To determine the effects of ingestion by birds on seed germination, we performed germination experiments in the field and laboratory with Sorbus commixta. The germination of four groups of seeds was compared: ingested seeds, seeds defecated in feces after feeding of fruits to birds; extracted seeds, seeds deliberately extracted from the fruit pulp; juiced seeds, seeds plus the juice of the pulp after seeds had been deliberately extracted from the pulp; intact seeds, seeds in untreated intact fruits. In the laboratory, intact and juiced seeds hardly germinated, but ingested and extracted seeds germinated. Thus, the pulp and its juice appeared to inhibit germination, but seeds could germinate without ingestion by birds once the seeds had been manually extracted from the pulp. In the field, intact fruits did not germinate in the first spring, because the seed was still covered with pulp. The pulp of intact seeds decomposed during the first summer, and thus, the seeds had the potential to germinate during the second spring. In fact, most intact seeds do not germinate during the second spring either, since they lose their viability during the first summer. Thus, under natural conditions, most seeds of Sorbus commixta cannot germinate without bird ingestion.
Decadal changes in masting behaviour—directional changes in seed production with fluctuations on a decadal time‐scale—are attracting widespread attention in the context of global climate change. However, our mechanistic understanding of the effects of climate on seed production on a decadal scale is unsatisfactory, partly because of the insufficient statistical analyses of long‐term data on masting. We detected decadal changes in masting behaviour in the Japanese oak Quercus crispula based on long‐term data (38 years: 1980–2017) from the Kitakami Mountains of Japan. The moving average of seed production in a 20‐year sliding window increased, whereas the coefficient of variation decreased. A wavelet power spectrum, as well as a second‐order log‐linear autoregressive (AR) model showed that masting intervals shortened from 3‐ or 4‐year cycle to a 2‐year cycle. The moving average of seed production increased linearly as the moving average of temperature increased. Temporal variations of the two AR model coefficients as a function of temperature were well described by concave curves. Synthesis. By conducting the statistical analyses of a long‐term seed production dataset, we obtained significant evidence of decadal changes in the masting behaviour of the Japanese oak and showed that the shortening of the masting interval was associated with rising temperature. A resource allocation shift and an environmental veto were discussed as possible mechanisms underlying the decadal change.
We used classification tree analysis to develop a climate-based distribution model for Fagus crenata forests in Japan. Four climatic variables judged likely to affect the distribution of the species (summer and winter precipitation, minimum temperature of the coldest month and Kira's warmth index) were chosen as independent variables for the model. Latitudinal and longitudinal information was also used to examine effects of spatial autocorrelation on the model. The climatic factors associated with the distribution of the forests were analysed using a classification tree to devise prediction rules. Predicted areas of high probability for forest occurrence lay mainly on the Sea of Japan side of northern Honshu and southern Hokkaido. This is consistent with actual forest distribution. Some areas with high predicted probabilities of F. crenata forest occurrence were beyond the current natural northern range limits of these forests. Since these areas were widely scattered, it was assumed that the species has been hindered from colonizing them due to dispersal limitations. Deviance-weighted scores, used to compare magnitudes of the contributions of predictor variables, revealed winter precipitation as the most influential factor, followed by the warmth index, the minimum temperature of the coldest month and summer precipitation. Attempts were made to generate ecological explanations for the effects of the four climatic factors on the distribution of F. crenata forests. Abbreviations: CA = Classification accuracy; DWS = Deviance weighted score; JMA = Japan Meteorological Agency; MER = Misclassification error rate; TMC = Minimum temperature of the coldest month; NSNE = National Survey on the Natural Environment; OE = Omission error; PRS = Summer precipitation; PRW = Winter precipitation; RMD = Residual Mean Deviance; WI = Warmth index.
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.
Abstract. We used classification tree analysis to develop a climate‐based distribution model for Fagus crenata forests in Japan. Four climatic variables judged likely to affect the distribution of the species (summer and winter precipitation, minimum temperature of the coldest month and Kira's warmth index) were chosen as independent variables for the model. Latitudinal and longitudinal information was also used to examine effects of spatial autocorrelation on the model. The climatic factors associated with the distribution of the forests were analysed using a classification tree to devise prediction rules. Predicted areas of high probability for forest occurrence lay mainly on the Sea of Japan side of northern Honshu and southern Hokkaido. This is consistent with actual forest distribution. Some areas with high predicted probabilities of F. crenata forest occurrence were beyond the current natural northern range limits of these forests. Since these areas were widely scattered, it was assumed that the species has been hindered from colonizing them due to dispersal limitations. Deviance‐weighted scores, used to compare magnitudes of the contributions of predictor variables, revealed winter precipitation as the most influential factor, followed by the warmth index, the minimum temperature of the coldest month and summer precipitation. Attempts were made to generate ecological explanations for the effects of the four climatic factors on the distribution of F. crenata forests.
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