Review: Using physiologically based models to predict population responses to phytochemicals by wild vertebrate herbivores

Abstract

To understand how foraging decisions impact individual fitness of herbivores, nutritional ecologists must consider the complex in vivo dynamics of nutrient–nutrient interactions and nutrient–toxin interactions associated with foraging. Mathematical modeling has long been used to make foraging predictions (e.g. optimal foraging theory) but has largely been restricted to a single currency (e.g. energy) or using simple indices of nutrition (e.g. fecal nitrogen) without full consideration of physiologically based interactions among numerous co-ingested phytochemicals. Here, we describe a physiologically based model (PBM) that provides a mechanistic link between foraging decisions and demographic consequences. Including physiological mechanisms of absorption, digestion and metabolism of phytochemicals in PBMs allows us to estimate concentrations of ingested and interacting phytochemicals in the body. Estimated phytochemical concentrations more accurately link intake of phytochemicals to changes in individual fitness than measures of intake alone. Further, we illustrate how estimated physiological parameters can be integrated with the geometric framework of nutrition and into integral projection models and agent-based models to predict fitness and population responses of vertebrate herbivores to ingested phytochemicals. The PBMs will improve our ability to understand the foraging decisions of vertebrate herbivores and consequences of those decisions and may help identify key physiological mechanisms that underlie diet-based ecological adaptations.

Fine-Scale Differentiation in Diet and Metabolomics of Small Mammals Across a Sharp Ecological Transition

“…Further analyses, including controlled feeding trials with individual plants, will be needed to characterize the unique metabolites we have discovered here. Likewise, further sampling of woodrat tissues/products including blood and urine will be needed to capture a more complete array of dietary compounds from these plants and their post-ingestion metabolites (Dunn et al, 2011;Forbey et al, 2018). Nonetheless, these fecal metabolomic profiles reflect the distinct chemistries of the habitat-specific diets in this system, along with how hill and flats woodrats are metabolically processing these diets.…”

“…In addition to sampling animal diet, plant chemistry should also be monitored through time at a site, although the method we describe here is intended to recover relatively stable chemical compounds and metabolites, and not volatile compounds. Overall, in this study system and others, additional work is needed to (1) refine primer sets and DNA databases so that fecal DNA read counts more accurately reflect herbivore diets, (2) identify specific metabolites and the metabolic processes they reflect, and (3) integrate this approach into wildlife monitoring plans to link diet-related physiology to population health and demography (Forbey et al, 2018). The application of these approaches will require close collaboration between ecologists and wildlife managers, and will result in unprecedented insight into how these and other herbivores interact with their environment at a highly mechanistic level.…”

“…For some herbivores, food consumption is ultimately a chemically-mediated ecological interaction wherein animals must balance the acquisition of nutrients while minimizing exposure to potentially toxic plant secondary compounds (Dearing et al, 2005). Some of the primary diet-related adaptations in these herbivores, then, are likely associated with how these animals protect themselves metabolically from overexposure to plant toxins (Skopec et al, 2008;Forbey et al, 2018). Identifying the underlying phenotypic plasticity and evolutionary potential (Sorensen et al, 2005;Magnanou et al, 2009;Gompert et al, 2015;Oh et al, 2019) of the traits that allow metabolic processing of plant toxins is central to understanding dietrelated ecological adaptation in herbivores.…”

“…Identifying the underlying phenotypic plasticity and evolutionary potential (Sorensen et al, 2005;Magnanou et al, 2009;Gompert et al, 2015;Oh et al, 2019) of the traits that allow metabolic processing of plant toxins is central to understanding dietrelated ecological adaptation in herbivores. Further, identifying how animals respond to changes in exposure to plant secondary compounds, spatially and temporally, will be critical in predicting how animals will respond to climate change, and the associated shifts in community composition and food availability (Estrada et al, 2016;Beale et al, 2018;Forbey et al, 2018).…”

Herbivore nutrition supporting sustainable intensification and agro-ecological approaches

“…Improving the efficiency of livestock production will be key to successful strategies to maintain wildlife. Forbey et al (2018) described a physiological model to help identify key physiological mechanisms that underlie diet-based ecological adaptations. The model is based on how both toxic and nutritional food constituents are metabolically processed, and provides a mechanistic link between foraging decisions in vertebrate herbivores and population consequences.…”