from the start of the experiments until the time when maturity was reached by each species (about 1 and 3 months for Lythrypnus and Coryphopterus, respectively), mortality was strongly density-dependent. Such strong density-dependent mortality virtually eliminated any linear relationship between adult density and "recruit" density. However, for both species, the relationship between these two variables was well fit by an asymptotic curve, with the asymptotic density of adults equal to c. 3/m for Coryphopterus, and c. 10/m for Lythrypnus. Natural recruitment (via settlement of larvae) to the reefs over the period of the study (9 months) was above the asymptotic densities of adults for the two species, even though the study did not encompass the periods of peak annual recruitment of either species. This suggests that adult populations of these two gobies may often be limited, and regulated, by post-settlement processes, rather than by input of settlers. Other studies have shown that mortality of the two species is density-independent, or only weakly density-dependent, on reefs from which predators have been excluded. Hence, it appears that predators cause density-dependent mortality in these fishes.

Habitat-dependent recruitment of two temperate reef fishes at multiple spatial scales

“…Recruitment (the number of new individuals in local populations that have survived to some arbitrary point in time after settlement) of these early life stages has been identified as a time at which the abundance of populations of reef fishes are determined by pre-settlement processes occurring during the pelagic phase (Doherty 1981, Victor 1983, Doherty & Fowler 1994, by subsequent post-settlement processes (Hixon & Carr 1997, Steele 1997b, Carr et al 2002, or probably by a combination of both (Jones 1991, Caley et al 1996. The prevalence of correlations between the abundance of recruits and specific habitat features suggests that the abundance and distribution of recently settled reef fishes are habitat-dependent (Carr 1991, 1994a, Levin 1991, Tolimieri 1995, Steele 1999.…”

“…Spatial and temporal variation in recruitment may be caused by the supply of larvae transported to a location (Doherty 1981, Victor 1983, Cowen 1985, Milicich et al 1992, Meekan et al 1993, larval behavior during settlement (Sweatman 1985, Holbrook & Schmitt 1997, early post-settlement processes, such as predatorinduced mortality (Hixon & Carr 1997, Steele 1997b, Schmitt & Holbrook 1999, Carr et al 2002, or postsettlement migration. Sources of variation in recruitment can be modified further by particular habitat features.…”

La notion de population en dynamique et génétique des populations

“…Il semble plutôt relever d'une discipline particulière, l'écologie marine, et caractérise des espèces au cycle de vie complexe dont l'un des stades au moins, en général les larves, se disperse totalement dans des espaces qui dépassent souvent nos capacités d'investigation, et dont au moins un autre stade est sédentaire (Sale, 1990 ;Steele, 1997 …”

The relative influence of abundance and priority effects on colonization success in a coral-reef fish

“…Recent work has shown that individual survival of reef fish settlers can depend on the timing of priority effects and that the strength of priority effects can vary dramatically within populations (Almany 2003;Munday 2004;McCormick 2014, 2015) and between habitats (Geange and Stier 2010;Adam 2011). However, these studies need to be reconciled against often large variation in settler abundance and earlier work showing that the abundance of settlers can determine their persistence by influencing density-dependent interactions (e.g., Steele 1997;Shima 2001;Shima and Osenberg 2003). Here, we factorially manipulated the abundance and sequence of settlement-stage damselfish arrival onto patch reefs to assess their relative contribution to reef fish survival.…”