How might an individual's ability to learn environmental information affect competitive interactions among species? Learned behavior can influence foraging decisions. Competition for food resources can influence patterns of species coexistence via habitat selection. I wondered if both learned behavior and competition might act together to influence interactions among species. I used Rosenzweig's shared-preference isoleg theory to predict four possible ways that differences in environmental information could affect density-dependent habitat selection. To test these predictions, I conducted field experiments to examine the foraging behavior of free-living hummingbirds. I studied black-chinned (Archilochus alexandri), blue-throated (Lampornis clemenciae), and magnificent (Eugenes fulgens) hummingbirds where they coexist in the Chiricahua Mts. of Southeastern AZ. I gave hummingbirds two types of habitats (rich and poor feeders) and let them learn to associate colors with feeder quality. I confirmed that learned color associations can increase hummingbird foraging efficiency. All birds shared a preference for the rich feeders. However, they will shift their preference toward poor feeders when competitor densities are high (Pimm et al. 1985). I quantified hummingbirds' preferences for the rich feeders when both competitor densities and information (via learned color cues) varied. The data support my fourth prediction---that birds foraging with complete information enjoy reduced negative effects from competition. Without complete information, the two subordinate species (black-chinned and magnificent) shifted their preference away from rich feeders in response to high densities of the dominant species (blue-throated). Each subordinate shifted in a unique way; the black-chinned reduced its foraging efficiency, while the magnificent reduced its total foraging time. Birds foraging with complete information remained highly selective on rich feeders even with high competitor densities. Thus, learned information affected competitive interactions (for rich feeders) among these species. My results require us to consider the information-gathering (e.g., learning) abilities of individual decision-makers when we evaluate density-dependent habitat selection. These results should help us better explain patterns of species diversity and distribution, especially for cases in which species learn environmental cues. This study provides the first demonstration, either theoretically or empirically, of a link between learned behavior and its cascading effects within a guild of coexisting species.

It is shown that the dynamics of models of predator-prey interactions in the presence of seasonality are profoundly structured by Hamiltonian limits, i.e., limiting cases where the flow satisfies Hamilton's canonical equations of motion. We discuss the dynamics at nonintegrable Hamiltonian limits, focusing on the existence of subharmonic periodic orbits, which correspond to multi-annual fluctuations. Perturbing away from a Hamiltonian limit, subharmonic periodic orbits are annihilated in tangent bifurcations, which compose the boundaries of resonance horns. All resonance horns emanate from the Hamiltonian limit and penetrate well into the realm of biologically-realistic parameter values. There, they indicate the "color" of the dynamics, i.e., the spectrum of dominant frequencies, whether the dynamics be regular or chaotic. Our observations provide both an account of the phase coherence often observed in population dynamics and a method for investigating more complex models of predator-prey dynamics, which may involve multiple Hamiltonian limits. This method is applied to the celebrated problem of the cyclic fluctuations of boreal hare populations. We present a model of the population dynamics of the boreal forest community based on known demographic mechanisms and parameterized entirely by measurements reported in the literature. The aforementioned method reveals the geometry potentially underlying the observed fluctuations. The model is quantitatively consistent with observed fluctuations. We derive specific, testable predictions of the model relating to the roles of herbivore functional response, browse abundance and regeneration, starvation mortality, and composition of the predator complex.

Temporal variability in the environment can affect population dynamics and life history strategies. Annual plants in desert environments are subject to large fluctuations in precipitation, both within and among years. I used a combination of field and laboratory studies to characterize variability in the populations dynamics and life history of a desert winter annual plant. I conducted demographic studies over four seasons in four populations of Plantago insularis Eastw. [Plantaginaceae] located along a precipitation gradient in the Sonoran Desert. I quantified the fates of germinated and non-germinated individuals by monitoring permanent quadrats and repeatedly sampling the soil seed bank. A fraction of seeds in all populations delayed germination and formed a persistent seed bank. Populations with more among-year variation in precipitation had greater variability in reproductive success for germinated seedlings, and the population in the most xeric environment was the most variable. Survival of non-germinated seeds was less variable than reproductive success of germinated seeds in all populations. Thus, non-germinating seeds reduced temporal variation in population dynamics by increasing population growth in dry years and decreasing growth in wet years. In this field study, populations in historically more xeric environments had lower mean germination fractions. Using geometric mean growth rate as an estimate of fitness, I demonstrate that germination fractions less than one were adaptive in three of four populations. Results of experimental studies with up to twelve populations of P. insularis, suggest that field germination responses emerged from a combination of two processes. Lower water availability during germination resulted in lower germination fractions. When water was amply available, all populations could express high germination fractions. A pattern of delayed germination consistent with bet-hedging as an adaptation to temporal variability in reproductive success arose in the field, in part, because frequencies of wet and dry germination conditions differed among populations. Phenotypic plasticity in germination response for seeds in the most xeric, environment conferred greater fitness than would have been possible with any one constant germination fraction.

This dissertation presents a four year field study on the movement patterns, community dynamics, and management of granivorous wintering grassland sparrows in Arizona. Chapter one focuses on within winter, local scale movement patterns. Recapture statistics and radiotelemetry both showed strong interspecific differences in movement, consistent with the idea that these species may partition niche space according to the regional coexistence mechanism. Both techniques ranked species from most to least sedentary as follows: Cassin's and Grasshopper sparrows, Baird's, Vesper, and Savannah and Brewer's sparrows. Data also indicated that fixed home range movements, and within-species constancy of movement behavior across years and study sites are generally the rule in this group. Correlations between bird abundance and summer rainfall suggest that movement may constrain large scale habitat selection processes. Chapter two presents larger scale movement data from grassland sparrows, along with a general discussion of facultative migration in birds. High between-year abundance fluctuations and low and variable rates of between-year recapture suggest that facultative migration strategies may be the rule in grassland sparrows. The use of alternative wintering sites by individual Grasshopper Sparrows provides direct evidence of limited facultative migration behavior. These patterns contrast with the largely non-facultative migration strategies that are the rule in birds. The evolution of facultative migration strategies is linked with unpredictable temporal variation in the spatial distribution of habitat conditions in the landscape. Chapter three presents three years of data on the effects of spring/summer burning and cattle grazing on wintering grassland sparrows. Vesper and Savannah sparrows responded positively to fire, while Cassin's Sparrows responded negatively. The ecologically and geographically restricted Baird's and Grasshopper sparrows utilized burned areas during the first post-bum winter and did not significantly respond to fire. Both Ammodramus sparrows also utilized the grazed pasture; they were more abundant there than in the ungrazed study area in one year. While field observations and a prior study suggest that heavy grazing can have a strong detrimental effect on Ammodramus sparrows, the results of this study suggest that moderate cattle grazing may be compatible with the conservation of these species.

Explanations for the transition from cosexuality to gender dimorphism have concentrated on overcoming the inherent 50% fitness loss of single-sexed nuclear gene mutants arising in cosexual populations. These mechanisms generally fall into two broad, non-exclusive categories: elimination of inbreeding depression by male-sterile mutants (i.e., selection for outcrossing) and compensatory resource reallocation following loss of one sexual function. This dissertation focuses on the relative importance of these mechanisms in the evolution of gender dimorphism in Lycium (Solanaceae) and then finds an emergent explanation. Plants of North American Lycium californicum, L. exsertum, and L. fremontii are either male-sterile or morphologically hermaphroditic, and populations are gynodioecious. Flowers on hermaphrodites are larger and have broader calyces and corollas than those on females. Phylogenetic relationships, using molecular and morphological data, indicate that gender dimorphism has evolved once in North America and have identified the cosexual relatives of the dimorphic taxa. Controlled pollinations and allozyme estimates of mating systems in cosexual relatives of dimorphic species indicate that gender dimorphism has evolved on a phylogenetic background of self-incompatibility. In contrast, studies of pollen tube growth indicate that hermaphrodites in the dimorphic species are self-compatible. To determine if females compensate for loss of male function, I estimated components of female reproduction for all three dimorphic and three cosexual species. I also investigated reallocation within flowers by quantifying the portion of total floral biomass allocated to each floral whorl. Despite substantial savings due to loss of male function, females do not produce increased numbers of seeds, fruits, or flowers, nor do they allocate additional biomass to gynoecia compared to cosexual relatives. Phylogenetic analysis suggests that the common ancestor of dimorphic Lycium in North America was self-compatible and polyploid. In contrast, relatives of the dimorphic clade are cosexual, self-incompatible diploids. This appears to have occurred independently in African Lycium. I describe a novel hypothesis for the evolution of separate sexes involving polyploidy. In this scenario, polyploidy disrupts self-incompatibility leading to inbreeding depression. Subsequently, male-sterile mutants invade and increase because they are fully outcrossed. Further evidence for this scenario is presented from 12 genera involving at least 20 independent evolutionary events.

Two research approaches were combined to study the perceptions, understandings and expectations of visitors, managers and local communities sharing the desert landscape within the recently created Pinacate Biosphere Reserve, Sonora Mexico. The psychophysical approach was applied to measure visitor's perceptions of scenic beauty and quality of outdoor experience in the Reserve. Students at the University of Arizona and tourists at Organ Pipe Cactus National Monument rated views from the road and major attractions presented as color slides arranged in a "virtual trip." Results indicated high internal reliability and consensus in ratings between groups. The highest ratings of scenic beauty were associated with lush vegetation, columnar cacti, rugged geological formations and volcanic features. Travel direction and order of "visitation" for the four major attraction sites were important variables affecting scenic beauty ratings (for road views) and enjoyment of the trip (for attractions), respectively. Questionnaires, structured and open interviews, and review of public meeting documents were used to assess and contrast the three different population's understandings and expectations regarding the shared desert landscape. The major themes that emerged focused on the trade-offs between environmental conservation goals and development needs of the communities living, or having vested interests in the Pinacate Reserve. Local community (Ejidos) members favored greater emphasis on utilization of natural resources for economic development. Biosphere managers held strongly to their environmental protection mandates, but struggled to find a balance between conservation goals and community needs. Eco-tourism was viewed by both populations as the most attractive option for achieving such a balance. Visitors agreed that tourism activities should contribute to the welfare of local residents, but in a direct trade-off they much more strongly favored management policies that protect the natural desert environment.

Impacts of vegetation manipulation treatments on the hydrologic regime of ponderosa pine watersheds in Arizona were evaluated in this dissertation. First, the Seasonal-Kendall test was applied to detect trends in the precipitation and water yield of the control watershed. Then the long-term implications of two levels of forest cutting (clear cut and strip cut with thinning) on the water yield of the treated watersheds were assessed by means of the traditional paired watershed method and plots of cumulative recursive residuals (CUSUM). CUSUM plots were proposed as a complementary tool to evaluate the duration of water yield changes following treatment. Next, BROOK90, a conceptual hydrologic model, was used to assess water yield changes of ponderosa pine watersheds associated with vegetative practices. The model was optimized and verified in the control watershed to determine if the model was applicable to the environment where the experiment was conducted. Then the model was optimized for the pre-treatment period of the treated watersheds and the optimized parameters were used to simulate the water yield of the post-treatment period. Finally, results obtained with the traditional paired watershed approach were compared with those obtained with the modeling simulation. The two methods were in reasonable agreement.

The Atacama Desert of northern Chile is one of the most arid regions on Earth. The central plateau, between the coastal escarpment and the Andes, is devoid of vegetation and receives only millimeters of rain every few years. Though plants are absent in the soils of this desert, perhaps bacteria can survive, and even thrive, in these hyperarid conditions. This dissertation represents the first comprehensive study of bacterial diversity in the driest central latitudes (approximately 24°S) of the Atacama Desert. Study 1 covers the development of a soil DNA extraction method for the study of soil bacterial populations. This method was field tested in an ecology study in the Santa Catalina Mountains of southern Arizona. In Study 2, Atacama soils were sampled in two transects at approximately 24°S and 25°S. The first transect runs across the absolute (plantless) desert and through several narrow bands of sparse vegetation at high altitudes in the Andes. The second transect is within the well-developed fog zone near Paposo on the Pacific coastal escarpment, where an endemic plant community called lomas is established. Analysis of DGGE profiles of bacterial !6S rRNA genes extracted from these soils with Kruskal's Isotonic Multidimensional Scaling indicates that the bacterial populations cluster into several groups, including the low diversity populations of the core absolute desert, and the higher diversity high elevation Andean populations influenced by the vegetation of Andean biomes. Only one group clustered in the lomas; the rest of the profiles were unique, demonstrating the high diversity of bacterial populations within this diverse vegetation community. Soil 3107, which is within the absolute desert, clustered with the Andean bacterial populations. This soil lies within the transition zone between the low precipitation of the absolute desert (approximately 2.4 mm per year) and the higher precipitation of the high elevation Andes (approximately 47.1 mm per year). This Andean bacterial population may extend further into the absolute desert than the Andean vascular plants due to superior aridity tolerance. Alternatively, this bacterial population may be a relic from when the Andean vegetation advanced through this elevation in a wet period 3000 years ago.

I tested three models for the evolution of cooperative breeding, as applied to Harris's Hawks. The ecological constraints model argues that cooperative breeding arises in response to habitat saturation or a harsh, variable climate. I assessed group size, territory quality, and reproductive success at 45 nests during 1986 through 1990. I found that reproductive success of pairs declined when rainfall and prey declined, while reproductive success of groups remained stable, suggesting that helping is favored under harsh conditions. I found no evidence of habitat saturation. Fisherian theory suggests that parents invest more resources in individual offspring of the larger sex, i.e., the female in Harris Hawks. According to the repayment model, however, cooperative breeders preferentially invest in male offspring. Both models predict male-biased sex ratios. I sexed 87 young fledged during 1986 through 1990 and found sex ratio bias only in 1990, when all female nestlings starved. I observed feeding at seven nests with bisexual broods and found that dominant females fed female offspring more than male offspring. According to the cooperative hunting model, Harris's Hawks form groups, because groups kill larger prey, obtaining a higher per capita caloric intake. This analysis fails to consider the importance of small prey items. I compared direct observations of the prey items eaten at 41 Harris's Hawk nests with prey remains found in 18 nests and with published reports, I showed that previous reports based on prey remains were biased in favor of large prey items. Nest attendance by female birds of prey has been linked to the female's role in antipredator defense. Dominant female Harris's Hawks with helpers to assist in nest defense should therefore attend the nest less than females lacking helpers. Females rearing broods in conspicuous nests should be more attentive than females with cryptic nests. I observed nest attendance and defense at 47 nests. I found that dominant females took the leading role in antipredator defense, especially against coyotes and Turkey Vultures. Females spent more time on conspicuous nests, due to the need to shade the young from direct sunlight. Helpers had no effect on attendance.

In order to test hypotheses of the selective advantage of sex, I have investigated three subjects: the timing of a sexual process, natural genetic transformation, in the bacterium Bacillus subtilis, the relationships between sex, dispersal and dormancy in a variety of organisms, and the evolutionary history of natural genetic transformation, in all living things. My investigation of B. subtilis concerns the relationship between the spore state and competence, the ability to undergo genetic transformation. I show that competence and spore-formation are alternative processes. This is unusual, since in most microorganisms, sex and sporulation are associated. The tradeoff between sex and the spore state found in B. subtilis contradicts ecological hypotheses for sex. These hypotheses predict that, when sex is facultative, it should be associated with the spore state, because that state is more dormant and more dispersible. I discovered that other microorganisms also violate these predictions: sex is either unassociated with dormancy, or unassociated with dispersal, or both. However, in most facultatively sexual organisms, sex, dormancy and dispersal are still associated. Two popular hypotheses for the selective advantage of sex make the wrong prediction for the usual dormancy-dispersal-sex relationship. Here I deduce that the red queen hypothesis and the sib-competition hypothesis incorrectly predict that sex should usually not be associated with dormancy and dispersal. Other hypotheses that I analyze make the correct prediction. Some of these hypotheses of sex make predictions about the history of (bacterial) sex, such as that competence should be ubiquitous. To test these predictions, I have reconstructed the evolutionary history of natural competence. My results show that competence is taxonomically widespread phylogenetically primitive, easy-to-lose, evolutionarily variable, and negatively correlated with certain habitats. These results confirm that competence is ubiquitous. However, the most notable result is that competence is primitive: the most parsimonious evolutionary hypothesis is that the universal ancestor of life was competent.