Long seed dispersal distances by an inquisitive flightless rail (Gallirallus australis) are reduced by interaction with humans.

Joanna K Carpenter,Elena Moltchanova,Dave Kelly,Colin F J O'Donnell

doi:10.1098/rsos.190397

Abstract

Human presence is becoming increasingly ubiquitous, but the influence this has on the seed dispersal services performed by frugivorous animals is largely unknown. The New Zealand weka (Gallirallus australis) is an inquisitive flightless rail that frequently congregates in areas of high human use. Weka are important seed dispersers, yet the seed dispersal services they provide are still poorly understood. We estimated seed dispersal distances of weka for two plant species (Prumnopitys ferruginea and Elaeocarpus dentatus) and tested how human interaction affected these dispersal distances. We estimated weka seed dispersal distances by combining GPS data from 39 weka over three sites with weka seed retention time data in a mechanistic model. The mean seed retention times were extremely long (38–125 h). Weka were highly effective dispersers, dispersing 93–96% of seeds away from parent canopies, and 1% of seeds over 1 km. However, we found evidence of a significant human impact on the seed dispersal distances of weka, with birds occupying areas of high human use performing 34.8–40.9% shorter distances than their more remote counterparts. This represents an example of cryptic function loss, where although weka are still present in the ecosystem, their seed dispersal services are impaired by human interaction.

Highlights

Human presence is becoming increasingly ubiquitous, but the influence this has on the seed dispersal services performed by frugivorous animals is largely unknown
The New Zealand weka (Gallirallus australis) is an inquisitive flightless rail that frequently congregates in areas of high human use
We found evidence of a significant human impact on the seed dispersal distances of weka, with birds occupying areas of high human use performing 34.8–40.9% shorter distances than their more remote counterparts. This represents an example of cryptic function loss, where weka are still present in the ecosystem, their seed dispersal services are impaired by human interaction

Summary

Introduction

Human presence is becoming increasingly ubiquitous, but the influence this has on the seed dispersal services performed by frugivorous animals is largely unknown. Seed deposition patterns affect recruitment and colonization rates, the ability of plants to escape climate change effects, gene flow between plant populations, and forest community composition [9,10,11,12] All these problems are magnified because at the same time as fragmentation reduces the mobility of seed dispersers, it increases the dispersal distances required to maintain gene flow and may reduce the density of dispersers. Even in landscapes that do not suffer from structural anthropogenic modifications like roads or habitat fragmentation, human presence is becoming increasingly pervasive, and this may directly affect the vagility and effectiveness of seed-dispersing animals. Understanding the dispersal distances provided by weka may give insights into the seed dispersal capabilities of flightless rails as a group, which were once common across the Pacific but have suffered widespread extinctions there in the last 3000 years [22]

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