Mixed-species herding levels the landscape of fear

Prey antipredator behaviours are influenced by perceived predation risk in
a landscape and social information gleaned from herd mates regarding
predation risk. It is well documented that high-quality social information
about risk can come from heterospecific herd mates. Here, we integrate
social information with the landscape of fear to quantify how these
landscapes are modified by mixed-species herding. To do this, we
investigated zebra vigilance in single- and mixed-species herds across
different levels of predation risk (lion vs. no lion), and assessed how
they manage herd size and the competition-information trade-off associated
with grouping behaviour. Overall, zebra performed higher vigilance in
high-risk areas. However, mixed-species herding reduced vigilance levels.
We estimate that zebra in single-species herds would have to feed for an
additional ~35 minutes per day in low-risk areas and ~51 minutes in
high-risk areas to compensate for the cost of higher vigilance.
Furthermore, zebra benefitted from the competition-information trade-off
by increasing the number of heterospecifics while keeping the number of
zebra in a herd constant. Ultimately, we show that mixed-species herding
reduces the effects of predation risk, whereby zebra in mixed-species
herds, under high-predation risk, perform similar levels of vigilance
compared to zebra in low-risk scenarios.

猎物的反捕食行为受景观中感知到的捕食风险，以及从同伴处获取的关于捕食风险的社会信息共同影响。已有充分研究表明，关于风险的高质量社会信息可来自异种群同伴（heterospecific herd mates）。本研究将社会信息与恐惧景观（Landscape of Fear）相结合，量化混合种群放牧如何改变此类景观。为此，我们研究了斑马在单种群与混合种群中，于不同捕食风险水平（有狮子vs无狮子）下的警觉性，并评估了它们如何管理种群规模，以及与集群行为相关的竞争-信息权衡（competition-information trade-off）。总体而言，斑马在高风险区域表现出更高的警觉性；但混合种群放牧降低了警觉性水平。我们估计，单种群中的斑马需在低风险区域每天额外觅食约35分钟，在高风险区域额外觅食约51分钟，以补偿更高警觉性带来的成本。此外，斑马通过增加异种个体数量同时保持种群中同种个体数量不变，从而从竞争-信息权衡中获益。最终，我们发现混合种群放牧可降低捕食风险的影响——高捕食风险下，混合种群中的斑马警觉性水平与低风险场景下的斑马相似。