Ward, David Mercer

[["dc.bibliographiccitation.firstpage","309"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Animal"],["dc.bibliographiccitation.lastpage","317"],["dc.bibliographiccitation.volume","11"],["dc.contributor.author","Accatino, F."],["dc.contributor.author","Ward, D."],["dc.contributor.author","Wiegand, K."],["dc.contributor.author","De Michele, C."],["dc.date.accessioned","2017-09-07T11:44:34Z"],["dc.date.available","2017-09-07T11:44:34Z"],["dc.date.issued","2017"],["dc.description.abstract","Assessing the carrying capacity is of primary importance in arid rangelands. This becomes even more important during droughts, when rangelands exhibit non-equilibrium dynamics, and the dynamics of livestock conditions and forage resource are decoupled. Carrying capacity is usually conceived as an equilibrium concept, that is, the consumer density that can co-exist in long-term equilibrium with the resource. As one of the first, here we address the concept of carrying capacity in systems, where there is no feedback between consumer and resource in a limited period of time. To this end, we developed an individual-based model describing the basic characteristics of a rangeland during a drought. The model represents a rangeland composed by a single water point and forage distributed all around, with livestock units moving from water to forage and vice versa, for eating and drinking. For each livestock unit we implemented an energy balance and we accounted for the gut-filling effect (i.e. only a limited amount of forage can be ingested per unit time). Our results showed that there is a temporal threshold above which livestock begin to experience energy deficit and burn fat reserves. We demonstrated that such a temporal threshold increases with the number of animals and decreases with the rangeland conditions (amount of forage). The temporal threshold corresponded to the time livestock take to consume all the forage within a certain distance from water, so that the livestock can return to water for drinking without spending more energy than they gain within a day. In this study, we highlight the importance of a time threshold in the assessment of carrying capacity in non-equilibrium conditions. Considering this time threshold could explain contrasting observations about the influence of livestock number on livestock conditions. In case of private rangelands, the herd size should be chosen so that the spatial threshold equals (or exceeds) the length of the drought."],["dc.identifier.doi","10.1017/s1751731116001531"],["dc.identifier.gro","3148929"],["dc.identifier.pii","S1751731116001531"],["dc.identifier.pmid","27452875"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/5570"],["dc.language.iso","en"],["dc.notes.intern","Wiegand Crossref Import"],["dc.notes.status","final"],["dc.notes.submitter","chake"],["dc.relation.issn","1751-7311"],["dc.relation.orgunit","Abteilung Ökosystemmodellierung"],["dc.rights","CC BY-NC-ND 4.0"],["dc.subject.gro","drought"],["dc.subject.gro","energy deficit"],["dc.subject.gro","foraging"],["dc.subject.gro","optimal herd size"],["dc.subject.gro","water point"],["dc.title","Carrying capacity in arid rangelands during droughts: the role of temporal and spatial thresholds"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.subtype","original_ja"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","617"],["dc.bibliographiccitation.issue","3"],["dc.bibliographiccitation.journal","Oecologia"],["dc.bibliographiccitation.lastpage","630"],["dc.bibliographiccitation.volume","172"],["dc.contributor.author","Ward, David"],["dc.contributor.author","Wiegand, Kerstin"],["dc.contributor.author","Getzin, Stephan"],["dc.date.accessioned","2017-09-07T11:44:35Z"],["dc.date.available","2017-09-07T11:44:35Z"],["dc.date.issued","2012"],["dc.description.abstract","Walter (Jahrb Wiss Bot 87:750-860, 1939) proposed a two-layer hypothesis, an equilibrium explanation for coexistence of savanna trees and grasses. This hypothesis relies on vertical niche partitioning and assumed that grasses are more water-use efficient than trees and use subsurface water while trees also have access to deeper water sources. Thus, in open savannas, grasses were predicted to predominate because of their water use efficiency and access to subsurface water. This hypothesis has been a prominent part of the savanna literature since first proposed. We review the literature on Walter's hypothesis and reconsider his original intentions. Walter intended this hypothesis to be restricted to dry savannas. In his opinion, mesic and humid savannas were controlled by biotic factors and disturbances. We surveyed the global savanna literature for records of vertical niche partitioning by grasses and trees. We find that, within the scope of Walter's original intentions, this hypothesis works remarkably well, and in some cases is appropriate for deserts as well as for dry temperate systems and even some mesic savannas."],["dc.identifier.doi","10.1007/s00442-012-2538-y"],["dc.identifier.gro","3148931"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/10315"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/5572"],["dc.language.iso","en"],["dc.notes.intern","Wiegand Crossref Import"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","public"],["dc.notes.submitter","chake"],["dc.relation.issn","0029-8549"],["dc.relation.orgunit","Abteilung Ökosystemmodellierung"],["dc.rights","Goescholar"],["dc.rights.uri","https://goescholar.uni-goettingen.de/licenses"],["dc.subject.gro","Codominance"],["dc.subject.gro","Equilibrium theory"],["dc.subject.gro","Patch dynamics"],["dc.subject.gro","Resource partitioning"],["dc.subject.gro","Root distributions"],["dc.subject.gro","Savanna"],["dc.subject.gro","Spatial heterogeneity"],["dc.subject.gro","Tree-grass coexistence"],["dc.subject.gro","Water"],["dc.title","Walter’s two-layer hypothesis revisited: back to the roots!"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.subtype","original_ja"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]