Year of Award


Document Type


Degree Type

Doctor of Philosophy (PhD)

Degree Name

Fish and Wildlife Biology

Department or School/College

College of Forestry and Conservation

Committee Chair

Lisa Eby

Commitee Members

Winsor Lowe, David Patterson, Michael Schwartz, Clint Muhlfeld


University of Montana


Habitat fragmentation and invasive species are two of the primary threats to global biodiversity, yet biologists have tested few guidelines for protecting species under these conditions. These threats are particularly relevant to conservation of freshwater species like the Cutthroat Trout (Oncorhynchus clarkii). Hybridization with introduced Rainbow Trout (O. mykiss) has already caused extinction of one subspecies and threatens extant populations. Additionally, Cutthroat populations have lost genetic diversity across their range due to habitat destruction and fragmentation. These threats create a catch-22 for managers, wherein treating one problem (connecting populations) may lead to the other (interactions with invasive species). Furthermore, little is known about requirements for persistence of populations isolated to protection against invasive species.

I assessed tradeoffs in conservation strategies for Westslope Cutthroat Trout (O. c. lewisi). In connected populations, steeper streams had smaller hybrid zones and less introgressive hybridization. I found that geomorphology (slope) limited hybridization between Rainbow and Cutthroat Trout and provided a natural refuge for native fish in connected systems.

Isolated Cutthroat populations residing in under 5km of habitat above anthropogenic barriers (<80yrs) suffered loss of genetic diversity independent of habitat size, quality, and time since isolation. Geologically isolated populations in larger fragments (up to 18km) also experienced loss of genetic diversity, likely from stochastic events causing population bottlenecks. Significant loss of genetic diversity compared to connected populations occurred despite exceeding habitat size and population recommendations derived from genetic theory for maintaining diversity. Thus over the long-term, isolated populations may not retain genetic diversity even if they meet suggested conservation thresholds.

In these anthropogenically isolated populations, population growth rate (lambda) was positively associated with water volume during summer base flow and declined with increasing land use in the watershed. Lambda was most sensitive to probability of maturity, and increased as size of maturity decreased. Populations with low adult survival had rapid somatic growth rates, thus reaching maturity sooner. This highlighted the potential for local adaption under isolation as populations adjust to shifting environmental conditions and life history tradeoffs. Although isolated population may have reduced genetic diversity, actions such as genetic rescue should be considered with caution.



© Copyright 2013 Kellie Jahan Carim