Thesis (M.S.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 227-234). Also available on the World Wide Web.

Thesis (M. Phil.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

The objective of this study was to examine the distribution of exotic plants and determine the potential threats in the mixedwood section of the boreal forest. The invasion of exotic plants into natural areas is a growing concern among ecologists. Exotic species have no previous exposure to the invaded area and have been introduced, either intentionally or accidentally, by humans. These plants have the potential to suppress surrounding vegetation and acquire the majority of available resources. This dominance alters important ecosystem functions and negatively affects ecosystem structure and composition. This study examined three types of land use (roadside right-of-way maintenance, timber harvesting and wildfire) to identify the density, frequency and cover of exotic plants within the mixedwood forest. There were also separate categories of the time since disturbance (re-current, recent and mature) for each disturbance type. Data were collected in the summer field seasons of 2000 and 2001 in and nearby the Prince Albert Model Forest (approximately 70 km north of Prince Albert, Saskatchewan). Surveying was completed in mature forest, harvested and wildfire areas using 10 x 10 m quadrats. These quadrats were adjacent to or remote from roadside right-of-ways that were deliberately seeded with exotic species. Seeding the right-of-ways with exotic species occurred along principal and secondary highways. Surveying was also conducted within roadside right-of-ways using 1 x 1 m quadrats. These quadrats were adjacent to the recently disturbed and mature quadrats surveyed in the previous year. Each plant species observed in the quadrats had a cover value assigned, while stem counts were also conducted for exotic species. A total of 23 exotic species were observed within the quadrats. The exotic herb species belong to the Gramineae (9 species), Leguminosae (7), Compositae (5) families with one species each in Plantaginaceae and Boraginaceae. No exotic trees or shrubs were observed within the study sites. Areas that were recently disturbed either by timber harvesting or wildfire had 6 different exotic species with an average density of 0.2 ± 0.1 stems/m2 and a frequency of 72 %. Similar exotic frequencies and species in both recently harvested and burned survey sites suggests that these disturbances have a comparable affect on exotic distributions. Exotic species capable of wind dispersal had the highest frequencies in the recently disturbed survey sites. Common dandelion (Taraxacum officinale) had a frequency of 57 %, perennial sow thistle (Sonchus arvensis) was observed in 38 % of the sites and annual hawksbeard (Crepis tectorum) was at 25 %. Mature forest had a lower population of exotic plants, with only 2 exotic species observed. Taraxacum officinale and Canada bluegrass (Poa compressa) were observed in 13 % of the mature quadrats with an average density of 0.002 ± 0.002 stems/m2. The right-of-way quadrats contained the highest amount of exotics with 22 observed species. The average density of exotic species in roadside right-of-ways was 117 ± 22 stems/m2 with 94 % of the quadrats containing at least one exotic plant. The deliberate introduction, frequency of disturbance and the physical environment of roadside right-of-ways appear to influence the distribution of exotic plant species. The most frequently observed exotic species in the right-of-way areas were Taraxacum officinale (observed in 73 % of the quadrats at 8 stems/m2) followed by alsike clover (Trifolium hybridum at 45 % and 17 stems/m2), Sonchus arvensis (43 % and 4 stems/m2), creeping red fescue (Festuca rubra at 36 % and 31 stems/m2) and smooth brome grass (Bromus inermis at 31 % and 17 stems/m2). These species are either common in urban areas, agricultural weeds or have been deliberately seeded into right-of-way areas. The distribution of exotic species suggests that land use contributes to increased densities and frequencies of exotic plants. Each exotic species observed was ranked according to a system developed by Hiebert and Stubbendieck (1993). The ranking system was used to determine the current and potential threat of exotic plant species to become detrimental to ecosystem structure, composition and function. The ranking identified 14 species that were a lesser threat and easy to control, 8 species that were a lesser threat and hard to control, and one species, Bromus inermis, that was ranked as a serious threat and hard to control. Additional monitoring is required as the species observed in this study may be exhibiting a lag phase of population expansion, which typically precedes an exponential increase. Other species (scentless chamomile (Matricaria perforata) and caragana (Caragana arborescens)) that were not observed in the study area, but are known to occur within the region, are also a concern with respect to future exotic species invasions. Anticipated climatic changes are also expected to increase the distribution of exotic species as changes to environmental attributes will produce a longer growing season and increased plant growth and productivity.

The objective of this study was to examine the distribution of exotic plants and determine the potential threats in the mixedwood section of the boreal forest. The invasion of exotic plants into natural areas is a growing concern among ecologists. Exotic species have no previous exposure to the invaded area and have been introduced, either intentionally or accidentally, by humans. These plants have the potential to suppress surrounding vegetation and acquire the majority of available resources. This dominance alters important ecosystem functions and negatively affects ecosystem structure and composition. This study examined three types of land use (roadside right-of-way maintenance, timber harvesting and wildfire) to identify the density, frequency and cover of exotic plants within the mixedwood forest. There were also separate categories of the time since disturbance (re-current, recent and mature) for each disturbance type. Data were collected in the summer field seasons of 2000 and 2001 in and nearby the Prince Albert Model Forest (approximately 70 km north of Prince Albert, Saskatchewan). Surveying was completed in mature forest, harvested and wildfire areas using 10 x 10 m quadrats. These quadrats were adjacent to or remote from roadside right-of-ways that were deliberately seeded with exotic species. Seeding the right-of-ways with exotic species occurred along principal and secondary highways. Surveying was also conducted within roadside right-of-ways using 1 x 1 m quadrats. These quadrats were adjacent to the recently disturbed and mature quadrats surveyed in the previous year. Each plant species observed in the quadrats had a cover value assigned, while stem counts were also conducted for exotic species. A total of 23 exotic species were observed within the quadrats. The exotic herb species belong to the Gramineae (9 species), Leguminosae (7), Compositae (5) families with one species each in Plantaginaceae and Boraginaceae. No exotic trees or shrubs were observed within the study sites. Areas that were recently disturbed either by timber harvesting or wildfire had 6 different exotic species with an average density of 0.2 ± 0.1 stems/m2 and a frequency of 72 %. Similar exotic frequencies and species in both recently harvested and burned survey sites suggests that these disturbances have a comparable affect on exotic distributions. Exotic species capable of wind dispersal had the highest frequencies in the recently disturbed survey sites. Common dandelion (Taraxacum officinale) had a frequency of 57 %, perennial sow thistle (Sonchus arvensis) was observed in 38 % of the sites and annual hawksbeard (Crepis tectorum) was at 25 %. Mature forest had a lower population of exotic plants, with only 2 exotic species observed. Taraxacum officinale and Canada bluegrass (Poa compressa) were observed in 13 % of the mature quadrats with an average density of 0.002 ± 0.002 stems/m2. The right-of-way quadrats contained the highest amount of exotics with 22 observed species. The average density of exotic species in roadside right-of-ways was 117 ± 22 stems/m2 with 94 % of the quadrats containing at least one exotic plant. The deliberate introduction, frequency of disturbance and the physical environment of roadside right-of-ways appear to influence the distribution of exotic plant species. The most frequently observed exotic species in the right-of-way areas were Taraxacum officinale (observed in 73 % of the quadrats at 8 stems/m2) followed by alsike clover (Trifolium hybridum at 45 % and 17 stems/m2), Sonchus arvensis (43 % and 4 stems/m2), creeping red fescue (Festuca rubra at 36 % and 31 stems/m2) and smooth brome grass (Bromus inermis at 31 % and 17 stems/m2). These species are either common in urban areas, agricultural weeds or have been deliberately seeded into right-of-way areas. The distribution of exotic species suggests that land use contributes to increased densities and frequencies of exotic plants. Each exotic species observed was ranked according to a system developed by Hiebert and Stubbendieck (1993). The ranking system was used to determine the current and potential threat of exotic plant species to become detrimental to ecosystem structure, composition and function. The ranking identified 14 species that were a lesser threat and easy to control, 8 species that were a lesser threat and hard to control, and one species, Bromus inermis, that was ranked as a serious threat and hard to control. Additional monitoring is required as the species observed in this study may be exhibiting a lag phase of population expansion, which typically precedes an exponential increase. Other species (scentless chamomile (Matricaria perforata) and caragana (Caragana arborescens)) that were not observed in the study area, but are known to occur within the region, are also a concern with respect to future exotic species invasions. Anticipated climatic changes are also expected to increase the distribution of exotic species as changes to environmental attributes will produce a longer growing season and increased plant growth and productivity.

Thesis (M. Phil.)--University of Hong Kong, 2007. / Also available in print.

Thesis (M. Phil.)--University of Hong Kong, 2005. / Title proper from title frame. Also available in printed format.

Thesis (M.S.)--Humboldt State University, 2007. / Includes bibliographical references (leaves 37-38). Also available via Humboldt Digital Scholar.

published_or_final_version / abstract / Ecology and Biodiversity / Master / Master of Philosophy

published_or_final_version / abstract / Biological Sciences / Master / Master of Philosophy

The interactions between plants and their insect herbivores are one of the main generators of biological diversity. A fundamental process generating this outstanding diversity is diet expansion to novel host plants. During the last four decades scientists accumulated evidence showing that co-adaptation between plants and herbivores is a major process assembling plant-herbivore interactions. However, rescent research suggests that adaptation is not always a prerequisite to generate novel plant-herbivore interactions. Novel associations between plants and insect herbivores may be assembled by ecological fitting - an ecological process whereby herbivores colonize novel host plants as a result of the suites of preadapted traits that they carry at the time of colonization. A widespread assumption concerning the architecture of insect herbivore genotypes is the "Jack of all trades master of none" principle. This principle proposes that there is a trade-off in genotype performances between host plants. The main prediction of this principle is that genotype performance will be negatively correlated among hosts. Genotypes displaying high performance on a given host will perform poorly on other hosts. This constraint of adaptation to multiple host plants implies that diet specialization will be selected over generalization. Contrary to these theoretical expectations, in most cases, genotypes that perform well in one host will also perform well in other host plants. Positive correlations in cross-host performance represent ecological and evolutionary dynamics opposite to the "Jack of all trades" principle. In this scenario genotypes with high performance on one host plant also have high performance on other plants, promoting generalization. The predictions of the current theory on the assemblage of novel plant-herbivore interactions focus on the fact that most insect herbivores are specialists. However, to fully understand the processes underlying the assembly of novel plant-insect interactions, it is necessary to study diet expansions in both specialist and generalist insect herbivores. This dissertation was performed at La Selva Biological Station, a tropical rain forest in Costa Rica, Central America. We studied a group of neotropical herbivores, the "rolled-leaf beetles" (Cephaloleia, Chrysomelidae: Cassidinae) and their host plants, neotropical plants in the order Zingiberales. Cephaloleia beetles have evolved with neotropical Zingiberales for the last 40-60 MY. Four paleotropical and one South American members of the Zingiberales have been introduced to La Selva during the last decade. After these introductions, currently seven Cephaloleia beetles are expanding their diets to exotic Zingiberales. These incipient diet expansions represent an opportunity to understand: 1) the relative roles of adaptation vs ecological fitting on the demography and colonization success of novel hosts in generalist and specialist herbivores and 2) whether genotypic performance across original and novel hosts are negatively correlated, as predicted by the "Jack of all trades" principle, or genotype performances across original and novel hosts are positively correlated. For most of the experiments included in this dissertation, I focused on the performance of larvae and adults of two generalist (Cephaloleia belti, C. dilaticollis) and two specialist beetles (Cephaloleia dorsalis, C. placida) reared in the laboratory on native or exotic Zingiberales. Generalist and specialist species display similar responses when changing their diets to novel hosts. Larvae preferred and performed better in the original than in the novel hosts. Adults usually displayed the opposite pattern, i.e. higher preference for and longevity on the exotic than on the novel hosts. In most novel interactions between Cephaloleia beetles and exotic Zingiberales, larval performance required adaptation, but adult performance was pre-adapted to the novel hosts. Therefore, both adaptation and ecological fitting are playing a role during diet expansions to novel hosts. Vital rates estimated through experimental demography show that population growth is reduced on novel host plants for both generalist and specialist Cephaloleia. Although in some cases population growth on the novel hosts is negative, suggesting the potential outcome of extinction after colonization or source-sink dynamics, several beetle species displayed positive population growth in the novel host plants. Positive instantaneous population growth rates in novel hosts supports diet expansions without substantial initial evolutionary change through ecological fitting. In quantitative genetics experiments testing for cross-host genetic correlations in performance between the original and novel host plants, we did not find evidence for negative genetic correlations, as predicted by the "Jack of all trades" principle. Most genetic correlations in performance between original and novel hosts were either not significant or they were positive. These results represent very different ecological and evolutionary dynamics than those predicted by the "Jack of all trades" principle. In this case, genotypes with high performance on original hosts also displayed high performance on novel hosts, promoting generalization. In conclusion, interactions between Cephaloleia beetles and plants from the order Zingiberales are labile. In some cases diet expansions may occur without substantial evolutionary change. In addition the genetic architecture of genotypes promotes generalization during diet expansions to novel hosts.