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Ecological traps are maladaptive behavioural scenarios in which animals
prefer to settle in habitats with the lowest survival and/or reproductive
success. Aquatic insect species, for example, are attracted to sources of
horizontally polarized light associated with natural water bodies, but
today they commonly prefer to lay their eggs upon asphalt roads and
buildings that reflect an unnaturally high percentage of polarized light.
Ecological traps are a rapidly emerging threat to the persistence of
animal populations, but the degree to which species vary in their
susceptibility to them remains uninvestigated. We designed a field
experiment to (1) assess the relative susceptibility of aquatic flies
(Diptera) to a single maladaptive behavioural cue: variation in degree of
horizontally polarized light (d), and (2) quantify how the isolation of an
ecological trap from a high-quality habitat affects its relative
attractiveness. We exposed wild dipterans to experimental test surfaces
varying in d at three distances from natural streams and mapped
behavioural reaction norms of habitat preference as a function of d and
distance from high-quality habitat. All seven of the dipteran families
were captured most in traps with progressively higher d values, especially
those (d = 90–100%) that exceeded that of natural water bodies (30–80%).
In most taxa, the height and slope of numerical responses to d were
influenced by the distance of an ecological trap from a natural water
body. Our results illustrate that dipterans have broadly evolved the use
of a habitat selection behaviour that treats more strongly polarized light
sources as indicative higher-quality habitats, making them broadly
susceptible to ecological traps driven by polarized light pollution. We
also found that the spatial isolation of ecological traps from
higher-quality, but less attractive, habitats can either increase or
reduce species' susceptibility to them.
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