Invasive Species Compendium

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Abstract

Seed dispersal by common ravens Corvus corax among island habitats (Canarian Archipelago).

Abstract

The role of the common raven (Corvus corax; Corvidae) as a seed dispersal agent for plants in the Canary Islands was studied by analysing 2672 pellets collected from all islands of the archipelago. Seeds of 16 species of phanerogams were found (four endemic to the Canaries, three endemic to the Macaronesian islands, six not endemic and three introduced by man). Vegetation in this archipelago is highly structured according to altitude, creating different types of macrohabitats. The quality of the transport of seeds between habitats was evaluated in a preliminary way by making use of the very high fidelity of the plant species to particular macrohabitats. Of the 102 580 potentially fertile seeds (excepting the other 51 061 infertile Ficus carica seeds) transported by common ravens, 76.5% were regurgitated in theoretically suitable habitat while the remaining 23.5% were taken to habitats that were not appropriate for establishment. Common ravens improved germination of six species, whereas an opposite effect was observed for three others. The percentage of viable seeds did not differ for any species between pellet seeds and seeds collected directly from the plants. Considering results from germination and viability experiments and macrohabitat patterns of dispersal, the common raven appears to be an important disperser for nine plant species: Lycium intricatum (Solanaceae), Opuntia ficus-indica (Cactaceae), Rubia fruticosa and Plocama pendula (Rubiaceae), Juniperus turbinata and J. cedrus (Cupressaceae), Phoenix canariensis (Arecaceae), Asparagus pastorianus (Liliaceae), and Myrica faya (Myricaceae).