Shrikes, lizards and Lycium intricatum (Solanaceae) fruits: a case of indirect seed dispersal on an oceanic island (Alegranza, Canary Islands)

Authors


M. Nogales (fax 22253344; e-mail mnogales@ull.es).

Summary

  • Indirect seed dispersal in the system Lycium intricatum (Solanaceae)–lizards (Gallotia atlantica)–shrikes (Lanius excubitor) was studied in Alegranza, a xerophytic small island of the Canarian archipelago.

  • A total of 835 seeds (224 obtained from lizard droppings and 611 from shrike pellets) was found by analysing 123 droppings and 146 pellets. Lycium fruit remains (including seeds) were observed in 31.7% of the lizard droppings and 50% of the shrike pellets.

  • As would be expected for legitimate seed dispersers, external seed damage produced by each species was negligible. Lycium seeds were significantly matched with the presence of lizard remains in shrike pellets. Seeds in shrike pellets have come from fruit consumed by lizards that have been predated by the shrikes, and not directly from bird frugivory.

  • Seeds from shrike pellets showed significantly higher germination rates than those from uneaten fruits and lizard droppings.

  • It seems probable that different treatments in the guts of each species and retention time are two main factors influencing the germination process. While gut pass time in G. atlantica has been estimated to be 2.42 days on average, the retention time of a seed inside a shrike gizzard is much shorter (45–55 min).

  • This is a new case of the scarcely known phenomenon of indirect seed dispersal, which seems to acquire a relatively important role in small islands where the animal–plant interaction is very intense and all the elements of the system are native.

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