Abstract
Hieracium pilosella has become a major concern in the high country grasslands of New Zealand. This thesis provides an understanding of the population dynamics of H. pilosella in an area which has supported the weed as a major component of the vegetation for more than 30 years. The study uses a combined modelling and experimental approach to determine vital rates and regulatory mechanisms. It then uses these to predict the rate of spatial spread, change in density, and the likely impact of biological control. Mature populations of H pilosella at Mt. John were found to be regulated by the interaction between density-dependent mortality and density-independent reproduction. The addition of water and/or fertiliser caused an increase in the reproductive vigour of the plant and a decrease in density while simulated grazing (i.e. mowing) had little effect on the population. A link was found between reproductive vigour and rosette size or age (50% of first year rosettes reproduced while only 11 % of older rosettes did), although the reproductive threshold size (23 mm diameter) appeared to be independent of age. Rosettes grown on soil which had previously supported H pilosella had lower growth and reproductive rates and produced fewer stolons of shorter length. However, there was little support for either the allelopathic or aluminium toxicity hypotheses for these lower growth rates. Spatial population models suggested that in the early stages of colonisation, H pilosella vital rates are such that it has the potential to occupy 100% of available space but as the population matures, vital rates change and it is unable to occupy all available space, probably because of intraspecific competition and a limit on plant size. Spread of patches was predicted to be 0.5 - 0.8 cm/yr by both explicit spatial simulation models and analytical diffusion models. Both spatial and non-spatial models predicted that the most effective agent for biological control would be one which caused an increase in mortality rather than a decrease in fecundity; to reduce a population by more than 50% a control agent would have to either increase mortality by 10 - 15 % or decrease daughter production by 80%.
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Claims 18
Claim · model-written summary
Mature H. pilosella populations at Mt. John were regulated by the interaction between density-dependent mortality and density-independent reproduction.
- Taxon
- H pilosella
_-_geograph.org.uk_-_1369110.jpg?width=60)
Pilosella officinarume0 - Outcome
- regulatede0
- Qualifier
- interaction between density-dependent mortality and density-independent reproductione0
- Setting
- Mt. Johne0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
_-_geograph.org.uk_-_1369110.jpg?width=500)
Verbatim
e0“Mature populations of H pilosella at Mt. John were found to be regulated by the interaction between density-dependent mortality and density-independent reproduction”
Claim · model-written summary
Adding water and/or fertiliser increased the reproductive vigour of H. pilosella.
- Taxon
- Hieracium PilosellaPilosella officinarumt1
- Treatment
- addition of water and/or fertilisere0
- Outcome
- reproductive vigour of the plante0
- Direction
- increasee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The addition of water and/or fertiliser caused an increase in the reproductive vigour of the plant and a decrease in density”
t1“Hieracium Pilosella”
Claim · model-written summary
Adding water and/or fertiliser decreased H. pilosella density.
- Taxon
- Hieracium PilosellaPilosella officinarumt1
- Treatment
- addition of water and/or fertilisere0
- Outcome
- densitye0
- Direction
- decreasee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The addition of water and/or fertiliser caused an increase in the reproductive vigour of the plant and a decrease in density”
t1“Hieracium Pilosella”
Claim · model-written summary
Simulated grazing (mowing) had little effect on the H. pilosella population.
- Taxon
- Hieracium PilosellaPilosella officinarumt1
- Treatment
- simulated grazing (i.e. mowing)e0
- Outcome
- populatione0
- Direction
- little effecte0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“simulated grazing (i.e. mowing) had little effect on the population”
t1“Hieracium Pilosella”
Claim · model-written summary
Reproductive vigour was linked to rosette size or age in H. pilosella.
- Taxon
- Hieracium PilosellaPilosella officinarumt1
- Organ / stage
- rosette size or agee0
- Outcome
- reproductive vigoure0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“A link was found between reproductive vigour and rosette size or age”
t1“Hieracium Pilosella”
Claim · model-written summary
About 50% of first year H. pilosella rosettes reproduced.
- Taxon
- Hieracium PilosellaPilosella officinarumt1
- Organ / stage
- first year rosettese0
- Outcome
- reproducede0
- Value
- 50%e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“50% of first year rosettes reproduced”
t1“Hieracium Pilosella”
Claim · model-written summary
Only 11% of older H. pilosella rosettes reproduced.
- Taxon
- Hieracium PilosellaPilosella officinarumt1
- Organ / stage
- older rosettese0
- Outcome
- dide0
- Value
- 11 %e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“only 11 % of older rosettes did”
t1“Hieracium Pilosella”
Claim · model-written summary
The reproductive threshold size (23 mm diameter) appeared independent of age.
- Taxon
- Hieracium PilosellaPilosella officinarumt1
- Outcome
- reproductive threshold sizee0
- Value
- 23 mm diametere0
- Qualifier
- independent of agee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the reproductive threshold size (23 mm diameter) appeared to be independent of age”
t1“Hieracium Pilosella”
Claim · model-written summary
H. pilosella rosettes grown on soil that previously supported the species had lower growth and reproductive rates.
- Taxon
- H pilosellaPilosella officinarume0
- Treatment
- soil which had previously supported H pilosellae0
- Outcome
- growth and reproductive ratese0
- Direction
- lowere0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Rosettes grown on soil which had previously supported H pilosella had lower growth and reproductive rates and produced fewer stolons of shorter length”
Claim · model-written summary
H. pilosella rosettes grown on soil that previously supported the species had fewer stolon number.
- Taxon
- H pilosellaPilosella officinarume0
- Treatment
- soil which had previously supported H pilosellae0
- Outcome
- fewer stolonse0
- Direction
- fewere0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Rosettes grown on soil which had previously supported H pilosella had lower growth and reproductive rates and produced fewer stolons of shorter length”
Claim · model-written summary
H. pilosella rosettes grown on soil that previously supported the species had shorter stolon length.
- Taxon
- H pilosellaPilosella officinarume0
- Treatment
- soil which had previously supported H pilosellae0
- Outcome
- shorter lengthe0
- Direction
- shortere0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Rosettes grown on soil which had previously supported H pilosella had lower growth and reproductive rates and produced fewer stolons of shorter length”
Claim · model-written summary
There was little support for the allelopathic or aluminium toxicity hypotheses as explanations of the lower growth rates.
- Taxon
- Hieracium PilosellaPilosella officinarumt1
- Outcome
- lower growth ratese0
- Qualifier
- little support for either the allelopathic or aluminium toxicity hypothesese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“there was little support for either the allelopathic or aluminium toxicity hypotheses for these lower growth rates”
t1“Hieracium Pilosella”
Claim · model-written summary
Spatial population models suggested that in early colonisation H. pilosella could occupy 100% of available space.
- Taxon
- H pilosellaPilosella officinarume0
- Outcome
- potential to occupy 100% of available spacee0
- Value
- 100%e0
- Qualifier
- early stages of colonisatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“in the early stages of colonisation, H pilosella vital rates are such that it has the potential to occupy 100% of available space”
Claim · model-written summary
Spatial models suggested that as the population matures H. pilosella cannot occupy all available space, probably because of intraspecific competition and a limit on plant size.
- Taxon
- Hieracium PilosellaPilosella officinarumt1
- Outcome
- unable to occupy all available spacee0
- Qualifier
- probably because of intraspecific competition and a limit on plant sizee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“as the population matures, vital rates change and it is unable to occupy all available space, probably because of intraspecific competition and a limit on plant size”
t1“Hieracium Pilosella”
Claim · model-written summary
Spread of H. pilosella patches was predicted to be 0.5 - 0.8 cm/yr by both spatial simulation and analytical diffusion models.
- Taxon
- Hieracium PilosellaPilosella officinarumt1
- Outcome
- Spread of patchese0
- Value
- 0.5 - 0.8 cm/yre0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Spread of patches was predicted to be 0.5 - 0.8 cm/yr by both explicit spatial simulation models and analytical diffusion models”
t1“Hieracium Pilosella”
Claim · model-written summary
Models predicted that the most effective biological control agent would increase mortality rather than decrease fecundity.
- Taxon
- Hieracium PilosellaPilosella officinarumt1
- Outcome
- most effective agent for biological controle0
- Qualifier
- increase in mortality rather than a decrease in fecunditye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Both spatial and non-spatial models predicted that the most effective agent for biological control would be one which caused an increase in mortality rather than a decrease in fecundity”
t1“Hieracium Pilosella”
Claim · model-written summary
To reduce a population by more than 50%, a control agent would have to increase mortality by 10 - 15%.
- Taxon
- Hieracium PilosellaPilosella officinarumt1
- Outcome
- increase mortalitye0
- Value
- 10 - 15 %e0
- Qualifier
- reduce a population by more than 50%e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“to reduce a population by more than 50% a control agent would have to either increase mortality by 10 - 15 % or decrease daughter production by 80%”
t1“Hieracium Pilosella”
Claim · model-written summary
To reduce a population by more than 50%, a control agent would have to decrease daughter production by 80%.
- Taxon
- Hieracium PilosellaPilosella officinarumt1
- Outcome
- decrease daughter productione0
- Value
- 80%e0
- Qualifier
- reduce a population by more than 50%e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“to reduce a population by more than 50% a control agent would have to either increase mortality by 10 - 15 % or decrease daughter production by 80%”
t1“Hieracium Pilosella”