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 we are causing the climate to change, which poses a major threat to biodiversity conservation worldwide.
While these represent the main threats to biodiversity conservation, our influence on the planet results in way more issues than the depletion of wildlife populations and biodiversity loss. For instance, we are also affecting the way wildlife populations look – their phenotype in scientific jargon – as well as their behaviour and life histories, which include aspects such as reproductive development, lifespan and adult size.
Hunting and poaching activities are usually targeted to animals with specific traits, which means that those animals will suffer from a greater human-related mortality risk than other individuals in their population that lack such traits. Over time, this may mean that certain phenotypes in wild populations will be lost by means of non-natural, or artificial, selection pressures.
This may be a conservation issue for two reasons: (i) by altering the morphology and behaviour of individuals we may be shifting 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; (ii) from a moral perspective, we would also be losing the “original” way wildlife populations looked.
Let’s take the example of African elephants which used to be regularly hunted for their tasks, and still are regularly poached for the same reason to date. Since elephants with tusks were – and still are – the ones targeted by poachers, over the last century there has been a strong anthropogenic selection pressure against tusked individuals – which continues to date.
In other words, hunting/poaching pressure is giving a biological advantage to elephants that don’t grow tusks, which means that more and more elephants are 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. Normally, tusklessness would 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
Another example is portrayed by the consequences of selective hunting on bighorn sheep on Ram Mountain near Nordegg, Alberta. A 2016 study published in Evolutionary Applications has found that the average size of a set of horns at Ram Mountain has declined more than 20 percent over 43 years due to pressures from hunting, as individuals with the largest horns are the most targeted ones3.
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, since it is now widespread in North American wolf populations.
Similarly, some bird populations in anthropogenic landscapes (e.g., blue tits in Britain5) may be evolving slender beaks to better reach and feed off the seeds inside bird feeders, which people have in their gardens.
While it may be difficult to tell exactly how artificial selection in wildlife populations may affect species conservation in the long-term, a conservative approach, and a moral case for preserving natural traits in wild populations, may guide us towards considering this issue a threat.
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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