Fruit consumption, seed dispersal and seed fate in the vine Strychnos erichsonii in a French Guianan forest

Abstract

Fruit removal and seed dispersal of three individuals of the vine Strychnos erichsonii (Loganiaceae) were investigated in a mature forest of French Guiana, during the season of minimal flower and fruit production. Five visitor species, birds and diurnal or nocturnal arboreal mammals, were observed, while one terrestrial rodent was collected in traps baited with S. erichsonii seeds or fruit pulp. One diurnal and one nocturnal mammal dispersed seeds at long distance. Arboreal frugivores consumed fruits as soon as they became ripe and also ate unripe fruits. Fruit-traps revealed a higher fruit removal during the night for the two more productive vines (‘instantaneous’ productivity). More than two-thirds of the seeds checked along transects until 30 m for the parent plant were dead or infested, without obvious relationship with the seed localisation (under or beyond the crown). However, the proportion of intact vs dead/infested seeds beyond the crown was higher for the more productive plant (‘overall’ productivity), suggesting predator satiation. Seed density decreased sharply in the first meters from the parent plant, but remained noticeable until 15 m after the crown on some transects. Seedlings were very few and distributed independantly of their position under or beyond the crown. A high seed mortality, a low number and a high turnover of seedlings under and in the vicinity of the parent plant suggest a crucial importance of long distance dispersal for the plant recruitment Seed dispersal seems to be performed by a small number of varied species. Based on its regular fruiting period during the season of flower and fruit scarcity, and its large place in the diet of several frugivores mammals, S. erichsonii is probably an importante resource for these species during the season of food scarcity.