title: Tradeoff between height and relative growth rate in a dominant grass from the Serengeti ecosystem.
abstract: We determined the relationship between plant height and whole-plant relative growth rate (g g-1day-1) for ten genotypes of Sporobolus kentrophyllus collected from an intensively grazed site on the Serengeti Plains, Tanzania. Plants were grown for 7 weeks in a greenhouse in Syracuse, N.Y., and harvested weekly. Plants that received simulated bovine urine showed a negative relationship between plant height and growth rate, suggesting a genetic tradeoff between competitive ability if ungrazed (height) and ability to recover from grazing (growth rate). There was no height-growth rate relationship under nitrogen addition rates similar to field mineralization rates. In addition, faster-growing, shorter plants tended to have relatively higher above-ground growth rates than slower-growing, taller plants. These results suggest that natural selection has maintained a gradient of morphologies within this species ranging from short, rapidly growing genotypes adapted to intense grazing conditions to tall, slow-growing, grazer-susceptible genotypes that are superior light competitors in absence of herbivory.
authors.affiliation: Biological Research Laboratories, Syracuse University, 130 College Place, 13244-1220, Syracuse, NY, USA.
authors.forename: G
authors.initials: G
authors.lastname: Hartvigsen
authors.affiliation: Biological Research Laboratories, Syracuse University, 130 College Place, 13244-1220, Syracuse, NY, USA.
authors.forename: S J
authors.initials: SJ
authors.lastname: McNaughton
keywords: Genotypic tradeoff; Plant height; Relative growth rate; Serengeti