Predation risk estimated on live and artificial insect prey follows different patterns

Models mimicking prey organisms are increasingly used in ecological
studies including testing fundamental ecological and evolutionary
theories. The general consensus is that predation risk estimated on
artificial models may not quantitatively correspond to predation pressure
on live prey, but it still can be used in various comparisons. We tested
whether the use of live and artificial prey reveals the same patterns of
variation in predation risk. We exposed live prey (blowfly larvae and
puparia) and plasticine models of blowfly puparia in two boreal forest
sites, both openly and in ant- and bird-exclusion treatments, and we
quantified attacks by both avian and invertebrate predators. Bird attack
rates were always higher on live puparia than on their plasticine models,
but the magnitude of this difference declined from 8.4-fold in early
summer to 2-fold in mid- and late summer. We attribute these changes to
different responses to prey by experienced adult birds that dominate the
bird communities in early summer versus explorative juvenile birds that
are abundant later in the season. Invertebrate daily predation rates on
maggots decreased from 56% in early summer to 28% in late summer, but
invertebrate attacks on plasticine models showed no seasonal changes.
Overall, invertebrate predation on maggots was 67-fold greater than their
predation on models. Observations showed that wood ants did not attack
plasticine models and did not leave on them any damage marks. Estimates
based on artificial prey indicate a much greater role of bird predation
than invertebrate predation, while estimates based on live prey suggest
the opposite pattern. Thus, using live and artificial prey may lead to
different conclusions about relative importance of different predator
groups in a locality. Moreover, for both avian and invertebrate predators,
predation risk based on artificial and live prey shows different seasonal
changes and may potentially demonstrate different spatial patterns.

模拟猎物的生物模型在生态学研究中的应用愈发广泛，此类研究包括对基础生态学与进化理论的验证。学界普遍认为，基于人工模型估算的捕食风险，或许无法与活体猎物所承受的捕食压力形成定量对应关系，但仍可用于各类比较研究。本研究旨在验证：采用活体与人工猎物是否能够揭示一致的捕食风险变异模式。我们在两处寒温带针叶林（boreal forest）样地中开展了野外暴露实验，受试对象包括活体猎物（丽蝇（blowfly）幼虫及蛹（puparia））以及丽蝇蛹的橡皮泥（plasticine）模型；实验设置了开放式暴露以及蚂蚁与鸟类排除处理组（ant- and bird-exclusion treatments）两种类型，并对鸟类捕食者（avian predators）与无脊椎动物捕食者（invertebrate predators）的攻击事件进行了量化统计。研究结果显示，鸟类对活体蛹的攻击率始终高于其橡皮泥模型，但二者的差异幅度从初夏的8.4倍降至仲夏与晚夏的2倍。我们将该差异的季节动态归因于鸟类群落组成的差异：初夏群落以经验丰富的成鸟为优势类群，其对猎物的响应模式与晚夏数量占优的探索性幼鸟显著不同。无脊椎动物对丽蝇幼虫（蛆）的日捕食率从初夏的56%下降至晚夏的28%，但无脊椎动物对橡皮泥模型的攻击率并未表现出季节性变化。总体而言，无脊椎动物对活体丽蝇幼虫的捕食强度是其对橡皮泥模型的67倍。观察结果表明，林蚁（wood ant）并不会攻击橡皮泥模型，也未在其表面留下任何损伤痕迹。基于人工猎物的评估结果显示，鸟类捕食的作用远大于无脊椎动物捕食；而基于活体猎物的评估则呈现出相反的格局。由此可见，采用活体与人工猎物，可能会对某一区域内不同捕食类群的相对重要性得出截然不同的结论。此外，无论是鸟类还是无脊椎动物捕食者，基于人工猎物与活体猎物估算的捕食风险，不仅表现出不同的季节动态特征，还可能呈现出相异的空间分布模式。