Foraging in patchy grasslands: diet selection by sheep and cattle is affected by the abundance and spatial distribution of preferred species

Abstract

-Understanding the distribution of grazing activity and its management is valuable to ensure the sustainability and productivity of heterogeneous grasslands. Controlled behavioural studies can provide insight into the cognitive abilities of herbivores and suggest new approaches to improve their grazing distribution. We compared the behaviour and diet selection of sheep and cattle in 1-ha fescue (Festuca arundinacea S.) plots, in which the number and size of preferred ryegrass (Lolium perenne L.) patches were varied. Five different patterns were used to investigate the effects of ryegrass abundance and spatial distribution on the searching success of the herbivores. Both heifers and ewes grazed ryegrass more when its abundance increased from 1.5 to 6% , and also when ryegrass was aggregated into a few 8 × 9-m patches, rather than being dispersed into a larger number of 3 × 3-m ones. Neither the interaction between ryegrass abundance and patch size, nor that between herbivore species and patch size was significant. At 6% abundance, aggregating ryegrass into a single 24 × 24-m patch tended to further increase its use by heifers, but not by ewes. Fescue less than 1 meter from the nearest ryegrass patch was usually selected more than the fescue located further away. Fescue between 1 and 5 m from the nearest patch was never selected more than the fescue located further away. Our results, together with those for the diet selected by sheep, cattle and deer, when offered patches of a preferred food in aggregated or dispersed patterns, indicate that over a wide range of abundance, it is advantageous for herbivores to forage on patchy resources when the preferred vegetation is aggregated. This corroborates the prediction that foraging costs associated with patch distribution are involved in determining diet selection in patchy grasslands, but our results suggest that it is also influenced by some social characteristics of the animals, such as their social attraction and social tolerance. Résumé -Dans une mosaïque de végétation, les choix des ovins et des bovins varient selon l'abondance mais aussi la distribution spatiale des placettes préférées. La compréhension des mécanismes qui gouvernent l'utilisation de pâturages hétérogènes permet de proposer des pistes pour conduire les parcelles et les troupeaux au mieux des attendus de l'élevage et de la préservation de la biodiversité. Les études comportementales en situation contrôlée peuvent aussi nous éclairer sur les capacités cognitives des herbivores. Ici, nous avons comparé le comportement et les choix alimentaires de génisses et d'agnelles dans des parcelles de fétuque (Festuca arundinacea S.) d'un hectare, dans lesquelles ont été implantées des placettes préférées de ray-grass (Lolium perenne L.) de diffé-rentes tailles et en différents nombres. Cinq combinaisons d'abondance et d'agrégation du ray-grass ont été proposées aux animaux. Ceux-ci ont plus sélectionné le ray-grass lorsque son abondance augmentait de 1,5 à 6 % . Ils l'ont également plus sélectionné lo...

Evaluation of n-alkanes and their carbon isotope enrichments (δ13C) as diet composition markers

“…Understanding the type of plant species selected by the animal and the contribution of each species to the total intake could give an insight into the nutritional status of the animal and offer a feasible range management strategy to optimise resource utilisation (Dumont et al, 2002). However, measurement of feed intake, diet composition and nutrient digestibility in free-ranging animals remains a challenge in nutritional studies -E-mail: derseh7@yahoo.com because of the inherent errors associated with the methods that are used at present (Dove and Mayes, 1991;Mayes and Dove, 2000).…”

Overgrazing in the Montado? The need for monitoring grazing pressure at paddock scale

“…Compared to sheep, cattle have lesser browsing ability because of their wider muzzle and other morpho-physiological characteristics. Cattle are mainly indiscriminate consumers of grass in the higher herbal layer while sheep are more selective grazers (Dumont et al 2002). As a consequence, in response to changing forage availability and phenological stages, different livestock species will behave differently (Stuth et al 1987).…”

Managing livestock using animal behavior: mixed-species stocking and flerds

“…These three broad classification categories place all seed-bearing plants within three broad categories: grasses, forbs (herbaceous dicots commonly referred to as weeds) and woody plants (phenology can range from shrubs to trees depending on their response to effective precipitation and past management practices). It is from among these three plant categories, often found in a patchy mosaic (Dumont et al, 2002), that most domestic ruminant livestock select their diets. Browsers and grazers differ in their foraging behavior (Gordon, 2003).…”

“…Recently, Laca (2009) suggested that when plant associations are 'less patchy' and 'well mixed' across a landscape, livestock apparently are less able to select a preferred diet. This phenomenon partially explains the heterogeneous use of large pastures (Vallentine, 1990) and the effect of plant spatial patterns on herbivore foraging (Anderson et al, 1985;Clarke et al, 1995;Hester et al, 1999;Dumont et al, 2002). Thus, understanding animal behavior is crucial to managing standing crop utilization.…”