Abstract
A classic system for studying trophic mismatch focuses on the timing of the spring caterpillar peak in relation to the breeding time and productivity of woodland passerine birds. Most work has been conducted in single-site oak woodlands, and little is known about how insights generalize to other woodland types or across space. Here we present the results of a 3-year study on the species composition and temporal distribution of the spring caterpillar peak on different tree taxa across 40 woodland sites spanning 2° of latitude in Scotland. We used molecular barcoding to identify 62 caterpillar species, with winter moth (Operophtera brumata) being the most abundant, comprising one-third of the sample. Oak (Quercus sp.) and willow (Salix sp.) hosted significantly higher caterpillar abundances than other tree taxa, with winter moth exhibiting similar trends and invariantly proportionate across tree taxa. Caterpillar peak phenology was broadly similar between tree taxa. While latitude had little effect, increasing elevation increased the height of the caterpillar peak and retarded timing by 3.7 days per 100 m. These findings extend our understanding of how mismatch may play out spatially, with caterpillar peak date varying with elevation and tree taxa varying in the caterpillar resource that they host.
Highlights
Trophic mismatches—where asynchrony between a consumer and an ephemeral resource negatively impacts the consumer’s fitness—have received much research attention (Durant et al 2007; Forrest and Miller-Rushing 2010)
This study identifies a diverse arboreal spring caterpillar peak dominated by a small number of species, in accordance with previous studies (Hunter 1992; Butler and Strazanac 2000; Wesolowski and Rowinski 2006), with winter moth accounting for one-third of all caterpillars identified and the three commonest species accounted for more than half of all caterpillars collected
Host tree taxon has a large effect on the availability of caterpillars in spring, including generalist winter moths, with oak and willow being the only two tree taxa significantly more likely to have a caterpillar sampled from them than the average tree taxon
Summary
Trophic mismatches—where asynchrony between a consumer and an ephemeral resource negatively impacts the consumer’s fitness—have received much research attention (Durant et al 2007; Forrest and Miller-Rushing 2010). Temperate deciduous woodlands comprise many different tree species across wide latitudinal and elevational gradients, and the passerine birds studied as part of this food chain typically forage and nest in a variety of woodland types (Perrins 1979; Blair and Hagemeijer 1997) To understand whether this induces spatial variation in phenological mismatch, we first need to gain insight into how the temporal distribution of caterpillars varies spatially and on tree species. A degree of buffering might arise if some caterpillar species (fig. 1C; dietary buffering hypothesis) or habitats provide a resource that is available for a longer duration
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