Missing the potential of evolutionary ecology
Monocultures, biodiversity and r-strategists
In modern, conventional agriculture the general principles is to mostly focus on the performance of an organism (crop) to produce a certain amount of yield. Human intervention makes sure the nutrient and energy input is given (fertilization, irrigation) and intervenes to supress unwanted interactions (parasitism, other plants). The population is often a one-clone population, whose density of growth is predetermined by plantation and nutrition. In this way, the system is relatively simple and so, predictable and controlable. On the other hand, since it relies on one organism, it is also more vulnerable and needs intervention in case of challenges (lack of water, pests, …).
However, the conception of agriculture as the reproduction of an organism in monoculture does not mean ecology is not playing a role. Indeed, it exists in a landscape and biosphere and can represent one source of food for a species that can then become invasive. This excellent food supply and the lack of predators favors type of predators /parasites of the type of r-strategists, spreading very fast due to their lack of density limitation. Annual plants in a monoculture represent the typical environment for those fast spreading species: temporary environments. They are a great food source for species which do not have a long life span and have many offsprings, thriving even in an only seasonal prosperity like mice or parasites or aphids (see definition box below 1). But those annuals offer on the other hand too unstable conditions to allow the establishement of longer-living predators (k-strategists) as prey birds for example. Indeed, permanently present predators are in need of life supporting conditions year round. The same is true for other species that are thriving on the long term, as some pollinators. Their thriving is compromised by annual monocultures or their equivalent: a short flowering season of a perennial monoculture2.
The lack of crop rotation is enhancing this risk because of the survival of these naturally oscillating r-strategists populations in the soil or in volontary plants until the next season. Moreover, a single solution for the problem (pesticides, or single adapted species) puts a huge and unidirectional selection pressure on the very same potentially invasive species on the longer term and promotes in this way adaptation mechanisms .
Permanent diversity pool is a way to escape this race against these strategists, by establishing the conditions for natural dynamics used to our own advantage instead of fighting unwanted consequences or side-effects. By ensuring a year-round shelter and food source to several species, it helps the establishment of population dynamics more favorable to k-strategists and therefore creates an environment more stable against sudden bursts of k-strategists. Furthermore, the more diverse the environement gets, the more intrinsic dynamics are present3 that can be used.
Dynamics are more resilient that statics – a case for genetic variety
Schematic representation of relative occurrence of different crops or different varieties of the same crop over time and changing conditions. After 4
Natural selection in one place is favoring one variety or one crop – or more, over the others but does not discard the others, less favored. Therefore, their characteristics are kept and take over when conditions are changing. The same principle could be extended to different species; some years might be more favorable to some crops than others, but it is still worth keeping all of them for their mutual support effect, even though it can mean changing the proportions and the dominant species.
Looking further, looking higher
Figure adapted after http://nsmn1.uh.edu/nholland/research.html. This represents the different levels of biological organization and the corresponding interactions with their predictability and complexity. It also shows that the higher levels exist only as a ensemble of many of the lower level and therefore large scale changes at one level brings consequences at a higher sphere.
The establishment of monocultures on large surfaces influences the population dynamics and the communities on those surfaces. Furthermore, the more widespread this model gets, the more influence it has on higher levels of biological organization, up to ecosystems, landscape and finally the biosphere. Can we, in the same way, find a local practice that would reconstruct ecosystems, so their effect, if widespread enough, would influence and balance even the climate?
… to be followed up…
1. Rafferty JP. K-related speies, R-related species. Encyclopædia Britannica. 2011.
2. Partap U and Ya T. The Human Pollinators of Fruit Crops in Maoxian County, Sichuan, China. Mountain Research and Development. 2012;32:176-186.
3. Allan E, Weisser W, Weigelt A, Roscher C, Fischer M and Hillebrand H. More diverse plant communities have higher functioning over time due to turnover in complementary dominant species. Proceedings of the National Academy of Sciences. 2017.
4. Ceccarelli S. Seeds of the future. Colloquium CERN 2015.