Can fear control ecosystems?






By Camilla Bertolini @CamiBe90

“We are more often frightened than hurt; and we suffer more from imagination than from reality” – Seneca

Now, imagine you are in the middle of a forest and you hear wolves howling in the distance, the noise getting closer and closer – your heart is probably pounding, pumping adrenaline into your blood, making you think clear about all the possible scenarios and way outs. The noise is now moving away again, after all the wolves were perhaps after some deer, but you are probably still scared and decide to get out of there as soon as possible.

Similar patterns occur in other realms of nature, governed by predator-prey interactions. And it is a known fact that these interactions can change ecosystems, and even have positive effects 1. Where consumptive effects (those where a predator actually eats its prey) exist, likely non-consumptive effects (those driven by the fear of being eaten) will be present too.Non-consumptive effects exist in both terrestrial and aquatic systems and include, but are not limited to: behavioural shifts, morphological modifications, changes in growth rates and changes in reproductive output.

In recent years many ecologists have begun to debate whether these can be more important in structuring populations than the classic consumptive effects 2. In a recent study, in which I collaborated as part of an internship, we found that non-consumptive effects of dogwhelks on barnacles had carry-over effects over multiple life stages, affecting the growth of barnacle from recruits to adults and in turn decreased their reproductive output, with potential negative effects for the barnacle population and with consequences for traits evolution3.

Non-consumptive effects can also themselves have indirect effects on other levels of the ecosystems. Studies of both terrestrial systems 4 and aquatic5 show non-consumptive cascading effects over multiple trophic levels. More research should focus on understanding how fear fits in the puzzle of ecosystem organization, but for now I think we are safe saying that fear is indeed an important component of interactions within an ecosystem. Think about that next time you hear a wolf howling in the distance, or maybe, let fear take control and run away.




1- very informative video on wolves role in the ecosystem

2- Peacor SD, Peckarsky BL, Trussell GC, Vonesh JR (2013) Costs of predator-induced phenotypic plasticity: a graphical model for predicting the contribution of non-consumptive and consumptive effects of predators on prey. Oecologia 171:1–10

3- Ellrich JA, Scrosati RA, Bertolini C, Molis M, in press, A predator has non-consumptive effects on different life-history stages of a prey. Marine Biology

4- Bestion E, Cucherousset J, Teyssier A, Cote J (2015) Non-consumptive effects of a top-predator decrease the strength of the trophic cascade in a four-level terrestrial food web. Oikos

5-      Grabowski JH, Huges AR, Kimbro DL (2008) Habitat complexity influences cascading effects of multiple predators Ecology 89:3413–3422


1 comment on Can fear control ecosystems?

  1. Oh yes!
    In other classic experiments, a few drops of “eau de trout” have small freshwater crustacea fleeing for cover rather than foraging: their productivity reduced in the longer run. Charles Krebbs et al. speculated that ‘stress’ reduced reproduction rates, contributing to the textbook case of snowshoe hare -lynx dynamics. Many marine organisms (quite sensibly) swim down to darker waters at dawn, presumably fearing the sighted predators and this influences many important ecological processes of the ocean.
    But how do we take account of fear over and above direct predation effects in population models? It is more complicated than merely adding a ‘fear multiplier factor’ because this fear does work to reduce individual mortality rates.
    Here we see potential conflict between the individual’s best interests and that of the population. If the prey’s fear response over-estimates predation risk then the multiplier should be greater than one, if not, it should be less than one. If there is a group of you being pursued by wolves, would it be better to spread out, or stick together? Hamilton’s selfish herd theory (allow me to plug: Beecham and Farnsworth (1999)) may provide a rational answer, and there is the old joke about putting on your running shoes: “you can’t outrun a wolf”, “no, but I can outrun you!”. Personally I would not be able to resist the temptation to haawwooool! back. But that’s just me.

    Nice post, by the way.

    JA Beecham, KD Farnsworth. Animal group forces resulting from predator avoidance and competition minimization. Journal of theoretical biology 198 (4), 533-548

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