Modelling large scale systems with natural and artificial components requires storage of voluminous amounts of knowledge/information as well as computing speed for simulations to provide reliable answers in reasonable time. Computing technology is becoming powerful enough to support such high performance modelling and simulation. This dissertation proposes a high performance simulation based optimization environment to support the design and modeling of large scale systems with high levels of resolution. The proposed environment consists of three layers--modeling, simulation and searcher layer. The modeling layer employs the Discrete Event System Specification (DEVS) formalism and shows how it provides efficient and effective representation of both continuous and discrete processes in mixed artificial/natural systems necessary to fully exploit available computational resources. Focusing on the portability of DEVS across serial/parallel platforms, the simulation layer adopts object-oriented technology to achieve it. DEVS is implemented in terms of a collection of classes, called containers, using C++. The searcher layer employs Genetic Algorithms to provide generic, robust search capability. In this layer, a class of parallel Genetic Algorithms, called Distributed Asynchronous Genetic Algorithm (DAGA), is developed to provide the speed required for simulation based optimization of large scale systems. This dissertation presents an example of DEVS modeling for a watershed, which is one of the most complex ecosystems. The example shows a well-justified process of abstraction from traditional differential equation models to DEVS representation. An approach is proposed for valid aggregation of spatially distributed systems to reduce the simulation time of watershed models. DEVS representation and spatial aggregation assure relative validity and realism with feasible computational constraints. Throughout the dissertation, several examples of GA optimization are presented to demonstrate the effectiveness of the proposed optimization environment in modeling large scale systems.

This dissertation reports on a study conducted to examine the morphological, behavioral, and environmental sources of variation in the structure of house cricket, Acheta domesticus, calling song. Song variations may be important in female mating decisions and influence male mating success. Eleven song parameters were measured: chirp duration, interchirp duration, syllable number, syllable duration, intersyllable duration, mean frequency, frequency intensity, minimum frequency, maximum frequency, syllable intensity, and intensity difference between syllable and frequency intensity. Morphological factors examined included body: mass, length, color, asymmetry, intactness; and male age. Behavioral factors were timing of song bouts and proclivity to sing. Environmental conditions of high population densities were simulated by temporarily placing males into an arena with three other males. The calling song structure of tactilely isolated males resulted in three factors: frequency (mean, minimum, and maximum frequencies); intensity (syllable intensity, and intensity difference); and variability (difference between syllable intensity and frequency intensity). Males with high body intactness sang at lower frequencies. Asymmetrical males sang more intense songs. Large males sang with more intensity and frequency variability. Intermale competitions resulted in distinguishable linear dominance hierarchies. Lower-ranking males sang less often than higher-ranking males, altered singing times, and sang quieter songs. Intermale competition resulted in males altering song structure. Analysis of post-competitive songs resulted in three factors: frequency (mean and maximum frequencies, and intensity difference); energy (duty-cycle, intensity, and minimum frequency) and variability (unchanged). Higher-ranking asymmetrical males sang at lower frequencies. Higher-ranking males sang with greater energy, and timed their singing to female receptive times. Higher-ranking, large, intact males sang with less variability. This study indicated that A. domesticus males signal phenotypic information via their calling song characteristics. More specifically, in low population densities males signal information concerning their fitness-related qualities. After having established dominance orders, the male signal information concerning their rank in conjunction with fitness. The implications of this study were that intermale competition altered the song cues available to the females and may alter female mating decisions.

A three-year randomized field study was undertaken to evaluate the effects of prescribed burning and the intense rainfall events associated with the summer monsoon of southern Arizona, specifically examining the interchange between the plant, soil and surface hydrologic processes within a savanna. The effects of fire and rainfall treatments were evaluated by examining their specific effects on vegetation, arbuscular mycorrhizal fungi (AMF), soil structure, soil nutrient capital, surface runoff and sediment. In addition to the field study, two factorial greenhouse studies were completed in conjunction with the field study. The objectives of the greenhouse studies were: (1) to test the effects of prescribed fire and high intensity rainfall on AMF infectivity potential, and (2) to examine the effect of mycotrophy on the biomass production of native and introduced grasses grown in pasteurized and native soils. A third study examined the development of an empirical model to estimate sediment production from the field study's plots. The objectives of this third study were: (1) to develop the empirical model using two years of collected sediment, and (2) to compare model estimates with the commonly used Revised Universal Soil Loss Equation (RUSLE) model. The results of these studies indicate that a integrated mechanism exists between the plant community and biotic and physical soil processes, which when disturbed affect the hydrology of the watershed.

In contrast to documented increases in woody plant dominance of former savannas and grasslands of North America, oak (Quercus L.) savannas that form lower treelines in the southwestern United States and northwestern Mexico have been relatively stable over the past millennium. This research identified potential biotic and abiotic constraints on seedling recruitment of Quercus emoryi Torr. (Emory oak) within the context of potential shifts in lower treeline. Field surveys were used to describe seedling distribution at and below lower treeline, and to determine the potential for acorn dispersal from lower treeline into adjacent grassland. Field and greenhouse experiments designed to determine constraints on seedling establishment included reciprocal soil transfers, nutrient amendment studies, provision of artificial shade, and manipulation of seasonal precipitation inputs. Results indicate that rates of Q. emoryi recruitment within grasslands below treeline are relatively low, and are constrained by low rates of seed dispersal coupled with a low probability of seedling emergence. Seedling recruitment rates were directly correlated with quantity of summer precipitation, but were independent of winter precipitation. Results of this and complementary research suggest that lower treeline in southern Arizona is stabilized by self-enhancing feedback mechanisms of overstory shade, seed dispersal, and seedling establishment coupled with strong abiotic constraints beyond the current ecotone. The observed shift in treeline in the last millennium was less likely the result of slow, spatial progression of autogenic safe sites than the result of episodic and infrequent allogenic processes that simulated, or negated the importance of, conspecific, biogenic safe sites. Increases in summer precipitation are one such process that would facilitate (historic or potential future) downslope shifts in lower treeline. This interpretation is consistent with observations that downslope shifts in lower treeline which occurred 700-1700 ybp coincided with a period of particularly high summer precipitation in the region (i.e., the "Medieval Warm" period, 645-1295 ybp).

Pandora moth (Coloradia pandora Blake) is a phytophagous insect, defoliating ponderosa pine trees in the western United States. However, long-term studies of this insect and its effects on the forest ecosystem have not been conducted. Using dendrochronological techniques, I examined past timing and intensity of defoliation through its effects on radial growth of trees in the forests of south central Oregon. Pandora moth leaves a distinctive ring-width "signature" that was easily identifiable in the wood. The growth for the first year of the signature was half the normal ring-width with narrow latewood. The following two years produced extremely narrow rings, with the entire suppression lasting from 4 to 18 years. Twenty-two individual outbreaks were reconstructed from this 620 year chronology. I found that pandora moth outbreaks were episodic on individual sites, with a return interval of 9 to 156 years. Conversely, on the regional scale of south central Oregon, outbreaks demonstrated a 37-year periodicity. On average, pandora moth defoliation caused a 29% mean periodic growth reduction in defoliated ponderosa pine trees. Spread maps of the first year that sites demonstrated suppression were plotted revealing an apparent annual spread of the outbreaks. Examination of a fire history on one pandora moth outbreak site suggested that pandora moth outbreaks delay fire by interrupting the needle fall needed for fire spread. Superposed epoch analysis showed that the year that the outbreak was first recorded was significantly dry and the fourth year prior was significantly wet. Therefore, climate may be a triggering factor in pandora moth outbreaks. The stem analysis demonstrated that the percent volume reduction was greatest at the base of the tree and declined further up the bole. The percent volume reduction in the canopy of the trees was variable with outlying high and low values. The mean volume reduction per outbreak was .053 m³ per tree. Although this insect is considered a forest pest and causes inconvenience for people living nearby, pandora moth is not as widespread and damaging as some other phytophagous insects. However, its very distinctive ring-width signature and the length of the ponderosa pine record enables reconstruction of very long outbreak histories, which may deepen our understanding of the interaction between defoliating insects and their ecosystem.

<p> Geophagy, the consumption of mineral soil, is believed to have several benefits for herbivores. Soils high in clay are often implicated in the detoxification of plant secondary metabolites. High mineral concentrations in soils may also provide nutrients that are poorly available from plants. Local observers report that snowshoe hares (Lepus americanus) use a lick in the foothills of the Brooks Range, Alaska. Using soil from this lick and other mineral supplements, I conducted a series of feeding trials on captive snowshoe hares fed felt-leaf willow (Salix alaxensis) or a formulated ration to determine whether geophagy resulted in a physiological benefit and, if so, which soil constituents are therapeutic. When fed willow leaves, hares ate more and lost less weight when they had access to soil. Access to soil increased sodium intake and dietary ratios of sodium to potassium in hares fed willow. Soil consumption resulted in higher calcium to phosphorous ratios for both diets. Across diets, higher sodium to potassium and lower calcium to phosphorus ratios corresponded to reduced weight loss. Access to pure calcium carbonate resulted in reduced weight loss in hares fed winter dormant willow twigs, suggesting that carbonates may also be an important component of this lick. </p>