New Zealand Journal of Agricultural Research abstracts
The assumption of optimality in foraging models: a simulated
experiment with dairy cows grazing grass pasture
Simon J. R. Woodward
Lincoln Ventures Limited
Private Bag 3062
Hamilton 3240, New Zealand
woodward@lvlham.lincoln.ac.nz
Louise M. Parsons
Institute for the Study of Earth, Oceans and Space
University of New Hampshire
Durham
NH 03824, USA
Vivien J. Kirk
Department of Mathematics
University of Auckland
Private Bag 92019
Auckland 1142, New Zealand
Abstract The “patch model” of optimal
foraging theory (OFT)
assumes that animals choose and exploit patches of food in order to
maximise their food intake rate and derives the foraging rules (patch
selection and exploitation) to achieve this. While evidence from field
studies has been found to be broadly consistent with the predictions of
OFT, this does not imply that animals actually forage using OFT rules,
however, as the same observations could possibly arise as the result of
non-optimising foraging rules (e.g., avoidance of low food intake
rate). Because OFT is potentially very useful for the purpose of
managing animal production systems (e.g., for predicting and
manipulating the intake of grazing dairy cows), it is of interest to
know to what extent OFT remains useful if animals actually behave
sub-optimally. This paper examines this question by simulating animals
foraging in a two-dimensional spatially heterogeneous environment (New
Zealand dairy cows grazing grass pasture) using six different foraging
rules with varying degrees of optimality. The results showed that both
optimal patch selection and optimal patch residence time rules
significantly increase intake rate in this type of environment, but
differences resulting from use of different variations of the patch
selection rules are small. Therefore, although OFT is highly
simplified, and animals’ senses and knowledge are imperfect, this need
not preclude the use of OFT in practical applications, as the
predictions of OFT are likely to be similar to the predictions of
other, more realistic, foraging strategies, even when these are quite
sub-optimal in formulation.
Keywords bite size; bite rate; grazing
behaviour; optimal
foraging theory; patch selection; sward heterogeneity
A07039; Online publication date 13 March 2008; Received 24 May 2007;
accepted 19 December 2007
New Zealand Journal of Agricultural Research, 2008, Vol. 51:
53–67
0028–8233/08/5101–0053 © The Royal Society of New Zealand 2008
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