Environmental Correlates of Habitat Distribution and Fitness Components in Impatiens Capensis and Impatiens Pallida

Publisher Website
Google Scholar
Abstract
(1) We correlated aspects of the growth and reproduction of Impatiens capensis and I. pallida (Balsaminaceae) with a broad range of availabilities of water, light and inorganic nutrients in diverse microhabitats on Mont St. Hilaire, Quebec, Canada. (2) Both species have distinct but overlapping distributions along environmental gradients on Mont St. Hilaire. Compared to I. capensis, I. pallida predominantly grows in a narrower range of habitats that are both significantly drier and richer in nitrate and phosphorus. Sites dominated by I. pallida also tend to be richer in potassium, to be relatively poor in calcium and magnesium, and to have significantly lower soil pH. (3) In the habitats on Mont St. Hilaire where each species commonly grows, I. pallida attains a significantly greater biomass and has higher fecundity than I. capensis, although the two species do not differ in numbers of cleistogamous capsules produced per plant. (4) Growth and reproduction are greatest on sites rich in potassium and phosphorus, and high in organic matter for I. capensis, and on sites rich in calcium and magnesium with high insolation for I. pallida. In I. pallida, fecundity increases with the availability of nitrate but decreases with ammonium. Waterlogged soils are detrimental to both species, but plant performance in most natural habitats of Impatiens on Mont St. Hilaire is not affected by water shortages in years of normal precipitation. (5) Based on these correlations, we believe that both the distribution of Impatiens in eastern deciduous forest ecosystems and the fitness of individuals in different habitats are mediated by the availability of inorganic nutrient resources to a greater degree than has previously been appreciated. Experimental investigations are necessary to actually define the interacting effects of different inorganic nutrients on growth and fecundity for both I. capensis and I. pallida.