Habitat partitioning in riverine macrophyte communities

1. Habitat partitioning has been extensively studied in terrestrial plant communities. By comparison, few studies have examined habitat partitioning in riverine macrophyte communities. Riverine environments are often highly heterogeneous with respect to current speed, depth, bottom sediment fertility and other biologically important properties. Thus, the potential for habitat partitioning in riverine macrophyte communities is great. 2. The objective of this study was to investigate how, or if, macrophyte species are differentially distributed with respect to abiotic gradients in a large river in central British Columbia, Canada. 3. A survey of macrophyte biomass and associated measures of current speed, depth and sediment texture showed that coexistence occurred both with and without habitat partitioning. 4. Coexistence in the absence of habitat partitioning was depicted by Potamogeton gramineus, Potamogeton berchtoldii, Myriophyllum exalbescens, Callitriche hermaphroditica and Potamogeton pectinatus such that they had a minimum and average niche overlap (NO) of 65% and 84%, respectively, for all measured abiotic variables. Similarly, the spatial niche of E. canadensis was close to that of Ceratophyllum demersum and M. exalbescens. 5. While several taxa seemed to occupy the same spatial niche, some taxa were distinguished from one another in terms of the types of microhabitats they utilized. Mosses, for example, were often the only occupants of sites having current speeds greater than 0.6 m s(-1) and substrates of bare rock. Ranunculus aquatilis was most abundant at sites having current speeds between 0.4 and 0.6 m s(-1) whereas most other taxa were restricted to slower waters. Habitat partitioning across depth contours, which occurred between several taxa, was most evident between P. pectinatus and C. demersum (NO=17%), C. hermaphroditica and C. demersum (NO=3%), C. demersum and P. richardsonii (NO=19%) and C. hermaphroditica and E. canadensis (NO=29%).