221. The ecological implications of body size extend from the biology of individual organisms 23 to ecosystem-level processes. Measuring body mass for high numbers of invertebrates can be 24 logistically challenging, making length-mass regressions useful for predicting body mass 25 with minimal effort. However, standardised sets of scaling relationships covering a large 26 range in body length, taxonomic groups, and multiple geographical regions are scarce. 27 2. We collected 6293 arthropods from 19 higher-level taxa in both temperate and tropical 28 locations to compile a comprehensive set of linear models relating live body mass to a range 29 of predictor variables. For each individual, we measured live weight (hereafter, body mass), 30 body length and width, and conducted linear regressions to predict body mass using body 31 length, body width, taxonomic group and geographic region. Additionally, we quantified 32 prediction error when using parameters from arthropods of a different geographic region. 33 3. Incorporating body width into taxon-and region-specific length-mass regressions yielded 34 the highest prediction accuracy for body mass. Using regression parameters from a different 35 geographic location increased prediction error, causing over-or underestimation of body 36 mass depending on geographical origin and whether body width was included.374. We present a comprehensive range of parameters for predicting arthropod body mass and 38 provide guidance for selecting optimal scaling relationships. Given the importance of body 39 mass for functional invertebrate ecology and a paucity of adequate regressions to predict 40 arthropod body mass from different geographical regions, our study provides a long-needed 41 resource for quantifying live body mass in invertebrate ecology research. 42 43 44 45 46 47Body size is one of the most fundamental traits of living organisms (Peters, 1983). From the 48 individual to the community level, a vast range of ecosystem properties scale with arthropod 49 body size. Body size determines various aspects of an organism's individual biology, such as 50 life-history, behaviour, range size, movement and physiology (Bekoff et al., 1981; 51 Woodward et al., 2005; White et al., 2007; Hirt et al., 2017). Aspects shaping arthropod 52 communities such as species abundance, biomass production, trophic link structure, and 53 interaction strengths are also related to the body size of constituent individuals and 54 populations (Boudreau et al., 1991; Belgrano et al., 2002; Brose et al., 2006; Riede et al., 55 2011; Rall et al., 2012; Kalinkat et al., 2013). As a result, arthropod body size determines 56 how individuals and communities carry out functions, making it a powerful predictor of 57 ecosystem performance (Barnes et al., 2018). 58Most biological rates scale with body size following a power-law relationship (Peters, 59 1983; White et al., 2007), which has important implications for individual and community 60 ecology. In the early 1930s, Kleiber (1932) propose...

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