Optimal foraging and community structure: The allometry of herbivore food selection and competition (original) (raw)
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Intra- and Interspecific Differences in Diet Quality and Composition in a Large Herbivore Community
PLoS ONE, 2014
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.
Foraging behaviour and diet selection in domestic herbivores
1998
— Foraging behaviour and diet selection determine both the nutrient intake by the animals and their impact on the vegetation. They are therefore of importance for animal and vegetation management. Animals exploit the heterogeneity of resources through selective grazing, choosing a diet of better quality than the average vegetation on offer. Recent increased effort has been made to develop models of the grazing process supported by theory, which should facilitate generalisation and application to a broad range of situations. Foraging involves the interactions between the characteristics of the animal and the characteristics of food in the environment. We review some of the animals' foraging decisions within the vegetation, morpho-physiological, digestive and behavioural constraints they face. The determinants of foraging behaviour and diet selection remain, however, somewhat obscure and a matter of debate. The complexity of the animal/vegetation interactions have prompted the development of simple experimental approaches, and further research is needed to extrapolate these to larger spatio-temporal scales. @ Elsevier / Inra foraging behaviour / dietary choices / grazing Résumé — Comportement d'ingestion et choix alimentaires au pâturage chez les herbivores domestiques. Le comportement d'ingestion et les choix alimentaires au pâturage conditionnent l'ingestion de nutriments par les animaux et leur impact sur la végétation. Une meilleure compréhension de leurs déterminants est donc importante pour gérer la dynamique des systèmes pâturés. Les animaux exploitent l'hétérogénéité des ressources en pâturant de manière sélective et en choisissant un régime de meilleure qualité que ce qui leur est offert. Un effort récent a été fait pour développer une approche hiérarchisée du processus de pâturage, étayée par des bases théoriques, afin de dégager des lois générales applicables à des situations variées. Le comportement d'ingestion et les choix alimentaires résultent de l'interaction entre les caractéristiques des animaux et celles de la végétation offerte. Cette revue présente certaines décisions des animaux face aux contraintes qu'ils rencontrent, qui sont liées à la végétation, à leurs caractéristiques morpho-physiologiques propres, ou au temps dont
Allometry and spatial scales of foraging in mammalian herbivores
Ecology Letters, 2010
Ecology Letters (2010) 13: 311–320Ecology Letters (2010) 13: 311–320AbstractHerbivores forage in spatially complex habitats. Due to allometry and scale-dependent foraging, herbivores are hypothesized to perceive and respond to heterogeneity of resources at scales relative to their body sizes. This hypothesis has not been manipulatively tested for animals with only moderate differences in body size and similar food niches. We compared short-term spatial foraging behavior of two herbivores (sheep and cattle) with similar dietary niche but differing body size. Although intake rates scaled allometrically with body mass (mass0.75), spatial foraging strategies substantially differed, with cattle exhibiting a coarser-grained use of the ‘foodscape.’ Selectivity by cattle (and not sheep) for their preferred food was more restricted when patches were smaller (< 10 m2). We conclude that differences in spatial scales of selection offers a plausible mechanism by which species can coexist on shared resources that exhibit multiple scales of spatial heterogeneity.Herbivores forage in spatially complex habitats. Due to allometry and scale-dependent foraging, herbivores are hypothesized to perceive and respond to heterogeneity of resources at scales relative to their body sizes. This hypothesis has not been manipulatively tested for animals with only moderate differences in body size and similar food niches. We compared short-term spatial foraging behavior of two herbivores (sheep and cattle) with similar dietary niche but differing body size. Although intake rates scaled allometrically with body mass (mass0.75), spatial foraging strategies substantially differed, with cattle exhibiting a coarser-grained use of the ‘foodscape.’ Selectivity by cattle (and not sheep) for their preferred food was more restricted when patches were smaller (< 10 m2). We conclude that differences in spatial scales of selection offers a plausible mechanism by which species can coexist on shared resources that exhibit multiple scales of spatial heterogeneity.
Oecologia, 1986
A particular linear programming model is constructed to predict the diets of each of 14 species of generalist herbivores at the National Bison Range, Montana. The herbivores have body masses ranging over seven orders of magnitude and belonging to two major taxa: insects and mammals. The linear programming model has three feeding constraints: digestive capacity, feeding time and energy requirements. A foraging strategy that maximizes daily energy intake agrees very well with the observed diets. Body size appears to be an underlying determinant of the foraging parameters leading to diet selection. Species that possess digestive capacity and feeding time constraints which approach each other in magnitude have the most generalized diets. The degree that the linear programming models change their diet predictions with a given percent change in parameter values (sensitivity) may reflect the observed ability of the species to vary their diets. In particular, the species which show the most diet variability are those whose diets tend to be balanced between monocots and dicots. The community-ecological parameters of herbivore body-size ranges and species number can possibly be related to foraging behavior.
Functional response of optimally foraging herbivores
Journal of Theoretical Biology, 1990
We present a general functional response model for herbivores exploiting well defined food items such as ramets of trees, shrubs and many herbs. The basic assumption in our analysis is that the partial consumption of ramets is a patch exploitation process. This allows us to derive not only testable, but also biologically realistic, functional responses with respect to both ramet and biomass density available to the herbivore. It is essential to know both measures in order to properly examine plant-herbivore dynamics. In both cases the functional response is typically Type II (continuously decelerating). Because individual ramets are treated as patches, the functional response to a given total available biomass density is sensitive to both the number and size of ramets in the stand. This may have considerable effects on the plant-herbivore dynamics and on the growth form and life-history strategies of the plants under exploitation.
Factors driving the within‐plant patterns of resource exploitation in a herbivore
Functional Ecology
1. Selective pressures exerted on the feeding behaviour of animals have been extensively studied to understand their foraging patterns. In herbivores, specific within-plant patterns of resource exploitation have been reported, but their determinants remain poorly understood. 2. Here, we describe and decipher the determinants of the foraging pattern of the pollen beetle Brassicogethes aeneus, a pollinivorous insect that is a pest of oilseed rape Brassica napus. This insect feeds from flowers for almost all of its life cycle, except for a couple of weeks preceding blossoming. During this period, only flower buds are available and the insect destroys them to feed from the pollen they contain, causing serious yield losses. 3. We found that during this critical period, pollen beetles exhibit a stereotypic intrainflorescence feeding pattern that depends on flower bud maturity. To explain this pattern, we first deciphered the selective pressures driving pollen beetles' feeding behaviour. Using a set of manipulative laboratory experiments, including behavioural experiments on plant tissues and artificial substrates, chemical characterization of plant tissues and performance experiments, we show that the pollen beetles' feeding behaviour does not seem to be driven by specialized metabolites or an attempt to reach an optimal nutrient balance, but rather by a process of maximization of total macronutrient intake. Next, using optimal diet choice models, we found that one aspect of the intra-inflorescence feeding pattern, the preference for young over old flower buds, could be well-explained through the lens of total macronutrient intake maximization per unit of time to access the resource. 4. Our study provides new insights into small-scale foraging patterns and highlights the need to characterize and assess the relative influence of several components of diet quality when deciphering selective pressures driving foraging patterns.
Selection and use of feeding sites and feeding stations by herbivores: A review
Annales De Zootechnie, 1998
A better understanding of the animal x plant interaction is needed to develop management practices which will maintain a sufficiently rich and abundant vegetation in the pastures. Such practices would permit the animals to meet their nutritional requirements, and to ensure a sufficient production, while contributing to the maintenance of the environment. This review, drawn on a large number of experimental studies, takes stock of the factors influencing the selection and use of feeding sites and stations by herbivores. First, we present the theoretical framework in which the experimental observations are discussed. The general context of optimal foraging theory (OFT) and its predictions are described. Its 'applicability', usefulness and validity to study the foraging behaviour of herbivores are then discussed. Second, we analyse how forage (quantity and quality, plant species, distribution), environment (topography, distance to water, predator risk) and some animal factors (cognitive abilities, social organisation) affect the choice and use of feeding sites and stations. In spite of some problems of definitions ('patch', 'prey' for an herbivore?) and of the herbivores' specific characteristics, the OFT has been successfully used to explain the foraging behaviour of herbivores. However, animals' choices are rarely as absolute as predicted. Under natural conditions, animals not only respond to food resource, but are also constrained by some non-alimentary environmental factors and by the limits of their cognitive abilities (memory, discrimination). Other complementary approaches, such as 'hedonism' and 'nutritional wisdom', can partly influence animals' choices and are also briefly discussed. (© Elsevier / Inra) grazing / herbivores / diet selection / optimal foraging theory / feeding site / feeding station Résumé -Sélection et utilisation des sites et stations alimentaires par les herbivores : Une revue. À terme, mieux comprendre la relation animalvégétation est nécessaire pour développer des systèmes de gestion qui favorisent le maintien par le pâturage d'une ressource suffisamment riche et abondante. Dans ces conditions, l'animal peut couvrir ses besoins nutritionnels et assurer une productivité suffisante, tout en participant à l'entretien du milieu. Cette revue fait le point, à partir d'un grand nombre de travaux expérimentaux, sur les facteurs qui influencent la sélection et l'utilisation
Resource-Ratio Theory Applied to Large Herbivores
The theoretical description of exploitation competition, known as resource competition theory (RCT) or resource-ratio theory, has been tested in terrestrial plant communities and microorganisms in laboratory cultures. Applications in animal ecology have been rare, although the theory itself is generic. A major difficulty is that the description of resources in RCT is fundamentally different from that used in classical studies of animal competition. In presenting the first fully specified RCT models for terrestrial animals, we distinguish between positive attributes (mineral elements) and negative attributes (plant defenses) as indicators of quality in animal resources. Using the latter we apply RCT to ungulate communities that exploit just two resources: the cell wall and cell contents of plant material. We show how coexistence in the same habitats depends on the strategy of resource exploitation. Ungulate species that differ in body size adopt a ‘‘demand-minimizing’’ strategy that permits them to coexist on ratios of the two resources by acquiring less of the resource that most limits their competitor. Ungulates that differ in mouth width adopt an ‘‘extractionmaximizing’’ strategy that leads to competitive exclusion because they acquire more of the resource that most limits their competitor. We conclude that differential resource utilization permits grazing herbivores of different body size to coexist on the same grassland habitats, but that the full diversity of grazing communities depends on spatial heterogeneity in plant defenses at the landscape level.
Diet preferences of herbivores at pasture
Annales de Zootechnie, 1997
— Preference is the discrimination among sward components displayed by animals when given free choice. Selection is the removal of certain sward components rather than others. Testing preferences can help to understand diet selection in more complex environments. We can measure these preferences when the animals are offered different swards provided as turves or trays indoors or forming adjacent homogeneous strips at pasture. A number of experiments have recently been con- ducted in this way. In this review, we summarize and discuss what the animals choose to eat given a minimum of constraints. We then focus on how behavioural and vegetation constraints influence diet selection. preference / diet selection / foraging abilities / herbivores Résumé -Préférences alimentaires des herbivores au pâturage. L'animal exprime ses préférences alimentaires quand il se trouve dans une situation de choix non contraignante. En pratique, une telle situation existe rarement dans les conditions habituelles du pâturage. On mesure alors la sélection ali- mentaire qui correspond à ce que l'animal prélève. La connaissance des préférences alimentaires des herbivores devrait aider à mieux comprendre les choix que ceux-ci réalisent dans la situation complexe du pâturage. Il est possible de les mesurer quand expérimentalement, les animaux ont le choix entre des micro-placettes ou entre des couverts homogènes adjacents. Un certain nombre d'expériences ont récemment été conduites ainsi, et cette revue a pour premier objectif de rassembler et de discu- ter leurs résultats. Ensuite nous montrons comment, au pâturage, les contraintes liées à la structure de la végétation et aux limites des aptitudes des animaux influencent ce qu'ils sélectionnent. préférences / sélection alimentaire / aptitudes au pâturage / herbivore