Effects of an invasive predator cascade to plants via mutualism disruption

Abstract

Invasive vertebrate predators are directly responsible for the extinction or decline of many vertebrate species, but their indirect impacts often go unmeasured, potentially leading to an underestimation of their full impact. When invasives extirpate functionally important mutualists, dependent species are likely to be affected as well. Here, we show that the invasive brown treesnake, directly responsible for the extirpation of forest birds from the island of Guam, is also indirectly responsible for a severe decline in plant recruitment as a result of disrupting the fruit-frugivore mutualism. To assess the impact of frugivore loss on plants, we compare seed dispersal and recruitment of two fleshy-fruited tree species on Guam and three nearby islands with intact disperser communities. We conservatively estimate that the loss of frugivorous birds caused by the brown treesnake may have caused a 61–92% decline in seedling recruitment. This case study highlights the potential for predator invasions to cause indirect, pervasive and easily overlooked interaction cascades.

Conflicting selection onCneorum tricoccon(Rutaceae) seed size caused by native and alien seed dispersers

“…; Rogers et al. ). Such impacts have been documented mostly on oceanic islands (e.g., Sax and Gaines ) but also on mainland areas (e.g., Ceballos et al.…”

Feminization of Male Brown Treesnake Methyl Ketone Expression via Steroid Hormone Manipulation

“…Through these faunal impacts, the brown treesnake is attributed with altering the native ecology of Guam (Mortensen et al 2008). For example, the loss of endemic bird species disrupted crucial mutualisms and caused a subsequent decline of rare plants (Rogers et al 2017;Traveset and Richardson 2006). To ameliorate the impacts of Boiga on Guam, primary management strategies have centered on trapping to maintain snake-free areas and/or distributing lethal baits specifically designed for wide-area suppression (Kimball et al 2016;Smith et al 2016).…”

Seed dispersal increases local species richness and reduces spatial turnover of tropical tree seedlings

“…These pronounced changes in patterns of seedling regeneration highlight the importance of dispersal in maintaining patterns of diversity in tropical forests. in the world to have lost vertebrate dispersal services (8), providing a unique opportunity to evaluate the role of dispersal in driving spatial patterns of diversity by comparing forest processes on Guam with those on neighboring islands.…”

“…Dispersal is thought to be a key process underlying this diversity, contributing to high local species richness by allowing the seeds arriving at a site to be drawn from a wide species pool (3,4) and influencing the spatial arrangement of species by moving seeds away from parent trees, reducing conspecific aggregation (4)(5)(6)(7)(8). However, it has proven extremely difficult to quantify the contribution of seed dispersal to local diversity and spatial patterning in forests because it is confounded with other processes, including environmental variation, to which species differentially respond (2,9); historical legacies, such as past disturbance (10); other biotic interactions, such as competition and predation (11,12); and stochastic variation (13).…”

“…1) and their presence on the nearby islands of Saipan and Rota (8,26,27), to quantify the contribution of vertebrate seed dispersal to local species richness (alpha diversity) and spatial turnover (beta diversity) of tree seedlings. The three islands have a similar climate and geology; contain native forests of very similar species composition; and originally had a similar composition of vertebrate seed dispersers, comprising only birds and bats with no native vertebrate herbivores.…”