POLLINATION OF ANGIOSPERMS IN CONTRASTING CONIFEROUS FORESTS

We studied the distributions of flower color, flower morphology, and putative pollinators in eight communities in the western Cascades of Washington and 14 communities in the eastern Cascades. These two forested regions differ in the proportions of species in each flower color and morphological type such that the eastern region is more complex. The putative pollinators of each species were determined from morphological and color properties of the flowers and from the recent, extensive literature. The floristic complement of the western region appears to be serviced by a collection of pollinators that is less diverse than that of the east. In each region there is a strong positive correlation between species richness and flower color diversity, floral morphology diversity, and putative pollinator diversity, respectively. These comparisons suggest the competition for pollinators has led to greater niche differentiation in the eastern regions and that this factor, combined with greater habitat complexity, results in the far greater species richness of the eastern region. POLLINATION ecology has entered a stage of synthesis and correlation. While it remains necessary, it is no longer sufficient merely to add more observations of how plants lure, seduce or antagonize animals into providing pollination service. While many details remain to be documented, the salient features of the mechanics of pollination biology are reasonably well known. The synthesis stage includes studies of evolutionary interactions at both population and community levels. Cruden (1972), Heinrich and Raven (1972), and Heinrich (1975) represent recent studies of pollination energetics. Several recent studies have been concerned with plant pollination systems on a community basis. Simpson (1977) studied pollination syndromes in the woody floras of amphitropical deserts. She concluded that despite numerous differences attributable to the absence of winter rainfall in Argentine deserts, the floral structure of the two communities was more similar to each other than it was to their respective surrounding vegetation. Her results provide evi1 Received for publication 9 May 1978; revision accepted 22 August 1978. We are indebted to M. F. Denton, A. R. Kruckeberg, B. J. D. Meeuse, G. Orians, S. L. Shepherd and an anonymous reviewer for many valuable suggestions on an earlier version of this paper. V. D. Adams has provided thoughtful comments throughout the study. We gratefully recognize the financial assistance of the Graduate School, University of Washington. The work reported in this paper was supported in part by National Science Foundation Grant No. DEB 74-20744 A06 to the Coniferous Forest Biome, Ecosystem Analysis Studies. This is contribution No. 334 from the Coniferous Forest Biome. dence for the effects of physical factors in structuring the spectra of pollinating systems. Moldenke (1976) published an extensive survey of species in the California flora and their observed pollinators. He noted that bees are the most important pollinators in montane forests; that in dense forests white flowers are at a competitive advantage over blue and violet flowers; and that where light conditions are extremely low, small flies dominate the pollinator guilds and that plant species diversity, floral color and diversity, and morphological diversity are low. Among other studies of pollination structure at the community level are: Kevan (1972), Macior (1974, 1975), Frankie (1975) and Percival (1975). In this paper we explore the following questions. What are the spectra of floral color and floral morphologies in two contrasting forest ecosystems in the central Washington Cascades? How do these spectra vary within each region? Is there a relationship between species richness and the complexity of floral characteristics in the community? What are the spectra of putative pollen vectors in the contrasting regions? We have attempted to answer these questions by use of primary survey data. The two study regions have been characterized in terms of their communities (del Moral, Watson, and Fleming, 1976) and gradient properties (del Moral and Watson, 1978). The western region occurs in what are termed the Tsuga heterophylla, Abies amabilis, and Tsuga mertensiana zones by Franklin and Dyrness (1973). The eastern region consists of stands referred to the Pseudotsuga menziesii, Abies amabilis, and A. lasiocarpa zones (Franklin and Dyrness, 1973). Primary sur-