Food selection by foragers is sensitive to the availability of resources, which may vary along geographical gradients. Hence, selectivity of food types by foragers is expected to track these resource gradients. Here we addressed this hypothesis and asked if foraging decisions of seed‐eating ants differ along a geographic gradient of habitat productivity. The study was carried out for two years at five sites along a natural climatic gradient, ranging from arid to Mediterranean, where plant productivity varies six‐fold across a short geographic distance of 250 km. We found that in ant colonies of the genus Messor, collective foraging decisions differed along the gradient. Specifically, at the high‐productivity sites, a stronger association was found between plant seed availability and selectivity, suggesting that colonies respond more accurately to within‐patch variation in food amounts. In contrast, colonies in low‐productivity sites foraged in patches with higher concentration of seeds, suggesting that they respond more accurately to among‐patch variation in food amounts. Moreover, at the high‐productivity sites, colonies were more discriminating in their choice of food and preferred bigger seeds, while in the low‐productivity sites, where smaller seeds were relatively more abundant, food collection depended mostly on seed availability. An experiment with artificial seed patches performed along the same climatic gradient, revealed no difference in food selectivity across sites when food type and availability were similar, and a general preference for bigger over medium‐sized seeds. Overall, our findings suggest that resource availability is an important factor explaining food choice along a climatic gradient and imply that in low‐productivity regions small‐seeded species incur high predation pressure, whereas in high‐productivity regions, large‐seeded species suffer higher predation. This could have important consequences for plant species composition, particularly at the face of climate change, which could dramatically alter the foraging decisions of granivores.

中文翻译：

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蚂蚁觅食策略随自然资源梯度而变化

觅食者的食物选择对资源的可用性敏感，资源的可用性可能随地理梯度而变化。因此，预计觅食者对食物类型的选择性将追踪这些资源梯度。在这里，我们解决了这一假设，并询问了食草蚂蚁的觅食决策是否沿着栖息地生产力的地理梯度变化。该研究在从干旱到地中海的自然气候梯度的五个地点进行了为期两年的研究，该地区的植物生产力在250 km的短地理距离内变化了六倍。我们发现，在梅塞尔属的蚁群中，集体觅食决策沿梯度不同。具体而言，在高产地，植物种子的可利用性与选择性之间存在更强的联系，这表明菌落对补丁内食物量变化的反应更加准确。相反，低产区的菌落在种子浓度较高的斑块中觅食，这表明它们对斑块间食物量变化的反应更准确。此外，在高产地，殖民地在选择食物和选择较大种子方面更具歧视性，而在低产地，种子较小的相对较多，种子的收集主要取决于种子的可利用性。沿着相同的气候梯度进行人工种子补丁的实验，研究表明，当食物类型和可获得性相似时，不同地点的食物选择性没有差异，并且普遍偏爱较大种子而不是中型种子。总体而言，我们的发现表明，资源的可获得性是解释沿气候梯度的食物选择的重要因素，这意味着在低生产率地区，小种子物种遭受高捕食压力，而在高生产率地区，大种子物种遭受更高的捕食。 。这可能会对植物物种的组成产生重要影响，尤其是面对气候变化时，这可能会大大改变食肉动物的觅食决策。我们的发现表明，资源的可获得性是解释沿气候梯度食物选择的重要因素，并暗示在低生产率地区，小种子物种遭受高捕食压力，而在高生产率地区，大种子物种遭受更高的捕食。这可能会对植物物种的组成产生重要影响，尤其是面对气候变化时，这可能会大大改变食肉动物的觅食决策。我们的发现表明，资源的可获得性是解释沿气候梯度食物选择的重要因素，并暗示在低生产率地区，小种子物种遭受高捕食压力，而在高生产率地区，大种子物种遭受更高的捕食。这可能会对植物物种的组成产生重要影响，尤其是面对气候变化时，这可能会大大改变食肉动物的觅食决策。