A caterpillar (Callopistria floridensis G. (Lepidoptera: Noctuidae)) accumulates arsenic from an arsenic‐hyperaccumulating fern (Pteris vittata L.).

1. The consumption of arsenic is toxic to most biota. However, a noctuid caterpillar was recently reported feeding on a plant known to hyperaccumulate arsenic. 2. The aim of this study was to investigate the effects of arsenic‐rich Pteris vittata L. consumption by Callopistria floridensis G., and measure differences in arsenic concentrations at various stages of development (larval and adult), and associated with exuviae and frass. 3. Callopistria floridensis accumulated extraordinary concentrations of arsenic. The relative accumulation of arsenic was highest in exuviae and larvae. Larvae invariably preferred P. vittata grown on low arsenic soil to P. vittata grown on higher soil arsenic concentrations, and appeared able to selectively forage on lower arsenic concentrations within each treatment. 4. These findings show that C. floridensis is tolerant of arsenic, and successfully develops to adulthood containing elevated concentrations of arsenic. Callopistria floridensis represents the only known terrestrial animal capable of accumulating arsenic, and may have developed novel physiological and behavioural adaptations to regulate the negative effects of arsenic.     

Soil feedback does not explain mowing effects on vegetation structure in a semi-natural grassland

Due to its ability to create aboveground conditions that favour plant diversity, mowing is often used to preserve the high conservation value of semi-natural species-rich grasslands. However, mowing can also affect belowground conditions. By decreasing plant carbon supply to soil, mowing can suppress the activity of soil decomposers, diminish plant nutrient availability and thus create a feedback on plant growth. In this study, we first documented the effects of three-year mowing on plant community structure in a species-rich grassland. We found that mowing decreased the total areal cover of woody plants and increased the total cover of leguminous forbs. At the species level, mowing further increased the cover of two non-leguminous forbs, Prunella vulgaris and Sagina procumbens. Mowing did not affect the species number, diversity or evenness of the plant community. To study whether any of these effects could be explained by mowing-induced changes in the soil, and particularly by reduced nutrient availability, we then collected soil from different treatment plots and monitored the growth of nine plant species in these soils in a greenhouse. Plant growth did not differ between soils collected from mowed and unmowed plots, suggesting that our mowing regimes did not impose such changes in soil decomposer activity and nutrient supply that would feedback on plant growth. Moreover, each of the nine species responded equally to the different nutrient availability in different parts of the grassland, which indicates that even if mowing had reduced plant nutrient supply, this would not have led to changes in plant community structure. It appears that those changes in aboveground vegetation that we recorded after three years of mowing were purely due to the aboveground effects, such as frequent cutting of woody plants and enhanced light availability for low-growing forbs.     

Spatio‐temporal variation in the effect of herbaceous layer on woody seedling survival in a Chilean mediterranean ecosystem

Questions: What is the effect of herbaceous layer on seedling establishment of three woody pioneer species in open areas of central Chile under a semi‐arid mediterranean climate? How do inter‐annual and habitat conditions (slope aspect) modulate this effect? Under high stress conditions such as the drier year and habitat (north‐facing slope) do herbs reach low abundance and have neutral effects on woody seedlings? Under medium stress conditions for these woody species, such as the wetter year and south‐facing slope, does the herbaceous layer reach greater abundance and have positive effects on woody seedlings due to increasing soil water content? Location: A watershed on the outskirts of Santiago, Chile, subjected to clearing of woody vegetation through firewood extraction and human‐set fires. Methods: In spring 2007, we set up 20 plots (3 m × 2 m). Half of each plot had herbs removed manually and by application of herbicide. In both halves of each plot, one seedling (8 months old) of each of the three native woody species (Colliguaya odorifera, Schinus polygamus and Quillaja saponaria) was planted and survival monitored subsequently. The experiment was repeated in two consecutive growing seasons (2007–2008 and 2008–2009) that differed significantly in total precipitation (152 and 256.5 mm, respectively), and replicated in two sites that differed in aspect and abiotic conditions: a moister south‐ and a drier north‐facing slope. Results: In the first and drier year, the herbaceous layer had low cover and no significant effect on seedling survival of woody species. During the second year, herbs had greater cover and a significant positive effect on spring survival of C. odorifera in the north‐facing slope, which was lost after summer. During this wetter year on the south‐facing slope, herb cover had a positive effect on survival of S. polygamus (mainly during summer). Conclusions: The role of mostly ruderal herbs on woody seedling establishment depended on the species, rainfall of the current year and slope aspect, and may be explained by soil moisture patterns. This suggests that the effect of ruderal herbs on woody seedlings shifts from neutral under high stress conditions produced by drought to positive under moderate stress conditions. Our results contribute to understand interactions between ruderal herbs and woody species under contrasting abiotic conditions. Therefore, control of the herbaceous layer may not be needed in restoration programmes for this region. Moreover, herbs may benefit restoration of woody cover in mesic habitats.     

Opposing forces of seed dispersal and seed predation by mammals for an invasive cactus in central Kenya

The invasive erect prickly pear cactus (Opuntia stricta) has reduced rangeland quality and altered plant communities throughout much of the globe. In central Kenya's Laikipia County, olive baboons (Papio anubis) frequently consume O. stricta fruits and subsequently disperse the seeds via defecation. Animal‐mediated seed dispersal can increase germination and subsequent survival of plants. However, consumption of seeds (seed predation) by rodents may offset the potential benefits of seed dispersal for cactus establishment by reducing the number of viable seeds. We investigated foraging preferences of a common and widely distributed small mammal—the fringe‐tailed gerbil (Gerbilliscus robustus), between O. stricta seeds deposited in baboon faeces versus control O. stricta seeds. In addition to providing evidence of seed predation on O. stricta by G. robustus, our data show that seed removal was higher (shorter time to use) for seeds within faeces than for control seeds. G. robustus clearly prefers seeds within faeces compared to control seeds. These results suggest that high abundances of rodents may limit successful establishment of O. stricta seeds, possibly disrupting seed dispersal via endozoochory by baboons.     

Do multitrophic interactions override N fertilization effects on <Emphasis Type="Italic">Operophtera</Emphasis> larvae?

We examined how performance of Operophtera brumata (Lepidoptera) larvae was affected by nitrogen (N) fertilization of boreal forest understorey vegetation. We monitored larval densities on Vaccinium myrtillus plants for a period of 7 years in a field experiment. Preliminary results indicated that the N effect on larval densities was weak. To examine if this was due to indirect interactions with a plant pathogen, Valdensia heterodoxa, that share the same host plant, or due to top-down effects of predation, we performed both a laboratory feeding experiment (individual level) and a bird exclusion experiment (population level) in the field. At the individual level, altered food plant quality (changes in plant concentration of carbon, N, phenolics, or condensed tannins) due to repeated infection by the pathogen had no effect on larval performance, but both survival to the adult stage and adult weight were positively affected by N fertilization. Exclusion of insectivorous birds increased the frequency of larval damage on V. myrtillus shoots, indicating higher larval densities. This effect was stronger in fertilized than in unfertilized plots, indicating higher bird predation in fertilized plots. Predation may thus explain the lack of fertilization effect on larval densities in the field experiment. Our results suggest that top-down effects are more important for larval densities than bottom-up effects, and that bird predation may play an important role in population regulation of O. brumata in boreal forests.Electronic Supplementary Material Supplementary material is available for this article at     

Spine production is induced by fire: a natural experiment with three Berberis species

Earlier studies indicate that some plant species allocate more mass to produce longer spines in shoots resprouting after browsing. Here we present, for the first time, evidence that fire induces a similar response. Many terrestrial herbivores may benefit from fire through the enhanced availability of fast growing species colonizing or re-sprouting in burned areas. It is less clear whether post-fire plant growth responds to the enhanced risk of herbivory by an increased investment in defensive traits. In this study, we tested whether the production of spines is influenced by the set of environmental conditions that result from fire events. We compared the resource allocation pattern of resprouting shoots from three Berberis species growing in two areas that burned 1999 with samples collected from unburned areas within the same plant communities. We divided the shoot into three main components: supporting tissue (twigs), assimilating tissue (leaves) and defensive structures (spines). We found that plants resprouting after fire allocated more mass to spines and leaves but not twigs. This resulted in a higher density of both spines and leaves. Spines were significantly longer in plants resprouting after fire. Leaves were shorter at the apical end of the shoot, but did not show any significant change in size following fire. We suggest that this type of post-fire response may be a general adaptation to pruning and leaf picking by browsing herbivores in arid and semi-arid regions. Changes in the browsing pressure following fire will determine the fitness value of this response.     

Herbivory and climatic warming: a Mediterranean outbreaking caterpillar attacks a relict, boreal pine species

Climate change can harm many species by disrupting existing interactions or by favouring new ones. This study analyses the foreseeable consequences of climatic warming in the distribution and dynamics of a Mediterranean pest that causes severe defoliation, the pine processionary caterpillar Thaumetopoea pityocampa, and the effects upon the relict Andalusian Scots pine Pinus sylvestris nevadensis in the Sierra Nevada mountains (southeastern Spain). We correlated a set of regional data of infestation by T. pityocampa upon Scots pine, from a broad ecological gradient, with climatic data for the period 1991–2001, characterized by alternating warm and cold winters. Defoliation intensity shows a significant association with previous warm winters, implying that climatic warming will intensify the interaction between the pest and the Scots pine. The homogeneous structure of the afforested pine woodlands favours the outbreak capacity of the newcomer, promoting this new interaction between a Mediterranean caterpillar pest and a boreal tree at its southern distribution limit.     

From protégé to nurse plant: establishment of thorny shrubs in grazed temperate woodlands

Question: Thorny shrubs play keystone roles in grazed ecosystems by defending non‐protected plants against herbivores, but their establishment in grazed ecosystems is poorly understood. Which factors control establishment of recruits of thorny nurse shrubs in grazed temperate woodlands? Location: Ancient grazed temperate woodlands (52°32′N, 6°36′E), The Netherlands. Methods: We surveyed biotic and abiotic factors for saplings of thorny nurse shrubs in plots with and without saplings. To disentangle these factors, we performed a transplantation experiment over two growing seasons with nurse shrub saplings (Prunus spinosa and Crataegus monogyna) planted in two dominant vegetation types – tall unpalatable swards and short grazed lawns – half of them protected from herbivory via exclosures. Results: Plots with shrub saplings had taller surrounding vegetation, higher soil pH and higher soil moisture than plots without saplings. These plots predominantly contained unpalatable sward species, while plots without saplings mainly contained palatable lawn species. After transplantation, sapling survival was higher in exclosures than in the open, and higher in sward exclosures than in lawn exclosures. Sapling growth was higher in swards than in lawns, higher inside than outside exclosures, and higher for Prunus than Crataegus, while browsing on saplings was higher in lawns. Conclusion: Unpalatable swards form essential establishment niches for thorny shrubs in grazed temperate woodlands: they protect against herbivores before thorns fully develop in saplings, and sapling growth is better due to improved micro‐environmental conditions. Once established and thorny, shrub saplings grow out of the protective range of the swards and in turn facilitate tree seedlings, which are essential for long‐term persistence of grazed temperate woodlands. This study shows that nurse plants may start as protégés before becoming facilitators for other plants in a later life stage. This may be common for nurse plants in various ecosystems. We argue that improved understanding of establishment of nurse plants and their constraining factors is crucial for effective conservation and restoration in various ecosystems.     

Bottom-up effects of nutrient availability on flower production, pollinator visitation, and seed output in a high-Andean shrub

Soil nutrient availability directly enhances vegetative growth, flowering, and fruiting in alpine ecosystems. However, the impacts of nutrient addition on pollinator visitation, which could affect seed output indirectly, are unknown. In a nutrient addition experiment, we tested the hypothesis that seed output in the insect-pollinated, self-incompatible shrub, Chuquiraga oppositifolia (Asteraceae) of the Andes of central Chile, is enhanced by soil nitrogen (N) availability. We aimed to monitor total shrub floral display, size of flower heads (capitula), pollinator visitation patterns, and seed output during three growing seasons on control and N addition shrubs. N addition did not augment floral display, size of capitula, pollinator visitation, or seed output during the first growing season. Seed mass and viability were 25–40% lower in fertilised shrubs. During the second growing season only 33% of the N addition shrubs flowered compared to 71% of controls, and a significant (50%) enhancement in vegetative growth occurred in fertilised shrubs. During the third growing season, floral display in N addition shrubs was more than double that of controls, received more than twice the number of insect pollinator visits, and seed output was three- to four-fold higher compared to controls. A significant (50%) enhancement in vegetative growth again occurred in N addition shrubs. Results of this study strongly suggest that soil N availability produces strong positive bottom-up effects on the reproductive output of the alpine shrub C. oppositifolia. Despite taking considerably longer to be manifest in comparison to the previously reported top-down indirect negative effects of lizard predators in the same study system, our results suggest that both bottom-up and top-down forces are important in controlling the reproductive output of an alpine shrub.     

Plant-microbe interactions to probe regulation of plant carbon metabolism

Plant growth and development is dependent on coordinated assimilate production, distribution and allocation. Application of biochemical and molecular techniques substantially contributed to a better understanding of these processes, although the underlying regulatory mechanisms are still not fully elucidated and attempts to improve crop yield by modulating carbon partitioning were only partially successful. Plant pathogens also interfere with source–sink interaction. To this end they have evolved a wide range of sophisticated strategies to allow their systemic spread, suppression of plant defence and induction of sink function to support nutrient acquisition for their growth. Studying compatible interactions of plants and pathogens like viruses, bacteria and fungi can be exploited to investigate different levels of source–sink regulation. The identification of microbial factors and their host targets involved in regulation of plant primary metabolism may allow developing novel strategies to increase crop yield. Here we will discuss recent studies on plant–microbe interactions aimed at elucidating mechanisms of compatibility.     

Impact of Archanara geminipuncta (Lepidoptera: Noctuidae) on aboveground biomass production of Phragmites australis

Management of invasive plants with biological control rests on the assumption of herbivores as structuring forces of plant community composition, but only 30% of programs achieve substantial plant suppression. Control is often caused by a few successful agents, and improvements in the ability to select the most promising species would greatly improve weed biocontrol programs. We evaluated impact of different larval stages and larval densities of the stem boring noctuid Archanara geminipuncta on height and biomass production of Phragmites australis in the field and in a common garden in the native European range. In the field, stem biomass was reduced 21.5–64.5% by A. geminipuncta attack with the largest reduction due to early larval feeding. In the common garden, P. australis performance declined linearly (stem height 40%, biomass 50%; and percentage of flowering stems 90%) as attack rates increased. Significant field and common garden impact and the large Eurasian distribution indicate great potential of A. geminipuncta for biocontrol of introduced P. australis in North America if host specificity tests produce favorable results. If approved for release, we anticipate that A. geminipuncta could establish throughout the range of introduced P. australis in North America. We also anticipate that this moth will build high populations with significant impact on height, aboveground biomass, and clonal expansion of P. australis. This attack is expected to reduce competitive ability of P. australis, favoring native wetland species and preventing further negative ecological impacts associated with the current spread of introduced P. australis in North America.     

Antagonistic selection and pleiotropy constrain the evolution of plant chemical defenses

When pleiotropy is present, genetic correlations may constrain the evolution of ecologically important traits. We used a quantitative genetics approach to investigate constraints on the evolution of secondary metabolites in a wild mustard, Boechera stricta. Much of the genetic variation in chemical composition of glucosinolates in B. stricta is controlled by a single locus, BCMA1/3. In a large‐scale common garden experiment under natural conditions, we quantified fitness and glucosinolate profile in two leaf types and in fruits. We estimated genetic variances and covariances (the G ‐matrix) and selection on chemical profile in each tissue. Chemical composition of defenses was strongly genetically correlated between tissues. We found antagonistic selection between defense composition in leaves and fruits: compounds that were favored in leaves were disadvantageous in fruits. The positive genetic correlations and antagonistic selection led to strong constraints on the evolution of defenses in leaves and fruits. In a hypothetical population with no genetic variation at BCMA1/3, we found no evidence for genetic constraints, indicating that pleiotropy affecting chemical profile in multiple tissues drives constraints on the evolution of secondary metabolites.