Our impact on the planet is unprecedented and utterly detrimental to biodiversity conservation. We are destroying, fragmenting and polluting natural landscapes, overharvesting wildlife populations beyond points of no return, and causing a rapid and catastrophic climate change.
While these represent the main threats to biodiversity conservation, our impact on the planet takes on many more forms. For instance, we are also unintentionally affecting the way wildlife populations look.
Hunting and poaching activities are usually targeted to animals with specific traits, which means that those animals will suffer from greater human-related mortality than other individuals in their population lacking such traits. Over time, this means that certain traits in wild populations could be lost by means of intensive artificial selection.
First, by altering the morphology and behaviour of individuals we may be changing their ecological function and even affecting the resilience of entire populations to environmental change, since we would be selecting for lower levels of intra-specific diversity. Second, by causing often irreversible changes to the way wildlife looks, we may also be inflicting a cultural and spiritual loss to all those human societies (e.g., indigenous communities) who may associate specific values with local species and wildlife.
Let’s take the example of African elephants which used to be regularly hunted for their tasks, and still are being regularly poached for the same reason. During the last century, strong selection pressure against the survival of tusked individuals resulted in more and more elephants being born tuskless.
A practical example of this is documented in one of the largest national parks in South Africa, Addo Elephant National Park, which counts over 300 female elephants and most of them (90-95%) lack tusks completely1. A similar situation is observed in Mozambique’s Gorongosa National Park2. Tusklessness would otherwise naturally occur only in about 2 to 4 percent of females in African elephant populations.
A tuskless elephant cow using her trunk to swat flies at the park.CreditFinbarr O’Reilly for The New York Times
Bighorn sheep hunting on Ram Mountain near Nordegg, Alberta is another example. A 2016 study published in Evolutionary Applications found that the average size of a set of horns at Ram Mountain declined by more than 20 percent during the course of 43 years because of severe hunting pressure, as the individuals bearing the largest horns are the most targeted ones by hunters3.
Big horn sheep. Image credits: https://bit.ly/2WPUcfI
Artificial selection on wildlife is increasingly documented across taxa, including on fish4, birds5 and mammals1,2,3. A rather controversial question is whether we should aim to conserve unnatural traits in wild populations in case these reveal to provide evolutionary advantages to a population.
For instance, while we are used to see black wolves in tv, documentaries and photos, especially in North America, wolves have likely derived such dark coat coloration unnaturally through interbreeding with domestic dogs6. This trait has likely brought evolutionary advantages to the wolves, such as greater camouflage ability, as this trait has become so widespread across North American wolf populations.
Less surprisingly, such artificial selection on wildlife also appears to be present on species that dwell in cities. For instance, some urban birds (e.g., blue tits in Britain5) are evolving slender beaks to better reach and feed off the seeds inside bird feeders which people put in their gardens. However, since cities are artificial environments, such trait changes are likely to be beneficial to the survival of urban wildlife. Contrastingly, in natural landscapes unnatural trait changes may have deleterious consequences for species.
While it is difficult to tell exactly how artificial selection in wildlife populations is likely to affect the conservation of wild populations in the long-term, a precautionary approach may guide us towards considering this issue as a threat, especially in natural landscapes.
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- Pigeon, G., Festa‐Bianchet, M., Coltman, D.W. and Pelletier, F., 2016. Intense selective hunting leads to artificial evolution in horn size. Evolutionary Applications, 9(4), pp.521-530.
- Jennings, S., Reynolds, J.D. and Mills, S.C., 1998. Life history correlates of responses to fisheries exploitation. Proceedings of the Royal Society of London. Series B: Biological Sciences, 265(1393), pp.333-339.
- Bosse, M., Spurgin, L.G., Laine, V.N., Cole, E.F., Firth, J.A., Gienapp, P., Gosler, A.G., McMahon, K., Poissant, J., Verhagen, I. and Groenen, M.A., 2017. Recent natural selection causes adaptive evolution of an avian polygenic trait. Science, 358(6361), pp.365-368.
- Anderson, T.M., Candille, S.I., Musiani, M., Greco, C., Stahler, D.R., Smith, D.W., Padhukasahasram, B., Randi, E., Leonard, J.A., Bustamante, C.D. and Ostrander, E.A., 2009. Molecular and evolutionary history of melanism in North American gray wolves. Science, 323(5919), pp.1339-1343.
featured image credits: https://bit.ly/2NPuFPI