HABITAT PARTITIONING IN RIVERINE MACROPHYTE COMMUNITIES

1. Habitat partitioning has been extensively studied in terrestrial pl ant communities. By comparison, few studies have examined habitat part itioning in riverine macrophyte communities. Riverine environments are often highly heterogeneous with respect to current speed, depth, bott om sediment fertility and other biologically important properties. Thu s, the potential for habitat partitioning in riverine macrophyte commu nities is great. 2. The objective of this study was to investigate how , or if, macrophyte species are differentially distributed with respec t to abiotic gradients in a large river in central British Columbia, C anada. 3. A survey of macrophyte biomass and associated measures of cu rrent speed, depth and sediment texture showed that coexistence occurr ed both with and without habitat partitioning. 4. Coexistence in the a bsence of habitat partitioning was depicted by Potamogeton gramineus, Potamogeton berchtoldii, Myriophyllum exalbescens, Callitriche hermaph roditica and Potamogeton pectinatus such that they had a minimum and a verage niche overlap (NO) of 65% and 84%, respectively, for all measur ed abiotic variables. Similarly, the spatial niche of E. canadensis wa s 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 s ites having current speeds greater than 0.6 m s(-1) and substrates of bare rock. Ranunculus aquatilis was most abundant at sites having curr ent speeds between 0.4 and 0.6 m s(-1) whereas most other taxa were re stricted to slower waters. Habitat partitioning across depth contours, which occurred between several taxa, was most evident between P. pect inatus and C. demersum (NO=17%), C. hermaphroditica and C. demersum (N O=3%), C. demersum and P. richardsonii (NO=19%) and C. hermaphroditica and E. canadensis (NO=29%).