Andreas Erhardt

Diurnal Lepidoptera: sensitive indicators of cultivated and abandoned Grassland

(1) In the subalpine region of Central Switzerland (Tavetsch Valley) studies were made of the day-active Lepidoptera faunas in different types of cultivated grassland, in various stages in the development of abandoned grassland and in woodlands (climax vegetation). (2) The results show a close correlation between bufferfly fauna and vegetation type concerning species composition and species richness of Lepidoptera. (3) Species richness of butterflies is highest in early abandoned stages and falls rapidly with the arrival of shrubs and trees. It is also high in traditionally lightly cultivated grassland (unfertilized mown and lightly grazed meadows), but it declines drastically with increasing intensity of cultivation. (4) In general, species richness of butterflies is closely correlated with species richness of vascular plants, but cultivation methods and the short time since abandonment (<5 years) of lightly cultivated grassland have strongly different influences on species richness of Lepidoptera and vascular plants. (5) The results are in contrast to former studies in Central Europe and parallel studies in England. (6) The natural primary habitats of butterflies living in the anthropogenetic types of vegetation investigated and the consequences for nature conservation are discussed.

Amino acids in nectar enhance butterfly fecundity: a long-awaited link.

Thirty years ago, researchers discovered that flowers pollinated by butterflies are consistently rich in nectar amino acids, and more recent findings have shown that butterflies prefer nectar with high amino acid content. These observations led to speculation that amino acids in nectar enhance butterfly fitness and that butterflies have acted as agents of natural selection on nectar composition. Despite a number of experimental efforts over the years, convincing proof that nectar amino acids affect butterfly fitness has been lacking. Here, we provide the first evidence that amino acids in nectar have a positive effect on fecundity of one butterfly species, supporting the existence of a relationship between nectar preferences and fitness benefits. Map butterflies (Araschnia levana L.) raised under natural larval food conditions laid more eggs when they were fed nectar containing amino acids, whereas nectar amino acids had no effect on the number of eggs laid by butterflies raised on larval food rich in nitrogen. Uptake and utilization of nectar amino acids by map butterflies appear to be compensatory mechanisms enabling them to override impacts of poor larval food. These results provide strong support for the long‐standing postulate that nectar amino acids benefit butterflies.

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.

Spatial bias in the GBIF database and its effect on modeling species' geographic distributions

Abstract Species distribution modeling, in combination with databases of specimen distribution records, is advocated as a solution to the problem of distributional data limitation in biogeography and ecology. The global biodiversity information facility (GBIF), a portal that collates digitized collection and survey data, is the largest online provider of distribution records. However, all distributional databases are spatially biassed due to uneven effort of sampling, data storage and mobilization. Such bias is particularly pronounced in GBIF, where nation-wide differences in funding and data sharing lead to huge differences in contribution to GBIF. We use a common Eurasian butterfly (Aglais urticae) as an exemplar taxon to provide evidence that range model quality is decreasing due to the spatial clustering of distributional records in GBIF. Furthermore, we show that such loss of model quality would go unnoticed with standard methods of model quality evaluation. Using evaluations of model predictions of the Swiss distribution of the species, we compare distribution models of full data with data where a subsampling procedure removes spatial bias at the cost of record numbers, but not of spatial extent of records. We show that data with less spatial bias produce better predictive models even though they are based on less input data. Our subsampling routine may therefore be a suitable method to reduce the impact of spatial bias to species distribution models. Our results warn of automatized applications of species distribution models to distributional databases (as has been advocated and implemented), as internal model evaluation did not show the decline of model quality with increased spatial bias (but rather the opposite) while expert evaluation clearly did.

Effects of elevated CO2 on flowering phenology and nectar production of nectar plants important for butterflies of calcareous grasslands

Abstract Effects of elevated CO2 on flowering phenology and nectar production were investigated in Trifolium pratense, Lotus corniculatus, Scabiosa columbaria, Centaurea jacea and Betonica officinalis, which are all important nectar plants for butterflies. In glasshouse experiments, juvenile plants were exposed to ambient (350 μl l−1) and elevated (660 μl l−1) CO2 concentrations for 60–80 days. Elevated CO2 significantly enhanced the development of flower buds in C. jacea. B. officinalis flowered earlier and L. corniculatus produced more flowers under elevated CO2. In contrast, the number of flowers decreased in T. pratense. The amount of nectar per flower was not affected by elevated CO2 in the tested legumes (T. pratense and L. corniculatus), but was significantly reduced (!) in the other forbs. Elevated CO2 did not significantly affect nectar sugar concentration and composition. However, S. columbaria and C. jacea produced significantly less total sugar under elevated CO2. The nectar amino acid concentration remained unaffected in all investigated plant species, whereas the total of amino acids produced per flower was reduced in all non-legumes. In addition, the amino acid composition changed significantly in all investigated species except for C. jacea. The observed effects are unexpected and are a potential threat to flower visitors such as most butterflies which have no alternative food resources to nectar. Changes in nectar production due to elevated CO2 could also have generally detrimental effects on the interactions of flowers and their pollinators.

Do Peacock butterflies (Inachis io L.) detect and prefer nectar amino acids and other nitrogenous compounds

Abstract The preferences for nectar amino acids, urea and ammonium ions of peacock butterflies, Inachis io, were tested experimentally. Females clearly preferred a mimic of Lantana camara nectar containing amino acids to an otherwise similar plain sugar solution, whereas males did not discriminate between these test solutions. Neither males nor females discriminated between the full mixture of amino acids in a mimic of L. camara nectar and similar test solutions containing only the single amino acids arginine or proline. Furthermore, the butterflies were not able to detect methionine in the test solutions. Both sexes detected and preferred ammonium ions in test solutions but showed no response to urea. These results support the hypothesis that butterflies can select for high amino acid concentrations in floral nectar. However, it seems unlikely that they select for particular amino acids. The rather unspecific response of I. io males to the nectar constituents tested may result from their relatively low demand for nitrogen for spermatophore and sperm production, while their high activity may make energy supply (i.e. sugar) more important. The preference for ammonium ions suggests that I. io could also acquire nitrogen from ammonium-contaminated soil by puddling, as has been shown for sodium in swallowtail butterflies.

LARVAL NUTRITION AFFECTS FEMALE NECTAR AMINO ACID PREFERENCE IN THE MAP BUTTERFLY (ARASCHNIA LEVANA)

Preference for nectar amino acids varies between different groups of pollinators. Females of several butterfly species have shown a clear preference for nectar mimics containing amino acids over nectar void of amino acids. This investigation examined how larval conditions affect nectar amino acid preferences of butterflies. Larvae of Araschnia levana were raised on low and high food quality diets. Female butterflies raised on the low quality larval diet were smaller and showed a significant preference for the nectar mimic with amino acids, whereas females raised on the high quality diet were larger and showed no preference. Larval food quality did not affect male mass, and male butterflies were indifferent to nectar amino acids. Consequently, female butterflies may compensate for poor larval nutrition by selectively feeding on nectar containing amino acids. These results demonstrate the nutritional plasticity of holometabolous insects and the potential evolutionary significance of nectar amino acids for both plants and their pollinators.

Nectar sugar and amino acid preferences of Battus philenor (Lepidoptera, Papilionidae)

Abstract. 1 Butterflies of Battus philenor were tested for their preferences for nectar sugars and amino acids in an outdoor cage experiment. 2 The butterflies clearly preferred both sucrose and fructose over glucose. They also preferred sucrose over fructose. 3 No other preferences were found to be statistically significant, although male butterflies tended to prefer a plain sugar solution over a sugar solution containing a mixture of amino acids: females consumed both of these solutions in almost equal proportions. 4 The results are discussed with respect to nectar composition of butterfly pollinated flowers, flower preferences, physiological and reproductive aspects of butterflies.

Pollen amino acids - an additional diet for a nectar feeding butterfly?

The increase of the amino acid concentration over different time intervals in artificial nectar (i.e., a sucrose solution) due to pollen contamination was investigated in four Californian plant species (Aesculus californica, Amsinckia lunaris, Brodiaea pulchella, Carduus pycnocephalus), which are important nectar resources for a Californian colony of the butterflyBattus philenor as well as for other insects. The increase of the amino acid concentration in the medium is different in all four species and seems to be determined by a variety of factors including permeability of the pollen grain wall and presence or absence of pores. The results suggest a passive diffusion process of the free pollen amino acids into the medium rather than an active release. Implications from the experiments forBattus philenor and for other nectar feeding pollinators are discussed. A possible complementary effect of free pollen and nectar amino acids is proposed for plant species in which pollen is likely to be knocked into nectar by their flower visitors. A possible evolutionary pathway from nectar feeding butterflies such asBattus philenor to the complex derived pollen feeding habit in theHeliconius butterflies is proposed.

Preferences and non-preferences for nectar constituents inOrnithoptera priamus poseidon (Lepidoptera, Papilionidae)

SummaryPreferences for nectar sugars and amino acids ofOrnithoptera priamus butterflies were tested experimentally. Both male and female butterflies clearly preferred a sucrose solution over a glucose solution of equal concentration (25%, weight to total weight) and equally a fructose solution over a glucose solution. A significant trend of males to prefer fructose over sucrose and of females to prefer sucrose over fructose was detected. However, neither males nor females discriminated between a mimic ofLantana camara nectar containing amino acids and a corresponding plain sugar solution. These results suggest that butterflies select against glucose in floral nectar but do not support the hypothesis that butterflies select for high levels of amino acids in nectar. The rather unspecific response ofOrnithoptera priamus butterflies to the tested nectar constituents may reflect a generalist feeding strategy of these long-lived and spectacular butterflies.