Estimation of biomass from body length and width for tropical rainforest canopy invertebrates

Abstract

Accurate estimates of invertebrate biomass are essential for quantifying community structure, food web dynamics and energy flow in terrestrial ecosystems. In this paper, length‐mass and length × width‐mass regressions were carried out for 18 invertebrate taxonomic groups collected from the canopy of an Australian tropical rainforest. In an additional analysis, invertebrates were divided among seven body shape categories based on the ratio of body length to body width (from short and squat to long and thin) in an attempt to develop accurate equations for estimating biomass that can be applied to any taxonomic group in any locality. For most groups, the inclusion of body width to the predictor variable improved the model, confirming that body shape is an important factor in the accuracy of biomass estimations. The most accurate method for estimating invertebrate biomass was the use of taxon‐specific equations, followed by equations based on body shape. Single whole‐fauna equations were very inaccurate for estimating biomass, especially for insects that are either very squat or very long and thin. In accordance with previous studies, it was concluded that the most accurate method for estimating invertebrate biomass from proxy body measurements is the use of taxon‐specific regression equations, especially those that incorporate body width in the model. However, equations based on body shape categories may be useful for estimating the biomass of groups for which no length‐mass relationship has been determined, while single, whole‐fauna equations should be avoided.

Estimating consumable biomass from body length and order in insects and spiders

“…& Enquist, 2009;Packard, 2009;Xiao et al, 2011). Previous studies estimating insect length-weight scaling relationships used quadratic functions for terrestrial insects (Sage, 1982) or log-log linear functions for Australian canopy insects (Wardhaugh, 2013). Xiao et al (2011) recommend using linear functions over nonlinear functions when data are log-normal, as ours were.…”

“…There has been a lively debate on the statistical methods used for allometric scaling functions for animals in general (Kerkhoff & Enquist, ; Packard, ; Xiao et al ., ). Previous studies estimating insect length–weight scaling relationships used quadratic functions for terrestrial insects (Sage, ) or log–log linear functions for Australian canopy insects (Wardhaugh, ). Xiao et al .…”

Applying generalized allometric regressions to predict live body mass of tropical and temperate arthropods

“…As more than 97% of the variance in body mass was described by length, width, taxonomic group, and geographic region, the benefit of adding body height would unlikely outweigh the added workload. Indeed, previous studies have shown that including body shape (i.e., body length and width) instead of taxonomy lead to more accurate body mass estimates at the order level, but not at higher taxonomic resolution (Gruner, ; Wardhaugh, ). Our results strongly support the finding that the accuracy in predicting body mass improves with adding further morphological traits, which are related to volume, in addition to body length for scaling relationships conducted at the order level.…”

“…Length-mass regressions have proven to be a powerful tool to predict body mass based on body length measurements (Benke, Huryn, Smock, & Wallace, 1999;Gruner, 2003;Johnston & Cunjak, 1999;Rogers, Buschbom, & Watson, 1977;Schoener, 1980;Wardhaugh, 2013), which are in some cases, easier to obtain than direct measurements of body mass. For living or particularly small organisms, direct measurement of body mass can be difficult and time-consuming.…”

“…Therefore, researchers requiring live body mass estimates are typically constrained to using rough conversion factors (Peters, 1983) or more elaborate dry mass-fresh mass regressions (e.g., Mercer, Gabriel, Barendse, Marshall, & Chown, 2001), which add further discrepancy to body mass predictions due to the very same sources of variation in length-mass scaling relationships (geographic origin, taxon-specificity, etc.). Considering the broad application of live body size data in ecological research, there are surprisingly few studies that provide length-body mass regression parameters for terrestrial arthropods, and most studies are restricted to one of either temperate or tropical animals, or to only a few taxonomic groups (Benke et al, 1999;Burgherr & Meyer, 1997;Gruner, 2003;Mercer et al, 2001;Schoener, 1980;Wardhaugh, 2013).…”