letters to nature NATURE | VOL 399 | 10 JUNE 1999 | www.nature.com 579 between 270 and 4,000 ms after target onset) and to ignore changes in the distractor. Failure to respond within a reaction-time window, responding to a change in the distractor or deviating the gaze (monitored with a scleral search coil) by more than 1Њ from the fixation point caused the trial to be aborted without reward. The change in the target and distractors was selected so as to be challenging for the animal. In experiments 1 and 2 the animal correctly completed, on average, 79% of the trials, broke fixation in 11%, might have responded to the distractor stimulus in 6% and responded too early or not at all in 5% of the trials. In Experiment 3 the corresponding values are 78, 13%, 8% and 2%. In none of the three experiments was there a difference between the performances for the two possible targets. Differences between average eye positions during trials where one or the other stimulus was the target were very small, with only an average shift of 0.02Њ in the direction of the shift of position between the stimuli. Only correctly completed trials were considered. Firing rates were determined by computing the average neuronal response across trials for 1,000 ms starting 200 ms after the beginning of the target stimulus movement. Tuning curves. Tuning curves were derived by fitting the responses to the 12 directions presented with gaussian functions: r null þ dirGain ϫ exp ð Ϫ 0:5‫ء‬ðdir Ϫ prefdirÞ 2 =width 2 Þ . The four parameters of a gaussian curve capture the four features of a direction-selective cell: preferred direction ( prefdir), response to the anti-preferred direction (r null ), the directional gain (dirGain; the maximal response modulation) and the selectivity or tuning width (width; the range of directions the neuron responds to).

Jason W. 2013 Multi-generational longdistance migration of insects: studying the painted lady butterfly in the Western Palaearctic. Ecography, 36 (4). 474-486. 10.1111/j.1600-0587.2012.07738.x Contact CEH NORA team at noraceh@ceh.ac.ukThe NERC and CEH trademarks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. (up to 60 degrees of latitude). The cycle comprises an annual poleward advance of the 73 populations in spring followed by an equatorward return movement in autumn, with returning 74 individuals potentially flying thousands of kilometres. We show that many long-distance 75 migrants take advantage of favourable winds, moving downwind at high elevation (from 76 some tens of metres from the ground to altitudes over 1,000 m), pointing at strong similarities 77 in the flight strategies used by V. cardui and other migrant Lepidoptera. Our results reveal the 78 highly successful strategy that has evolved in these insects, and provide a useful framework 79 for a better understanding of long-distance seasonal migration in the temperate regions 80 worldwide. 81 82 5

ResearchCite this article: Betzholtz P-E, Pettersson LB, Ryrholm N, Franzén M. 20 With that diet, you will go far: trait-based analysis reveals a link between rapid range expansion and a nitrogen-favoured diet. Recent global change has had a substantial influence on the distribution of organisms, and many species are currently expanding their ranges. To evaluate the underlying processes, long-term data with good geographic resolution are essential. One important but generally overlooked data source is offered by the taxon-specific national catalogues of first provincial records that are kept in many countries. Here, we use such data to quantify traitbased influences on range expansion in Swedish butterflies and moths between 1973 and 2010. Of 282 species meeting pre-defined quality criteria, 170 expanded their northern range margin, with a mean expansion rate of 2.7 km per year. The analyses demonstrate that habitat and diet generalists, forest species and species active during warm conditions have expanded their ranges more rapidly than other species. Notably, range expansion in diet specialists was positively related to a nitrogen-favoured larval diet, an effect not found among oligo-or polyphagous species. In contrast to the general view, this shows that specialist species can undergo rapid range expansion. We suggest that increased areas of nitrogen-rich habitat, and increased availability of a nitrogen-favoured diet, are among the most important drivers of range expansions, potentially having far-reaching consequences for a wide variety of organisms.

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We provide a comprehensive overview of those Lepidopteran invasions to Europe that result from increasing globalisation and also review expansion of species within Europe. A total of 97 non-native Lepidoptera species (about 1% of the known fauna), in 20 families and 11 superfamilies have established so far in

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Climate and land use change can alter the incidence and strength of biotic interactions, with important effects on the distribution, abundance and function of species. To assess the importance of these effects and their dynamics, studies quantifying how biotic interactions change in space and time are needed. We studied interactions between nettle-feeding butterflies and their shared natural enemies (parasitoids) locally and across 500 km latitudinal gradient in Sweden. We also examined the potential impact of the range-expansion of the butterfly Araschnia levana on resident butterflies via shared parasitoids, by studying how parasitism in resident butterflies covaries with the presence or absence of the newly-established species. We collected 6777 larvae of four nettle-feeding butterfly species (Aglais urticae, Aglais io, Ar. levana and Vanessa atalanta), over two years, at 19 sites distributed along the gradient. We documented the parasitoid complex for each butterfly species and measured their overlap, and analysed how parasitism rates were affected by butterfly species assemblage, variations in abundance, time, and the arrival of Ar. levana. Parasitoids caused high mortality, with substantial overlap in the complex of parasitoids associated with the four host butterflies. Levels of parasitism differed significantly among butterflies and were influenced by the local butterfly species assemblage. Our results also suggest that parasitism in resident butterflies is elevated at sites where Ar. levana has been established for a longer period. In our study system, variations in butterfly species assemblages were associated in a predictable way with substantial variations in rates of parasitism. This relationship is likely to affect the dynamics of the butterfly host species, and potentially cascade to the larger number of species with which they interact. These results highlight the importance of indirect interactions and their potential to reorganise ecological communities, especially in the context of shifts in species distributions in a warmer world.