Disrupted learning: habitat degradation impairs crucial antipredator responses in naive prey

Abstract

Habitat degradation is a global problem and one of the main causes of biodiversity loss. Though widespread, the mechanisms that underlie faunal changes are poorly understood. In tropical marine systems, corals play a crucial role in forming habitat, but coral cover on many reefs is declining sharply. Coral degradation affects the olfactory cues that provide reliable information on the presence and intensity of threat. Here, we show for the first time that the ability of a habitat generalist to learn predators using an efficient and widespread method of predator learning is compromised in degraded coral habitats. Results indicate that chemical alarm cues are no longer indicative of a local threat for the habitat generalist (the damselfish, Pomacentrus amboinensis), and these cues can no longer be used to learn the identity of novel predators in degraded habitats. By contrast, a rubble specialist and congeneric (Pomacentrus coelestis) responded to olfactory threat cues regardless of background environment and could learn the identity of a novel predator using chemical alarm cues. Understanding how some species can cope with or acclimate to the detrimental impacts of habitat degradation on risk assessment abilities will be crucial to defining the scope of resilience in threatened communities.

Fisheries productivity under progressive coral reef degradation

“…Reefs dominated by dead coral may also be less productive than our model predicts due to ecosystem consequences relating to losses of live coral obligates that we do not explicitly consider. A number of reef fish species preferentially recruit to live corals (Coker, Graham, & Pratchett, 2012;Feary, Almany, McCormick, & Jones, 2007;McCormick, Moore, & Munday, 2010), others depend on acoustic settlement cues provided by healthy reef habitats (Simpson, Meekan, Montgomery, McCauley, & Jeffs, 2005), and others still use live corals for predator avoidance cues (McCormick, Chivers, Allan, & Ferrari, 2016;McCormick & Lönnstedt, 2016) and food (Pratchett, Wilson, Baird, et al, 2006). The prevalence of coral specialists in the reef fish assemblage, their trophic importance, and the extent to which they are replaced by more generalist species when live corals die will ultimately determine whether food web dynamics and fisheries productivity will be negatively affected by their loss.…”

Risk assessment and predator learning in a changing world: understanding the impacts of coral reef degradation

“…A few studies have recently suggested that risk assessment by Ambon damselfish (Pomacentrus amboinensis) may be compromised in degraded habitats 23 24 25 . Indeed, these damselfish have a limited ability to use alarm cues for risk assessment when their alarm cues have been mixed with even small amounts of water from degraded coral habitats.…”

Interspecific differences in how habitat degradation affects escape response

“…This finding takes on even greater significance when paired with recent evidence showing that chemicals from degraded coral habitats negate the innate response of some fishes to damage-released odours from conspecifics 29 . Fishes of the same, closely-related or ecologically similar species elicit an innate antipredator response to these alarm odours because they represent a reliable indicator of an active predator in the vicinity 30, 31 .…”

“…Fishes of the same, closely-related or ecologically similar species elicit an innate antipredator response to these alarm odours because they represent a reliable indicator of an active predator in the vicinity 30, 31 . Research to date has shown that the ability to use alarm odours in degraded habitats is species specific, with one species no longer able to use alarm odours to inform risk (Ambon damselfish, Pomacentrus amboinensis ), while another species (the neon damsel, P. coelestis ) was not adversely affected 29 .…”