Intra- and interspecific differences in diet quality and composition in a large herbivore community

Species diversity in large herbivore communities is often explained by niche segregation allowed by differences in body mass and digestive morphophysiological features. Based on large number of gut samples in fall and winter, we analysed the temporal dynamics of diet composition, quality and interspecific overlap of 4 coexisting mountain herbivores. We tested whether the relative consumption of grass and browse differed among species of different rumen types (moose-type and intermediate-type), whether diet was of lower quality for the largest species, whether we could identify plant species which determined diet quality, and whether these plants, which could be "key-food-resources'' were similar for all herbivores. Our analyses revealed that (1) body mass and rumen types were overall poor predictors of diet composition and quality, although the roe deer, a species with a moose-type rumen was confirmed as an "obligatory non grazer'', while red deer, the largest species, had the most lignified diet; (2) diet overlap among herbivores was well predicted by rumen type (high among species of intermediate types only), when measured over broad plant groups, (3) the relationship between diet composition and quality differed among herbivore species, and the actual plant species used during winter which determined the diet quality, was herbivore species-specific. Even if diets overlapped to a great extent, the species-specific relationships between diet composition and quality suggest that herbivores may select different plant species within similar plant group types, or different plant parts and that this, along with other behavioural mechanisms of ecological niche segregation, may contribute to the coexistence of large herbivores of relatively similar body mass, as observed in mountain ecosystems

Coefficient of coinertia between diet composition in terms of plant types and diet quality, per species and period.

<p>Table gives coefficient of inertia (RV), sample size (N) and significance values obtained by bootstrapping (P) for period 1 (September to mid November) and period 2 (mid-November to January) for the 4 herbivore species.</p

Patterns of diet composition according to species, periods and plant types.

<p>A. Position of herbivore species and periods on the two first axes of the between-PCA performed on the number of plant-type items per rumen. “P1” stands for Period 1 and “P2” for Period 2, “Cha” for Chamois, “Mou” for Mouflon, “Roe” for Roe deer, and “Red” for Red deer. Grey stars relate individual points for a given species and period to its gravity center. The shift in gravity centres from period 1 to period 2 is indicated by a coloured line for each species. B. Contribution of the first most important plant types to the axes of the between-PCA. “Ever. Tree” and “Ever. Shrub” are abbreviation for “Evergreen tree” and “Evergreen shrub” respectively. C to G. Variations in the percent of “Forb”, “Fruit”, “Grass”, “Evergreen shrub” and “Evergreen tree” respectively in the diet according to date for the four herbivore species as predicted from the best models.</p

Relationship between the percentage of grass content in the rumen and diet quality.

<p>A–E. Expected values of respectively “Nitrogen”, “Helicellulose”, “Lignin”, “Cellulose”, and “Soluble Fraction” according to the grass content in the rumen, species and period. Average values of grass content per herbivore species and period and their corresponding predicted value are added to help visualising the gravity centres of the actual data in terms of both grass content and chemical component.</p

Patterns of diet quality according to species, periods and nutrients.

<p>A. Position of herbivore species and period on the two first axes of the between-PCA performed on the analyses of rumen nutrient content. “P1” stands for Period 1 and “P2” for Period 2, “Cha” for Chamois, “Mou” for Mouflon, “Roe” for Roe deer, and “Red” for Red deer. Grey stars relate individual points for a given species and period to its gravity center. The shift in gravity centres from period 1 to period 2 is indicated by a coloured line for each species. B. Contribution of each chemical component to the between PCA. “N” stands for “Nitrogen”, “SF” for “Soluble Fraction”, “Lig” for “Lignine”, “Cel” for “Cellulose”, and “Hem” for “Hemicellulose”. C to G. Variations in the percent of “Nitrogen”, “Soluble Fraction” “Lignine”, “Cel” for “Cellulose”, and “Hem” for “Hemicellulose” respectively dry matter according to date for the four herbivore species as predicted from the best models.</p

Classification of roe deer, chamois, mouflon and red deer according their body mass, digestive morphophysiology (“moose-type” to “cattle-type”) and diet category (browser to grazer).

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Niche breadth and overlap in diet among the four herbivore species.

<p>(A) Shannon-Wiener index of niche breadth according to julian date (1 being the 1^st of September). The predicted regression line is represented for all species combined. The dashed vertical line corresponds to the cutting date between periods 1 and 2 (15^th of November). (B) Schoener’s Index of overlap in periods 1 and 2. Schoener’s Index of overlap is given for the 6 combinations of species pairs and per period. The symbol colour is the colour corresponding to the smallest species in the pair, as used throughout the figures (green = roe deer, red = chamois, blue = mouflon, black = red deer ). The black line represents the expected values if there was no period effect.</p