Marcel Goverde

Small-scale habitat fragmentation effects on pollinator behaviour: experimental evidence from the bumblebee Bombus veteranus on calcareous grasslands

We examined visiting patterns of pollinators of Betonica officinalis L. (Lamiaceae) in experimentally fragmented calcareous grasslands and corresponding control plots at two study sites (Movelier and Nenzlingen) in the north-western Swiss Jura mountains. Fragments (1.5×1.5 m) were isolated by a 5-m wide strip of frequently mown vegetation while the control plots were situated in the adjacent undisturbed vegetation. The most common pollinator, the bumblebee Bombus veteranus (Apidae), visited fragments 53.7% less frequently than control plots. Furthermore, a change in foraging behaviour of Bombus veteranus was observed. In fragments the bumblebees visited more inflorescences, flew longer total visiting distances and the visiting time per patch tended to be higher than in control plots. The distribution of angles between arrival and departure direction (turning angles) differed from a uniform distribution in fragments but not in control plots. The increased directionality of bumblebee flight might be due to a decrease in floral rewards. Our results show that small-scale habitat fragmentation can affect plant pollination at two levels both relevant for plant fitness. First, lower visitation rates indicate a limitation of pollinators which might result in reduced seed set of the pollinated plant. Second, changes in pollinator behaviour might reduce pollen dispersal among flowers, increase inbreeding and hence reduce genetic variability in populations of this bumblebee pollinated plant.

Influence of atmospheric carbon dioxide enrichment on induced response and growth compensation after herbivore damage in Lotus corniculatus

Abstract 1. Plant growth and chemical defence compounds in four Lotus corniculatus genotypes exposed to factorial combinations of ambient and elevated carbon dioxide, and herbivory by caterpillars of Polyommatus icarus were measured to test the predictions of the carbon/nutrient balance hypothesis.

IN SITU DEVELOPMENT OF A SATYRID BUTTERFLY ON CALCAREOUS GRASSLAND EXPOSED TO ELEVATED CARBON DIOXIDE

Elevated atmospheric CO2 can affect plant–insect herbivore interactions, primarily due to changes in leaf nutritional quality. However, current experimental evidence is predominantly based on greenhouse studies, and there is a paucity of data gained in natural plant communities growing under natural climatic conditions. We investigated the development of larvae of the satyrid butterfly Coenonympha pamphilus in seminatural calcareous grasslands that had been exposed to elevated CO2 for five growing seasons in the northwestern Swiss Jura mountains. Late second-instar larvae were grown until adult eclosion in cages containing a natural mixture of grassland plant species. Leaf nitrogen concentration of the grass species present decreased at elevated CO2, while nonstructural carbohydrates increased. Total polyphenolics were unaltered, but condensed tannins increased marginally significantly. Lipid concentration in freshly emerged butterflies of C. pamphilus increased, and females tended to have higher numbers ...

Genotype-specific response of a lycaenid herbivore to elevated carbon dioxide and phosphorus availability in calcareous grassland

Effects of elevated CO2 and P availability on plant growth of the legume Lotus corniculatus and consequences for the butterfly larvae of Polyommatus icarus feeding on L. corniculatus were investigated in screen-aided CO2 control chambers under natural conditions on a calcareous grassland in the Swiss Jura mountains. Elevated CO2 conditions and P fertilisation increased the biomass production of L. corniculatus plants and affected the plant chemical composition. CO2 enrichment increased the C/N ratio and sugar concentration and decreased the N and P concentrations. C- and N-based allelochemicals (cyanoglycosides, total polyphenols and condensed tannins) were only marginally affected by CO2 enrichment. P fertilisation increased the specific leaf area and concentrations of water, N, sugar and P, while the C/N ratio and the concentration of total polyphenols decreased. Furthermore, P availability marginally enhanced the effect of elevated CO2 on the total dry mass and sugar concentration while the opposite occurred for the total polyphenol concentration. The changes in food-plant chemistry as a result of P fertilisation positively affected larval mass gain and accelerated the development time of P. icarus. Only a marginal negative effect on larval mass gain was found for CO2 enrichment. However, we found genotype-specific responses in the development time of P. icarus to elevated CO2 conditions. Larvae originating from different mothers developed better either under elevated CO2 or under ambient CO2 but some did not react to CO2 elevation. As far as we know this is the first finding of a genotype-specific response of an insect herbivore to elevated CO2 which suggests genetic shifts in insect life history traits in response to elevated CO2.

Species-specific reactions to elevated CO2 and nutrient availability in four grass species

The objective of this study was to determine effects of elevated CO₂ and soil nutrient availability on growth and plant tissue quality in four grass species, Agrostis stolonifera, Anthoxanthum odoratum, Festuca rubra and Poa pratensis, native in Western European calcareous grassland. Plants were grown for 65 days in the greenhouse in pots with untreated soil from calcareous grassland under ambient (350 ppm) and elevated (700 ppm) CO₂ either with or without fertilisation. In general, elevated CO₂ increased plant height, total biomass, starch and sugar concentrations, and decreased water and nitrogen concentrations. However, the response to CO₂-enrichment depended strongly on the grass species investigated. Fertilisation enhanced most effects of elevated CO₂ Biomass production in fertilised plants increased more under elevated CO₂ than in unfertilised plants whereas leaf nitrogen concentration of fertilised plants decreased more at elevated CO₂ than it did in unfertilised plants. Furthermore, a species-specific response to elevated CO₂, depending on soil nutrient availability was detected in starch and sugar concentrations (three-way interaction). The data from this study indicate that grass species vary in their response to elevated CO₂ in biomass production and tissue quality. Furthermore, increasing nutrient availability can substantially alter effects of elevated CO₂. Since the investigated grass species are important larval food-plants of insect herbivores on calcareous grassland, the observed species-specific reactions to CO₂-enrichment and high nutrient availability in tissue quantity and quality are discussed with respect to their effects on insect performance and thus abundance and biodiversity of these insects.

Positive effects of cyanogenic glycosides in food plants on larval development of the common blue butterfly.

Cyanogenesis is a widespread chemical defence mechanism in plants against herbivory. However, some specialised herbivores overcome this protection by different behavioural or metabolic mechanisms. In the present study, we investigated the effect of presence or absence of cyanogenic glycosides in birdsfoot trefoil (Lotus corniculatus, Fabaceae) on oviposition behaviour, larval preference, larval development, adult weight and nectar preference of the common blue butterfly (Polyommatus icarus, Lycaenidae). For oviposition behaviour there was a female-specific reaction to cyanogenic glycoside content; i.e. some females preferred to oviposit on cyanogenic over acyanogenic plants, while other females behaved in the opposite way. Freshly hatched larvae did not discriminate between the two plant morphs. Since the two plant morphs differed not only in their content of cyanogenic glycoside, but also in N and water content, we expected these differences to affect larval growth. Contrary to our expectations, larvae feeding on cyanogenic plants showed a faster development and stronger weight gain than larvae feeding on acyanogenic plants. Furthermore, female genotype affected development time, larval and pupal weight of the common blue butterfly. However, most effects detected in the larval phase disappeared for adult weight, indicating compensatory feeding of larvae. Adult butterflies reared on the two cyanogenic glycoside plant morphs did not differ in their nectar preference. But a gender-specific effect was found, where females preferred amino acid-rich nectar while males did not discriminate between the two nectar mimics. The presented results indicate that larvae of the common blue butterfly can metabolise the surplus of N in cyanogenic plants for growth. Additionally, the female-specific behaviour to oviposit preferably on cyanogenic or acyanogenic plant morphs and the female-genotype-specific responses in life history traits indicate the genetic flexibility of this butterfly species and its potential for local adaptation.