Data from: Size-mediated priority and temperature effects on intra-cohort competition and cannibalism in a damselfly

1. A shift in the relative arrival of offspring, e.g., a shift in hatching
time, can affect competition at the intraspecific level through
size-mediated priority effects, where the larger individuals gain more
resources. These priority effects are likely to be affected by climate
warming and the rate of intraspecific predation, i.e., cannibalism. 2. In
a laboratory experiment, we examined size-mediated priority effects in
larvae of the univoltine damselfly, Lestes sponsa, at two different
temperatures (21°C and 23°C). We created three size groups of larvae by
manipulating hatching time: early hatched with a large size
(extra-advanced), intermediate hatched with an intermediate size
(advanced) and late hatched with a small size (non-advanced). Thereafter
we reared the larvae from these groups in non-mixed and mixed groups of 12
larvae. 3. We found strong priority and temperature effects. First,
extra-advanced larvae most often had higher survival, growth and
development rates than non-advanced larvae in mixed groups, compared to
groups that consisted of only extra-advanced larvae. Second, temperature
increased growth and development rates and cannibalism. 4. However, the
strength of priority effects did not differ between the two experimental
temperatures, because there was no statistical interaction between
temperature and treatments. That is, the mixed and non-mixed groups of
non-advanced, advanced and extra-advanced larvae showed the same relative
change in life history traits across the two temperatures. 5. Non-advanced
and advanced larvae had similar or higher growth rate and mass in mixed
groups compared to non-mixed groups, suggesting that predation from
advanced larvae in the mixed group released resources for the non-advanced
and advanced larvae that survived despite cannibalism risk. Thus, a
thinning effect occurred due to cannibalism caused by priority effects. 6.
The results suggest that a shift in the relative arrival of offspring can
cause temperature-dependent priority effects, mediated through
cannibalism, growth and development, which may change the size
distribution and abundance of emerging aquatic insects.

1. 后代相对出现时间的改变（例如孵化时间的偏移）可通过体型介导的优先效应（size-mediated priority effects）影响种内竞争——体型较大的个体在此效应下会获得更多资源。这些优先效应可能受到气候变暖及种内捕食率（即同类相食）的影响。
2. 在实验室实验中，我们于两种温度条件下（21°C和23°C），研究了单世代豆娘（Lestes sponsa）幼虫的体型介导的优先效应。通过调控孵化时间，我们将幼虫分为三个体型组：早孵化的大型个体组（extra-advanced）、中孵化的中型个体组（advanced）及晚孵化的小型个体组（non-advanced）。随后，我们将这些组的幼虫以12只为一组，分别饲养在非混合组与混合组中。
3. 我们发现了显著的优先效应与温度效应。首先，在混合组中，extra-advanced幼虫的存活率、生长速率及发育速率通常高于non-advanced幼虫——这一差异相较于仅含extra-advanced幼虫的组别更为明显。其次，温度升高会提升生长发育速率及同类相食行为的发生率。
4. 然而，优先效应的强度在两种实验温度间并无差异，这是由于温度与处理组间不存在统计学交互作用。具体而言，non-advanced、advanced及extra-advanced幼虫的非混合组与混合组，其生活史性状在两种温度下表现出相同的相对变化趋势。
5. 相较于非混合组，混合组中的non-advanced与advanced幼虫具有相似或更高的生长速率及体重，这表明混合组中advanced幼虫的捕食行为释放了资源，供那些在同类相食风险下存活的non-advanced与advanced幼虫利用。因此，优先效应引发的同类相食行为产生了种群稀疏效应（thinning effect）。
6. 研究结果表明，后代相对出现时间的改变可通过同类相食、生长及发育过程介导，引发温度依赖性的优先效应——这可能改变羽化水生昆虫的体型分布及种群丰度。