Invasive predator tips the balance of symmetrical competition between native coral‐reef fishes

Abstract

The importance of competition and predation in structuring ecological communities is typically examined separately such that interactions between these processes are seldom understood. By causing large reductions in native prey, invasive predators may modify native species interactions. I conducted a manipulative field experiment in The Bahamas to investigate the possibility that the invasive Pacific red lionfish (Pterois volitans) alters competition between planktivorous fairy and blackcap basslets (Gramma loreto and Gramma melacara, respectively). Competition between these coral-reef fishes is known to have symmetrical effects on the juveniles of both species, whereby the feeding positions under reef ledges and growth rates of these individuals are hindered. Following baseline censuses of local populations of competing basslets, I simultaneously manipulated the abundance of lionfish on entire reefs, and the abundance of basslets in local populations under isolated ledges within each reef, resulting in three treatments: unmanipulated control populations of both basslets, reduced abundance of fairy basslet, and reduced abundance of blackcap basslet. For eight weeks, I measured the change in biomass and feeding position of 2-5 cm size classes of each basslet species and calculated the growth rates of ~2 cm individuals using a standard mark-and-recapture method. Experimental populations were filmed at dusk using automated video cameras to quantify the behavior of lionfish overlapping with basslets. Video playback revealed lionfish hunted across all ledge positions, regardless of which basslet species were present, yet lionfish differentially reduced the biomass of only juvenile (2 cm) fairy basslet. Predation reduced the effects of interspecific competition on juvenile blackcap basslet as evidenced by corresponding shifts in feeding position toward coveted front edges of ledges and increases in growth rates that were comparable to the response of these fish in populations where competition was experimentally reduced. Thus, an invasive marine predator altered the outcome of interspecific competition via differential predation, which tipped the balance of competition between native prey species from symmetrical to asymmetrical effects on juveniles. This study reveals a newly demonstrated context in which predation can indirectly facilitate prey, further broadening our understanding of the interactive effects of predation and competition in the context of invasive species.

Frenemy at the gate: Invasion by Pheidole megacephala facilitates a competitively subordinate plant ant in Kenya

“…In contrast, P. megacephala invasion generates a landscape of unoccupied, low‐reward host plants, which shifts competition among acacia ants to the colony founding stage, favoring more strongly colonizing species with lower energetic requirements. Our results are consistent with other studies demonstrating that invasive species can facilitate natives (Rodriguez 2006, Collins et al 2017, Kindinger 2018, Goodman and Warren 2019, Rees et al 2019). For example, Kindinger (2018) showed that invasive lionfish ( Pterois volitans ) facilitated the native blackcap basslet ( Gramma melacara ) through differential predation on the basslet’s competitor on Bahamian reefs.…”

“…Our results are consistent with other studies demonstrating that invasive species can facilitate natives (Rodriguez 2006, Collins et al 2017, Kindinger 2018, Goodman and Warren 2019, Rees et al 2019). For example, Kindinger (2018) showed that invasive lionfish ( Pterois volitans ) facilitated the native blackcap basslet ( Gramma melacara ) through differential predation on the basslet’s competitor on Bahamian reefs. Reductions in the competitor’s abundance allowed the blackcap basslets to occupy more favorable foraging territories on the reef, leading to higher growth rates of this fish in the presence of the invader.…”

“…This facilitation can occur via a number of mechanisms; for example, invasive species can exert direct positive effects on native species by creating or modifying habitat (Wonham et al 2005, Thomsen 2010, Norkko et al 2012, Ramus et al 2017, Fill et al 2019), or by providing food (Chittka and Schurkens 2001, Shapiro 2002) or mutualistic services such as pollination (Moragues and Traveset 2005) or seed dispersal (Cumberland and Kirkman 2013). Alternatively, invasive species may indirectly benefit native species, for example by enhancing the services of shared mutualists (reviewed in Traveset and Richardson 2006, Bjerknes et al 2007; but see Morales and Traveset 2009), or by reducing the abundance or impact of a native species’ predators (Nelson et al 2010, Doody et al 2013) or competitors (Grosholz et al 2000, Kindinger 2018).…”

Shelter use interactions of invasive lionfish with commercially and ecologically important native invertebrates on Caribbean coral reefs

“…In addition to exerting non-consumptive effects, lionfish can also be subjected to these effects by humans; lionfish hide deeper in the reef and are more wary of humans as a consequence of lionfish culling programs [37,38]. Lionfish also exert non-consumptive effects through 'transmitter' species, for example lionfish predation on fairy basslet releases blackcap basslet from competition and allows them to occupy prime feeding locations on the reef [39]. Another type of non-consumptive impact is competition.…”

Behavioural Competition in the Intertidal Shore Crab, Petrolisthes elongatus

“…Intraspecific competition is thought to be more intense than interspecific competition due to the similar characteristics of individuals from the same species (Connell, 1983). Because it is such an important selection force, competition is often considered a main evolutionary driver of behavioural and physiological traits, as well as a key factor in affecting community structure (Connell, 1961;Bonin et al, 2015;Kindinger, 2018).…”