A COMPARISON OF RARE AND COMMON GRASSES OF THE STIPEAE .1. GREENHOUSESTUDIES OF GROWTH AND VARIATION IN 4 SPECIES FROM PARAPATRIC POPULATIONS

This is a comparative study of variation and growth rates between the widespread grasses Achnatherum (Stipa) lemmonii, Achnatherum (Stipa) t hurberiana, and Achnatherum (Stipa) occidentale and their rare relativ e Achnatherum (Oryzopsis) hendersonii growing in shallow, frost-distur bed soils in central Washington. We assess two hypotheses: rare plants are less variable and do not compete as well as widespread plants. Th e former thesis will manifest itself in lower variation and more highl y constrained integration; the latter by lower growth rates. The rare species usually has a lower growth rate and level of variation, especi ally in vegetative shoots, which are those most likely to affect survi val. For reproductive shoots, A. hendersonii shows weaker integration in terms of the absolute level assessed, but integration appears stron ger when relative levels are examined; the results for vegetative shoo ts are inconsistent. The lower growth rate of A. hendersonii may precl ude its survival away from its typical habitat. The lower levels of va riation may reflect selection at the native sites of A. hendersonii an d thus contribute to its rarity. The lower level of variation in A. he ndersonii contrasts with its local abundance at the study site, as com pared with the more variable A. lemmonii, A. thurberiana, and A. occid entale. Local abundance combined with a low level of morphological var iation may indicate A. hendersonii is genetically depauperate.