Potential role of frugivorous birds in the recovery process of forest vegetation after feral goat eradication in Mukojima Island, the Bonin Islands

Abstract

Some introduced frugivorous birds disperse introduced plants and are thus a substitute for extinct native birds. Introduced birds have negative and/or infrequently positive effects on local ecosystems. It is important for management of the ecosystems to understand the relationships between native and introduced frugivorous and plant species. In this study, we elucidated these relationships in Mukojima Island, the Bonin Islands, where was anthropologically deforested and Japanese White-eye Zosterops japonicus and some plants were already introduced. We examined the habitat selection of frugivorous birds, actual dispersed seeds in bird feces, and the distribution of the potentially dispersed plant species. The Japanese White-eye and the native, Blue Rockthrush Monticola solitarius, were dominant on this island. The former mainly used the forest area and dispersed only small seeds and frequently introduced plant seeds. The latter mainly used the open area and dispersed both small and large seeds. Some small-seed plants occurred not only in the forest but also in the open area. Their seedlings were distributed farther from their adult trees than the large-seed species. These indicate that small-seed plants would be more spread than the large-seed plants because the two bird species disperse their seeds in different environments. This introduced bird species may be important in vegetation recovery, although it may contribute to the distribution of introduced plants on this island.

Fruit colour conceals endocarp dimorphism from avian seed dispersers in a tropical beach plant,Scaevola taccada(Goodeniaceae), found in Okinawa

“…In fact, frugivorous birds seem not to distinguish the morphotypes as they consumed C+ fruits (Emura et al . 2012, Kawakami et al . 2009) in areas where both morphotypes were found (Emura et al .…”

“…The single-and double-cone sensitivity of the blue tit Cyanistes caeruleus (Hart et al 2000) with its cone abundance (Hart 2001) were adopted because observed seed dispersers of the plant are the blue rock-thrush Monticola solitarius (Emura et al 2012) and the browneared bulbul Hypsipetes amaurotis stejnegeri (Kawakami et al 2009), both of which are classified as Passerida, and thus, likely to have the UVS (ultraviolet sensitive) vision (Ödeen et al 2011).…”

“…It is likely that S. taccada seeds are dispersed by ocean currents as well as by frugivorous birds (Emura et al . 2012, Howarth et al . 2003).…”

“…Scaevola taccada is a widely distributing tropical beach plant, whose fruits have an endocarp composed of a cork substrate around the seed, facilitating flotation (Emura et al 2014). It is likely that S. taccada seeds are dispersed by ocean currents as well as by frugivorous birds (Emura et al 2012, Howarth et al 2003. However, Emura et al (2014) discovered a cryptic dimorphism in the endocarp of this plant: although most plants bear fruit with the cork endocarp (C+), fruits of some individuals consistently lack such a structure (C-), even though both types of fruit have sugar-containing flesh around the seed.…”

Dimorphism of the seed‐dispersing organ in a pantropical coastal plant, Scaevola taccada: heterogeneous population structures across islands

“…In addition, both fruit types are foraged by frugivorous birds, such as the Blue Rock Thrush Monticola solitarius and the Brown-eared Bulbul Hypsipetes amaurotis (C-morph: Kawakami et al 2009;Emura et al 2012;NC-morph: Emura, unpublished). However, because the NC-morph fruit has characters adapted for bird dispersal, it may be more useable by frugivorous birds than the C-morph fruit.…”