Compositional Changes in Foliage Phenolics with Plant Age, a Natural Experiment in Boreal Forests

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.

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“…), varying, for example, with plant ontogenetic stage (Boege and Marquis , Wam et al. ), seasonality, and site conditions (Stolter et al. , ).…”

Section: Resultsmentioning

confidence: 99%

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

Felton

Wam

Stolter³

et al. 2018

Ecosphere

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“…, Wam et al. , b). In our study, we did observe a slightly higher diet content of browse for moose in control areas compared to sympatric moose, potentially explaining their higher fecal N. It could be that because browse includes more perennial plant parts, they also have more condensed tannins than other plant groups.…”

Section: Discussionmentioning

confidence: 99%

“…What matters to the foraging animal is how much of which nutrients it is able to process without aversive effects, and this may largely vary even within a given plant species (Wam et al. ). Unfortunately, obtaining comprehensive profiles of nutrient intake is challenging in natural settings (Felton et al.…”

Section: Introductionmentioning

confidence: 99%

Subtle foodscape displacement of a native ungulate by free‐ranging livestock in a forest agroecosystem

Wam

Herfindal

2018

Ecosphere

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The prevalence of livestock grazing in wildlife areas is increasing. This transformation of ecosystems into agroecosystems is concerning because the introduction of new species may cause niche displacement of the functionally related native species. We used a large‐scale fence scheme and fecal analyses to study the influence of free‐ranging livestock on moose diet on three boreal forest ranges. We found low interspecific diet overlap between moose and livestock (mean Pianka's O across ranges = 0.21, SD = 0.104), and the diet overlap with livestock did not differ between moose in areas with livestock and in adjacent control areas without livestock. Still, moose sympatric with livestock had less fecal nitrogen (a proxy for diet quality) than moose in the control areas. Our findings suggest that interspecific interactions other than direct food competition contributed to reduce the moose’ foraging opportunities, such as altered forage abundance and composition, or behavioral avoidance of livestock. We caution that displacement in the foodscape (i.e., spatiotemporal use of food) can occur through pathways not evident in niche indices based on composition of plant species in the diet.

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“…Across the ecosystem, tannins are widely distributed within living plant matter, litter, and soil. Tannins are complex molecules that are energetically costly to synthesize, so their widespread distribution and abundance indicates that they play an important role in plant function and evolution (Kraus et al 2003;Wam et al 2017).…”

Section: Introductionmentioning

confidence: 99%

Seasonal variation and ecological importance of tannin and nutrient concentrations in Casuarina equisetifolia branchlets and fine roots

Zhang

Zhang²,

Gong-fu³

et al. 2019

J. For. Res.

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In this study, we investigated the effects of environmental factors on plant phenolic variability, seasonal dynamics of total phenolic content (TP), extractable condensed tannins (ECT), protein-bound condensed tannins (PBCT), fiber-bound condensed tannins (FBCT), total condensed tannins (TCT), protein precipitation capacity (PPC) and nutrient content in the branchlets and fine roots of Casuarina equisetifolia. TP and TCT concentrations in branchlets were lowest in the spring, then increased in summer and autumn, similar to the seasonal dynamics in air temperature. TP and TCT concentrations in fine roots were highest in summer, coinciding with heavy precipitation. In general, TP and TCT concentrations were higher in branchlets than in fine roots. No significant difference was found in C concentration among various seasons for either branchlets or fine roots. Branchlets had significantly higher N and P concentrations than fine roots in most seasons. The C/N and N/P ratios in branchlets were significantly lower than in fine roots in all seasons, except summer. The relationship between branchlets and fine roots was significant for C, P and FBCT, but no significant relationships were found for N, TP, ECT, PBCT and TCT. Additionally, TP and TCT content were each significantly correlated with PPC in branchlets and in fine roots. Both TP/N and TCT/N ratios were highest in the autumn for the branchlets and in the summer for fine roots. The results indicate that high temperatures lead to increased tannin production in branchlets, but that the tannin content in fine roots is mainly affected by precipitation. Tannin content was greater in branchlets than in fine roots, which may indicate that selective pressure is greater on branchlets than on fine roots.

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Compositional Changes in Foliage Phenolics with Plant Age, a Natural Experiment in Boreal Forests

Cited by 26 publications

References 80 publications

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

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

Subtle foodscape displacement of a native ungulate by free‐ranging livestock in a forest agroecosystem

Seasonal variation and ecological importance of tannin and nutrient concentrations in Casuarina equisetifolia branchlets and fine roots

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