“Batesian” behaviour of non-venomous snakes as a threatening signal against potential predators Interestingly enough, mimicry behaviour has been observed between species since 1862 by Bates who discovered that a harmless species imitates a defensive signal of a dangerous species and thus can protect itself against its predators. According to research, colouration and body patterns are the most important factors contributing to the protection of prey animals, but behaviour, body shape and odour play a role as well in reducing their predation. (Janne K. Valkonen, Ossi Nokelainen, Johanna Mappes, 2011) The importance of head triangulation in non-venomous snakes as a mimicry behaviour from European vipers has recently started to be investigated and researched in depth. But does this kind of behavioural mimicry really help the non-toxic snakes to defend themselves against predators and therefore prevent their extinction? Viperine (Natrix mauna), grass (Natrix natrix) and smooth snakes (Coronella austriaca) belonging to the family Colubridae are some of the most common species exhibiting the behavioural mimicry of head triangulation. Particularly, these species when they feel threatened tend to flatten their body especially in the head and neck region resulting in a larger, triangular shaped head characteristic to the European vipers. (Janne K. Valkonen, Ossi Nokelainen, Johanna Mappes, 2011) At the same time, as a second type of warning signal, viperine and grass snakes such as Natrix natrix cypriaca excrete a garlic-like, strongsmelling liquid from their anal glands which may (Wikipedia) repel their predators. Needless to say, both types of Batesian behaviours may play an important role in the maintenance of fauna and life chain in countries of origin of these species but also contribute to the management of rapidly growing populations of rodents, amphibians, insects which serve as feed for these snake species. Last but not least some of these species being endemic to their countries contribute to the culture and image of the countries to the outside world attracting the attention of tourists and scientists interested in them. 1 Eirini Stylianou Wildlife Ecology & Management 2014 On one hand, the special phenotypic characteristics of European vipers are the dorsal zig-zag pattern and triangular head. On the other hand, the non-venomous grass and smooth snakes exhibit a narrower, more rounded head and pattern- less dorsal aspect while the also non-venomous viperine snakes beside the narrower head show the dorsal zigzag pattern of vipers. (Janne K. Valkonen, Ossi Nokelainen, Johanna Mappes, 2011) In order to prove the adaptive importance of heat triangulation as a warning signal, a set of trials was carried out by the researchers with four kinds of artificial, plasticine made snakes: (a) viper-type head snakes with zig-zag dorsal pattern (b) without dorsal pattern (c) narrow- head snakes with dorsal zig-zag pattern and (d) without dorsal pattern. (Janne K. Valkonen, Ossi Nokelainen, Johanna Mappes, 2011) Potential predators of which attacks were recorded are small mammalian species like foxes and cats, raptors, owls, corvids and storks. 2 Eirini Stylianou Wildlife Ecology & Management 2014 According to the above figure, there isn’t an important difference in the number of attacks between the viper head zigzag snakes and the colubrid head zigzag snakes suggesting that zigzag pattern alone can sufficiently act as a defensive signal against the predators and at the same time triangular head doesn’t increase the efficacy of zigzag pattern. The efficacy of zigzag pattern can also be proved from the fact that even though colubrid head zigzag snakes do not exhibit triangular head,they weren’t attacked more than those with triangular head. Secondly, the number of attacks in colubrid head patternless snakes is significantly higher than that in viper head patternless snakes saying it is true that head triangulation can really be used by nonvenomous snakes for their survival against predators. Lastly, in patternless snakes a higher number of attacks were recorded in comparison to the zigzag patterned snakes. The above mentioned observations were recorded in the group of raptors as predators suggesting that raptors tend to avoid attacking triangular viper head snakes, bearing in mind that these snakes might be poisonous. However, this tendency is significantly different in case of mammalian predators and the reason lies in the fact that mammals use their olfaction rather than their vision during hunting. As a result, head triangulation, with few exceptions, is not recognized by mammals as a threatening signal of their prey. In conclusion, head triangulation, secretion of strong-smelling liquids and other behavioural mimicries can be considered beside warning signals, also a way of protection of prey animals against their potential predators and as a consequence, this can prevent the extinction of such species that play important role in the maintenance of wildlife and biodiversity. As far as I am concerned predators of such species cannot only be considered different animal species but also human, one of the most dangerous species that God created. In fact, in my country Cyprus, the habitat of Natrix natrix cypriaca, humans have managed to destroy the natural environment of this subspecies by constructing huge buildings around lakes, polluting the water of the lakes with rubbishes and industrial wastes and by hunting around the area. (Hans-Jorg Wiedl, 2010) So what would happen if humans misunderstood a non-venomous snake as a venomous one? They would simply avoid doing such terrible things to natural habitats being afraid of their lives, resulting in the maintenance of populations of such creatures and consequently of the entire ecosystem. References: The essay is based on the following research paper: • Valkonen JK, Nokelainen O, Mappes J (2011) Antipredatory Function of Head Shape for Vipers and Their Mimics. PLoS ONE 6(7): e22272. doi:10.1371/journal.pone.0022272 3 Eirini Stylianou Wildlife Ecology & Management 2014 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3144867/pdf/pone.0022272.pdf Background information was obtained from the following sources: 1. David W. Pfennig, Sean P. Mullen, Allopatric mimics. Review by Proc. R. Soc. B (2010) 277, 2577–2585, doi:10.1098/rspb.2010.0586: Mimics without models: causes andconsequences of allopatry in Batesian mimicry complexes • http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2982051/pdf/rspb20100586.pdf 2. WIKIPEDIA, The free encyclopedia • http://en.wikipedia.org/wiki/Grass_snake 3. Rochfordessex • http://rochfordessex.net/cyprusreptiles/wpcontent/uploads/2010/12/Endangerment-of-the-Cyprus-Grass-Snake.pdf Pictures were taken by the following sources: 1) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2982051/pdf/rspb20100586.pdf 2) http://www.fieldherpforum.com/forum/viewtopic.php?f=2&t=9418 3) http://www.iucnredlist.org/details/14368/1 4 Eirini Stylianou Wildlife Ecology & Management 2014
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