Poulos, Davina E., Brooker, Rohan M., and McCormick, Mark I. (2025) Prior residents mediate density-dependent success in newly arriving reef fish. Coral Reefs, 45. pp. 625-634.

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Abstract

Many populations of organisms experience periodic inputs or ‘pulses’ of new individuals, with varying numbers arriving to habitats occupied by varying numbers of prior residents. Identifying the behavioural mechanisms that determine individual success is central to understanding the factors shaping population structure. Using a juvenile damselfish, we investigated how prior residents (early arrivers) influenced the success of newly arriving individuals (late arrivers) and how this changed over time as successive pulses of conspecifics were experimentally introduced at varying densities. We conducted a manipulative field experiment using a two-factor crossed design to examine behaviours and mortality trajectories, focussing on: (a) time of arrival (first to fourth pulses, staggered at ~ 10–12 d intervals to mimic natural settlement patterns), and (b) conspecific density (two, five or ten individuals per pulse). Our results showed that growth was negatively density-dependent, decreasing at higher conspecific densities. In addition, activity was influenced by both space limitations (due to density) and dominance status (due to priority of arrival). Aggressive interactions occurred most strongly between individuals closest in the social hierarchy, and between individuals in low-density assemblages, partially explaining mortality trajectories. These findings highlight the key role of priority effects in structuring fish assemblages and determining size- and age-based hierarchies. Given ongoing disturbances to coral reef ecosystems, understanding how prior residents influence recruitment success has important implications for population resilience and conservation interventions, such as fish restocking in degraded habitats.

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