Theses and Dissertations at Montana State University (MSU)
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Item Using genetic and genomic techniques to uncover cryptic diversity for improving aquatic invasive plant management(Montana State University - Bozeman, College of Agriculture, 2021) Chorak, Gregory Michael Thomas; Chairperson, Graduate Committee: Ryan Thum; This is a manuscript style paper that includes co-authored chapters.Genetic diversity can be important at many levels of invasive species management. And, for different questions, it matters at which level we measure diversity to understand its relevance. Some invaders may look similar to other species, so identifying the species to be managed may be difficult without genetic tools. Once the species has been identified, understanding the diversity in that species may be important to identify management units, invasive traits, and the possibility of spread. Finally, understanding how the alleles an individual possesses determine the traits expressed can give managers the tools to control for unwanted traits of an invasive species. In this body of work, I uncover diversity at the species/taxon level, the genotype/clone level, and finally at the gene level in invasive aquatic weed species. At the taxon level, I found that one invasion of aquatic weeds in the northeastern US was actually two or more separate invasions and taxa. At the genotype level, I found that the same genotype responds the same to a common herbicide management regardless of where it is found, and that different genotypes have varying responses to a common herbicide treatment. And, at the gene level, I found that different genotypes with different growth rates have different gene expression in the control and transcriptional response to a common herbicide treatment. At each of these levels, managers have questions and concerns about management decisions. Understanding that there were two unique taxa in what was considered one invasion informed managers that there may be variance in management relevant traits between the two. In the genotype level study, we learned that determining which clones are present in a lake slated for herbicide management may inform which herbicides to use. And, at the gene level, we are starting to understand the molecular process of management relevant phenotypes so that one day managers can screen for molecular markers that will reveal herbicide response of individuals slated for management.Item Coexistence between a native (Valvata humeralis) and a non-native (Potamopyrgus antipodarum) gastropod in the Middle Snake River, Idaho : implications for invasive species impact(Montana State University - Bozeman, College of Letters & Science, 2012) Gates, Kiza Kristine; Chairperson, Graduate Committee: Billie L. Kerans; Billie. L. Kerans was a co-author of the article, 'Spatial, temporal, and diet partitioning combine with environmental stochasticity to enable coexistence between an invasive and a native gastropod' in the journal 'Biological invasions' which is contained within this thesis.; Billie. L. Kerans was a co-author of the article, 'Biotic interaction gradients between native and invasive species' in the journal 'Ecology' which is contained within this thesis.; Billie. L. Kerans was a co-author of the article, 'Competitive and facilitative mechanisms of a biotic interaction gradient' in the journal 'Oecologia' which is contained within this thesis.The dominant competitive abilities of many invasive species are frequently assumed to preclude biologically similar native species over time, but there has been little research exploring how interactions between invasive and native species may change with changes in biotic and abiotic conditions. Introduction of the invasive New Zealand mud snail Potamopyrgus antipodarum in the Snake River in the late 1980's raised many concerns for the native gastropods of this region; however, the native gastropod Valvata humeralis has maintained large populations and continued to coexist with P. antipodarum. I investigated the coexistence of P. antipodarum and V. humeralis in the Vista reach of the Middle Snake River. Diet, spatial, and temporal partitioning of V. humeralis were explored in populations that were invaded by P. antipodarum and uninvaded. A field growth experiment was used to measure the net intra- and interspecific effects of V. humeralis and P. antipodarum at varying densities and species proportions. Results of the field growth experiment were compared with field survey data. A laboratory growth experiment and a stoichiometric experiment were used to identify the interaction mechanisms between species. Valvata humeralis juveniles appeared to shift diet in the presence P. antipodarum. There was evidence of spatial partitioning from P. antipodarum by V. humeralis at the among population scale but not the within population or patch scales. The field growth experiment indicated that interspecific net effects of P. antipodarum on V. humeralis changed in direction with increasing P. antipodarum density. Field surveys showed a similar pattern. The laboratory growth experiment indicated that direct interference competition was the negative mechanism of the species interaction and confirmed field experimental results. Stoichiometric analyses suggested that P. antipodarum juveniles require more phosphorus than V. humeralis juveniles, but that stoichiometric facilitation was not likely an interaction mechanism. Facilitated growth of V. humeralis in the presence of P. antipodarum may have been caused by increased access to food and/or P. antipodarum digestive food conditioning. Results suggest that the impact of an invasive species on the native community may be a complex interplay between invader density, native species behavior, invader nutrient use, and environmental conditions.