<i>Rhinocyllus conicus</i>
            : initial evaluation and subsequent ecological impacts in North America.

Gaßmann, A.; Louda, Svaťa M.

doi:10.1079/9780851994536.0147

Cited by 47 publications

(51 citation statements)

References 65 publications

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“…First, capitulum diameter information is necessary to correct for differences in drying time and seed production (larger capitula produce more seeds). Second, florivory by R. conicus reduces the number of seeds available for release during wind tunnel trials (Gassmann and Louda 2001;Sezen 2007). Finally, both field VPD and precipitation information allow the effect of natural conditions in the field to be quantified.…”

Section: Discussionmentioning

confidence: 99%

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Water loss from flower heads predicts seed release in two invasive thistles

Marchetto

Jongejans

Shea

et al. 2012

Plant Ecology & Diversity

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Background: Non-random seed release caused by plant responses to weather conditions is important for seed dispersal. Much is known about the effects of wind speed and turbulence, but our understanding of the effects of water loss on seed release is either qualitative, or indirect and phenomenological. Aims: To quantify the empirical relationship between water loss and seed release. Methods: Capitula of the invasive thistles Carduus acanthoides and C. nutans were collected from the field and treated for either 0, 1, or 2 days in the laboratory at three different vapour pressure deficit levels (3.4, 9.5, and 17.0 hPa) to cause a range of water loss values. Total seed release was quantified before and during wind tunnel trials. Results: Water loss was the only significant predictor of whether or not capitula released any seeds. The number of seeds released was predicted by water loss, capitulum diameter, and herbivore damage, with the same amount of water loss having less effect on larger capitula. Conclusions: These results represent an important step towards using weather data to predict seed release for many xerochastic species. Incorporating the effects of water loss on seed release into mechanistic seed dispersal models will greatly improve predictions of when and how far seeds disperse. While initiation of dispersal in some species is more likely during precipitation events (Pufal and Garnock-Jones 2010), a majority of wind dispersed angiosperms and gymnosperms are xerochastic, meaning that drying enhances seed abscission and release (Greene et al. 2008). For many Asteraceae species, including the invasive thistles Carduus nutans L. and Carduus acanthoides L. (Figure 1), drying causes cohesion tissues located on the outer side of the involucral bracts to lose turgidity and buckle, causing the bracts to be lowered away from the seeds and thus exposing seeds to the wind (Fahn 1990). Drying may also cause contraction of the receptacle away from seeds (Smith and Kok 1984).The ubiquity of xerochastic plant species suggests that seed dispersal models could be made more realistic and accurate for a wide range of species if weather data describing potential evaporation could be used to mechanistically predict seed release. Two important pieces of information need to be re-examined to accomplish this goal. First, we must predict water loss from inflorescences using weather data. A number of models already exist that use weather data to predict water loss from entire plants (de Bruin and Holtslag 1982;Sumner and Jacobs 2005), and even from capitula separately from vegetative structures (Guilioni and Lhomme 2006). The second necessary piece of information, the relationship between water loss and seed release, must still be documented and is the focus of this paper.Currently, our understanding of the effects of water loss and weather on seed release is either qualitative or phenomenological. Physiologically, we understand what effects dry conditions have on capitula (Smith and Kok 1984;Fahn 1990) and seed attachm...

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Section: Discussionmentioning

confidence: 99%

“…(a biocontrol agent) were counted to quantify florivory in each capitulum. This damage is known to reduce seed production (Gassmann and Louda 2001;Sezen 2007).…”

Section: Capitulum Dissectionsmentioning

confidence: 99%

Water loss from flower heads predicts seed release in two invasive thistles

Marchetto

Jongejans

Shea

et al. 2012

Plant Ecology & Diversity

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“…thistles, especially musk thistle, C. nutans L. (Zwölfer and Harris 1984;Gassmann and Louda 2001). The weevil oviposits on external bracts of developing flower heads, covering each egg with an obvious case of masticated plant tissue.…”

Section: Natural History and Backgroundmentioning

confidence: 99%

“…We used regression (PROC REG: SAS 1999) to identify the model with the lowest mean square error and fewest nonsignificant variables. We included as explanatory variables only those climate variables that our literature review indicated were likely to affect thistle development, or weevil activity, survival, or development (Rathcke and Lacey 1985;Tauber et al 1986;Tauber et al 1998;Gassmann and Louda 2001). For R. conicus egg cases per wavyleaf flower head, weevil abundance, and weevil-plant phenological synchrony, we examined both precipitation and GDD in the previous summer, previous autumn, preceding winter and spring; winter and spring relative humidity; and days until both last hard freeze and last freeze in spring.…”

Section: Influence Of Climatic Variablesmentioning

confidence: 99%

Indirect interaction between two native thistles mediated by an invasive exotic floral herbivore

Russell

Louda

2005

Oecologia

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., "Indirect interaction between two native thistles mediated by an invasive exotic floral herbivore" (2005). Faculty Publications in the Biological Sciences. 58. http://digitalcommons.unl.edu/bioscifacpub/58 AbstractSpatial and temporal variation in insect floral herbivory is common and often important. Yet, the determinants of such variation remain incompletely understood. Using 12 years of flowering data and 4 years of biweekly insect counts, we evaluated four hypotheses to explain variation in damage by the Eurasian flower head weevil, Rhinocyllus conicus, to the native North American wavyleaf thistle, Cirsium undulatum. The four factors hypothesized to influence weevil impact were variations in climate, weevil abundance, phenological synchrony, and number of flower heads available, either on wavyleaf thistle or on the other co-occurring, acquired native host plant (Platte thistle, Cirsium canescens), or on both. Climate did not contribute significantly to an explanation of variation in R. conicus damage to wavyleaf thistle. However, climate did influence weevil synchrony with wavyleaf flower head initiation, and phenological synchrony was important in determining R. conicus oviposition levels on wavyleaf thistle. The earlier R. conicus was active, the less it oviposited on wavyleaf thistle, even when weevils were abundant. Neither weevil abundance nor availability of wavyleaf flower heads predicted R. conicus egg load. Instead, the strongest predictor of R. conicus egg load on wavyleaf thistle was the availability of flower heads on Platte thistle, the more common, earlier flowering native thistle in the sand prairie. Egg load on wavyleaf thistle decreased as the number of Platte thistle flower heads at a site increased. Thus, wavyleaf thistle experienced associational defense in the presence of flowering by its now declining native congener, Platte thistle. These results demonstrate that prediction of damage to a native plant by an exotic insect may require knowledge of both likely phenological synchrony and total resource availability to the herbivore, including resources provided by other nontarget native species.

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“…In the northern plains, it is a taprooted, short-lived, iterocarpic perennial (Great Plains Flora Association 1986). In Nebraska, C. undulatum bolts in mid to late May, begins flowering in early June, and disperses most seeds in late July (McCarty 1982, Louda 1998 (Zwölfer andHarris 1984, Gassmann andLouda 2001).…”

Section: Natural History Of Study System and Study Sitesmentioning

confidence: 99%

Variation in Herbivore-Mediated Indirect Effects of an Invasive Plant on a Native Plant

Russell

Louda

Rand

et al. 2007

Ecology

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2001 -2003), the number of eggs laid by R. conicus on C. undulatum always decreased significantly with distance (0 -220 m) from a musk thistle patch. Neither the level of R. conicus oviposition on C. undulatum, nor the strength of the distance effect, were predicted by local musk thistle patch density or by local C. undulatum density (< 5 m). The results suggest that high R. conicus egg loads on C. undulatum near musk thistle resulted from the native thistle's co-occurrence with the co-evolved, preferred exotic host plant and not from the weevil's response to local host plant density. Mean egg loads on C. undulatum also were greater at sites with higher R. conicus densities. We conclude that both plant proximity and herbivore density strongly affected the herbivore-mediated indirect interaction, and that such interactions are important pathways by which invasive exotic weeds can indirectly impact native plants. (240 words)

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Rhinocyllus conicus : initial evaluation and subsequent ecological impacts in North America.

Cited by 47 publications

References 65 publications

Water loss from flower heads predicts seed release in two invasive thistles

Water loss from flower heads predicts seed release in two invasive thistles

Indirect interaction between two native thistles mediated by an invasive exotic floral herbivore

Variation in Herbivore-Mediated Indirect Effects of an Invasive Plant on a Native Plant

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