Habitat Partitioning and Competitive Displacement in Cattails (Typha): Experimental Field Studies

Abstract

The aquatic plants Typha latifolia and T. angustifolia are observed to be strongly segregated along a gradient of increasing water depth with T. latifolia restricted to depths of less than 80 cm and T. angustifolia to depths greater than 15 cm. Transplantation of both species along the gradient in the absence of competitors showed that T. latifolia was little affected by the presence of T. angustifolia but T. angustifolia was capable of growing over the entire gradient. The loss of precompetitive distribution was not statistically significant for T. latifolia compared to a 39.6% loss for T. angustifolia. It was further observed that overlap was reduced by 43.5% during the course of the growing season. Rhizomes transplanted into natural stands failed to survive, further demonstrating that competition was actively operating to maintain zonation between species. The basis for habitat partitioning appears to be a difference in morphology whereby T. latifolia was prevented from growing in deep water because of the higher cost of producing broader leaves but better able to compete for light in shallow water because of its greater leaf surface area. Coexistence is largely the result of a deep-water refuge for the competitively inferior T. angustifolia although other factors may be involved.