Effects of within‐plant variability in seed weight and tannin content on foraging behaviour of seed consumers

Abstract

Summary Individual plants provide a habitat patch for foragers where the sought‐after resources (e.g. leaves, fruits and seeds) are clustered in locally dense aggregations. Characteristics of these resources often vary greatly even within individual plants, which is known as within‐plant or subindividual variation. To best describe properties of the patch (individual plants), the higher moments of trait‐value distributions must be included in addition to the mean values. However, the question whether differences in within‐plant variability of a given trait influence the foraging behaviours of consumers has been mostly untested. To test the hypothesis that differences in within‐plant variation of traits can influence the patch selection behaviour of seed consumers, we used the mean, coefficient of variation (CV) and skewness of within‐plant distributions of two Quercus serrata (Thunb) seed traits (weight and tannin content) as descriptors of plant phenotypes. We then examined the relationships between these descriptors and patch selection by the wood mouse Apodemus speciosus, where individual Quercus trees formed a foraging patch for seed removal. We collected 8594 seeds from 26 individual trees in a forest in northern Japan. We then measured their weight and tannin content, marked and returned them to the locations where they were found, and traced their fates in relation to seed removal by the wood mouse. Tannin content was nondestructively estimated using near‐infrared spectroscopy (NIRS). There was notable within‐plant variation in seed weight and tannin content. Generalized additive modelling revealed that trees with a large mean and CV of seed weight and those with a small CV and skewness of tannin content had a high frequency of seed removal. These results highlight the importance of considering the within‐plant distribution of seed trait values, in addition to the mean trait values of individual seeds, when describing plant phenotypes. The inclusion of these data is essential to understand the ecological and evolutionary processes at work in plant–animal interactions.

Deciphering seed dispersal decisions: Size, not tannin content, drives seed fate and survival in a tropical forest

“…, Shimada et al. ). Seed‐caching rodents in other systems preferentially hoard seeds with 5–25% tannin content, but with a preference for seeds of intermediate tannin content (Wang and Chen , ).…”

“…, Shimada et al. ). More valuable food items, from the perspective of a seed hoarder, are likely to be buried far away from their source location, escaping high threats from natural enemies concentrated near parent plants (Janzen , Connell , Wang and Corlett ).…”

Scatter‐hoarding rodents select different caching habitats for seeds with different traits

“…For example, larger and more nutritious seeds are more likely to be removed and are transported further (Jansen et al 2004, Moore et al 2007, Wang and Chen 2009, Vander Wall 2010. Defensive compounds (e.g., tannins) have also been found to influence seed caching probability and dispersal distance (Xiao et al 2008, Wang and Chen 2009, Vander Wall 2010, Shimada et al 2015.…”

Variation in seed packaging of a fleshy‐fruited conifer provides insights into the ecology and evolution of multi‐seeded fruits

“…, ; Shimada et al . ) and might influence the structure and functioning of ecological networks (González‐Varo & Traveset ). However, whether the variation in seed size within fruits has any adaptive significance is still unclear (Bañuelos & Obeso ; Obeso ).…”