Abstract

Orconectes hylas is native to the Black River, Meramec River and Big River drainages in Missouri, USA. Following introduction to the St Francis River drainage, it expanded its range there into portions of several streams. Simultaneously, two imperiled endemic species, Orconectes peruncus and Orconectes quadruncus, were eliminated from those locations. Our objectives were to determine life histories in one O. hylas population in the Black River drainage and two populations in the St Francis River drainage; to compare fecundity and instar growth between O. hylas and O. peruncus; and to compare O. hylas’ life history with published data for O. peruncus and O. quadruncus to determine possible mechanisms that might facilitate displacement of these endemics. Monthly collections (August 1998 - July 1999) indicated that life cycles among the O. hylas populations were generally similar, with some timing differences. Introduced populations of O. hylas from the St Francis River drainage grew larger and had attained a larger size upon reaching sexual maturity than those from the indigenous population. Densities were high in all populations. Orconectes hylas appeared more fecund and its instars grew faster than O. peruncus. Orconectes hylas showed potential to release young earlier and grew larger than the endemics. This study revealed life history differences between introduced O. hylas and native O. peruncus and O. quadruncus that may facilitate the apparent displacement of the endemics in portions of the St Francis River drainage in Missouri, USA.

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