Influence of moonlight on temporal overlap intensity
We calculated the Relative Abundance Index (RAI) at each trap site as
the number of detections per 100 camera-trap days of every species in
the two seasons (Yang et al., 2019) (Table 2). Each camera trap was
considered as an independent spatial point for determining animal
nocturnal activity by selecting records occurring between sunset and
sunrise. The clock time of sunrise and sunset varies slightly over the
course of the year depending on distance from the equator and time of
year. To account for these successive changes of daylight hours
throughout the year (Nouvellet et al., 2012), we used the ‘sunTime’
function of the ‘overlap’ package version 0.3.2 in R to map times to
radians for analysis (see (Meredith and Ridout, 2020) for details). The
activity pattern of each species was fitted non-parametrically as kernel
density functions with the package ‘Overlap’ using the default bandwidth
parameters (Meredith and Ridout, 2014, Meredith and Ridout, 2020),
following the assumption that animals are equally likely to be ‘trapped’
throughout any period of their activity (Linkie and Ridout, 2011).
Circular density curves were compared using the coefficient of
overlapping (‘overlap coefficient’∆), with values ranging from 0 (no
overlap) to 1 (complete overlap), as proposed by (Ridout and Linkie,
2009). Lunar activity was categorized using Moonrise 3.5 software (Free
data source https://moonrise.informer.com) to obtain the moon phase for
each observation based on moon phase data stamped on camera trap images,
location of study area and its date. Moon phase was scaled to radians so
that 0 corresponds to New Moon, π/2 as First Quarter, π as Full Moon,
and 3π/2 as Last Quarter, as described by (Pratas‐Santiago et al., 2017,
Prugh and Golden, 2014) and further details to see the conceptual model
in (e.g. Figure 2).
We estimated the overlap coefficient (∆) for nocturnal activity between
leopard-prey species pairs and night vs daytime for each species sets at
four moon phases. In addition, to test the predictions of the predation
risk and visual acuity hypotheses, we computed the number of independent
records in each quarter of the moon phase for each species at the night
by dividing the moon phase cycle from 0 to 2π using four identical
quadrants centered on every moon phase (for illustration: First Quarter
from 1/4 π to 3/4π). The percentage of records in each lunar phase for
each species was calculated, with the assumption that lack of any
pattern would be shown by 25% of activity occurring during each of the
four lunar phases. A deviation from 25% activity during the full moon
phase was interpreted as follows: (1) species with less than or equal to
20% of records during full moon were classified as lunar phobic; (2)
those with more than or equal to 30% of records during full moon were
considered lunar philic (e.g; Figure 2), and; (3) species that did not
qualify as lunar phobic or lunar philic exhibited no pattern or
irregular (Prugh and Golden, 2014).