Summary1. The source of seed or plant material can have profound implications for the success of restoration efforts because most species exhibit adaptive genetic variation within their range. Understanding the geographical distribution of ecologically relevant genetic variation and the environmental factors driving adaptive divergence within species will help to ensure appropriate sourcing of material for ecological restoration. 2. We present a study of geographical variation of ecologically important traits of the forest tree jarrah Eucalyptus marginata from a 15-year-old provenance trial in southwestern Australia. We assessed trait variation in association with rainfall, latitude and slope position at the site of origin. 3. Survival and stem diameter varied at the largest scale, between northern and southern jarrah forest provenances. Stem diameter also varied among rainfall zones, while latitude was a more important determinant of variation of reproductive traits (flowers and buds). None of the environmental variables accounted for significant variation of height, growth form or the presence of capsules. Slope position at the site of origin did not account for significant variation of any trait. 4. Trees from low rainfall sites had smaller stem diameters, possibly reflecting selection for slower growth. Such a strategy could prevent drought stress and may explain why trees from the high rainfall southern jarrah forest, which showed the fastest growth, had the poorest survival at the drier northern trial site. 5. Variation in the presence of buds and flowers among latitudinal divisions may be because of variation in flowering time, which has been observed previously among E. marginata populations. However, variation among replicate blocks within the trial suggests that the environment also strongly influences expression of these traits. 6. Synthesis and applications . We have demonstrated divergence of several ecologically important traits in association with different types of environmental variation. Our findings support an argument for 'habitat matching' when sourcing material for restoration; however, differences among trait types in the distribution of variation highlight the need to consider environmental variation at a range of geographical scales. Consideration of ecologically important genetic variation within species is important and this information should be integrated into seed collection strategies for ecological restoration.

Predicting how species will respond to the rapid climatic changes predicted this century is an urgent task. Species distribution models (SDMs) use the current relationship between environmental variation and species' abundances to predict the effect of future environmental change on their distributions. However, two common assumptions of SDMs are likely to be violated in many cases: (i) that the relationship of environment with abundance or fitness is constant throughout a species' range and will remain so in future and (ii) that abiotic factors (e.g. temperature, humidity) determine species' distributions. We test these assumptions by relating field abundance of the rainforest fruit fly Drosophila birchii to ecological change across gradients that include its low and high altitudinal limits. We then test how such ecological variation affects the fitness of 35 D. birchii families transplanted in 591 cages to sites along two altitudinal gradients, to determine whether genetic variation in fitness responses could facilitate future adaptation to environmental change. Overall, field abundance was highest at cooler, high-altitude sites, and declined towards warmer, low-altitude sites. By contrast, cage fitness (productivity) increased towards warmer, lower-altitude sites, suggesting that biotic interactions (absent from cages) drive ecological limits at warmer margins. In addition, the relationship between environmental variation and abundance varied significantly among gradients, indicating divergence in ecological niche across the species' range. However, there was no evidence for local adaptation within gradients, despite greater productivity of high-altitude than low-altitude populations when families were reared under laboratory conditions. Families also responded similarly to transplantation along gradients, providing no evidence for fitness trade-offs that would favour local adaptation. These findings highlight the importance of (i) measuring genetic variation in key traits under ecologically relevant conditions, and (ii) considering the effect of biotic interactions when predicting species' responses to environmental change.

The analysis of interaction networks across spatial environmental gradients is a powerful approach to investigate the responses of communities to global change. Using a combination of DNA metabarcoding and traditional molecular methods we built bipartite Drosophila – parasitoid food webs from six Australian rainforest sites across gradients spanning 850 m in elevation and 5°C in mean temperature. Our cost‐effective hierarchical approach to network reconstruction separated the determination of host frequencies from the detection and quantification of interactions. The food webs comprised 5–9 host and 5–11 parasitoid species at each site, and showed a lower incidence of parasitism at high elevation. Despite considerable turnover in the relative abundance of host Drosophila species, and contrary to some previous results, we did not detect significant changes to fundamental metrics of network structure including nestedness and specialisation with elevation. Advances in community ecology depend on data from a combination of methodological approaches. It is therefore especially valuable to develop model study systems for sets of closely‐interacting species that are diverse enough to be representative, yet still amenable to field and laboratory experiments.

The analysis of interaction networks across spatial environmental gradients is a powerful approach to investigate the responses of communities to global change. Using a combination of DNA metabarcoding and traditional molecular methods we built bipartite Drosophila-parasitoid food webs from six Australian rainforest sites across gradients spanning 850 m in elevation and 5° Celsius in mean temperature. Our cost-effective hierarchical approach to network reconstruction separated the determination of host frequencies from the detection and quantification of interactions. The food webs comprised 5-9 host and 5-11 parasitoid species at each site, and showed a lower incidence of parasitism at high elevation. Despite considerable turnover in the relative abundance of host Drosophila species, and contrary to some previous results, fundamental metrics of network structure including nestedness and specialisation did not change significantly with elevation. Advances in community ecology depend on data from a combination of methodological approaches. It is therefore especially valuable to develop model study systems for sets of closely-interacting species that are diverse enough to be representative, yet still amenable to field and laboratory experiments.