Abstract
The ways in which spines and thorns on plants affect browsing behavior and instantaneous intake rate (IIR) have been investigated for several medium and large ungulates, with most authors concluding that spines either affect the ability to obtain a full bite, or prevent the removal of twig material. We investigated how a very small ruminant, the blue duiker (Philantomba monticola; mass 5 kg), altered its feeding strategy when confronted with intact or despined branches of three species of woody plant that differed in leaf and spine size, density, and arrangement, viz. Dichrostachys cinerea africana, Vachellia (Acacia) karroo and Ziziphus mucronata. Increasing spine length and density reduced IIR (g/min), while bite size was directly related to leaf area. Bite rate and the lag time to taking the first bite did not differ among treatments. In all treatments, blue duikers cropped leaves in preference to pruning shoots. High spine density forced duikers to crop leaves at the ends of branches where spines were softer. At low spine density and on despined treatments, leaves midway along branches were preferred. Single bites (using incisors) were used preferentially in the presence of spines, with a shift to cheek bites on despined branches. We conclude that, as found with larger browsers, spines coupled with small leaf size provide the best defense against defoliation.
Highlights
In African savanna ecosystems, plants have co‐evolved with a suite of mammalian herbivores, ranging in size from tens of grams to several tonnes (Augustine & McNaughton, 1998; du Toit, Bryant, & Frisby, 1990)
Given the plants utilized in this study, we predicted that the greatest instan‐ taneous intake rate (IIR) and bite mass would be achieved on despined D. cinerea, and the lowest on intact Z. mucronata
These experiments clearly show that the combination of leaf size, leaf arrangement and spine size and density affect browsing behavior and IIR by a small antelope
Summary
In African savanna ecosystems, plants have co‐evolved with a suite of mammalian herbivores, ranging in size from tens of grams to several tonnes (Augustine & McNaughton, 1998; du Toit, Bryant, & Frisby, 1990). The type of defense is typically linked to the suite of herbivores removing signifi‐ cant biomass, but may be effective against herbivores that were unlikely to have applied strong evolutionary pressure (Belsky, 1984; Hanley, Lamont, Fairbanks, & Rafferty, 2007). The rate at which food can be acquired by a feeding herbivore is a function of the time it takes to crop a mouthful, the amount of ma‐ terial cropped, bite rate, and the handling time—that is, the time re‐ quired to chew and swallow (Trudell & White, 1981)
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