Data from: Cannibalism and activity rate in larval damselflies increase along a latitudinal gradient as a consequence of time constraints

Background: Predation is ubiquitous in nature. One form of predation is cannibalism, which is affected by many factors such as size structure and resource density. However, cannibalism may also be influenced by abiotic factors such as seasonal time constraints. Since time constraints are greater at high latitudes, cannibalism could be stronger at such latitudes, but we know next to nothing about latitudinal variation in cannibalism. In this study, we examined cannibalism and activity in larvae of the damselfly Lestes sponsa along a latitudinal gradient across Europe. We did this by raising larvae from the egg stage at different temperatures and photoperiods corresponding to different latitudes. Results: We found that the more seasonally time-constrained populations in northern latitudes and individuals subjected to greater seasonal time constraints exhibited a higher level of cannibalism. We also found that activity was higher at north latitude conditions, and thus correlated with cannibalism, suggesting that this behaviour mediates higher levels of cannibalism in time-constrained animals. Conclusions: Our results go counter to the classical latitude-predation pattern which predicts higher predation at lower latitudes, since we found that predation was stronger at higher latitudes. The differences in cannibalism might have implications for population dynamics along the latitudinal gradients, but further experiments are needed to explore this.

背景：捕食作用（predation）在自然界中广泛存在。其中一类捕食形式为同类相食（cannibalism），其受体型结构、资源密度等多种因素共同影响。然而，同类相食还可能受到季节性时间约束等非生物因子的调控。由于高纬度地区的时间约束更为严苛，高纬度环境下的同类相食行为可能更为强烈，但目前学界对同类相食的纬度变异几乎一无所知。本研究以欧洲沿纬度梯度分布的豆娘（Lestes sponsa）幼虫为研究对象，探究其同类相食行为与活动能力。我们通过在匹配不同纬度的温度与光周期条件下，从卵期开始饲养幼虫开展了相关实验。
结果：我们发现，高纬度地区受季节性时间约束更强的种群，以及承受更强季节性时间约束的个体，其同类相食水平均更高。同时我们还观测到，高纬度环境下的个体活动能力更强，且活动能力与同类相食水平呈正相关，这表明活动行为可介导时间约束动物的同类相食水平升高。
结论：本研究结果与经典的纬度-捕食模式相悖——该经典模式预测低纬度地区的捕食作用更强，但我们的研究发现高纬度地区的同类相食作用更为强烈。同类相食的纬度差异可能对沿纬度梯度的种群动态产生潜在影响，但仍需开展进一步实验对此展开探究。