DOI: 10.5061/dryad.31zcrjdn6
title: Data from: Can matrix structure affect animal navigation between fragments? A dispersal experiment using release platforms

description: The persistence of species in fragmented landscapes relies on landscape
 connectivity and individuals’ ability in dispersing among habitat patches.
 Accordingly, matrix structure can affect the orientation of dispersing
 individuals across the landscape. In this study, we measured the impact of
 matrix structure on the dispersal performance of the white-eared opossum
 (Didelphis albiventris). We released individuals in three types of matrix:
 bare field, corn crops and soybean crops, with distances of 30, 50 and 100
 m to the nearest habitat patch. To test if the release height would affect
 the individuals' dispersal performance, we released animals from the
 ground and from 2 m high platforms. We released and tracked 14 individuals
 in bare field on the ground; 30 in corn crops, 22 on the ground and 8 on
 platforms; 17 on soybeans crop, 12 on the ground and 5 on platforms. The
 type of matrix influenced the perceptual range. Perceptual range was 100 m
 in bare field, 50 m in cornfield and less than 30 m in soybean field. The
 platforms only increased the perceptual range of individuals in the
 cornfield from 50 to 100 m. Visual and olfactory cues would cause this
 effect. We conclude that matrix structure affects dispersal performance,
 and that vertical elements of the matrix, such as scattered trees, may
 increase orientation in crop fields during inter-patch dispersal.
description: 2.1 Study species As a model organism, we
 chose the white-eared-opossum, Didelphis albiventris (Lund 1840), which
 occurs from French Guyana until Argentina, except in the Amazon Basin
 (Emmons & Feer, 1990). This species is common in the Brazilian
 savanna and easily found in urban areas within the region. D. albiventris
 is the largest Brazilian didelphid; it is nocturnal, solitary, habitat
 generalist, scansorial and omnivorous (Cabrera & Yepes, 1960;
 Cáceres, 2002; da Fonseca et al., 1982). Studies on patch occupancy,
 inter-patch movements, or environmental requirements of this species are
 rare. In the Atlantic Forest D. albiventris was captured only inside
 forest patches (Umetsu et al., 2008) and, although it is able to maintain
 populations in small fragments, it was absent in most of them (Asfora
 & Pontes, 2009). Regarding matrix use, D. albiventris usually
 is<br> not found at crops (Gheler-Costa et al., 2012; Scheibler
 & Christoff, 2007), or is found in very low abundance and usually
 near to the forest border (Bilenca et al., 2007). Taken together, these
 studies suggest that non-forest matrices are not suitable habitats for D.
 albiventris. This avoidance of deforested matrices, coupled with its
 easiness to capture, makes D. albiventris an excellent model to understand
 inter-patch movements and dispersal in fragmented landscapes.
 2.2 Animal Capture and Translocation We
 captured D. albiventris individuals in urban forest fragments, houses and
 commercial buildings in the municipality of Campo Grande, state of Mato
 Grosso do Sul, Brazil. The annual average temperature in the study area is
 23°C and the annual average precipitation is 1.500 mm (Coleti et al.,
 2007). Forest fragments in Campo Grande are woodland savanna remnants,
 with tropical climate (Aw Köppen), dry winter and wet summer. Most
 captures occurred around and inside the Federal University of Mato Grosso
 do Sul campus (20°29'59"S, 54°36'49"W). We captured
 individuals using Tomahawk live traps (40.6 x 12.7 x 12.7cm). We
 distributed five to forty traps randomly in the urban forest fragments,
 houses, and building roofs, where the species was reported. We did not use
 in the experiments, and we released on the capture sites, young
 individuals and pregnant or lactating females. Other individuals were
 placed in individual cages and kept at the laboratory from 4 to 72h before
 translocation and release. The laboratory was a large climate-controlled
 room. We offered to the animals enough food and water for the duration of
 their stay. All individuals used in the experiment were weighted, sexed,
 marked with ear-tags, and had their age estimated by counting the number
 of molars (Macedo et al., 2006). We observed the individuals, and
 individuals who appeared unhealthy, or had atypical behaviour were not
 used in the experiment. From the laboratory, we carried the individuals in
 opaque fabric bags to the experimental area. These bags precluded
 individuals from seeing the environment, thus reducing possibility of
 orientation before release; they also reduced the stress of manipulation
 during transport. All procedures were approved by Brazilian Institute of
 Environment (License n°.: 51900) and Committee on Animal Research and
 Ethics (CEUSUFMS n°.:745/2016). 2.3 Release
 Experiment We released individuals on a crop matrix
 close to a single isolated woodland savanna forest fragment in the rural
 area of Campo Grande (20°36'39" S, 54°33'14"O) (Fig.
 1). Using this strategy, we were able to standardize soil, relief, forest
 horizon angle and woodland high, variables that could interfere in our
 treatments (Zollner & Lima, 1997). The trees within the forest
 fragment are 15m high on average, the canopy is continuous and the
 understory is open.The forest is semi deciduous, with loss of some of its
 canopy during dry season. Is possible to observe some human interference,
 likely due to selective logging. The target fragment had about five
 hectares in area, and it was located at least 800m from other fragments,
 and at least 10km from the places where we captured individuals. We
 assumed that this distance was enough to avoid animals returning to their
 original environment (homing behavior) or having any previous knowledge
 about the release site (Forero-Medina & Vieira, 2009). The matrix
 was composed of corn (April to August), soybean (December to February) or
 bare filed (between cultures, typically March, October, and November; Fig.
 1). We are aware that the effect of our treatments (matrix type) could be
 confounded with the time of the year and climate variables. To mitigate
 the possibility of a climate interference, we released individuals at each
 treatment at least in two different years. In addition, all release events
 happened in similar temperatures and in sunny days. The releases on bare
 field occurred in March 2017 and from September to November 2018. The mean
 temperature (temp.) and the mean air humidity (humi.) during such releases
 were 27.8±4.5°C, and 62±16%, respectively. On corn, we released
 individuals from May to July 2017, and in July 2018 (temp. 27.2±3.4°C,
 humi. 38±13%). On soybean, we released individuals in 2016 December and
 2019 February (temp. 28.9±3.4°C, humi. 65±16%). We released all
 individuals on the southern face of the fragment. This standardization
 aimed to reduce environmental variation such as wind direction, vegetation
 high, row direction, and relief that could affect our results. We released
 animals at  round 30 m from the forest fragment (mean = 26.95m, varying
 from 17.05 to 33.95m), 50m (48.89m, from 38.04 to 55.75m) and 100m
 (100.59m, from 88.48 to 108.36m), at ground height at the 3 types of
 matrix (Figure S1). We chose those distances, to match previous studies
 (e.g. Prevedello et al., 2011) and allow better comparisons and future 
 eta-analyses. Seeding, harvesting and the maintenance of crops were
 mechanized in the study area. Therefore, well-defined plantation rows and
 spray lines characterized both crops (Fig. 1). The plantation rows (~0.6
 m) were diagonally oriented in relation to the fragment for both crops.
 However, at 20 m to the fragment, the rows changed the directions and went
 around the fragment as a halo, which had 20 m width. From walking in the
 field during the study and observing the crop structure at the ground
 level, we noticed that a substantial difference in blockage between corn
 and soybean crops. When individuals were moving perpendicularly to these
 plantation rows, corn provided less obstructions to the small animals
 because corn plants do not develop ramifications at small mammals height
 (~30 cm). Spray lines (~80 cm) were in pairs, spaced 5 m within pair and
 20 m among pairs. These spray lines were arranged perpendicularly to
 plantation rows and resulted from the soil compaction caused by machines
 tires during spray pulverization. Because our experiments involve animal
 translocation and could affect the populations from where the animals came
 from and the population at the release site, we tried to reduce the number
 of individuals used. Therefore, we only performed platform experiments at
 distances beyond the D. albiventris' perceptual range, based on our
 ground experiment. Using this strategy, we were able to test if the
 platform increases individual perceptual range, orientation, tortuosity,
 and dispersal success using the minimum number of translocated individuals
 as possible. Platform experiments were only performed on corn and soybeans
 matrices, at the 50 and 100m distances to the fragment. We used the
 Forero-Medina and Vieira (2007) apparatus to release the individuals. To
 make this apparatus we used two wooden rods. One was  m long, and the
 other was 0.7m long. We fixed them with spikes in an upside-down
 "L" shape. We set the longer side of the "L" in the
 soil. The corner and the shorter "L"  side received a pulley
 each. We used a bucket as a release box. From this box, a rope was driven
 through the pulley and we could, using the rope, release the animals from
 at least 30m distance (Fig 1). The operator location was chosen
 haphazardly but the he would never stand between the fragment and the
 bucket. This distance aims to reduce the influence that the presence of
 the researcher could have on animal behaviour. After the box rose,
 individuals had 360° view of the surrounding landscape and could decide
 the way to follow. To simulate the crow's nest effect of scattered
 trees, independent from other resources that scattered trees may offer, we
 developed a wood platform. The platforms were 2m height in average, with a
 tripod shape. The three legs could be removed using a simple system of
 nuts and bolts. At the top of the legs, there was a wood squared surface
 where the same upside down “L” structure was present (Fig 1). 2.4
 Post-release Animal tracking We tracked individuals using spool-and-line
 cocoons glued on the fur between the individuals' shoulder blades
 with Super Bonder® (see Vieira & Loretto, 2004). The cocoons
 weighted approximately 5g and had no internal reel. The line goes out
 through the centre of the cocoon that were wrapped with plastic wrapping
 and adhesive tape. After wrapped the cocoons were glued and the free side
 was tied at the release apparatus. After released the animal could walk
 normally. While it walks, the line could exit from the cocoons, recording
 its movements. Walked distances, hereafter referred to as “step lengths”,
 and direction changes, hereafter “turning angles”, were measured using
 measuring tape and compass. We considered only turning angles greater than
 10°. The distance between two turning angles is the step length. We
 tracked the D. albiventris from the release site until the end of the line
 or until the animal reached the fragment. 2.5 Data
 analysis<br> 2.5.1 Perceptual range For each
 tracked individual we calculated both: 1. the direction (angle) that
 should be used to travel from the release place to the fragment using the
 shortest path, and 2. The angular mean of turning angles along the
 individual path, weighted by their respective step lengths. Then, we used
 these two values to calculate the angular divergence, which represented
 how oriented an individual moved toward the target fragment. Angular
 divergence ranged from -180º to 180º, with values around 0º depicting
 highly oriented individuals (i.e. individuals following theshortest path
 direction), while higher values depicted divergence for right (positive
 values) or left (negative values), until a complete opposite path
 (~|180º|). For each combination - distance, matrix type and release height
 - we used the Rayleigh test to check if angular divergence were different
 from 0º. Based on Rayleigh test, we considered as perceptual range the
 longer release distance at which angular divergence did not differ from 0º
 (following Zollner & Lima, 1997; Flaherty et al., 2008; Bridgman
 et al., 2012) 2.5.2 Effects on tortuosity, orientation ability and
 dispersal success We calculated three metrics to represent the path of
 individuals: sinuosity, orientation ability and dispersal success. We used
 the sinuosity index to measure tortuosity. Sinuosity index combines the
 mean cosine of direction changes with the mean step length, and it has
 been shown to have superior performance over alternative indexes to
 capture tortuosity of simulated paths (Benhamou, 2004). Orientation
 ability was measured as the angular divergence between the angular mean of
 turning angles, and the direction of the shortest distance to fragment
 (see details in perceptual range section: sensu Schooley and Wiens 2003;
 Forero-Medina and Vieira 2009; Prevedello et al. 2011). Dispersal success
 was measured in a binary way, in which individuals that reached the
 fragment edge were considered successful (coded as 1’s) and those that did
 not reach were unsuccessful (coded as 0’s) (Prevedello et al., 2011;
 Zollner & Lima, 1999, 2005). To statistically analyse these
 metrics, we built a total of 6 generalized linear models, in two sets of
 three models. In the first set, we considered only ground releases. We
 tested the effect of release distance and matrix type on the three
 metrics: tortuosity, orientation ability, and dispersal success. In the
 case of dispersal success, we used binomial distribution error because of
 the binary nature of this response variable. The other two variables had a
 normal error distribution. For the second set of models, we also tested
 the effect of the platforms. However, to do so, we had to restrict our
 analysis to corn and soybean fields at 50 and 100 m distance to the
 fragment. Once again, we had three models, one for each metric, with the
 dispersal success model having a binomial error distribution. For all six
 models, we ran a full parametrized model (including all interactions).
 Non-significant interaction terms were dropped, and models were ran again.
 Because the reduced number of individuals released in platforms, we
 performed a set of complementary analyses grouping releases at 50 and
 100m, and compared the platform effect separately for each crop using
 Wilcoxon test. This set of follow up analyses must be interpreted
 cautiously All data was analysed using R (R Core Team, 2019). Complete
 dataset is provided in Table S1.
description: id: a sequential number of the individual according with the
 capture order <br> sp: Species of the individual that was
 captured<br> id_l: ear ring attached at the left ear<br> id_r:
 ear ring attached at the right ear<br> date_cap: the day that the
 individual was captured<br> mass: mass of the individual in
 kilogram <br> l_skull: length of the individual skull in
 centimeter<br> w_skul: width of the individual skull in
 centimeter<br> sex: sex of the individual<br> age: age class
 estimated using the molar teeth<br> date_rel: The day that the
 individual was released<br> dist: the distance from the fragment
 from where the individual was released <br> x: the latitude of the
 place where the individual was released<br> y: the longitude of the
 place where the individual was released<br> matrix: the kind os
 matrix where the individual was released<br> time: the time of the
 day when the individual was released<br> azi_l: at the release
 place, using a compass, this is the azimuth to te left limit of the target
 fragment<br> azi_r: at the release place, using a compass, this is
 the azimuth to te right limit of the target fragment<br> azimuth:
 using a compass, the direction to where the individual moved<br>
 move: the distance moved in the previous azimuth<br>
 time_orientation: we measured to some individuals, how long they took to
 iniciate the movement. These data were not used at this papper.<br>
 arrive:if the individual reached the target fragment, the value is 1, if
 not, the value is 0<br> row: if the movement was realized at the
 plantation row, the value is 1, if not, the value is 0<br> platform:
 if the release happened from a plataform, the value is one, if not, the
 value is 0