Abstract
AbstractThe effect of habitat loss on the decline of habitat specialists has been well documented in coral reef fishes, since they have a restricted habitat preference. However, the different competitive advantages of specialists and generalists can impact their performance within varying habitat conditions. The order in which species arrive into a community influences competitive outcomes; these ‘priority effects’ may modify communities within degrading resource scenarios as individuals migrate in search of higher quality resources. In this study, we investigated: how sequence and timing of arrival affects interactions between a habitat generalist and a specialist in healthy and degrading environments, and how prior residency interacts with habitat quality and species identity to affect propensity to migrate. We conducted manipulative field studies using the damselfishes Pomacentrus amboinensis, a habitat generalist, and Pomacentrus moluccensis, a live coral specialist, on live or dead coral habitats, with timing of arrival differing between early and late arrivers (residents and intruders, respectively) by 1, 3 or 24 h. Our results demonstrated that the strength of priority effects (i.e., aggression intensity) increased with increasing timing of arrival when the P. moluccensis arrived after P. amboinensis, suggesting that as the perceived value of the habitat patch increased (owing to increasing ownership duration and defence investment), the tendency to defend it increased. Propensity to migrate from dead to live coral was greater for P. moluccensis compared to P. amboinensis; however, arriving after P. amboinensis significantly reduced willingness to migrate to its preferred live coral habitat, indicating an inhibitory priority effect, directly affecting future persistence. The degree that ecological versatility and priority effects combine to modify competitive outcomes in coral reef fishes has important consequences for the persistence of specialist species in the face of environmental degradation, and has implications for predicting how our changing environment will affect fish communities.
Highlights
Environmental and anthropogenic-induced changes are causing increased stress to natural systems, resulting in a decline, and in extreme events a loss, of species worldwide (Ceballos et al 2017; Sanchez-Bayo and Wyckhuys 2019; Smale et al 2019; Kleypas et al 2021)
This was caused by P. amboinensis becoming more aggressive with residence time, and early-arrivers that had been on the patch for an hour tending to be more aggressive on dead coral than live (Fig. 1b)
The present study demonstrates that priority effects modify how two species, which differ in their ecological versatility, perform in healthy and degrading habitats
Summary
Environmental and anthropogenic-induced changes are causing increased stress to natural systems, resulting in a decline, and in extreme events a loss, of species worldwide (Ceballos et al 2017; Sanchez-Bayo and Wyckhuys 2019; Smale et al 2019; Kleypas et al 2021). This loss of biodiversity has emphasised the importance of determining which species are most at risk, the factors directly influencing the decline in abundance of vulnerable species, and how their decline alters the dynamics of communities (Feary et al 2014; Madin et al 2016; McKenzie et al 2016; Gladstone-Gallagher et al 2019). Species with a high level of habitat specialisation (specialists) are restricted to a small number of preferred habitats, whilst species that are versatile in their habitat use (generalists) use a range of different habitat types within their local environment (Feary 2007; Berkstrom et al 2012)
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