Abstract
Habitat quality has direct effects on the evolutionary fitness of breeding organisms, which is why it is believed that animals tend to have an evolved preference for the best possible habitats. However, some animals may mistakenly choose to reproduce in habitats that decrease their fitness, resulting in ‘ecological traps’. In this study, we tested whether great tits (Parus major) attracted to areas affected by outbreaks of the great web-spinning sawfly (Acantholyda posticalis) had fitness detriments characteristic of ecological traps. Sawfly larvae consume pine needles, which decreases resource availability for birds co-habiting the forest. Using artificial nesting sites, we found that great tits inhabiting areas of sawfly outbreaks had similar clutch sizes as tits breeding in healthy forest patches; however, the fledgling number was significantly lower, and fledgling condition was worse in the damaged forests. While moth larvae are the most important food for bird nestlings, the forest patches damaged by sawflies had lower larval biomass. Although most ecological traps occur in environments altered by humans, this study shows that pest insects can lower habitat quality, forming ecological traps. Our results indicate that attracting cavity-nesting birds should be done with caution because it may negatively impact birds’ nutritional status and reproductive fitness.
Highlights
Evolution creates variation in the genetic tapestry of life via natural selection
We show that forests damaged by pest insects are transformed into ecological traps in such cases when artificial nest boxes are provided for hole-nesting birds
The use of nest boxes to attract cavity-nesting birds to areas of insect outbreaks is a traditional measure to protect forest ecosystems. These forests can become deteriorated by pest insects so that the attracted birds lack sufficient resources to feed their offspring
Summary
Evolution creates variation in the genetic tapestry of life via natural selection. One of the principal drivers of natural selection is adaptation to different environments or ecological niches: some genetic variants become favored over others in certain environments (Schluter 2009; Luoto 2019a, b; Rees et al 2020), resulting in variation in the diverse forms that life takes (Darwin 1859). When environments change rapidly, and when organisms lack adequate genetic, behavioral, and/or phenotypic plasticity, organisms may end up choosing habitats that are detrimental to their fitness. Such outcomes are termed ‘ecological traps’ (Sherley et al 2017; Sun et al 2020).
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