Patterns of predator neophobia: a meta-analytic review

Abstract

Neophobia, the fear of novel stimuli, plays a major role in animal ecology. Here, we review studies on predator neophobia and explore its underlying patterns within an ecological framework. Predator neophobia is typically assessed by observing behaviours in novel areas that bring potential risk from unknown predators, or by observing behaviours towards certain kinds of objects and odours that are novel. We conducted a literature review across taxa, surveying research on baseline and induced neophobia versus controls. We calculated effect sizes for the intensity of neophobic responses, and categorized data according to six factors (taxa, age class, background type, trophic position, test cue type and experimental treatment type). While accounting for each of the other factors, we found that baseline neophobia was stronger among birds and mammals, and towards novel areas, relative to other taxa and cue types. Baseline neophobia was lower for wild-caught animals and for those that were higher in trophic position, compared with those reared in captivity and from lower trophic levels. By contrast, induced neophobia was similar in intensity across taxa, background types and testing cue types, while again being lower among upper trophic-level members and among juvenile animals. Although induced neophobia occurred across all treatment types, brain lesions induced stronger neophobia than predation risk or social isolation. We discuss potential mechanisms underlying these results and highlight gaps in the literature.

Keywords: fear; noetic; novelty; predation; risk; uncertainty.

Figure 1.

(a) The ‘neophobia threshold hypothesis', adapted from Greenberg [11], predicting that the probability of gaining novel resources depends on aversion to novelty, whereby generalist species are less neophobic and gain novel resources more than specialist species. (b) The ‘dangerous niche hypothesis’, adapted from Greenberg [33], where neophobia increases with the level of danger in the niche. (c) Theoretical model where neophobia decreases with age in some species as threats become less dangerous versus a model where species become more neophobic with age because they have more assets to protect [34]. (d) Theoretical effect of the frequency of novelty on predator neophobia in high- and low-risk environments in the context of the ‘risk allocation hypothesis' [35]. (e) Theoretical model for how neophobia in animals that are certain about risk may be influenced by a risk threshold.

Figure 2.

Estimated marginal means (±s.e.) for baseline neophobia scores by (a) taxa (Actinopterygii, Amphibia, Aves, Gastropoda, Malacostraca, Mammalia), (b) age class, (c) background type, (d) trophic position and (e) test cue type. Numbers above bars represent data replicates. Asterisks indicate significant differences, and bars sharing the same letter are not statistically different (n.s., non-significant). The neophobia score compares levels of each factor independently of other factors (i.e. not the raw/uncorrected levels of neophobia).

Figure 3.

Estimated marginal means (±s.e.) for induced neophobia scores. Details are as in figure 1, with the addition of the inducing treatment type (brain lesion, castration, drugs, predation-related cues, isolation). (a) Act, Actinopterygii; Amp, Amphibia; Ave, Aves; Mam, Mammalia.