Plant Trait Assembly Affects Superiority of Grazer's Foraging Strategies in Species-Rich Grasslands

Abstract

BackgroundCurrent plant – herbivore interaction models and experiments with mammalian herbivores grazing plant monocultures show the superiority of a maximizing forage quality strategy (MFQ) over a maximizing intake strategy (MI). However, there is a lack of evidence whether grazers comply with the model predictions under field conditions.Methodology/FindingsWe assessed diet selection of sheep (Ovis aries) using plant functional traits in productive mesic vs. low-productivity dry species-rich grasslands dominated by resource-exploitative vs. resource-conservative species respectively. Each grassland type was studied in two replicates for two years. We investigated the first grazing cycle in a set of 288 plots with a diameter of 30 cm, i.e. the size of sheep feeding station. In mesic grasslands, high plot defoliation was associated with community weighted means of leaf traits referring to high forage quality, i.e. low leaf dry matter content (LDMC) and high specific leaf area (SLA), with a high proportion of legumes and the most with high community weighted mean of forage indicator value. In contrast in dry grasslands, high community weighted mean of canopy height, an estimate of forage quantity, was the best predictor of plot defoliation. Similar differences in selection on forage quality vs. quantity were detected within plots. Sheep selected plants with higher forage indicator values than the plot specific community weighted mean of forage indicator value in mesic grasslands whereas taller plants were selected in dry grasslands. However, at this scale sheep avoided legumes and plants with higher SLA, preferred plants with higher LDMC while grazing plants with higher forage indicator values in mesic grasslands.ConclusionsOur findings indicate that MFQ appears superior over MI only in habitats with a predominance of resource-exploitative species. Furthermore, plant functional traits (LDMC, SLA, nitrogen fixer) seem to be helpful correlates of forage quality only at the community level.

Livestock Type is More Crucial Than Grazing Intensity: Traditional Cattle and Sheep Grazing in Short‐Grass Steppes

“…A possible explanation could be that dominant plants in stressed habitats are highly adapted to abiotic stress, resource competition and have the ability to form strong and deep root system and tussock‐form canopy structure, which make them also highly resistant to grazing (Osem et al, , Lezama et al, , Kelemen et al, ). This phenomenon also could be partly explained by the habitat dependent strategy shift between maximising for forage quality and maximising intake strategy of sheep grazing stressed by Mladek et al (). However, it also should be taken in account that several studies indicated that sheep grazing can be highly selective for forbs (see details for example in Jerrentrup et al, ).…”

“…These results are also well in line with that the sheep were highly selective for forb species, especially for legume species. It was found by Mladek et al (2013) that sheep grazing affected in higher magnitude the late flowering grasses than the early flowering ones. The late flowering species provide a higher forage quality for longer period (typically until the flowering) than the early flowering ones.…”

Spatial distribution of thermal refuges analysed in relation to riverscape hydromorphology using airborne thermal infrared imagery

“…Jacobs' index values computed for each class were assigned 95% confidence intervals using the method of Strauss (1979); the 'selectivity' of a particular value was considered significant (p b 0.05) if the confidence intervals did not include zero (eg. Boulanger et al, 2009;Kauhala & Auttila, 2009;Mládek et al, 2013;Monterroso, Brito, Ferreras, & Alves, 2009). A range of regression models were fitted between the refuge density dataset and the various landscape metrics.…”

Vegetation type and grazing intensity jointly shape grazing effects on grassland biodiversity

“…This can be explained by the general grazing habit of cattle, and thus, its magnitude is highly grazer dependent. Jerrentrup et al (2015) and Rook et al (2004) reported that cattle was less selective to forbs compared to sheep, and cattle, in general, was more likely characterized by a "maximising intake" strategy (see Mládek et al, 2013); therefore, selecting patches with higher biomass instead of selecting for individual species, that is, with lower SLA (see also Török, Valkó, Deák, Kelemen, & Tóthmérész, 2014). This behavior suggests that in cases of low and medium density cattle grazing, cattle likely suppress the dominant species of the respective habitat, in most cases characteristic graminoid species, causing an increase in functional diversity .…”