A global systematic review of frugivorous animal tracking studies and the estimation of seed dispersal distances

Abstract

Seed dispersal is one of the most important ecosystem functions globally. It shapes plant populations, enhances forest succession, and has multiple, indirect benefits for humans, yet it is one of the most threatened processes in plant regeneration, worldwide. Seed dispersal distances are determined by the diets, seed retention times and movements of frugivorous animals. Hence, understanding how we can most effectively describe frugivore movement and behaviour with rapidly developing animal tracking technology is key to quantifying seed dispersal. To assess the current use of animal tracking in frugivory studies and to provide a baseline for future studies, we provide a comprehensive review and synthesis on the existing primary literature of global tracking studies that monitor movement of frugivorous animals. Specifically, we identify studies that estimate dispersal distances and how they vary with body mass and environmental traits. We show that over the last two decades there has been a large increase in frugivore tracking studies that determine seed dispersal distances. However, some taxa (e.g. reptiles) and geographic locations (e.g. Africa and Central Asia) are poorly studied. Furthermore, we found that certain morphological and environmental traits can be used to predict seed dispersal distances. We demonstrate that flight ability and increased body mass both significantly increase estimated seed dispersal mean and maximum distances. Our results also suggest that protected areas have a positive effect on mean seed dispersal distances when compared to unprotected areas. We anticipate that this review will act as a reference for future frugivore tracking studies, specifically to target current taxonomic and geographic data gaps, and to further explore how seed dispersal relates to key frugivore and fruit traits.

Keywords: GPS transmitter; animal behaviour; animal movement; frugivore; radio transmitter; seed dispersal; tracking.

FIGURE 1

The number of published studies per years that used tracking technology (GPS, radio transmitters or resource tracking) on frugivorous species (a) and the number of published studies per years that either calculated seed dispersal distances or focussed on other themes (b) between 1978 and 2022.

FIGURE 2

The geographic distribution of 162 frugivore tracking publications undertaken between 1978 and 2022. Number of studies per location are denoted by point size, with black points denoting studies undertaken inside protected areas, and red outside protected areas. Corresponding pie charts show the proportion of focal taxa represented in studies from each continent (Purple = Bird; Blue = Mammal; Green = Reptile; Yellow = Fish). Map colours represent the 14 biomes taken from Ecoregion Snapshots: Descriptive Abstracts of the Terrestrial Ecoregions of the World. 2021. Developed by One Earth and RESOLVE. Version 2021 <www.oneearth.org>. Downloaded on [April 2021].

FIGURE 3

The mean body mass of species tagged, with either GPS tags or radio transmitters, per study during 1978–2022, for frugivorous birds, and frugivorous mammals.

FIGURE 4

A comparison between tracking method (GPS & radio transmitters) and animal taxa (bird and mammal) with respect to (a) the mean number of tagging days and (b) the mean number of total location points collected per individual species per study.

FIGURE 5

The estimated (a) mean and (b) maximum seed dispersal distances of bird and mammal species in relation to their body mass. Regression lines for volant/non‐volant species are denoted by colour and show standard errors with a 95% confidence interval. Point shape denotes whether the study was conducted in a protected area or not. Images indicate the species for the closest circled point and from left to right indicate Oilbird (Steatornis caripensis), Central American agouti (Dasyprocta punctata), African forest elephant (Loxodonta cyclotis), Large Japanese field mouse (Apodemus speciosus), Straw‐coloured fruit bat (Eidolon helvum) and Southern cassowary (Casuarius casuarius).