The complexity of interacting nutritional drivers behind food selection, a review of northern cervids

Abstract

Abstract. The research literature on food selection by large herbivores is extensive. Still, we are generally lacking in our knowledge of the influence of potentially interacting chemical contents of the food. We made a qualitative review of a systematic literature search of studies that empirically link chemical contents of food to the food selection by northern cervids (genera Alces, Capreolus, Cervus, Dama, Odocoileus, Rangifer). We found that although the majority of the 98 relevant studies measuring any given food constituent (energy, protein, fiber, minerals, plant secondary metabolites) provided support for it acting as a driver of food selection (in either a negative or positive way), there was little support for the traditional hypotheses of maximization or limitation of any single constituent. Rather, because of the animals' need to acquire an appropriate intake of several constituents at the same time, our review highlights how new empirical studies need to focus on several food constituents in synchrony: (1) Study designs should capture sufficient variation in the content of food constituents in order to tease apart their many co-variations; and (2) insights about nutritional drivers may be lost if one uses only composite currencies such as crude energy, crude fiber, ash, or tannins, which may mask contrasting selection patterns of the lumped constituents. Season had an apparent influence on the selection of some food constituents, particularly various fiber fractions. In contrast, our review revealed a lack of evidence that cervids more strongly select for protein in summer than they do in winter. Our overall conclusion of the review is that interacting chemical contents of food make the nutritional value of a given food type into a varying entity. To better elucidate this variation, we need new technologies that non-invasively capture nutrient intake of free-ranging animals, across seasons.

New approaches to tannin analysis of leaves can be used to explain in vitro biological activities associated with herbivore defence

“…This is not necessarily surprising, because eucalypt species with the same total polyphenol concentration can have vastly different polyphenol profiles (Marsh et al, 2017a). Nevertheless, researchers frequently (and often unsuccessfully) attempt to relate total tannin concentrations to, for example, various measures of herbivory (Ayres et al, 1997;Wang et al, 2014;Masette et al, 2015;Volf et al, 2015;Felton et al, 2018).…”

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“…From a conservation perspective, extensive grazing with livestock species and wildlife has become an established and suitable tool to maintain semi-natural grasslands (Van Wieren 1995;Bunzel-Dr€ uke 2008;Rosenthal et al 2012;Borer et al 2014). The spatial distribution and activities of large herbivores are affected by the availability and quality of potential forage areas, and so is their impact on the ecosystem through grazing, trampling and dispersion of wastes (Palmer et al 2003;Catorci et al 2016;Merkle et al 2016;Raynor et al 2016;Fløjgaard et al 2017). Therefore, spatially explicit information about forage quantity and quality is of critical importance for active grazing management in order to conserve seminatural grasslands.…”

“…In the context of conservation of semi-natural grassland ecosystems, this might include a cost efficient, easy to apply and robust technique to provide timely information about forage quantity and quality. As several components of the forage and not a single parameter seems to influence the grazing behaviour of herbivores, there is a need to consider forage quantity and quality parameters at the same time (Felton et al 2018). Forage quality depends on a large number of chemical and physical biomass characteristics.…”

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“…24 Baltzinger et al 2016;Cocquelet et al 2019. 25 Merceron et al 2004;Felton et al 2018. 26 Licoppe 2006. paradumus daļēji nosaka un ietekmē mācīšanās process 27 .…”