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Data from: Vertebrate herbivory weakens directional selection for earlier emergence in competition

Waterton, Joseph1; Cleland, Elsa1

Published Jun 22, 2026 on Dryad. https://doi.org/10.5061/dryad.hf70r6p

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Jun 22, 2026 version files 46.57 KB

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Abstract

The timing of seedling emergence is strongly linked with fitness because it determines the biotic and abiotic environment experienced by plants following dispersal. Hence, emergence timing is expected to be under strong selection to shift in concert with climate change. Experiments and observations consistently find that earlier emerging plants have a competitive advantage over those emerging later. However, emergence timing varies substantially within and among plant populations, making it important to understand the selective forces maintaining this variation. In seasonal herbaceous communities, mammalian herbivores may maintain variation in emergence timing by weakening directional selection for earlier emergence in competitive environments. To investigate this, we carried out phenotypic selection analyses on emergence timing in two California grass species, the native Stipa pulchra and non-native Bromus diandrus, growing in close competition with and without mammalian herbivore exclusion. Mammalian herbivores consistently weakened directional selection for earlier emergence independently of reductions in mean fitness. Our results demonstrate that mammalian herbivores play an underappreciated role in shaping emergence timing in plant populations, with implications for the potential of species to adapt to current and future global changes.