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Cripps M.G.,Lincoln University at Christchurch | Edwards G.R.,Lincoln University at Christchurch | Bourdot G.W.,Agresearch Ltd. | Saville D.J.,Saville Statistical Consulting Ltd. | And 2 more authors.
Plant Ecology

Cirsium arvense (L.) Scop. (Californian, Canada, or creeping thistle) is an exotic perennial herb indigenous to Eurasia that successfully established in New Zealand (NZ) approximately 130 years ago. Presently, C. arvense is considered one of the worst invasive weeds in NZ arable and pastoral productions systems. A mechanism commonly invoked to explain the apparent increased vigour of introduced weeds is release from natural enemies. The enemy-release hypothesis (ERH) predicts that plants in an introduced range should experience reduced herbivory, particularly from specialists, and that release from this natural enemy pressure facilitates increased plant performance in the introduced range. In 2007, surveys were carried out in 13 populations in NZ (7 in the North Island and 6 in the South Island) and in 12 populations in central Europe to quantify and compare growth characteristics of C. arvense in its native versus introduced range. Altitude and mean annual precipitation for each population were used as covariates in an attempt to explain differences or similarities in plant traits among ranges. All plant traits varied significantly among populations within a range. Shoot dry weight was greater in the South Island compared to Europe, which is in line with the prediction of increased plant performance in the introduced range; however, this was explained by environmental conditions. Contrary to expectations, the North Island was not different from Europe for all plant traits measured, and after adjustment for covariates showed decreased shoot density and dry weight compared to the native range. Therefore, environmental factors appear to be more favourable for growth of C. arvense in both the North and South Islands. In accordance with the ERH, there was significantly greater endophagous herbivory in the capitula and stems of shoots in Europe compared to both NZ ranges. In NZ, capitulum attack from Rhinocyllus conicus was found only in the North Island, and no stem-mining attack was found anywhere in NZ. Thus, although C. arvense experiences significantly reduced natural enemy pressure in both the North and South Islands of NZ there is no evidence that it benefits from this enemy release. © 2010 Springer Science+Business Media B.V. Source

Cripps M.G.,Lincoln University at Christchurch | Bourdot G.W.,Agresearch Ltd. | Saville D.J.,Saville Statistical Consulting Ltd. | Hinz H.L.,CABI Europe Switzerland | And 2 more authors.
Biological Invasions

Introduced weeds are hypothesized to be invasive in their exotic ranges due to release from natural enemies. Cirsium arvense (Californian, Canada, or creeping thistle) is a weed of Eurasian origin that was inadvertently introduced to New Zealand (NZ), where it is presently one of the worst invasive weeds. We tested the 'enemy release hypothesis' (ERH) by establishing natural enemy exclusion plots in both the native (Europe) and introduced (NZ) ranges of C. arvense. We followed the development and fate of individually labelled shoots and recorded recruitment of new shoots into the population over two years. Natural enemy exclusion had minimal impact on shoot height and relative growth rate in either range. However, natural enemies did have a significant effect on shoot population growth and development in the native range, supporting the ERH. In year one, exclusion of insect herbivores increased mean population growth by 2. 1-3. 6 shoots m-2, and in year two exclusion of pathogens increased mean population growth by 2. 7-4. 1 shoots m-2. Exclusion of insect herbivores in the native range also increased the probability of shoots developing from the budding to the reproductive growth stage by 4. 0× in the first year, and 13. 4× in the second year; but exclusion of pathogens had no effect on shoot development in either year. In accordance with the ERH, exclusion of insect herbivores and pathogens did not benefit shoot development or population growth in the introduced range. In either range, we found no evidence for an additive benefit of dual exclusion of insects and pathogens, and in no case was there an interaction between insect and pathogen exclusion. This study further demonstrates the value of conducting manipulative experiments in the native and introduced ranges of an invasive plant to elucidate invasion mechanisms. © 2011 Springer Science+Business Media B.V. Source

Nboyine J.A.,Lincoln University at Christchurch | Saville D.,Saville Statistical Consulting Ltd. | Boyer S.,Lincoln University at Christchurch | Boyer S.,Unitec Institute of Technology | And 2 more authors.
Journal of Pest Science

The effects of the association between grasses and fungal endophytes on orthopterans are very poorly studied although they are important grassland pests. Here, the endemic New Zealand weta, Hemiandrus sp. ‘promontorius’, and Festulolium loliaceum infected with Epichloë uncinata, were used to study the effect of endophyte-mediated resistance in grasses on this large orthopteran insect in the laboratory, and the effects of this interaction on the grass. The insect was presented with F. loliaceum with and without E. uncinata infection in no-choice and paired choice experiments. Other controls were Epichloë festucae-infected Festuca rubra and endophyte-free Lolium perenne. In no-choice experiments, persistent attempts by the insect to graze the endophyte-infected grasses (but promptly abandoning them) resulted in a significantly higher number of plants lost due to excision at their stems after the first bite (P = 0.004). The inability of affected grasses to compensate for the lost biomass resulted in a lack of significant difference between the dry biomass of endophyte-infected and endophyte-free controls (P = 0.206). However, in choice experiments, there was a preference for the endophyte-free controls when they were paired with the endophyte-infected grasses (P < 0.05). The current work shows that endophyte-infected grasses can sustain high plant losses when attacked by an orthopteran insect in the absence of an alternative food source. This contrasts other endophyte/herbivory experiments in which high herbivory occurs because chemical plant defences are at a low concentration or the endophytes have other non-toxin roles in the plant. © 2016 Springer-Verlag Berlin Heidelberg Source

Lamoureaux S.L.,Agresearch Ltd. | Bourdot G.W.,Agresearch Ltd. | Saville D.J.,Saville Statistical Consulting Ltd.
Acta Oecologica

Nassella trichotoma established in modified tussock-grasslands in New Zealand from about 1860. Management programmes since 1946 have reduced populations to levels no longer impacting pastoral production. Optimising future management requires knowledge of the trajectory of population growth and its regulating demographic processes. To that end, four long-term field experiments were conducted. Net reproductive rate varied from 1.021 to 1.237year-1 and growth in plant basal diameter from 8.1 to 16.6mmyear-1. The probability of flowering increased with basal diameter and was essentially unity above 50mm diameter. Populations grubbed annually declined abruptly but recruitment was unaffected and extinction did not occur. Of seeds sown into disturbed and intact pastures, 0-51% produced seedlings and more arose on sunny slopes and from disturbed than intact pasture. Death rates were high; 7 years after sowing, surviving plants represented only 0-9% of the seed sown. Seeds buried 25mm deep in the pasture litter on two occasions declined in viability at rates of 74 and 89% in the first year and first three months respectively and 26 and 0% year-1 thereafter. Seed production plant-1 (square root scale) increased linearly with plant basal diameter; for example, plants of 11 and 100mm diameter are predicted to produce 0 and 11,092 spikelets (each with one seed) respectively. We estimate that a N. trichotoma population today will, in the absence of management, take 210 years to increase to 90% of its carrying capacity supporting the hypothesis that population growth in this species is slower than occurred historically. We show that the rates of some demographic processes may be much lower than in the past and suggest this is due to more competitive vegetation resulting from improved management. The size-dependence of many processes supports the need for a size-structured model to explain population growth in this weed. © 2011 Elsevier Masson SAS. Source

Bourdot G.W.,Agresearch Ltd. | Hurrell G.A.,Agresearch Ltd. | Saville D.J.,Saville Statistical Consulting Ltd.
New Zealand Plant Protection

A gel preparation of mycelia of the plant pathogen Sclerotinia sclerotiorum was applied to the pasture weeds Carduus nutans L., Carduus tenuiflorus L., Cirsium arvense (L.) Scop., Jacobaea vulgaris L. and Ranunculus acris L. Doses ranging from 0 to 1,000 μl gel/plant were applied as 10 or 50 μl droplets, one per leaf axil. Statistically significant responses to dose were evident in C. arvense, J. vulgaris and R. acris, leading to 90, 74 and 100% reductions in living tissue respectively at 200 μl/plant compared to the control 29 days after treatment. For C. nutans and C. tenuiflorus, where even low doses gave good control, the reductions (averaged over all doses) were 98 and 88% respectively indicating that these two annual thistles were exceptionally susceptible to this S. sclerotiorum formulation. For C. nutans, 1 litre of the gel would, if precision applied, be sufficient to control at least 20,000 plants, suggesting broad-acre use may be commercially viable. Source

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