Kaczmarek Jan M, Kaczmarski Mikołaj, Mazurkiewicz Jan, Kloskowski Janusz
Department of Zoology Poznań University of Life Sciences Poznań Poland.
Department of Inland Fisheries and Aquaculture Poznań University of Life Sciences Poznań Poland.
Ecol Evol. 2020 Nov 24;10(24):13705-13716. doi: 10.1002/ece3.6956. eCollection 2020 Dec.
Many chemically defended aposematic species are characterized by relatively low toxin levels, which enables predators to include them in their diets under certain circumstances. Knowledge of the conditions governing the survival of such prey animals-especially in the context of the co-occurrence of similar but undefended prey, which may result in mimicry-like interactions-is crucial for understanding the initial evolution of aposematism. In a one-month outdoor experiment using fish (the common carp ) as predators, we examined the survival of moderately defended aposematic tadpole prey (the European common toad ) with varying absolute densities in single-species prey systems or varying relative densities in two-species prey systems containing morphologically similar but undefended prey (the European common frog ). The density effects were investigated in conjunction with the hunger levels of the predator, which were manipulated by means of the addition of alternative (nontadpole) food. The survival of the tadpoles was promoted by increasing their absolute density in the single-species prey systems, increasing their relative density in the two-species prey systems, and providing ample alternative food for the predator. Hungry predators eliminated all individuals regardless of their proportion in the prey community; in treatments with ample alternative food, high relative density supported survival. The results demonstrated that moderately defended prey did benefit from high population densities (both absolute and relative), even under long-term predation pressure. However, the physiological state of the predator was a crucial factor in the survival of moderately defended prey. While the availability of alternative prey in general should promote the spread and maintenance of aposematism, the results indicated that the resemblance between the co-occurring defended and undefended prey may impose mortality costs on the defended model species, even in the absence of actual mimicry.
许多具有化学防御能力的警戒色物种的毒素水平相对较低，这使得捕食者在某些情况下能够将它们纳入食谱。了解此类猎物动物生存的条件——尤其是在相似但无防御能力的猎物同时出现的情况下，这可能导致类似拟态的相互作用——对于理解警戒色的初始进化至关重要。在一项为期一个月的户外实验中，我们以鱼类（鲤鱼）作为捕食者，研究了在单物种猎物系统中具有中等防御能力的警戒色蝌蚪猎物（欧洲普通蟾蜍）在不同绝对密度下的生存情况，以及在包含形态相似但无防御能力的猎物（欧洲普通青蛙）的双物种猎物系统中不同相对密度下的生存情况。我们结合捕食者的饥饿程度来研究密度效应，通过添加替代（非蝌蚪）食物来控制饥饿程度。在单物种猎物系统中增加蝌蚪的绝对密度、在双物种猎物系统中增加蝌蚪的相对密度以及为捕食者提供充足的替代食物，都能提高蝌蚪的存活率。饥饿的捕食者会消灭所有个体，无论它们在猎物群落中的比例如何；在有充足替代食物的处理中，高相对密度有助于生存。结果表明，即使在长期捕食压力下，具有中等防御能力的猎物确实从高种群密度（绝对密度和相对密度）中受益。然而，捕食者的生理状态是具有中等防御能力的猎物生存的关键因素。虽然一般来说替代猎物的可获得性应该会促进警戒色的传播和维持，但结果表明，即使在没有实际拟态的情况下，同时出现的有防御能力和无防御能力的猎物之间的相似性可能会给有防御能力的模式物种带来死亡成本。
