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Plant defence syndromes on islands

Citation

Moreira, Xoaquín (2021), Plant defence syndromes on islands, Dryad, Dataset, https://doi.org/10.5061/dryad.qbzkh18jf

Abstract

Aim: It has been hypothesised that insular plant taxa have evolved reduced defences in response to lower herbivore pressure on islands. However, the few studies testing this hypothesis have addressed variation in individual defensive traits, without paying attention to patterns of correlated trait expression (i.e. defence syndromes).

Location: Balearic and Canary Islands.

Taxon: Ninety-one woody plant species.

Methods: We tested whether plant species with contrasting histories of insularity (namely: endemics, non-endemic natives, and exotics) differed in their patterns of variation for a suite of morphological and chemical traits putatively associated with herbivory. For this, we measured eight leaf traits of 42 endemic, 29 native non-endemic, and 20 introduced species for which specimens were sourced from botanical gardens found in two archipelagos: the Balearic and Canary Islands.

Results: We conducted phylogenetic-controlled analyses which showed that, contrary to predictions, insular taxa (endemics and non-endemic natives) across both archipelagos similarly exhibited thicker, smaller, leaves with less nutrients and were physically more defended (especially the Balearic species) than exotic species. There were no differences in chemical defence (phenolic compounds) between endemics, non-endemic natives, and exotics. Finally, we also found what appeared to be differential syndromes between archipelagos: whereas species from the Balearic Islands were more physically defended, on average, those from the Canary Islands had higher chemical defences.

Main conclusions: Overall, these results point to a functional-physical defence syndrome characteristic of insular plant taxa that is indistinct for endemic and non-endemic taxa, relative to introduced species, as well as quantitative and qualitative differences in defences between archipelagos owing to differences in species composition and likely also to different histories of biotic or abiotic pressure.