DOI: 10.25338/b8rw6j
title: Personality, spatiotemporal ecological variation, and resident/explorer movement syndromes in the sleepy lizard

description: Individual variation in movement is profoundly important for fitness and
 offers key insights into the spatial and temporal dynamics of populations
 and communities. Nonetheless, individual variation in fine-scale movement
 behaviours are rarely examined even though animal tracking devices offer
 the long-term, high-resolution, repeatable data in natural conditions that
 are ideal for studying this variation. Furthermore, of the few studies
 that consider individual variation in movement, even fewer also consider
 the internal traits and environmental factors that drive movement
 behaviour which are necessary for contextualising individual differences
 in movement patterns. In this study, we GPS-tracked a free-ranging
 population of sleepy lizards, Tiliqua rugosa, each Austral spring over
 five years to examine consistent among-individual variation in movement
 patterns, as well as how these differences were mediated by key internal
 and ecological factors. We found that individuals consistently differed in
 a suite of weekly movement traits, and that these traits strongly covaried
 among-individuals, forming movement syndromes. Lizards fell on a primary
 movement continuum, from ‘residents’ that spent extended periods of time
 residing within smaller core areas of their home range, to ‘explorers’
 that moved greater distances and explored vaster areas of the environment.
 Importantly, we also found that these consistent differences in lizard
 movement were related to two ecologically important animal personality
 traits (boldness and aggression), their sex, key features of the
 environment (including food availability, and a key water resource),
 habitat type, and seasonal variation (cool/moist vs hot/drier) in
 environmental conditions. Broadly, these movement specialisations likely
 reflect variation in life-history tactics including foraging and mating
 tactics that ultimately underlie key differences in space use. Such
 information can be used to connect phenotypic population structure to key
 ecological and evolutionary processes, for example social networks and
 disease-transmission pathways, further highlighting the value of examining
 individual variation in movement behaviour.
description: The following description is from Michelangeli et al. (2021) but
 modified for brevity. Note that citations have been removed, but can be
 found in Michelangeli et al. (2021) <b>Study
 system</b> The sleepy lizard is a common skink
 species to South Australia. They are large-bodied (adults are 400 – 950g,
 snout-vent-length 25 – 35 cm), long-lived (up to ~48 years) and
 slow-moving. They have been found to maintain relatively stable and
 consistent home ranges (HR) over multiple years (our tracking covering up
 to 8 years; mean 95% HR area in hectres [95% CI]; females: 3.53 [3.07,
 4.01] and males: 4.91 [4.42, 5.43]). We studied a population within a
 ~1.2km<sup>2</sup> field site near Bundey Bore Station
 (33.888240 S, 139.310718 E). Our field site has semi-arid Mediterranean
 climate and is primarily chenopod shrubland dominated by bluebush
 (<i>Maireana sedifolia</i>) and some black oak
 (<i>Casuarina cristata</i>). Various annual plants, including
 the lizards’preferred food item, the invasive Ward’s weed,
 <i>Carrichtera annua</i> , tend to grow around and under these
 shrubs. The field site has a seasonal dam that retains water and soil
 moisture for longer than other parts of the area. Lizards at this field
 site are primarily active from September (early spring) to December (early
 summer). The beginning of the lizard’s activity period is characterised by
 moderate temperatures and higher relative abundance of food and water.
 Early spring is also the breeding season in which lizards form monogamous
 pairs for up to 10 weeks before they mate. During this time males perform
 more scent-marking and competition is higher, potentially leading to sex
 differences in movement behaviour early in the season. On the other hand,
 the late season is hotter and drier, and food and water resources become
 increasingly scarce and patchier in distribution.  
 <strong>GPS data collection</strong>
 Sleepy lizards were GPS tracked during their activity season
 between 2013-2017. The GPS data was filtered to remove all errors and
 points that were outside a lizards primary activity period (between 06:00
 and 20:00). The data was also thinned to follow a 20 min resolution. Using
 the wrangled GPS data, we calculated six movement metrics - daily distance
 travelled, max daily displacement, straightness index, residence time,
 home range size and home range use ratio. These metrics are commonly used
 to represent a range of possible movement and spatial patterns that we
 predicted might vary among lizards. To enable comparison between all
 metrics, we averaged the daily scale metrics within weeks. To eliminate
 correlation between the number of weekly GPS points and corresponding
 movement metric value, we only included weeks in our analysis with at
 least 120 GPS locations (which represents ~ 3.5 days of GPS data). we
 obtained GPS data from 128 lizards and a total of 569341 GPS fixes (after
 sub-sampling that data to 20 min intervals). From these data, we obtained
 on average 17 ± 11.6 (mean ± SD; range 2 – 45) weekly replicates for each
 movement metric over an average of 2.35 ± 1.4 (range 1-5) years per
 lizard. Each weekly replicate contained on average 189.64 ± 30.00 GPS
 points <strong>Measurement of lizard internal
 traits</strong> In addition to the movement data,
 we also collected data on each lizards size every 2 weeks. Between
 2015-2017 seasons, lizard aggression and boldness behaviour was also
 assayed 2-3 times per year, with each trials occuring at least 2 weeks
 apart. . To assess a lizard’s boldness, we measured a lizard’s response to
 a preferred food item (a piece of banana) in the presence of a potential
 threat (a looming observer). A lizard’s boldness was ranked based on their
 response, from quickly approaching the food item and the observer (high
 boldness rank), to showing very little response (intermediate boldness),
 to quickly fleeing from the observer into refuge (shy). Boldness was
 ranked on a 1-10 scale in 2015 and on a 1-7 scale in 2016-2017, but higher
 ranks always referred to bolder animals and thus ranks were standardized
 within year (by subtracting the mean and dividing by the standard
 deviation). To assess a lizard’s aggression, we ranked a lizard’s response
 to a simulated capture attempt by an observer which involved the
 observer’s hand coming to within ~10 cm of the lizard’s head. Responses
 were ranked on a scale of 1-11, from fleeing the observer into refuge
 (passive = 1) to attempting to bite the observer (high aggression = 11).
 Both aggression and boldness have shown to be repeatable over an 8-year
 period (r ± SE = 0.43 ± 0.05 and r = 0.27 ± 0.04, respectively), and are
 only weakly positively correlated suggesting independence between the
 traits (correlation coefficient ± 95% CI = 0.15 [-0.07, 0.39]). In the
 present study, we used the average personality score for each individual
 within each year in our analysis
 <strong>Measurment of environmental
 variables</strong> From the movement trajectories
 within each year, we calculated an individual’s mean weekly distance from
 the dam (DamDist) and the number of unique visits to the dam (i.e.
 DamVisits). A unique visit to the dam involved a lizard entering and then
 leaving a 15m radius around the dam. The dam is the only reliable water
 resource at our field site, and lizards are often observed in this area,
 but we also know that approximately only about 50% of our study population
 access the dam within a given year. We also calculated a lizard 95% weekly
 HR overlap with ‘forested’ habitat (ForestHR). Forested areas tend to
 contain denser vegetation and refuge for lizards and may be preferred by
 lizards seeking shelter. Forested habitats were defined by drawing
 polygons around forested regions based on satellite images from Google
 Earth. During 2015 -2017, we also conducted habitat surveys of food
 quality in 123 quadrats distributed in a grid over the field site. Within
 each quadrat, we surveyed a 40m radius around a central point, and ranked
 the availability of moist food (i.e. primarily Ward’s weed) on a 1-5
 scale. Since lizard HRs could include multiple quadrats, we averaged the
 quadrat food scores within a lizard’s 95% HR, weighted by the usage of
 that quadrat (relative to usage of all quadrats within the focal lizard’s
 95% HR), within each week, (FoodQualityHR).