The Plant Vigour Hypothesis Revisited: How Is Browsing by Ungulates and Elephant Related to Woody Species Growth Rate?

• Published in: Plant ecology Vol. 184; no. 1; pp. 163 - 172
• Main Authors: Makhabu, Shimane W., Skarpe, Christina, Hytteborn, Håkan, Mpofu, Zenzele D.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer 01.05.2006; Springer Nature B.V
• Subjects: Browsing; Elephants; Flowers & plants; Growth rate; Herbivores; Indigenous species; Leaves; Loxodonta africana; Nutrient concentrations; Plant ecology; Plant species; Plants; Principal components analysis; Shoots; Species; Tannins; Ungulates; Woody plants
• ISSN: 1385-0237; 1573-5052; 1573-5052
• DOI: 10.1007/s11258-005-9060-9

The way herbivores select what to eat is of considerable practical and theoretical interest, and has given rise to different theories and hypotheses. The plant vigour hypothesis predicts that herbivores feed preferentially on vigorous, i.e., large and/or fast-growing plants or plant parts. These predictions have previously primarily been tested on variation within plant species. Here we test whether differences in vigour among plant species in the same environment can explain differences in herbivore attack. We studied variation in browsing pressure by a guild of large herbivores on different woody species in an African savanna ecosystem. Shoot growth rate, annual shoot length, basal shoot diameter and annual shoot volume of 14 woody plant species were measured in the field. Plant species' shoot vigour represented by the first PCA axis scores generated from the four shoot variables were then related to browsing pressure (% utilisation) on each of the species by native ungulates and elephant. Nutrient and fibre concentrations and tannin activity were also determined for the 14 woody plant species. We found ungulate browsing pressure to show a unimodal relationship with plant species' shoot vigour. The heaviest browsing pressure was on plant species with shoots of intermediate vigour. We suggest that species with less vigorous shoots had low nutrient and high fibre concentrations and offered small bite sizes, whereas species with vigorous shoots had high nutrient concentrations but larger shoot diameters than the bite diameters of browsing ungulates. Elephant browsing pressure was not related to plant species' shoot vigour.