DOI: 10.5061/dryad.j9kd51cgt
title: Data for: Elevational changes in insect herbivory on woody plants in six mountain ranges of temperate Eurasia: Sources of variation

description: Current theory predicts that the intensity of biotic interactions, and
 particularly herbivory, decreases with increasing latitude and elevation.
 However, recent studies have revealed substantial variation in both the
 latitudinal and elevational patterns of herbivory. This variation is often
 attributed to differences in study design and type of data collected by
 different researchers. Here, we used a standardised sampling protocol
 along elevational gradients in six mountain ranges, located at different
 latitudes within temperate Eurasia, to uncover the sources of variation in
 elevational patterns in insect herbivory on woody plant leaves. We
 discovered the considerable variation in elevational patterns among
 different mountain ranges; nevertheless, herbivory generally decreased
 with increasing elevation at both the community-wide and individual plant
 species levels. This decrease was mostly due to openly living defoliators,
 whereas no significant association was detected between herbivory and
 elevation among insects living within plant tissues (i.e. miners and
 gallers). The elevational decrease in herbivory was significant for
 deciduous plants but not for evergreen plants, and for low-stature plants
 but not for tall plants. The community-wide herbivory increased with
 increases in both specific leaf area and leaf size. The strength of the
 negative correlation between herbivory and elevation increased from lower
 to higher latitudes. We conclude that elevational gradients in herbivory
 demonstrate considerable variation, and that this variation is mostly
 associated with herbivore feeding habit, some plant traits and latitude of
 the mountain range.
description: <em>Sampling
 protocol</em> The
 sampling was conducted in the second half of the growth season, when the
 majority of insect herbivores had completed their feeding, but well before
 the start of leaf fall at any of the study sites. At each site,
 we collected a total of 15‒25
 branches (greater numbers corresponded to more diverse plant communities)
 from common woody plant species. We selected
 branches for sampling while standing at a distance of 5‒10
 m away (at this distance, the level of herbivory on the selected branch
 could not be assessed visually) to avoid unconscious selection bias. We
 disregarded a few branches that were grazed by
 vertebrate herbivores, which usually remove the entire shoots or greater
 parts of adjacent leaves; this ‘coarse’ damage is easily distinguished
 from a ‘fine’ and relatively minor damage imposed on individual leaves by
 invertebrate herbivores. All samples
 were collected and processed by the same persons (MVK and VZ) who had no a
 priori knowledge of the herbivory levels in the visited regions and/or on
 the collected plant species. In the Alps
 and in Cairngorms, we first selected up to five woody plant species that
 dominated the community (i.e. that comprised the greater part of foliar
 biomass), and we then haphazardly collected one branch (or
 group of branches) from each of five mature individuals of each selected
 species (on a first-found, first-sampled
 basis). In the other mountain ranges, we
 did not select the species to be collected. Instead, we collected
 one branch from
 each of 15‒25 individuals of woody plants irrespectively of their identity
 using the following procedure. Each of two collectors walked along a
 straight line, making stops at approximately 10 m intervals and collecting
 a branch from a species which had the greatest foliar biomass (as
 estimated visually) within a 2 × 10 m plot behind the collector.
 This change was introduced to better
 reflect herbivory in species-rich plant communities and to avoid possible
 subjectivity in the selection of plant species to be collected. All other
 details of the protocol were the same across all regions, and
 we assumed that under both these
 protocols the numbers of sampled individuals of each species were roughly
 proportional to the contributions of these species to the community-wide
 foliar biomass. Importantly, the sampling protocol was always
 identical within each gradient, and thus a minor difference outlined above
 is unlikely to influence the results of meta-analysis based on
 correlations between herbivory and elevation within individual
 gradients. <em>Measurements of
 herbivory</em> In the laboratory, each leaf was carefully
 examined for the presence of damage imposed by chewing, galling and mining
 invertebrates. In conifers, we classified current-year needles that were
 missing from the shoot as having been consumed by insects, because
 undamaged needles of
 evergreen conifers generally persist for several
 years.
 We assigned
 each leaf/needle (leaf hereafter) to one of the damage classes according
 to the percentage of the leaf area that was consumed or otherwise damaged
 by insects, as follows: 0 (intact leaves), 0.01–1%, 1–5%, 5–25%, 25–50%,
 50–75% and 75–100%. The last class included the petioles of fully consumed
 leaves and missing needles. We calculated the proportion of foliage area
 lost to insects (i.e. the leaf herbivory level) by multiplying the numbers
 of leaves in each damage class by the respective median values of the
 damaged leaf area (i.e. 0 for intact leaves, 0.5% for the damage class
 0.01–1%, etc.); the obtained values were then summed for all damage
 classes and divided by the total number of leaves (including undamaged
 ones) in a sample. <em>Measurements of leaf
 traits</em> We measured leaf traits from each branch
 collected from Altai, Avachinskij, Caucasus and Troodos, but only from one
 of several conspecific branches collected from the same site in the Alps
 and in Cairngorms. Soon after branch collection, when the plant leaves
 were still turgid, we sampled 1‒125 undamaged leaves (depending on leaf
 size; the median value was 8 leaves) and weighed them to the nearest 1 mg.
 We then punched out 5‒12
 discs (4.5, 8 or 12 mm in diameter, depending on leaf size) from those
 leaves, dried the discs and the remaining parts of leaves for 24 h at
 105ºC and then weighed them to the nearest 0.1 mg. When the leaves were too small to
 allow punching of leaf discs, we press-dried the leaves and measured their
 total area from their photographs using Adobe Photoshop 2020. This
 measured area was then divided by 0.902 to correct for leaf shrinkage
 during drying. This correction factor was obtained by averaging the ratio
 between dry and fresh areas of 60 leaf discs collected from leaves of 20
 plant species from our study regions. We did not measure SLA in
 needle-bearing plants. The dry weight of an individual leaf was calculated
 by dividing the weight of the punched leaves plus discs by the number of
 leaves. The water content in leaf tissues was calculated by dividing the
 difference between the wet and dry weight of a leaf by its wet weight. The
 SLA was calculated as the total area of the discs or leaves
 (mm<sup style="text-indent:1cm;">2</sup>) divided by their dry weight (mg).
 Leaf area (mm<sup style="text-indent:1cm;">2</sup>) was calculated by multiplying dry
 leaf weight (mg) by SLA (mm<sup style="text-indent:1cm;">2</sup> mg<sup style="text-indent:1cm;">-1</sup>).
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