Behavioral Ecology Advance Access originally published online on September 3, 2007
Behavioral Ecology 2007 18(6):1065-1072; doi:10.1093/beheco/arm080
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Patch density determines movement patterns and foraging efficiency of large herbivores
a Resource Ecology Group, Centre for Ecosystem Studies, PO Box 47, Wageningen University, 6700 AA Wageningen, The Netherlands b Grassland Science, School of Biological and Conservation Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville 3209, Pietermaritzburg, South Africa
Address correspondence to H.J. de Knegt. E-mail: henjo.deknegt{at}wur.nl.
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Abstract |
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Few experimental studies have tested theoretical predictions regarding the movement strategies of large herbivores and their consequences for foraging efficiency. We therefore analyze how the movement and foraging behavior of goats are related to patch density, with patches being trees and bushes. We show that their movements become slower and more tortuous when patch density increases, resulting in shorter steps, more acute turns, and a lower net displacement. Furthermore, the movements of the goats can be well described by Lévy walks (LWs). In agreement with hypotheses generated by LW models, the goats move with µ 
2 at low patch density but with µ 3 when patches are abundant. However, simplified statistical descriptors of movement patterns like the shape of the step/flight length and turn angle distributions become insufficient in predicting foraging efficiency when patch density is high because then the sequence of steps and turns becomes an important determinant of foraging efficiency. By changing their movements and behavior with increasing patch density, the goats intensify their utilization of resources and consequently are able to raise the efficiency of the foraging process more than proportional to the increase in patch density. This resembles the concept of area-restricted search, stating that animals concentrate their foraging effort in areas with high reward, thereby increasing the efficiency of foraging. The findings as presented in this paper provide support for theoretical expectations on the movement and foraging behavior of large herbivores in relation to resource density.
Key words: foraging behavior, Lévy walk, movement strategy, patch density.
Received 7 January 2007; revised 28 July 2007; accepted 1 August 2007.