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Abstract Helical drives (sometimes known as Archimedes’ screws) are a class of propulsion mechanism with the potential for application in amphibious, multi-terrain robotic ground vehicles such as Arctic rovers. Despite their simplistic construction, consisting of a screw-like rotating drum with a helically wound blade, their propulsion dynamics are complex and not well understood. There is a need for an experimental testing environment capable of controlling and recording the variables that characterize the dynamics of this terrestrial propulsion mechanism in order to experimentally validate dynamic and energetic modelling. Such variables include displacement, velocity, and acceleration of the mechanism in question in the x, y and z directions, as well as terramechanical properties such as substrate moisture content, subsequent density, and particulate size. This environment would also ideally be designed with modularity in mind in order to easily adapt to multiple different test conditions and terrestrial propulsion mechanisms. This paper describes the design of the experimental testing rig created to serve the above-described purpose. The apparatus is tested with an example of a helical screw drive at three different rover weights. Results of an initial test are shown, and the trends shown in the x position (longitudinal travel), z position (vertical travel), and effective pitch length are discussed. 

Abstract Niche theory suggests that the realized niche occupied by an organism in the field is a subset of the fundamental niche space of the organism, absent additional biotic and abiotic factors. Though often assumed, this discrepancy is rarely tested for specific organisms, and could act as a source of error in model predictions of biogeographical shifts resulting from temperature change which assume niche theory constraints. Here, we quantify the difference between fundamental and realized temperature niches for four dominant ecotypes ofProchlorococcus, including eMED4, eMIT9312, eMIT9313, and eNATL2A, and ask whether the realized temperature niches of each ecotype vary across ocean basins. The realized niches for the four ecotypes are, on average, 3.84°C ± 1.18°C colder (mean ± SD across all ocean basins and ecotypes) and 2.15°C ± 1.89°C wider than the lab‐measured fundamental niches. When divided into four ocean regions—North Atlantic, South Atlantic, North Pacific, and South Pacific—we find that the realized temperature niche optimum for a given ecotype compared to the fundamental temperature niche optimum differs across regions by as much as 7.93°C, while the niche width can differ by up to 9.48°C. Colder and wider realized niches may be a result of the metabolic risk associated with living in variable environments when the mean temperature is too close to the optimal temperature for growth or due to physical processes such as dispersal. The strong differences in temperature niches across ocean basins suggest that unresolved genetic diversity within ecotypes, local adaptation, and variable interactive ecological and environmental factors are likely to be important in shapingProchlorococcusrealized temperature niches.