Abstract
Global climate change has sparked a vast research effort into the demographic and evolutionary consequences of mismatches between consumer and resource phenology. Many studies have used the difference in peak dates to quantify phenological synchrony (match in dates, MD), but this approach has been suggested to be inconclusive, since it does not incorporate the temporal overlap between the phenological distributions (match in overlap, MO).We used 24 years of detailed data on the phenology of a predator–prey system, the great tit (Parus major) and the main food for its nestlings, caterpillars, to estimate MD and MO at the population and brood levels. We compared the performance of both metrics on two key demographic parameters: offspring recruitment probability and selection on the timing of reproduction.Although MD and MO correlated quadratically as expected, MD was a better predictor for both offspring recruitment and selection on timing than MO. We argue—and verify through simulations—that this is because quantifying MO has to be based on nontrivial, difficult‐to‐verify assumptions that likely render MO too inaccurate as a proxy for food availability in practice.Our results have important implications for the allocation of research efforts in long‐term population studies in highly seasonal environments.
Highlights
Organisms in seasonal environments, where the phenology of resource abundance varies from year to year, need to adjust their timing of reproduction to match this variation to ensure successful reproduction (Kokko, 1999; Lepage, Gauthier, & Reed, 1998; Plard et al, 2014; Réale, Berteaux, McAdam, & Boutin, 2003; Reid et al, 2018; Siikamäki, 1998; Smith & Moore, 2005; Verboven &Visser, 1998)
This synchrony between consumer and resource phenology can be described as the difference between the dates when the phenological distributions of the consumer and the resource peak
Our empirical results show that the phenological synchrony of food availability and food requirements in our population can be better estimated as the difference in days between the mean phenology (MD) than as the relative degree of overlap of these two distributions (MO), even though match in peak dates (MD) and MO correlated with one another in a predictable fashion, both at the population level (Figure S2) and the brood level
Summary
Organisms in seasonal environments, where the phenology of resource abundance varies from year to year, need to adjust their timing of reproduction to match this variation to ensure successful reproduction We tested which of the two quantifications of phenological synchrony—the match of peak dates and the phenological overlap—correlated better with selection and offspring recruitment in a wild population of great tits Great tits in this population depend strongly (albeit not exclusively) on caterpillars (mainly Operopthera brumata and Tortrix viridana) to raise their offspring (Van Balen, 1973), which are available to them over a span of a few weeks during the breeding season. Egglaying date in this population is under increased directional selection due to climate warming, which has been linked to the decreased temporal synchrony with caterpillar abundance (Reed et al, 2013; Visser et al, 2006). We discuss important limitations of constructing food availability and food requirement distributions as well as the appropriateness of using either measure of phenological synchrony to describe ecological interactions between trophic levels
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