Abstract
Trait-mediated indirect interactions (TMII) can be as important as density-mediated indirect interactions. Here, we provide evidence for a novel trait-mediated cascade (where one TMII affects another TMII) and demonstrate that the mechanism consists of a predator eavesdropping on chemical signaling. Ants protect scale insects from predation by adult coccinellid beetles – the first TMII. However, parasitic phorid flies reduce ant foraging activity by 50% – the second TMII, providing a window of opportunity for female beetles to oviposit in high-quality microsites. Beetle larvae are protected from ant predation and benefit from living in patches with high scale densities. We demonstrate that female beetles can detect pheromones released by the ant when attacked by phorids, and that only females, and especially gravid females, are attracted to the ant pheromone. As ants reduce their movement when under attack by phorids, we conclude that phorids facilitate beetle oviposition, thus producing the TMII cascade.
Highlights
Long appreciated by traditional naturalists, the idea of a trophic cascade gained popularity in the ecological literature through debates that emerged from Hairston, Smith, and Slobodkin’s publication of the famous “green world hypothesis” (Hairston et al 1960)
Testing mated and unmated females demonstrated that the attraction to ant pheromones is manifested only after mating, and that before mating, female beetles have an aversion to ant pheromones (Fig. 4A)
Female beetles collected from the field showed an intermediate level of attraction to ant pheromones between that of unmated and mated females (Fig 4A)
Summary
Long appreciated by traditional naturalists, the idea of a trophic cascade gained popularity in the ecological literature through debates that emerged from Hairston, Smith, and Slobodkin’s publication of the famous “green world hypothesis” (Hairston et al 1960). At least since Darwin, are the indirect effects on morphologies (and/or physiologies and/or behaviors, etc....) so predominant in nature In modern literature, these special indirect effects that involve some sort of “trait” of the organism are distinguished from those that affect only the density or biomass of the organism and are termed trait-mediated indirect interactions (TMII). One’s imagination can create long links from simple natural history storytelling. This sort of linkage between TMII units has been discussed in the literature
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