18.1750

18.1750

40.3515

40.3515

2019-09-01

2019-11-27

Species

Gammarus insensibilis

Info and download page on the LifeWatch Italy Data Portal

DOI

OSF

University of Salento

principalInvestigator

CNR

principalInvestigator

University of Salento

principalInvestigator

University of Salento

principalInvestigator

University of Salento

principalInvestigator

University of Salento

principalInvestigator

University of Salento

Professor

principalInvestigator

For detailed experimental method see Shokri et al., 2021 following DOI: 10.1002/ece3.7129. Experimental setup The experimental system consisted of a number of mazes made of transparent Plexiglas and designed specifically for measuring aquatic macroinvertebrate space use behavior, which were placed on top of a near infrared (NIR) backlight source. Each maze was in the shape of an isosceles trapezoid [with the parallel sides measuring 70 and 40 cm and each nonparallel side measuring 70 cm], inside which were six circular patches [13 cm in diameter, 3 cm high], each with an area of 0.013 m2, connected by a network of channels [2.5 cm wide, 3 cm high], with a total surface area of 0.08 m2 (Figure 1). For each experimental trial, 1 g DW of conditioned leaf fragments was uniformly distributed across the surface of one patch, 0.5 g of conditioned leaf fragments was placed in another patch (thereby simulating two resource patches), and the other four patches were left empty. The distribution of the resource patches was randomized in each test to prevent any effect of microcosm geometry. Individual movement in the experimental maze was recorded by cameras (Basler, aca1300‐60gm) equipped with infrared pass filters (850 E, 35.5 mm; Heliopan, Germany). The cameras were supported by an aluminum framework and positioned 60 cm above the maze with an aerial view of the microcosm and channels in order to detect individual movements (Figure 1). Because all the channels are in a radial position with respect to the center of the patches, placing the camera above the center of a patch ensured that it could capture everything occurring inside the patch and the channels connected to it. The setup of the cameras was crucial to the method, since the small size of the aquatic invertebrates is compounded by their tendency to thigmotaxis, which causes them to crawl or swim along the walls and would make it easy to miss an animal if a wall were blocking the view of the cameras. To this end, three cameras were placed at 60 cm above each maze. Each camera covered a view of two patches and the channels connected to them with a visual radius of 21 cm .

Automated tracking Space use was measured for one individual at a time in an experimental maze, meaning that it was possible to know the position of the animal at any moment. Recordings were initiated 10 min after the specimen was placed in the maze and lasted for 6 hr. Videos were recorded at 25 frames per second with 1,280 × 1,024 spatial resolution. The video files were then processed automatically by Ethovision XT 14 in batch acquisition mode (Noldus Information Technology BV) [see Noldus et al. (2001) for more details on Ethovision software]. Specimens were directly identified by the software as moving elements compared to the static background, thus allowing detection even if the specimen was not moving. Ethovision XT 14 makes it possible to set transition thresholds and thus determine each transition between patches (an illustrative video is publicly accessible at https://osf.io/7ezm5/). The channels were divided into three zones (a, b, and c) (Figure 2), with transition being counted once the animal passed all three zones along the channel depending on the direction, the transition was counted as positive or negative and exported as text files. The output of Ethovision XT 14 was then fed into a Microsoft Excel Macro©™ which computed the time spent in each patch during each visit, as well as the number of patches visited, a visit being defined as each time an individual passes through a channel and enters a patch.

System variables In terms of space use behavior, the present case study made use of four descriptors: The number of visits to each patch; a visit being defined as each time the animal entered a patch and remained in the patch for at least 30 s. The giving‐up time (GUT), defined as the duration of a single visit (Krebs et al., 1974), computed here as the average time spent in a resource patch during each visit. The total time spent by individuals in any patch in absolute terms (min) and as a fraction (%) of the experimental time. The individual cumulative space used, defined as the total area of the resource patches used by individuals during the experimental time (ca. 360 min), and it was computed simply as the number of visits to a resource patch × the resource patch area (0.01 m2).