The relationship of total and per-gram rankings in competitive effect to the natural abundance of herbaceous perennials

Howard, TG

Tg. Howard, The relationship of total and per-gram rankings in competitive effect to the natural abundance of herbaceous perennials, J ECOLOGY, 89(1), 2001, pp. 110-117

42

INGLESE

Article

Environment/Ecology

JOURNAL OF ECOLOGY

0022-0477 → ACNP

89

1

2001

110 - 117

ISI

0022-0477(200102)89:1<110:TROTAP>2.0.ZU;2-3

1 Using a field experiment and a garden experiment, I estimated the ranking s in total and per-gram competitive effect of non-woody perennial old-field species. 2 Total competitive effects were defined as the relative reduction in growt h of a target from no-neighbour to with-neighbour conditions. Per-gram comp etitive effects were defined as the per-unit relative reduction in target g rowth among increasing neighbour densities and were determined from the sha pe of a nonlinear curve fit through a distribution of normalized target per formance against neighbour mass. 3 In both experiments, mean total competitive effect differed significantly among species indicating a strong competitive hierarchy. In the garden exp eriment only species at opposite ends of the ranking differed significantly in per-gram competitive effect, resulting in a weaker competitive hierarch y based on this measure. 4 Nonetheless, rankings of per-gram competitive effect were more strongly c orrelated with rank in abundance than were rankings of total competitive ef fect. 5 Per-gram competitive effect may be more predictive of natural abundance t han total competitive effect for at least two reasons. The effects of neigh bour abundance on targets are nonlinear, and unlike total effects, per-gram estimates of competitive effect may therefore indicate how competition cha nges over time with changing neighbour densities Also, if higher per-gram c ompetitive effect reflects higher per-unit nutrient uptake rates, it would probably be advantageous to a species throughout the individual's life span , rather than only when the individual is larger than its surrounding neigh bours.