Date of Graduation

8-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Biology (PhD)

Degree Level

Graduate

Department

Biological Sciences

Advisor/Mentor

Magoulick, Daniel D.

Committee Member

Naithani, Kusum J.

Second Committee Member

Willson, John D.

Third Committee Member

Tipton, John R.

Keywords

Invasive species; Mammoth Spring Crayfish; Drought; Stream permanence

Abstract

Freshwater crayfish constitute one of the most-threatened taxonomic groups in North America. Invasion by other crayfish species as well as habitat degradation through alteration of natural flow regime are two of the most prominent threats to crayfish persistence. Additionally, extreme weather events like droughts can amplify threats posed by other stressors on crayfish populations and are expected to increase in frequency, magnitude, and/or duration in the future, which may negatively influence narrow-ranged endemic crayfish populations typical of the Southeast. The Mammoth Spring Crayfish, Faxonius marchandi, is a narrow-ranged endemic that occurs in the Spring River drainage of Arkansas and Missouri where it is both geographically and genetically isolated. Additionally, F. marchandi populations may be faced with a spreading invader, F. neglectus chaenodactylus, the Gap Ringed Crayfish. This dissertation sought to examine the influence of invasion and drying on F. marchandi growth and survival using mescosm experiments, the desiccation tolerance of the invader versus F. marchandi using experimental chambers, the influence of stream permanence and drying on crayfish density, occupancy, detection, colonization, and extinction using a multi-season dynamic occupancy model, and the predicted extinction risk and population viability of F. marchandi under future invasion and drought scenarios using a stage-based demographic metapopulation model. In the mesocosm experiment, there was a significant negative interspecific competition effect on change in length, and the experimental chamber experiment found differential tolerance to desiccation for all populations, with larger individuals tending to live longer. Additionally, the population models found negative effects under severe invasion and only under severe drought. These results indicate F. marchandi may show resilience when faced with F. neglectus invasion and drying will likely not play a part in their dynamics. The dynamic occupancy results showed context-dependent differences in density, detection, colonization, and extinction. This dissertation shows how crayfish may respond to environmental changes and invasive species in the coming years and gives potential implications about their persistence.

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