Data from: eDNA concentration, population size structure, and mark-recapture data

Organism abundance is a critical parameter in ecology, but its estimation
is often challenging. Approaches utilizing eDNA to indirectly estimate
abundance have recently generated substantial interest. However,
preliminary correlations observed between eDNA concentration and abundance
in nature are typically moderate in strength with significant unexplained
variation. Here we apply a novel approach to integrate allometric scaling
coefficients into models of eDNA concentration and organism abundance. We
hypothesize that eDNA particle production scales non-linearly with mass,
with scaling coefficients < 1. Wild populations often exhibit
substantial variation in individual body size distributions; we therefore
predict that the distribution of mass across individuals within a
population will influence population-level eDNA production rates. To test
our hypothesis, we collected standardized body size distribution and
mark-recapture abundance data using whole-lake experiments involving nine
populations of brook trout. We correlated eDNA concentration with three
metrics of abundance: density (individuals/ha), biomass (kg/ha), and
allometrically scaled mass (ASM) (∑(individual mass0.73)/ha). Density and
biomass were both significantly positively correlated with eDNA
concentration (adj. r2 = 0.59 and 0.63, respectively), but ASM exhibited
improved model fit (adj. r2 = 0.78). We also demonstrate how estimates of
ASM derived from eDNA samples in ‘unknown’ systems can be converted to
biomass or density estimates with additional size structure data. Future
experiments should empirically validate allometric scaling coefficients
for eDNA production, particularly where substantial intraspecific size
distribution variation exists. Incorporating allometric scaling may
improve predictive models to the extent that eDNA concentration may become
a reliable indicator of abundance in nature.