An invasive tree alters the structure of seed dispersal networks between birds and plants in French Polynesia

Abstract

Aim We studied how the abundance of the highly invasive fruit‐bearing tree Miconia calvescens DC. influences seed dispersal networks and the foraging patterns of three avian frugivores. Location Tahiti and Moorea, French Polynesia. Methods Our study was conducted at six sites which vary in the abundance of M. calvescens. We used dietary data from three frugivores (two introduced, one endemic) to determine whether patterns of fruit consumption are related to invasive tree abundance. We constructed seed dispersal networks for each island to evaluate how patterns of interaction between frugivores and plants shift at highly invaded sites. Results Two frugivores increased consumption of M. calvescens fruit at highly invaded sites and decreased consumption of other dietary items. The endemic fruit dove, Ptilinopus purpuratus, consumed more native fruit than either of the two introduced frugivores (the red‐vented bulbul, Pycnonotus cafer, and the silvereye, Zosterops lateralis), and introduced frugivores showed a low potential to act as dispersers of native plants. Network patterns on the highly invaded island of Tahiti were dominated by introduced plants and birds, which were responsible for the majority of plant–frugivore interactions. Main conclusions Shifts in the diet of introduced birds, coupled with reduced populations of endemic frugivores, caused differences in properties of the seed dispersal network on the island of Tahiti compared to the less invaded island of Moorea. These results demonstrate that the presence of invasive fruit‐bearing plants and introduced frugivores can alter seed dispersal networks, and that the patterns of alteration depend both on the frugivore community and on the relative abundance of available fruit.

Connecting Resource Tracking by Frugivores to Temporal Variation in Seed Dispersal Networks

“…Since evidence suggests that neighborhood effects in interspecific neighborhoods are likely to be facilitative (Carlo et al, 2007), the introduction of plants may increase fruit removal of neighbors (Gleditsch and Carlo, 2010; Figure 2A). However, competition for dispersers can also occur (Aslan, 2011;Spotswood et al, 2012). Introduced plants can change habitat structure, thereby influencing disperser foraging behaviors (Traveset and Richardson, 2006).…”

“…The resultant novel fruiting community would likely select for frugivores that are not neophobic, suggesting that they would be diet generalists. Introduced frugivores are often considered to be inferior dispersers of native plants compared to native frugivores (Chimera and Drake, 2010;Culliney et al, 2012;Spotswood et al, 2012;Wu et al, 2014). For example, the Hawaiian Islands have lost a majority of their native frugivorous birds, with only two thrush species remaining: the puaiohi (Myadestes palmeri) and the 'ōma'o (M. obscurus; Pejchar, 2015).…”

Seed dispersal networks in the Galápagos and the consequences of alien plant invasions

“…The end result might thus be a simplified plant community, which would tend to promote a less diverse community of dispersers [21].…”

“…In recent years, this growing realization has lifted the focus of conservation efforts from species to ecosystems [1,19]. While there is an increasing number of studies documenting different aspects of the dispersal of native and invasive plants by frugivores [10,20], the consequences of the integration of alien plants into seed dispersal networks has been poorly explored [21]. By contrast, several studies have evaluated the impact of alien plants upon pollination networks.…”

Protocol for Transferring Bare-rooted Native Plant Seedlings to Restoration Sites - Preventing the Spread of Invasive Species Contaminants

“…On Tahiti, key habitats for the Tahiti monarch are highly threatened by several introduced tree species such as miconia (Miconia calvescens) and the African tulip tree (Spathodea campanulata) which can form monospecific stands, overtaking native habitats and altering ecosystems (Meyer, 1996;Spotswood et al, 2012). A project aiming to restore the monarch's habitats through revegetation with native tree species and control of invasive tree species is currently underway.…”