The influence of loss of diversity on community dynamics and ecosystem functioning has recently received considerable attention. Although study of biodiversity has a long history within ecology, empirical investigations exploring consequences of loss have been rare. Because many factors confound diversity comparisons, experimental manipulations of diversity offer the most direct way of attributing cause to diversity loss. The effects of reduction in number of species will depend on the strength and sign of species interactions affected by loss of diversity. An experiment performed on a high zone, rocky intertidal community in which macroalgal diversity was manipulated demonstrated that effects of diversity loss will be highly dependent on which species are removed. However, effects of diversity reductions were strongest at the harsh end of a stress gradient where interactions were more positive. Thus, factors that affect the strength and sign of species interactions such as the degree of physical stress may serve as a rough guide to where the effects of diversity loss will be most severe. An assessment of the influence of diversity on community response to a strong physical perturbation was performed using an experimentally-induced thermal stress. Higher diversity treatments were most strongly affected directly by the stress because such treatments had higher abundance and therefore more biomass to lose. However, those same treatments recovered more quickly from the stress. Community recovery of initially low diversity treatments was slowed by persistence of non-typical states or slow recovery of dominant species. A simulation study was performed to assess the ability of different experimental designs to detect biodiversity effects. Our ability to predict consequences of changes in diversity will be dependent on our ability to distinguish the most influential biodiversity "components" within a system. This study uncovered a phenomenon that will be common in biodiversity studies: misidentification of one biodiversity component (e. g., an effect of a keystone species) as a different component (e. g., an effect of the number of species). I call this phenomenon "aliasing." Because of the complexity of biodiversity, experiments and observational studies will be highly susceptible to aliasing and, thus, results will require careful interpretation. / Graduation date: 1997

This work examined the importance of structural complexity of habitat, availability of prey, and competition with ants as factors influencing the abundance and community composition of arboreal spiders in western Oregon. In 1993, I compared the spider communities of several host-tree species which have different branch structure. I also assessed the importance of several habitat variables as predictors of spider abundance and diversity on and among individual tree species. The greatest abundance and species richness of spiders per 1-m-long branch tips were found on structurally more complex tree species, including Douglas-fir, Pseudotsuga menziesii (Mirbel) Franco and noble fir, Abies procera Rehder. Spider densities, species richness and diversity positively correlated with the amount of foliage, branch twigs and prey densities on individual tree species. The amount of branch twigs alone explained almost 70% of the variation in the total spider abundance across five tree species. In 1994, I experimentally tested the importance of needle density and branching complexity of Douglas-fir branches on the abundance and community structure of spiders and their potential prey organisms. This was accomplished by either removing needles, by thinning branches or by tying branches. Tying branches resulted in a significant increase in the abundance of spiders and their prey. Densities of spiders and their prey were reduced by removal of needles and thinning. The spider community of needle-sparse branches was dominated by orb weavers (Araneidae), whereas tied branches were preferably colonized by sheet-web weavers (Linyphiidae and Micryphantidae), and nocturnal hunting spiders (Anyphaeilidae and Clubionidae). Spider species richness and diversity increased in structurally more complex habitats. In 1994 and 1995, I excluded foraging Camponotus spp. ants from canopies of sapling Douglas-fir. Biomass of potential prey organisms, dominated by Psocoptera, increased significantly by 1.9 to 2.4-fold on the foliage following ant exclusion. Hunting spiders, dominated by the Salticidae, increased significantly by 1.5 to 1.8-fold in trees without ants in the late summer. The exclusion of ants did not affect the abundance of web-building spiders. Documented aggressive behavior of aphid-tending ants suggests interference competition between hunting spiders and ants. / Graduation date: 1996

Typescript. Includes vita and abstract. Bibliography: Includes bibliographical references (leaves 114-132). Description: xiii, 132 leaves : ill. (some col.), charts ; 29 cm. / Larvae of the limpets Lottia digitalis and LOffia asmi, as well as larvae of the flat abalone Halioits walallensis. develop into lecithotrophic veliger larvae and settle into benthic habitat after a breif planktonic stage. Larvae of 1. digitalis settled and metamorphosed upon rocky substrata, as well as the barnacle P. polymerus, collected from an adult habitat high in the rocky intertidal. In contrast, substrata from mid and low intertidal zones failed to induce settlement and metamorphosis in larvae of L. digitalis. These results suggest that recruitment into high intertidal habitat is driven by settlement rather than post settlement processes. New recruits within an adult habitat were most abundant low within the adult range and upon north-facing slopes of rocks. Larvae ofH walallensis that experienced a five-day extension of their competence period exhibited accelerated rates of metamorphosis, as well as accelerated juvenile growth rates, relative to larvae that were presented with settlement surfaces at initial competence.

Waldo Lake, located in the Oregon Cascades, is considered to be one of the most dilute lakes in the world. Even with very low nutrient concentrations and sparse populations of zooplankton, introduced fish in the lake are large in size and in good condition when compared to fish from other lakes. Fish were originally stocked in Waldo Lake in the late 1800's. The Oregon Department of Fish and Wildlife began stocking in the late 1930's and continued stocking until 1991. Species existing in Waldo Lake today include brook trout, rainbow trout, and kokanee salmon. The overall objective of this thesis was to increase the understanding of the interrelationships that affect the age, growth, and diet of fish in Waldo Lake. The specific objectives were to summarize and synthesize available information on the substrate, climate, water, and biota of the Waldo Lake Basin; describe the cultural history and current cultural values of the Waldo Lake Basin; determine the age, growth, length, weight, condition, diet, and reproduction of introduced fish species in Waldo Lake; interrelate the above information to show how these components of the natural-cultural system are related. Fish were collected one week per month from early June through mid-October in 1992 and 1993. Variable mesh experimental gillnets set in nearshore areas were used to capture fish in 1992. During the 1993 sampling period, experimental gillnets and trapnets were set in the nearshore areas of the lake. Relative age specific growth rates of brook trout in Waldo Lake are comparable to brook trout growth rates in other lakes. Brook trout growth rates generally decreased with age, however, there were no significant differences in the growth rate of each age class between 1991 and 1993. The condition of brook trout in Waldo Lake is also comparable to brook trout in other lakes. The same is true for rainbow trout and kokanee salmon. Fish in Waldo Lake are large in size and in good condition due, in part, to the availability of benthic macroinvertebrates. Taxa found in stomach contents of fish captured in Waldo Lake consisted primarily of aquatic benthic macroinvertebrates, but terrestrial vertebrates and vertebrates, although infrequently consumed, were also part of the total diet. Rainbow trout in Waldo Lake consumed primarily chironomidae larvae and pupae although odonata larvae, ephemeroptera larvae, and amphipods were also consumed. Kokanee salmon fed almost exclusively on chironomid larvae although small numbers of ephemeroptera larvae, odonata larvae, and coleoptera were also consumed. The most important macroinvertebrate taxon consumed by Waldo Lake brook trout was chironomid larvae and pupae, although other species also were important. The diet of Waldo Lake brook trout varied in a complex way that appeared to be related to the relative abundance of macroinvertebrate taxa, feeding location in the lake, and time of year. Brook trout diet also varied by size class. The components of the Waldo Lake natural-cultural system are complexly interrelated and the nature of these relationships are constantly changing. Each component in some way affects and is, in turn, affected by each of the other components. Changes in some components, such as substrate, affect other components along geologic time scales. Other components, such human culture and biota, may change rapidly within a decade. The capacity of natural-cultural systems, such as Waldo Lake, to change over time makes it possible to view the present state of the system only as a snapshot in time. This dynamic nature of the Waldo Lake natural-cultural system is not unique to Waldo Lake, but is expressed in all natural- cultural systems. / Graduation date: 1997

The vegetative communities in the subalpine meadows of Hunts Cove, Mt. Jefferson, and some of the major environmental factors affecting them were studied in the summer of 1971. Hunts Cove is in the subalpine Tsuga mertensiana parkland of the Central Oregon High Cascades. Habitats within the Cove vary considerably; elevation changes from 1500 m to 1900 m; water regime ranges from bogs and seeps to desert; snowlie varies as much as two months at different points in the same year. Estimates of vegetative cover and frequency were taken on 300 quadrats. Snow lie was monitored on a weekly basis. Soils were collected and analyzed. Eleven meadow communities were distinguished. They are: A. The short sedge communities, 1) Carex nigricans-Aster and 2) Carex nigricans-Polytrichum on late snowfree, poorly drained sites; B. Bryophyte, on very late snowfree, damp, shaded soil; C. Heath communities on well drained sites, 1) Phyllodoce-Cassiope on exposed late snowfree slopes, 2) Vaccinium deliciosum on moderately late snowfree slopes and 3) Potentilla-Carex nigricans on very late snowfree sites with rodent activity; D. Senecio lush herb on mesic warm sites; E. Hydric communities, 1) Eleocharis-Aulacomnium occurring in stagnant water, 2) Carex rostrata-Sphagnum in freely moving water, 3) Carex scopulorum in seeps and bogs with permanent water supply, probably an edaphic climax, and 4) Carex sitchensis in swamps flooded during meltoff. These communities were arrayed in a floristic ordination and the position of all hydric, lush herb, and short sedge sample plots was found to parallel snowfree dates. Well drained heath communities became snowfree in the order expected from other studies. Comparison of the communities with other studies from the Northwest suggests Phyllodoce-Cassiope, Vaccinium deliciosum and the Carex nigricans communities to be parts of a consistent vegetative pattern extending north into Southern B. C. / Graduation date: 1973

Thesis (Ph.D.)--Oregon, Dept. of Biology Vita Bibliography: l. 118-122

I examined the biomechanical factors that influence the sizes of intertidal macroalgae by studying a population of Fucus gardneri at Fogarty Creek Point, OR. I constructed a mathematical model to predict optimal sizes and probabilities of survival for Fucus under conditions of high and low wave exposure. Predicted optimal sizes of Fucus closely matched the mean observed sizes of plants collected from wave-exposed and protected locations. To test this hypothesis in the field, I reciprocally transplanted Fucus between wave-exposed and wave-protected sites and found that the degree of wave exposure did not affect survival, but did influence size. Large Fucus were tattered by waves at exposed sites, and small Fucus grew at protected sites. These results support the hypothesis that wave forces can set mechanical limits to size in Fucus. I experimentally examined the relative influences of wave-induced disturbance, competition and predation on the sea palm, Postelsia palmaeformis and its understory community at a wave-exposed site at Depoe Bay, OR. Postelsia recruitment was affected by seasonal variations in disturbance and was greatest in areas disturbed in winter. Postelsia were most abundant at mid-zone, wave-exposed sites, and their restriction to wave-exposed sites seems to be due both to; 1) the occurrence of predictable winter disturbances at these sites which remove mussels, thereby stimulating sea palm growth from the underlying rock, and 2) high water motion which enhances sea palm growth by increasing nutrient exchange and photosynthesis and preventing desiccation at low tide. Competition, disturbance and grazing were all important factors in structuring the Postelsia understory community. Postelsia were dominant competitors and their holdfasts overgrew low-lying plants which were torn loose with Postelsia when this kelp was dislodged by winter storm surf. In the absence of this predictable, seasonal disturbance, competitive understory species, such as Corallina dominated primary space. Intermediate levels of disturbance allowed for the highest understory species diversity. Limpets played a keystone role by grazing Postelsia, the competitive dominant during most of the year, and maintained high levels of species diversity in the algal understory. / Graduation date: 1995

Typescript. Includes vita and abstract. Bibliography: Includes bibliographical references (leaves 102-110). Description: xiii, 110 leaves : ill. ; 29 cm.

This study consisted of two research projects in the Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis (Beetle & A. Young) S.L. Welsh) alliance, the most extensive of the big sagebrush complex in the Intermountain West. In the first project, we intensively sampled 107 relatively undisturbed, late seral Wyoming big sagebrush sites across the High Desert, Humboldt, and western Snake River Ecological Provinces to investigate vegetation heterogeneity and the relationship of environmental factors with vegetation characteristics. Vegetation characteristics were highly variable across the region. Perennial grass and total herbaceous cover varied more than six and sevenfold, respectively between minimum and maximum values. Sagebrush cover averaged 12%, but ranged between 3 and 25%. With the exception of perennial grass cover (p<0.0001, r²=0.52), limited variability in other vegetation characteristics was explained by environmental variables. In the second project, we investigated the functional role of Wyoming big sagebrush by using undisturbed and sagebrush removed (with burning) treatments and comparing vegetation and microsite characteristics under (subcanopy) to between sagebrush canopy (interspace) zones. Wyoming big sagebrush influenced associated vegetation and microsites. On sites receiving high incidental radiation, perennial grass and total herbaceous cover and density were greater in the subcanopy than interspace zones (p<0.05). On north aspects, these differences were not as pronounced suggesting sagebrush's influence on associated vegetation is site dependent. Temperature extremes were mediated and soil water content was greater in the subcanopy than interspace zones during the growing season. Results indicated that the subcanopy zone can be a more favorable environment to herbaceous vegetation than the interspace zone. Wyoming big sagebrush is important to community resource capture and use. Plots with sagebrush had greater soil water content at the start of the growing season and produced more total biomass compared to where sagebrush had been removed in both post-fire years (p<0.05). However, higher Thurber's needlegrass photosynthetic rates and greater herbaceous cover and production where sagebrush had been removed suggested that more resources were available to herbaceous vegetation in the absence of sagebrush. / Graduation date: 2006

Samples of benthic organisms off the coast of Oregon, taken from depths varying from 50 to 2900 meters, have been analyzed in terms of diversity at a given station, and similarity and ecological distance to other stations. Estimates of epifauna abundance were also made. In the analysis an important distinction is made between diversity, abundance, and variety indices; the three measures are considered independent pieces of information relevant to the ecological structure of the population of interest. Two types of sampling gear were used. Large epifauna were sampled with a beam trawl. Polychaetous infauna were sampled with an anchor-box dredge. The diversity index chosen is Simpson's index; the measures of similarity and ecological distance are related. These measures are preferred because of their ease in calculation and basic simplicity. In addition these measures may be interpreted as estimates of well-defined population parameters (as Simpson has pointed out) which have straightforward probabilistic interpretation. A valid measure of diversity is one piece of relevant information necessary for elucidating the sufficient parameters of ecological systems. Therefore the methodology presented has broad application to studies of population structure. / Graduation date: 1970