Validating a high-throughput tracking system: ATLAS as a regional-scale alternative to GPS

Fine-scale tracking of animal movement is important to understand the proximate mechanisms of animal behaviour. While GPS tracking is an excellent tool for measuring animal movement, trade-offs between tag weight, cost and lifespan limit its application to relatively large species, a small number of individuals or short tracking durations, respectively. The reverse-GPS system – ATLAS – uses lighter, cheaper tags compared to GPS tags, that can also last long periods of time at high sampling frequencies. Six systems are now operational worldwide and have successfully tracked over 50 species in various landscape types. This growing use of ATLAS to track animal movement motivates further refinement of best-practice application and an assessment of its accuracy.Here, we test the accuracy and precision of the largest ATLAS system, located in the Dutch Wadden Sea using concurrent GPS measurements as a reference. This large-scale ATLAS system consists of 26 receivers and covers 1326 km2 of intertidal region, with almost no physical obstacles for radio signals, providing a useful baseline for other systems. To measure accuracy, we calculated the distance between ATLAS and GPS location estimates for a route (mobile test) and 16 fixed locations (stationary test) on the Griend mudflat.ATLAS-derived location estimates differed on average 4.2 m from GPS-estimated stationary test sites and 5.7 m from GPS tracks taken whilst moving between them. Signals that were collected by more receiver stations were more accurate, although even 3-receiver localisations were comparable with GPS localisations (∼10 m difference). Higher receiver stations detected the tag at longer distances.Future ATLAS users should consider the height of receivers, their spatial arrangement, density and the movement mode of the study species (e.g., ground-dwelling or flying). In conclusion, ATLAS provides an accurate, regional-scale alternative to global GPS-based tracking with which hundreds of relatively small-bodied species can be tracked simultaneously for long periods of time. Our study shows that ATLAS is a valid alternative, providing comparable location estimates to GPS.

The Use of Water Vapor Isotopes to Determine Evapotranspiration Source Contributions in the Natural Environment

Water balance measurements are the simplest and most direct means of estimating evapotranspiration (ET). However, numerous factors relating to climate and terrain characteristics contribute to the variability that makes the assessment of evapotranspiration challenging at the ecosystem or even the plot scale. Alternative methods, such as an isotope mass balance (IMB), can provide evapotranspiration estimates. This paper illustrates two IMB examples of partitioning evaporation and transpiration. The first example demonstrates at the laboratory scale how accurate mass-balance measurements provide a complete validation and refinement of the isotope mass balance methods. The second IMB case uses similar data processing methods for an experimental field design. These methods are further validated by comparison with previous laboratory and field studies. Finally, this paper presents a comparison between partitioned ET ratios from a nearby U.S. Geological Survey (USGS) microclimate site produced using the Flux Variance Similarity (FVS) method. The results suggest the potential of employing these methods to estimate evaporation and transpiration source contributions at various scales. This technique and its further development show IMB methods are an appropriate tool for partitioning evapotranspiration.

Brouwer, L.E.J. (1881–1966)

L.E.J. Brouwer was a mathematician and philosopher. He graduated from the University of Amsterdam in 1907 and remained there, from 1913 to 1951, as full professor. Brouwer was a founding father of modern topology. In the foundations of mathematics he launched ‘intuitionism’: a mathematical ontology and epistemology, based on a philosophy of mind, that yields a form of constructive mathematics. Although intuitionism was designed as a Kantian approach, Brouwer’s conception of the intuition of time supports a much richer mathematics than Kant’s. Arguably, a closer affinity with Husserl’s transcendental phenomenology transpired as the latter was being developed. A by-product of intuitionism, intuitionistic logic, found application independently of the foundational programme. Intuitionism presented the first full-scale alternative to classical mathematics and logic. Brouwer was also interested in mysticism, and in language reform in the service of spiritual and political progress.