Theses and Dissertations at Montana State University (MSU)
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Item Olfactory preference and reproductive isolation of two Mecinus species (Coleoptera: curculionidae): implications for biological control of dalmatian, yellow, and hybrid populations of Toadflax, Linaria species(Montana State University - Bozeman, College of Agriculture, 2016) Hubbard, Charles Eli; Chairperson, Graduate Committee: David WeaverClassical biological control of the exotic, invasive toadflaxes Linaria vulgaris (L.) Mill. and Linaria dalmatica Mill. has had both successes and failures. One of the new challenges land managers face is the apparent increase in vigor shown by naturally occurring hybrid populations of the two toadflax species. This has presented practical problems because managers now are unable to decide which weevil species to use on these hybrids: Mecinus janthinus, which is found on L. vulgaris, or M. janthiniformis which has preference for L. dalmatica. This key question was addressed using olfactometer experiments to determine if the volatile profile for each plant establishes host fidelity for the naturally-occurring associated Mecinus species. Adults of both insect species were paired in cages on clones of naturally occurring and synthetic reciprocal cross hybrids and the parent toadflax species to quantify mating events and to determine the number of offspring produced on clones of each plant type of plant in incomplete randomized blocks. We did this using both intraspecific and interspecific pairs of Mecinus species to determine how many offspring are produced by intraspecific adults and also to explore the possibility of establishing a hybrid weevil population using clones of each plant type. Host plant preference for both Mecinus species is influenced by olfactory responses, but this was only evident for adult females. Our first series of no-choice experiments with intraspecific mating pairs indicated that M. janthiniformis is more successful in terms of offspring produced for all types of hybrid toadflax tested. The results also showed that M. janthinus had a higher percentage of survival on all types of hybrids. As expected each Mecinus species performed best on its natural host plant. The results of our second series of no-choice experiments suggest that these two weevil species can produce viable interspecific offspring on clones of most of the plant types evaluated. This suggests that the newly described M. janthiniformis is very similar to M. janthinus and the separation between the two species is controlled at least in part, by olfactory cues from the favored host. In the future, land managers can better decide which Mecinus species to use based on whether the hybrid weed species is influenced more by L. vulgaris, or L. dalmatica.Item Habitat selection of a reintroduced beaver population in the Absaroka-Beartooth Wilderness(Montana State University - Bozeman, College of Agriculture, 2011) Scrafford, Matthew Allan; Chairperson, Graduate Committee: Duncan T. Patten; Geoffrey Poole (co-chair)In 1986, a beaver reintroduction program was initiated in the Absaroka-Beartooth Wilderness (AB), Montana, in an effort to restore this species to the landscape after a nearly 40 year absence. Since reintroduction, the AB has been inventoried yearly by the U.S.F.S. Gardiner Ranger District to document the location of active beaver structures. This study utilized the beaver structure inventory to report habitat characteristics associated with successful beaver colonies in the AB over a 24 year period. In meadows along 3rd order streams, colonies beaver established early (1986 - 1993) were more successful through 2010 than those established later (1994 - 2006), likely because habitat selected early was of higher quality. Odds of beaver colony success increased with greater stream sinuosity and depth, less distance to secondary channels, and less area of point/gravel bars. The amount of willow, although abundant at all locations, was not significantly different for beaver colony locations with varying levels of success. The best habitat for beaver colonies in meadows along 3rd order streams appeared to be on or within close proximity of secondary channels (e.g., sloughs, tributaries) because these locations were sheltered from destructive main stem flooding such that colonies and their structures were more permanent. Locations with evidence of historic use by beaver in meadows along 3rd order streams had less area of point/gravel bars, greater stream depth, and more willow than locations which had never been used by beaver. Successful beaver colonies were also found in smaller meadows on 1st and 2nd order streams although there was less available willow and streams could be intermittent in flow. After 24 years, the beaver population appears to be at carrying capacity, although there is no evidence that willow harvest rates are excessive or even negative. The success of reintroduced beaver populations in the AB is in contrast to conditions on the nearby northern Yellowstone winter range, where colony density is lower, likely because riparian woody vegetation shows more evidence of suppression from ungulate browsing, site potential for willow growth may be less, and negative anthropogenic effects persist.