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The role of local adaptation and factors other than climate in determining extinction probabilities of species under climate change has not been yet explicitly studied. Here we performed a field experiment with annual plants growing along a steep climatic gradient in Israel to isolate climatic effects for local trait expression. The focus trait was seed dormancy, for which many theoretical predictions exist regarding climate-driven optimal germination behaviour. We evaluated how germination is consistent with theory, indicating local adaptation to current and changing climatic conditions, and how it varies among species and between natural and standardised soil conditions. We reciprocally sowed seeds from three or four origins for each of three annual species, Biscutella didyma, Bromus fasciculatus and Hymenocarpos circinnatus, in their home and neighbouring sowing locations along an aridity gradient. Our predictions were: lower germination fraction for seeds from more arid origins, and higher germination at wetter sowing locations for all seed origins. By sowing seeds in both local and standard soil, we separated climatic effects from local conditions. At the arid sowing location, two species supported the prediction of low germination of drier seed origins, but differences between seed origins at the other sites were not substantial. There were no clear rainfall effects on germination. Germination fractions were consistently lower on local soil than on standard soil, indicating the important role of soil type and neighbour conditions for trait expression. Local environmental conditions may override effects of climate and so should be carefully addressed in future studies testing for the potential of species to adapt or plastically respond to climate change.

Dormant seeds in permanent soil seed banks change their germination probability with age, but little is known about the causes of this behavior. Since current adaptive models do not consider the age structure of the seed bank, the sole explanation is that changes in germination probability with age are due to passive accidental factors or to decay of seeds. Here we present a theory, which shows that such changes might be adaptive. In particular, in density-regulated populations, the evolutionarily stable fraction of germinating seeds in each age class increases with age whenever age-dependent mortality of dormant seeds remains constant or increases with age.

Heavy metal hyperaccumulation (MH) is a rare trait found in plant species that inhabit metal‐contaminated soils. Two main hypotheses proposed to explain the selective advantage of MH are the elemental defence hypothesis and elemental allelopathy hypothesis. The elemental defence hypothesis suggests that MH functions as defence against herbivores while the elemental allelopathy hypothesis suggests that MH acts to inhibit the growth of neighbours. Nevertheless, these hypotheses are not likely to be mutually exclusive. Here, we present the first study to test both hypotheses simultaneously. We examined these hypotheses with the Cd hyperaccumulator, Arabidopsis halleri, which inhabits both metalliferous and non‐metalliferous soils, thus providing an opportunity to test the hypotheses of both habitats.Arabidopsis halleri plants originating from several populations in both metalliferous and non‐metalliferous soils were grown in a greenhouse in soils with or without cadmium (Cd). Their leaves were used in a feeding experiment with a specialist herbivore and in a set of leaf‐leachate experiments that tested their effect on seed germination and seedling establishment of species co‐occurring with A. halleri. Finally, a field survey in several A. halleri populations was conducted to compare herbivore load between A. halleri and neighbours from metalliferous versus non‐metalliferous soils.Results of the feeding experiment and field survey suggest that Cd accumulation in A. halleri leaves could provide it with defence against herbivores. Results of the leaf‐leachate experiments reveal that Cd accumulation has no effect on seed germination of neighbouring species but inhibits seedling establishment, particularly of plant species originating from non‐metalliferous soils.Our results suggest that both herbivores and competing neighbours may jointly select for MH in plants. Moreover, MH could provide a selective advantage particularly in non‐metalliferous soils, where neighbouring plants lack metal tolerance. These results highlight the importance of including different origins and populations of both the target species and its neighbouring plant species when studying the ecological role of MH. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

A key hypothesis that has been proposed to explain plants' invasive success suggests that some invasive species produce allelochemicals that are novel against naïve neighbours at the introduced range and therefore provide an advantage there (novel weapons hypothesis - NWH). However, a seldom-studied hypothesis suggests that invasive populations could not only possess novel weapons, but might also evolve their enhanced production. Moreover, so far no study has examined both the novelty and evolution of allelopathic effects. Here, we examined these two hypotheses in a set of experiments with the highly invasive plant Impatiens glandulifera. In the first experiment, we examined the evolution of allelopathic ability by comparing the inhibitory effects of leaf extracts from native versus invasive I. glandulifera on the germination success of its dominant neighbour Urtica dioica. In the following experiments, we examined the NWH by comparing the germination success of U. dioica seeds collected at the native versus invasive range of I. glandulifera, in response to either leaf extracts or soil trained with invasive I. glandulifera. The results of the first experiment indicate that invasive I. glandulifera exert a stronger inhibitory effect on the germination of U. dioica compared to their native counterparts, providing support for the hypothesis that allelopathic ability can evolve at the invasive range. However, the results of the two following experiments reveal no difference in the response of U. dioica from the native versus invasive range of I. glandulifera, to the allelopathic effects of either the leaf extracts or the trained soil. These results therefore do not provide support for the NWH, and suggest that increased allelopathy in invasive I. glandulifera might have been selected for by other processes. The results of this study call for biogeographical experiments that will examine not only the novelty but also the evolution of allelopathic effects in invasive plants. [ABSTRACT FROM AUTHOR]

Seed dormancy is thought to be a key mechanism allowing annual plants to spread extinction risk in unpredictably varying environments. Theory predicts increasing germination fractions with increasing probability of reproductive success but solid empirical evidence is scarce and often confounded with environmental factors. Here we provide an empirical test of bet-hedging via delayed germination for three annual plant species along a 'predictability gradient' in Israel. We excluded confounding environmental and maternal effects by raising inbred seed families and germinating them under controlled conditions. Additionally, we germinated field-collected seeds in three consecutive seasons to compare their germination with inbred families where maternal effects were removed. Risk of reproductive failure was quantified using demographic data from the field and from second-generation inbred lines raised in a rainfall gradient in the greenhouse. Our findings were consistent with bet-hedging theory in that germination fraction was negatively related to species- and site-specific risk of reproductive failure. Both field and hand-raised seeds of one species exhibited higher dormancy with increasing risk of reproductive failure across sites, and hand-raised seeds of another species showed the same pattern. The third species exhibited a rather random pattern of germination between years and sites, corresponding to the lack of site-specific risk of reproductive failure. Species-specific patterns of dormancy and risk could be related to alternative risk-spreading strategies such as high adult survival, but were also affected by phylogeny. We provide strong empirical evidence for seed dormancy being a mechanism to reduce the risk of reproductive failure in highly variable environments, but a larger number of rigorous experimental tests of bet hedging germination are needed. Specifically, the genetic basis of bet-hedging must be shown in species with different life histories, for demonstrating that dormancy is adaptive and how it is modified by other risk-spreading traits. [ABSTRACT FROM AUTHOR]

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