The Impact of Local Plant Density on Plant-Pollinator Interactions and Plant Reproduction in a Fragmented Landscape: A Comparative Approach

Abstract

In the study of the "fragmentation paradigm" researchers variously measure parameters such as isolation, connectivity, patch size or population size, at different spatial and temporal scales. All of these aspects have been implicated (both positively and negatively) in shaping species' responses and interactions to fragmentation. Clarity is required here however, about the relative importance of ecological factors that can influence species' resilience and persistence. In addition, studies are often zoologically inclined. A problem with plant-based studies has been the bias towards herbaceous temperate species that exist in European landscapes, which have experienced Pleistocene glacial episodes and subsequent agrestral activities. The utility of ecological work from these ecosystems to for example, Australian ecosystems requires close scrutiny. The study of plant and pollinator responses to fragmented and altered landscapes in the last two decades has shown that the landscape context and time since fragmentation is important in shaping species persistence and resilience. Furthermore, local density effects may in fact be more influential on plant performance than currently assumed. This study focuses upon the effects of local patch density (sparse versus dense) on floral visitation and plant fecundity within naturally occurring populations in a fragmented landscape occurring on the New England Tablelands in New South Wales, Australia. In this thesis, I use three plant species with different breeding systems and floral morphology as vehicles for examining the impacts of local density on floral visitation rates, fecundity and offspring fitness; 'Dillwynia sieheri' (Fabaceae), an obligate outcrossing shrub, 'Wahlenbergia luteola' (Campanulaceae), a facultative outcrossing herb and 'Thesium australe' (Santalaceae) a hemiparasitic herb which displays high levels of selfing. Fruit: flower ratios, seed: fruit ratios, and components of offspring fitness such as seed weight and germinability were included as performance indicators in this study.