Improved estimation of gut passage time considerably affects trait‐based dispersal models

Abstract

Animals are important vectors for transporting seeds, nutrients and microbes across landscapes. However, models that quantify the magnitude of these ecosystem services across a broad range of taxa often rely on generalised mass‐based scaling parameters for gut passage time. This relationship is weak and fundamentally breaks down when considering individual species, indicating that current models may incorrectly attribute or estimate the magnitude of dispersal. We collated a large dataset of gut passage time for endothermic animals measured using undigested markers (n = 391 species). For each species, we compiled trait data, including body mass, morphology, gut physiology, diet and phylogeny. We then compared the ability of five statistical models (constant, generalised least squares, phylogenetic generalised least squares, general linear model and random forest) to estimate the time of first marker appearance (transit time; TT) and mean marker retention time (MRT) for particle and solute markers in mammals and birds separately. For mammals, we found that the inclusion of additional traits appreciably reduced the median root‐mean squared error across all markers in a leave‐one‐out cross validation. For birds, however, additional traits did not significantly improve our ability to predict gut passage time across markers. This may have occurred due to the smaller number of bird species included in our analysis or the absence of important explanatory factors such as differences in gastrointestinal morphology. Using the MRTparticle random forest model from this study, we updated two trait‐based dispersal models for seed and nutrient movement by mammals. The magnitude of dispersal in our updated predictions ranged from 66% to 176% of the original model formulation for different scenarios, highlighting the importance of gut passage time for dispersal models. Furthermore, the contribution by individual or groups of species was found sizeably altered in our updated models. Future modelling studies of dispersal by mammals, for which empirical estimates of gut passage time are absent, will benefit from predicting gut passage time using statistical models that incorporate traits including animal morphology, diet and gut physiology. A free Plain Language Summary can be found within the Supporting Information of this article.

Long Distance Seed Dispersal by Forest Elephants

“…The specific environmental characteristics of sites that influence disperser movements need to be investigated, particularly in the face of global climate change, habitat fragmentation, and diminishing intact wilderness. In addition, life history strategies and stages of individuals, such as phenotypic, size-, and age-related variation influence animal GPTs and movements (Byrne et al, 2019;Abraham et al, 2021). While we identified individual variation in elephant movement, individual variation in fruit consumption rates and seed deposition patterns could also strongly influence the patterns and outcomes of seed dispersal (Markl et al, 2012).…”

“…Sex-based effects are likely even stronger than our findings because males are large, have higher energy needs, and therefore likely consume more fruit and disperse more seeds than females. In addition, mammalian GPT tends to scale with mass (Abraham et al, 2021); thus, male GPTs should be slower than female GPTs.…”

Understanding anthropogenic impacts on zoogeochemistry is essential for ecological restoration

“…While this suite of models has allowed us to appreciate the importance of animals as agents within local and global biogeochemical cycles in a computationally efficient manner (Schmitz et al 2018; Abraham et al 2022 a ), there are several shortcomings. These include issues related to poorly mapped underlying element distributions (Wolf et al 2013), a bias toward large vertebrate herbivores (Doughty et al 2016), compound effects of using inaccurate mass‐based scaling parameters such as gut passage time (Abraham et al 2021 a ), unrealistic movement strategies which are approximated to Brownian motion (Wolf et al 2013), and no feedback between animals and their elemental environment—an important relationship that drastically impacts animal movement (McInturf et al 2019). As a result, precise estimation of how human activities influence element recycling and redistribution by animals in any one place is inherently uncertain, which has precluded the application of these models for modern‐day wildlife and landscape management.…”

Factors shaping the abundance and diversity of archaea in the animal gut

“…Information on body weight were also gathered on this website. Information about coefficients of gut differentiation, pH, diet fibre content, and intestinal tract structure and mean retention time were gather from 3,86,[110][111][112][113][114] . Information on methanol, H CO and CH 4 in the gut and in marine sediments originate from 18,46,115-123 .…”