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Previous work has demonstrated that coflowering plant species (those that flower simultaneously in the same place) can potentially compete for pollination services. Competition for pollination among plant species can negatively impact their reproductive success. To minimise competition, plants can partition the activity of shared pollinators through releasing their floral resources at different times. Resource partitioning has been studied in several individual plant species, and some guilds of plants (e.g. African acacias), but little is known about temporal changes in resources at a community level. This thesis examines the spatiotemporal changes of floral resources at a community level and its implications for pollinator activity patterns. The temporal patterns of nectar and pollen provision of 70 plant species in two different plots were investigated at Mpala, in north central Kenya between 2004 and 2006. The communities studied showed that seasonal and daily microclimatic fluctuations significantly affect flowering patterns, times of flower opening, dehiscence and nectar production; and consequently the overall amount of pollen mass and nectar volume available at different times. I explored the effects of daily temporal changes in floral resource availability on pollinator activity patterns both in a guild of Malvaceae plant species, and at the community level through pollination webs. Detailed observations of daily patterns of resource provision and floral visitation in six Malvaceae plant species showed that plants can effectively avoid competition through attracting different pollinators, and via resource partition. Examination of daily changes in resource availability and the links portrayed in plant-visitor webs revealed that visitors move from one plant species to another, actively tracking changes in floral resource provision. These results suggest that in combination with physiological limitations imposed to the pollinators by temperature, bottom-up influences are a main force shaping daily pollinator activity patterns at a community level. Competition for pollination can only occur if plant species flower simultaneously and share pollinators within the same geographic area. Competition for pollination has been investigated in at least two African communities, but none of these studies have assessed the geographic spatial scale over which competition among coflowering species might happen. With the aim of measuring the geographic distance that pollinators visiting African acacias fly whilst foraging, I used molecular techniques to conduct paternity analysis as a proxy of how far pollen is carried away from particular trees within a population of Senegalia (Acacia) mellifera. The paternity analysis showed that pollinators move on average a maximum of 60 metres from the sampled trees, and that trees producing more flowers (resources) receive more visits, confirming that if sufficient resources are available pollinators can stay within relatively small geographic areas. Pollen movement only provides a partial measurement of the genetic neighbourhood of individual plants, because genes via seed dispersal can travel longer distances than those encompassed by the pollinators foraging areas. To investigate patterns of genetic variability in S. mellifera, I used microsatellites to conduct landscape genetic analyses including 25 adult populations and 9 seedling populations. Fourteen distinctive genetic clusters separated by four main geographic barriers were identified in the analyses. Significantly higher inbreeding was found in the seedling populations than in the adult populations. I discuss the possibility that this situation has been caused by anthropogenic exploitation and fragmentation of the adult stands.

Water is a critical resource for which plants compete in many terrestrial communities. In arid communities where water most limits plant growth, rainfall events occur in discrete, pulsed events. These pulses of water create highly variable soil moisture availabilities. Plant species respond differently to variation in soil water availabilities throughout a season and between years. How species vary in their responses to a range of water availabilities is thought to influence community and ecosystem properties. Many previously proposed hypotheses are not suitable to explain rapidly fluctuating resource availabilities or numerous input events throughout the growing season. This dissertation uses variation in water availability as a model resource to examine how species characteristics influence the process of exploitation competition within plant communities.Experiments were conducted to examine variation in growing season, exploitation competition between several pairs of co-occurring species in the Sonoran desert. Three separate studies evaluated several components of community dynamics thought to be influenced by exploitation competition. Spatial attributes of exploitation competition were assessed by measuring the performance of a deep-rooted species across the boundary of a natural expansion of a shallowly rooted species. Then, neighborhood composition was varied for species of similar growth-form to address the affects of species characteristics to shifts in abundances under field conditions. Lastly, species from the neighborhood composition study were placed under controlled, manipulated water availabilities to measure their fundamental operational conditions.Performances of plant species in all experiments were assessed using a combination of physiological and vegetative measurements, capturing the responses of the plants to both the dynamic growth conditions during the growing season, and integrated measures of plant performance post growth season. A shared preference was found for all species, where the performance of all species was greatest when water was most available in the soil profile. This work suggests the mechanism within a functional type by which plants coexist at various abundances is in part due to the variation in responses to temporal resource gradients. The variation in availability of resources and the species composition within the community should be considered in studies of competition between plant species.

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This project interrogates the claims made for the possibility of collapsing all the various disciplines into one discipline, probably physics, and surely a science, in the name of making clearer the relations between our various fields of knowledge. This is the aim of the radical reductionist, and I take E. O. Wilson's Consilience as exemplary of such attempts. Central to Wilson's method of achieving unity is the new science of evolutionary psychology - itself a re-working of the sociobiology with which Wilson first achieved notoriety. In the on-going project of explaining culture under a Darwinian description, the evolutionary psychologists have begun to suggest explanations for the popularity and content of narrative fiction. Because they are consonant with the rest of science, these biologistic accounts of fiction might be preferable to the accounts traditionally offered by Literary Studies. Consequently, there is a risk that the traditional practices of Literary Studies will be made redundant within the academy and gradually atrophy. The demand is that Literary Studies either makes itself rigorous like the sciences (as with such projects as Northrop Frye's Anatomy of Criticism), or else forfeit its claims to produce knowledge. Aware of this threat, some literary critics embrace forms of relativism in an attempt to deny the unity or effectiveness of scientific knowledge and so neuter the threatened takeover. Among these forms of relativism, Richard Rorty's account seeks to collapse the hierarchy of disciplines and seemingly offers Literary Studies a means of retaining its distinctive approach without denying the effectiveness of scientific knowledge. I aim to show that Literary Studies need not become a science, and that such sciences as evolutionary psychology are neither as threatening as some had feared, nor as useful to literary study as some have hoped.

Differences in reproductive strategies are a major factor influencing the patterns of genetic variability. Inbreeding and other non-recombining breeding systems can have profound effects on the efficacy of natural selection, which should be manifested in the patterns of genetic diversity within and between species. The impact of an organism’s breeding system can be investigated through a number of approaches. In this thesis, I use mathematical modelling, computer simulations, breeding schemes, quantitative life history measures, and molecular biological techniques to explore many of the consequences of breeding system evolution. Following a general introduction in Chapter 1, I explore the dynamics of transposable elements (TEs)—selfish mobile sequences of DNA that have deleterious effects upon their hosts. Sexual reproduction and recombination are important for constraining TE abundance, and in the absence of sex, an unchecked proliferation of TEs may cause a population to go extinct. In Chapter 2, I use a theoretical framework to analyze TE dynamics under asexual reproduction. Here, I show that while small populations are driven to extinction by element accumulation, large asexual populations can prevent this fate and be cured of vertically transmitted TEs. These results may help explain an "evolutionary scandal": the persistence of ancient asexual lineages, such as the bdelloid rotifers. In Chapter 3, I extend the computer simulations used in the previous chapter to explore the effects of reduced recombination on the distribution and abundance of TEs in sexual populations. I show that TEs become fixed as a result of Hill-Robertson effects in the form of Muller’s ratchet, but only in regions of extremely low recombination when excision is effectively absent and synergism between elements is weak. These results should help explain genomic patterns of TE distributions. In the remainder of the thesis, I turn to testing the genetic effects of androdioecy—the breeding system in which populations are comprised of separate male and hermaphrodite individuals—using the nematode Caenorhabditis elegans and related species. This unusual breeding system promotes high levels of inbreeding, yet males are maintained at appreciable frequencies. In Chapter 4, I measure lifehistory traits in the progeny of inbred versus outcrossed C. elegans and the related outcrossing species, C. remanei, to compare levels of inbreeding depression. I show that highly inbred C. remanei show dramatic reductions in brood size and relative fitness compared to outcrossed individuals, whereas pure strains of C. elegans performed better than crosses between strains, indicating outbreeding depression. The results are discussed in relation to the evolution of androdioecy and the effect of mating system on the level of inbreeding depression. Like C. elegans, C. briggsae reproduces by self-fertile hermaphrodites, and both species have similarly low levels of molecular diversity. But the global sampling of natural populations has been limited and geographically biased. In Chapter 5, I describe the first cultured isolates of C. elegans and C. briggsae from sub-Saharan Africa, characterize these samples for patterns of nucleotide polymorphism and vulva precursor cell lineage variation, and conduct a series of hybrid crosses in C. briggsae to test for genetic incompatibilities. With the new African isolates, I show distinct differences in levels of genetic and phenotypic diversity between the two species. Despite many similarities between C. elegans and C. briggsae, the results indicate that there may be more subtle, and previously unknown, differences in their natural histories. Finally, I return to the question of the impact of reduced recombination on TE dynamics in Chapter 6, by comparing population frequencies of TEs in natural populations of selfing and outcrossing Caenorhabditis species. I show that in the selfing species, C. elegans, transposons are less polymorphic and segregate at higher frequencies compared with the outcrossing species, C. remanei. Estimates of the intensity of selection based on the population frequencies of polymorphic elements suggest that transposons are selectively neutral in C. elegans, but subject to weak purifying selection in C. remanei. These results are consistent with a reduced efficacy of natural selection against transposable elements in selfing populations.