In this dissertation, the evolutionary and ecological determinants of host range of nematode parasites (Tylenchida: Allantonematidae: Howardula, Parasitylenchus) of mushroom-breeding Drosophila (Diptera: Drosophilidae) are examined. These nematodes are horizontally transmitted, obligate parasites, often with severe effects on host fitness. Phylogenetic analysis of Drosophila and Howardula DNA sequences shows little congruence between host and parasite phylogenies, with frequent host colonizations and losses. Drosophila -parasitic Howardula are not monophyletic, with host switches occurring between Drosophila and distantly related mycophagous sphaerocerid flies. Molecular analysis reveals eight new Howardula species. The ability of five nematode species to infect and develop in 24 taxonomically diverse Drosophila species is assessed. All nematode potential host ranges but one are large, even for host specialists. Novel hosts that are distantly related from the native host are less likely to be infected, but among closely related hosts there is variation in susceptibility. Potential host ranges differ greatly between related parasite species. Most novel infections do not cause reductions in host fecundity, with the exception of P. nearcticus. Thus, Drosophila-nematode associations are dynamic, and appear to be driven by a combination of repeated opportunities for host colonization due to shared mushroom breeding sites, and large nematode potential host ranges. Recent colonization of novel host species may explain the striking differences in virulence observed in natural Drosophila-nematode associations. For example, Nearctic species of the Drosophila testacea group are more severely affected by infection than Palearctic species, including complete female sterility. Cross-infection experiments reveal that virulence is evolutionarily labile in testacea-Howardula associations, and that high levels of virulence manifested in some host-parasite combinations are due to a lack of host resistance. Finally, ecological determinants of host range are considered. First, competition between a generalist and a specialist parasite of D. recens is assessed by comparing nematode infection success and reproduction in single and double infections. Second, differences between the actual and potential host ranges of Howardula neocosmis are documented. This parasite appears restricted to D. acutilabella in nature, yet successfully parasitizes the closely related, microsympatric D. cardini. Neither differential virulence nor competitive interactions between hosts explain the host range differences.

Population viability analyses based on matrix population models provide important information for species management. These analyses enable biologists to predict future population size and structure, assess extinction risk, and identify the stages and transitions in a species' life history that have the largest effects on population growth rate (lambda). It is also possible, using these analyses, to weigh the relative effectiveness of different management strategies. In this study, I constructed a matrix population model for a threatened Hawaiian plant species, the Haleakala silversword (Argyroxiphium sandwicense ssp. macrocephalum), in order to assess the viability of this population under different disturbance and management regimes. Over five years, I assessed annual variation in seed set and quantified reproductive vital rates for use in a matrix model. These data were combined with long-term demographic data in order to construct a stage-based matrix model for the Haleakala silversword. Using this model, I examined temporal and spatial variation in silversword demography. I also used the model to evaluate management strategies for the Haleakala silversword and the related subspecies, the endangered Mauna Kea silversword (Argyroxiphium sandwicense ssp. sandwicense). Using deterministic and stochastic models, I compared the relative impacts of different threats on silversword persistence, and weighed the relative effectiveness of different management options. The Haleakala silversword was self-incompatible, and percent seed set was positively correlated with annual flowering plant abundance. Individuals were pollen-limited only in low flowering years, suggesting a pollinator-mediated Allee effect in this species. Seeds remained viable in the field for multiple years, suggesting that a seed stage should be incorporated into the matrix model. Reproductive output (e.g., number of capitula and capitulum size) was strongly correlated with rosette diameter, allowing for size-based estimates of reproduction. Vital rates and population growth rates varied over time and space. In all years and plots, adult survival had the greatest impact on lambda. Thus, factors influencing adult survival, such as browsing and outplanting, had larger effects on lambda than did factors influencing seed set. Management strategies aimed at increasing germination rates or adult survival rates will be most effective in ensuring the persistence of silversword populations.

Why some organisms reproduce just once in their lifetime (semelparity), while others reproduce more than once (iteroparity), has been a central question of life history theory since it was posed by Cole (1954). I used comparative studies at large (phylogenetic) and small (demographic) scales to address this question in a group of evening primroses (the Sections Anogra and Kleinia, genus Oenothera, Onagraceae) found in the arid and semiarid region west of the 100th meridian in North America. In the phylogenetic study, I found that changes in habit were not associated with the changes in aridity that I expected, based on the classic demographic model of Charnov and Schaffer (1973). Instead, this study suggested that changes to the annual habit were associated with increased temperature. I propose that temperature is an important factor influencing the favorability of the annual habit via the effect that temperature has on growth rate. The remaining two studies, comparing the performance of a closely-related desert annual and desert perennial in natural and experimental settings, also indicated that temperature correlated with habit. Using demographic data from natural populations, I evaluated seed banking and iteroparity as alternative means of bet hedging. I found evidence that bet hedging occurs via seed banking in both populations, and may occur via post-reproductive survival in the perennial populations. The demographic data did not clearly show the patterns expected to favor one form of bet hedging over the other. Based on an analysis of climate data, I suggest that cold temperatures are unfavorable to the annual habit. I compared the performance of the same species pair directly in two common environments. In this reciprocal common garden experiment, the annual outperformed the perennial when conditions were good, and when conditions became stressful relatively early. The annual, with lower leaf mass per area, more rapid above ground growth, and accelerated phenology, exhibits the classic stress-avoiding strategy of desert annuals, explaining the conditions under which it excelled. Relative to the annual, I describe the perennial as a stress-tolerator, and discuss water and temperature stress as two forms of stress it may excel at tolerating.

Reproduction constitutes the principle determinant of organismal fitness and, therefore, a central theme in biology is devoted to understanding variation in the mode of reproduction and its effects within and among species. Different breeding systems lead to varying levels of inbreeding, outcrossing, and sex ratios---with concomitant effects on patterns of genetic variation, effective population size, and adaptation by natural selection. Theoretical studies have proposed many mechanisms to explain the diversity of breeding systems observed in nature, several models of which invoke deleterious effects of mutation as a dominant force in patterning breeding system evolution. These notions motivated the present investigations into (1) the factors contributing to outcrossing rates and sex ratio in Caenorhabditis elegans and their population genetic effects, and (2) the general importance of deleterious mutation in the evolution of breeding system, emphasizing the Caenorhabditis clade. Nematodes of the genus Caenorhabditis provide a convenient system for studying these issues because species vary in breeding system, self-fertile C. elegans hermaphrodites can be genetically transformed into females to create dioecious populations, and complete genomic sequences of two species allow genomic analysis. With this context, I constructed a quantitative model describing sex ratio and outcrossing as a function of male copulatory ability and sex-chromosome non-disjunction (as a consequence of the XO sex-determination mechanism). The sex ratio and amount of outcrossing in C. elegans were then predicted from laboratory experiments and nucleotide polymorphism data, by applying population genetic theory of selection at linked sites when partial selfing is taken into account. These analyses suggest that outcrossing occurs on the order of one percent. Subsequent computational and multigeneration experimental evolution studies of the potential influence of deleterious mutations on breeding system evolution demonstrated that (1) selfing species do not exhibit lower rates of deleterious mutation than outcrossing species, (2) a higher deleterious mutation rate does not prevent the invasion of selfing alleles into a population, and (3) adaptive modulation of sex-chromosome non-disjunction is unlikely to underlie the persistence of males in androdioecious species. These results indicate that mutational theories are unlikely to fully explain the evolution of breeding system and sex.

This dissertation is a report on the investigation of the vocal behavior of free-living Grey Parrots (Psittacus erithacus) that inhabit the Congo Basin in Central Africa. I observed Grey Parrots in the Central African Republic and Cameroon and made audio recordings of their vocalizations. The results of spectrographic analysis of vocalizations lend support to the assertion that Grey Parrots produce calls that fall into four major acoustical classes--tonal, harmonic, noisy-harmonic, and noisy--and that these call classes may be subdivided into as many as 39 different acoustical types. A reliability study of this classification scheme demonstrated that both clustering of these acoustical types into aggregate categories and the combined method of visual inspection and basic spectrographic measurement enable reliable classification of calls into classes, types and also subtypes. The majority of calls in the observed repertoire belong to pure tonal call class, which may suggest that a large proportion of Grey Parrot calling behavior is adapted for tonal call production. Grey Parrots may also adjust the acoustic characteristics of their calls to better adapt them to their environment and communication needs. Both observations of Grey Parrots and analysis of the acoustic and production characteristics of their calls indicate that Grey Parrots may share functional call types of some New World and Australian parrot species. Some Grey Parrot calling vocal behavior parallels that of captive Grey Parrots in the laboratory. I conclude with an exploration of possible reasons why Grey Parrots possess such a diverse vocal repertoire.

Social spiders most likely evolved from subsocial-like ancestors, species in which siblings remain together for part of their life cycle but disperse prior to mating. Understanding the ecological conditions that favor small colony sizes and periodic dispersal in subsocial species vs. large multigenerational colonies in the social species may provide insight into this evolutionary transition. The biogeography of these spiders and the ability of prey supplementation to delay dispersal in subsocial species implicate prey abundance as an important ecological factor influencing this process. I propose a conceptual framework in which environmental prey abundance determines the rate at which prey contact webs per unit web area, colony size determines web area and prey capture success, and per capita prey capture affects when spiders disperse. To further understand how prey abundance may have influenced the evolution of sociality, I have empirically explored aspects of this framework. Within the genus Anelosimyyus, I studied two social species inhabiting an Ecuadorian lowland rain forest, a subsocial species along the edge of an Ecuadorian cloud forest, and another subsocial species occupying a temperate riparian area of Arizona. In a comparative study examining relationships among sociality, prey availability, and prey capture rate across these species, the environments of social species tended to have relatively large prey and high overall prey biomass, but not the highest numbers of prey items. Relationships among colony size, web size, and prey capture within three of these populations revealed significant foraging-related costs of increasing colony size that could be offset by the availability of high prey biomass in the form of large prey items. Finally, I conducted an experiment manipulating prey capture rate in a subsocial species that resulted in higher prey levels delaying dispersal within and among colonies. This effect often led to a single, relatively large individual remaining in nests of colonies that had been provided more prey. Overall, these findings indicate that, while the availability of high prey biomass may have allowed sociality to evolve, the concentration of prey biomass into large, but not necessarily more prey may have selected for the larger, longer-lived colonies characteristic of social species.

Cooperative breeding (CB) is found in a wide diversity of avian lineages and can be explained at several levels of analysis. After a brief introduction to the theory explaining CB, I take an historical approach to examine CB evolution in the bee-eaters (Family Meropidae). Parsimony analyses of plumage color and shape characters yielded a number of phylogenetic hypotheses. The best supported phylogenies are six fully resolved trees from three analyses and a strict consensus tree from another analysis. These trees are used to examine the possible patterns of evolution in CB and how transition correspond to transitions in other ecological and behavioral traits. Bee-eaters were also studied in Thailand. Little green bee-eaters, Merops orientalis, breed cooperatively and predation pressure may be high in this species. Blue-tailed bee-eaters, M. philippinus, breed cooperatively in dense colonies and show signs of potential extra-pair copulation and intraspecific brood parasitism. Observations of the bay-headed bee-eater, M. leschenaulti, and the blue-bearded bee-eater, Nyctyornis athertoni, document CB in the former and support non-CB designation for the latter. Cooperative breeding is either primitive in bee-eaters or evolved early in the family. Reversals to non-CB occurred in one to three lineages. Transitions in breeding systems are not generally correlated with the transitions in nesting requirements, habitat utilization, migratory behavior, or diet. Evidence suggests correlated evolution between CB and both foraging mode (weak evidence) and social systems (stronger support). This study does not support any single hypothesis for the adaptive basis of CB across the family. Social system evolutionary patterns do suggest the importance of kin selection in several lineages. Lack of change in breeding systems, given diverse ecological and behavioral circumstances, means either cooperative breeding is malleable (selectively advantageous in a variety of ecological conditions) or represents phylogenetic inertia. A final analysis demonstrates that phylogenetic confidence indices fail to express the degree to which characters in a matrix are non-conflicting and congruent (for a given level of noise) and show only limited abilities to distinguish among probabilities of analyses making type II errors.

Fifteen canyons in the Coronado National Forest, in southeastern Arizona were sampled in order to study the woody riparian overstory. Vegetative and environmental data were collected from 99 high elevation (>1050 meters) sites within these canyons that had a woody riparian overstory. Vegetative data included abundance and diameter at breast height (DBH) of each woody tree, and abundance and root collar diameter of each woody shrub in the sample plot. Environmental site data included elevation, stream gradient, stream width and depth, terrace height, stream direction, and watershed area. The vegetative data for each site were classified into one of six possible community types using an average linkage/euclidean distance clustering algorithm. Clustering was performed using DBH data and abundance data in order to compare the two types of approaches. This study suggests that in high elevation areas, typical riparian community vegetation include shrub species such as Baccharis and Robinia, as well as facultative upland species such as Abies, Acer, Juniperus and Ouercus. Platanus and Salix are also commonly found, while Populus is rare. The environmental data were summarized by community type. Binary recursive partitioning was used to produce a classification structure to determine which environmental variables were most effective to differentiate between the communities and the larger sample set. Elevation and stream gradient were the most important parameters when measuring communities by their relative abundance. Elevation was the most important parameter when measuring communities by DBH.

The Rubiaceae, with a world-wide distribution, have a variety of pollinator syndromes and include the greatest number of heterostylous species of any angiosperm family. Variation in heterostyly among taxa of Rubiaceae is often attributed to potential incidences of independent evolution. I documented incompatibility systems, floral dimensions at anthesis, and floral development for three heterostylous taxa in Rubiaceae. I collected data from populations of hummingbird-pollinated Psychotria poeppigiana at La Selva Biological Station, Costa Rica and Soberania National Park, Panama, and from a population of hawkmoth-pollinated P. chiapensis also at La Selva. My study populations of hummingbird-pollinated Bouvardia ternifolia were in the Catalina and Santa Rita Mountains near Tucson, Arizona. To characterize incompatibility, I recorded inhibition sites of illegitimate pollen tubes. For B. ternifolia, locations of inhibition sites were similarly variable for each floral morph. In both species of Psychotria, incompatibility reactions of short-styled (SS) flowers typically occurred within stigmas whereas in long-styled (LS) flowers, incompatibility reactions most often occurred in styles. For all three species, I found significant differences in stigma and anther heights at anthesis corresponding to floral morph. However, because of extensive variation among individuals of both floral morphs, stigma and anther heights of LS and SS flowers are not strictly reciprocal. Mean anther height per plant forms a near continuum from LS to SS plants in most populations. Stigma heights of different floral morphs overlap in several plants of B. ternifolia and of P. chiapensis. Only for stigmas of P. poeppigiana did the organs of both floral morphs fall into distinct height categories. To study floral ontogeny, I measured buds representative of different developmental stages. For all species, height differences between anthers of LS and SS flowers at anthesis result from differences in relative growth rates. For B. ternifolia, a dimorphism in corolla size also contributes to anther height differences between floral morphs. Style heights of LS and SS flowers of B. ternifolia result from differences in relative growth rates between floral morphs. Contrasting with the Psychotrias, where style height differences are established early in development and maintained as styles elongate at the same relative rate.

Traditional approaches to theoretical ecology have focused on the behavior of observable patterns. Presumably, the observed pattern reflects a statistical characterization of the underlying processes. I apply probability theory to model species-area curves and population dynamics. In both cases, new insights result connecting details of lower level process to higher order pattern. Chapter 1 details the development and testing of a new theory species-area curves (SPARs). The new theory predicts z-values near 0.77 while previous theory claims z-values of about 0.26. We arrived at our prediction using two independent methods: we performed computer simulations of the scheme and we derived its analytical equation. However, although logically accurate, the new theory has an empirical problem: real SPARs tend to have z-values in the interval 0.1-0.2. To obtain these, we assumed that range size and abundance are positively correlated according to a power function. Chapter 2 examines a real data set for the power function assumed in chapter 1. Using data from the North American Breeding Bird Survey (BBS) project, I found that both least squares regression and principal components analysis (PCA) discover a significant positive correlation between range size and abundance. From the BBS data I fit this power function to the data and estimate the value of the relationship's parameter to be c = 0.27. The resulting fit accounts for 91% of the variance in the data. In the final chapter of the dissertation, I use stochastic processes to model both the spatial distribution and the birth and survival mechanism of individuals living in an environment of identical, but independent patches. It turns out that linear individual level density dependence easily produces non linear population level dependence. I present the first derivation of the Ricker map and show that patch number interacts with recruitment and survival to generate the carrying capacity parameter. Finally, I combine Monte Carlo simulations and Markov chain theory to study statistical properties population dynamics such as mean time to extinction.