The allometry of plant spacing that regulates food intake rate in mammalian herbivores.
The distance that mammalian herbivores can travel without interrupting food processing corresponds to a distance threshold (d*) in plant spacing where change occurs in the mechanisms regulating the functional response. The instantaneous rate of food consumption is controlled by food encounter rate when plant spacing exceeds d*. Below this threshold, food processing in the mouth controls instantaneous intake rate. The distance threshold provides a mechanistic definition of the scale of heterogeneity of the food resource. Recent work indicates that d* should scale positively with the body mass of mammalian herbivores. Here I evaluated the empirical evidence for this positive scaling by investigating (1) herbivores consuming only alfalfa (Medicago sativa), (2) grazers, and (3) herbivores consuming any kind of vegetation. Overall, I found greater evidence for a negative than for a positive scaling of d*. Out of the three groups, only herbivores consuming alfalfa could yield a positive covariation between d* and body mass. However, even this positive scaling became negative when herbivores consumed bites of alfalfa that were only a fraction of their maximum size. Finally, d* also scaled negatively among herbivores foraging in similar food patches. Overall, differences in foraging decisions among mammalian herbivores seem more likely to have been shaped by a negative than a positive scaling of d*.
Fortin
Daniel
D
Département de biologie, Université Laval, Sainte-Foy, Québec GLK 7P4, Canada. Daniel.Fortin@bio.laval.ca
D000818:Animals; D001835:Body Weight; D005247:Feeding Behavior / Q000502:physiology*; D008322:Mammals / Q000502:physiology*; D000455:Medicago sativa / Q000502:physiology*; D008954:Models, Biological; D011156:Population Density