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).

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Climate changes have profound effects on the distribution of numerous plant and animal species 1-3 . However, whether and how different taxonomic groups are able to track climate changes at large spatial scales is still unclear. Here, we measure and compare the climatic debt accumulated by bird and butterfly communities at a European scale over two decades (1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008). We quantified the yearly change in community composition in response to climate change for 9,490 bird and 2,130 butterfly communities distributed across Europe 4 . We show that changes in community composition are rapid but different between birds and butterflies and equivalent to a 37 and 114 km northward shift in bird and butterfly communities, respectively. We further found that, during the same period, the northward shift in temperature in Europe was even faster, so that the climatic debts of birds and butterflies correspond to a 212 and 135 km lag behind climate. Our results indicate both that birds and butterflies do not keep up with temperature increase and the accumulation of different climatic debts for these groups at national and continental scales.Species are not equally at risk when facing climate change. Several species-specific attributes have been identified as increasing species' vulnerability to climate change, including diets, migratory strategy, main habitat types and ecological specialization [5][6][7] . Moreover, although phenotypic plasticity may enable some species to respond rapidly and effectively to climate change 8,9 , others may suffer from the induced spatial mismatch and temporal mistiming with their resources 10,11 . For instance, species such as great tits and flycatchers have been shown to become desynchronized with their main food supply during the nesting season 12 .However, beyond individual species' fates, climate change should also affect species interactions and the structure of species assemblages within and across different taxonomic groups over large spatial scales [13][14][15] . For instance, ectotherms should be more directly affected by climate warming and taxonomic groups with short generation time should favour faster evolutionary responses to selective pressures induced by climate changes 13 . Yet, whether different taxonomic groups are tracking climate change at the same rate over large areas is still unclear, and methods to routinely assess the mismatch between temperature increases and biodiversity responses at different spatial scales are still missing 16 .Here, we used extensive monitoring data of birds and butterflies distributed across Europe to assess whether, regardless of their species-specific characteristics, organisms belonging to a given group are responding more quickly or more slowly than organisms belonging to another group over large areas. We characterized bird and butterfly communities in 9,490 and 2,130 sample sites respectively by their community temperature index (CTI) for ea...

Intensification or abandonment of agricultural land use has led to a severe decline of semi-natural habitats across Europe. This can cause immediate loss of species but also time-delayed extinctions, known as the extinction debt. In a pan-European study of 147 fragmented grassland remnants, we found differences in the extinction debt of species from different trophic levels. Present-day species richness of long-lived vascular plant specialists was better explained by past than current landscape patterns, indicating an extinction debt. In contrast, short-lived butterfly specialists showed no evidence for an extinction debt at a time scale of c. 40 years. Our results indicate that management strategies maintaining the status quo of fragmented habitats are insufficient, as time-delayed extinctions and associated co-extinctions will lead to further biodiversity loss in the future.

Biological responses to climate change have been widely documented across taxa and regions, but it remains unclear whether species are maintaining a good match between phenotype and environment, i.e. whether observed trait changes are adaptive. Here we reviewed 10,090 abstracts and extracted data from 71 studies reported in 58 relevant publications, to assess quantitatively whether phenotypic trait changes associated with climate change are adaptive in animals. A meta-analysis focussing on birds, the taxon best represented in our dataset, suggests that global warming has not systematically affected morphological traits, but has advanced phenological traits. We demonstrate that these advances are adaptive for some species, but imperfect as evidenced by the observed consistent selection for earlier timing. Application of a theoretical model indicates that the evolutionary load imposed by incomplete adaptive responses to ongoing climate change may already be threatening the persistence of species.