Colonization of an island volcano, Long Island, Papua New Guinea, and an emergent island, Motmot, in its caldera lake. V. Colonization by figs (Ficus spp.), their dispersers and pollinators

Abstract

Abstract Aim This study considered the colonization of disturbed island ecosystems by Ficus species (Moraceae). Specifically, we examined the extent of colonization (compared with source areas), differential roles of seed dispersing birds and mammals, and the Ficus fruit characters influencing mode of colonization. Location Research was conducted on Long Island (5°20′S; 147°10′E), a volcanic island 55 km from Papua New Guinea, which erupted catastrophically in c. 1645 with probable extirpation of all life. Renewed volcanic activity in the early 1950s produced a series of temporary islands in the volcano's caldera lake. One island, Motmot, present since 1968 has persisted. Methods Long Island and Motmot were surveyed over 15 days for Ficus species and their vertebrate dispersers and pollinating wasps. The Ficus community was compared with that of mainland sources areas and Ficus species present were characterised according to their figs' size, colour, crop size and height. Observations of frugivory and literature records were used to determine Ficus dispersal guild membership. Results At least 31 Ficus species have colonized Long Island since its eruption. Evidence of pollinator wasp colonisation was found for all sixteen Ficus species observed fruiting. Thirty‐six vertebrate species occurring on Long Island are identified as potential seed dispersers. Of these, fruit bats and pigeons are likely to have been instrumental in the island's early colonization with subsequent spread being facilitated by these frugivores as well as a number of smaller birds, and an introduced cuscus. Comparisons of fruit characters and frugivore attraction between Ficus species reveal two broad dispersal guilds. Members of the first guild produce relatively large, green figs in the lower strata of the forest and attract fruit bats. The second guild includes species that attract both birds and fruit bats with generally smaller, red figs produced throughout the vertical structure of the forest. Eight Ficus species have colonized Motmot, a 31‐year‐old emergent island in the volcano's crater lake. However, only one furgivore species was recorded alive on the island. Fig seeds are likely to have arrived during rare over‐flights or roosting visits by frugivores, or in the bodies of prey brought to Motmot by raptors. We found no evidence of pollinator presence on Motmot. Most Ficus individuals on Motmot remain immature and the figs of the only three individuals observed with crops had not been pollinated. Main conclusions Their numerical abundance and frequency of fruiting make figs an important resource in regenerating ecosystems. Ficus species differ in their ability to colonise degraded habitats because of differences in the design and presentation of their figs. Fruit bats are likely to be of special importance early in succession. Once the Ficus species on Motmot start to produce fruit regularly we can expect a rapid increase in the numbers of fleshy‐fruited plant species colonising the island.