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.

研究背景：捕食行为在自然界中广泛存在。其中一类为同类相食（cannibalism），其受多种因素影响，例如种群体型结构与资源密度。然而，同类相食还可能受非生物因子调控，如季节性时间限制。由于高纬度地区的季节性时间限制更为严苛，高纬度区域的同类相食行为可能更强，但目前学界对同类相食的纬度变异几乎一无所知。本研究针对欧洲境内沿纬度梯度分布的狭翅豆娘（Lestes sponsa）幼虫的同类相食与活动水平展开探究，通过从卵期开始饲养对应不同纬度温度与光周期（photoperiods）条件下的幼虫完成实验。
研究结果：我们发现，高纬度地区受季节性时间限制更为严苛的种群，以及承受更强季节性时间限制的个体，其同类相食发生率更高。同时我们还发现，高纬度条件下幼虫的活动水平更高，且该活动水平与同类相食行为呈正相关，这表明该行为是受时间限制的动物同类相食程度升高的介导机制。
研究结论：本研究结果与经典纬度-捕食格局相悖，该格局预测低纬度地区的捕食压力普遍更高，而我们发现高纬度地区的同类相食行为更为强烈。同类相食行为的纬度差异可能对纬度梯度上的种群动态产生潜在影响，但仍需开展进一步实验以验证该推论。