Date of Graduation


Document Type


Degree Name

Master of Science in Biology (MS)

Degree Level



Biological Sciences


Daniel D. Magoulick

Committee Member

Michelle Evans-White

Second Committee Member

John D. Willson


Crayfish, Drought, Invasive species, Morphology, Source population


Invasive species are a global problem and their effects on recipient ecosystems may be mediated by disturbance and intraspecific variation. Crayfish can substantially influence stream structure and function, and invasive crayfish often have differential impacts than native crayfish in aquatic ecosystems. Since species traits often vary across a distribution, it is possible that invasive crayfish from different source populations may have distinct impacts on recipient ecosystem structure and function. In the Ozark Highlands of Arkansas and Missouri, USA, invasive O. neglectus (the Ringed Crayfish) may be leading to the displacement of native O. eupunctus (the Coldwater Crayfish). The objective of this thesis is to assess variation in the impacts of O. eupunctus and O. neglectus from multiple source populations. First, we experimentally examine the effects of crayfish source population and drought on stream structure and function and crayfish growth and survival. We found growth rates differed between O. eupunctus and O. neglectus, and also between O. neglectus from different source populations. In addition, we found O. neglectus from different source populations differentially affected stream structure, and O. eupunctus and O. neglectus differentially affected stream function. Drought and crayfish source population had interactive effects on macroinvertebrate richness, but no other variables. Important aspects of stream structure and function were also influenced by drought. In the second study, we assessed variation in morphology and traits related to invasiveness for O. eupunctus and O. neglectus from multiple source populations. We examined variation in chelae size in order to investigate potential competitive ability for O. eupunctus and O. neglectus. We found O. eupunctus had larger chelae than O. neglectus indicating that displacement of O. eupunctus by O. neglectus may not be related to competitive dominance. In addition, we found O. neglectus morphology varied across source populations. The results of these studies indicate that morphology and impacts of invaders from different source populations may vary, and disturbance and invasive species may have compounding effects on recipient ecosystems. Therefore, abiotic disturbance and the source population of an invasive species are important considerations when addressing and predicting invasion impacts.