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Title: Density-dependence in plant populations : multiple processes and multiple scales
Author: Gunton, Richard Michael
ISNI:       0000 0001 3522 4168
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2007
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The abundance of conspecific neighbours is one detenninant of individual plants' fitness. Moreover, intraspecific interactions' are essential to the temporal and spatial dynamics of populations, which detennine a species' local pers'istence or extinction. In this thesis I explore how different measures of neighbourhood density (in particular, those obtained by varying the area over which density is measured) may explain the perfonnance ofindividuals, using white campion (Silene /atifolia) as a model species. During establishment of seedlings, a glasshouse experiment showed that the intensity of competition depends on the size and. species-frequency of neighbours, reducing growth rates and increasing mortality at higher densities. Growth rate over the '' first 11 days was best explained by the size of neighbours within 3.2-cm squares, but by 55 days the .frequency of grass neighbours within 16-cm squares had be~ome the most important factor. A 2-year field experiment showed negative effects of conspecific density on herbivory that were strongest among density treatments'in 4-m squares. There were also positive effects on survival; an improved analysis using neighbourhood circles showed . peak effects in neighbourhoods extending to 0.24 m (0.48 m diameter). Seed production was negatively related to densities of plants at much coarser scaies (around 15 m radius); here a better predictor was the density of female flowers, which had negative ... effects peaking in neighbourhoods between 13 and 67 m in extent. A specialist seed herbivore inflicted the most damage in 6-m neighbourhoods with more female or fewer male flowers, although a model combining male flowers at 20 m and female flowers at 0.5 m showed positive effects ofboth sexes in one ofthe two years. The generality of these conclusions was explored by analysing data from a seminatural population. This emphasises the variability ofdensity effects and the importance of dealing with spatial autocorrelation whet) analysing effects at multiple scales. I conclude that much remains to be done if population ecology is to explain the spatial patterns ofplant populations at multiple scales.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available