2.2 Data extraction
For each study, data were extracted that detailed: 1) year of study, 2)
tracking method, 3) overall purpose of study, 4) country of study, 5)
habitat type, 6) taxonomic group and 7) species tracked (see
Supplementary Material 1). Quantitative information including the number
of individuals tracked, the average number of tracking days and the
average number of location points collected per individual tag were also
collated (see Supplementary Material 1). This information was calculated
from tracking summary results only when the total number of location
points and deployment days were stated. Some articles did not provide
sufficient information for these metrics to be calculated and these
studies were omitted from further analyses. Tracking method included
either radio transmitters (VHF), GPS or resource tracking with attached
radio/GPS tags. Frugivore species data included taxonomic group at a
species level, the number of species studied and the number of
individuals per species per study.
The mean number of tag days was calculated for each study where data
were provided. This was the mean number of days reported per study where
data were collected across all tracked individuals per species. The mean
number of tracking locations per species per study was also calculated
when this information was provided (see Supplementary Material 1).
Mean and maximum seed dispersal distances were stated in 45 and 56
publications, respectively (see Supplementary Material 2). When
publications presented estimates for different sized seeds or different
seasons, we took an average across the different estimates as there was
too much variability among studies to sub-divide data into different
seed sizes, season or different sexes etc.
To explore what factors influenced dispersal distance, we extracted
frugivore morphological traits and environmental variables from each
study to be used as predictors for our models. Estimates of mean species
body mass (g) for birds and mammals were extracted from Wilman et al
(2014). We categorised species as either volant (i.e.,
capable of flying) or nonvolant. This is functionally informative,
because in our data set a large proportion of the mammals studied were
bat species, while birds included some flightless species such as
cassowaries and emus.
If not mentioned in the publication, the geographic coordinates of each
study were derived from Google Earth to determine whether the study was
undertaken in a protected area. The study was defined as,such if the
animal was recorded within a protected area (i.e., national park or
reserve) at some point during the study. Each study site was categorised
by biome; these data were 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). The global
distribution of studies was also mapped. Temperate climates are
described as being > 35° or < -35° N and tropical
climates between 23.4° and -23.4° N. The Human Footprint Index (HFI)
value was extracted from Venter et al (2016) for each of the studies
where GPS coordinates were included. These coordinates were either the
coordinates given for the study area from the publications, or if not
mentioned, the coordinates of where the animal was released. In addition
to protected areas, HFI can be used as a proxy for identifying the
impact of human-modified landscapes on seed dispersal. Two studies, Weir
& Corlett (2007), and Wotton & Kelly (2012), were omitted from the
seed dispersal analysis as there was no HFI data available for these
locations. The HFI values extracted here use data from 2009 and do not
align exactly with the dates of our studies estimating seed dispersal
distances (ranging from 1987-2022), however we use these values as a
broad-scale indicator of human disturbance.