More than a century and a half after he formulated his hypotheses, Charles Darwin is still supported by the empirical data gathered by scientists, although sometimes with some nuance.
This time it was the turn of a prediction made by the British naturalist in 1859 : that the expansion of species across a territory is more limited by climatic factors in hostile environments (for example, very cold or very dry places), while what weighs the most in mild environments are interactions with other species, that is, competition or pollination, in the case of plants.
Precisely, the new research, carried out by experts from the University of Boulder in Colorado, has put the focus on the plant kingdom. The experts studied the population dynamics – physiological changes, age distribution, etc. – of the flowering species Hibiscus meyeri at three locations in central Kenya, where varying degrees of aridity reigned, over a total period of four years. Their results have been published in the journal Proceedings of the National Academy of Sciences (PNAS).
The general conclusion is that, broadly speaking, Darwin was right : the effects of inter-species relationship and competition increase in conjunction with decreasing climatic and environmental pressure.
As expected, pollination, higher or lower consumption by herbivorous animals and competition with rival herbaceous and shrubs played an important role in the more humid areas. And in the driest places, the biological success of Hibiscus meyeri was not so dependent on those factors .
Effects of stress
And what is the – small – hit then? This is how Allison Louthan, the expert who has directed the work and who is now investigating at Duke University, in North Carolina, explains: “Both Darwin and other evolutionists argued that what drives this model are the gradients –variations– in the density and diversity of the interacting species, but in reality it appears to be an effect of stress on the growth, survival, reproduction and germination of plant species .
This research provides a guide to where and when relationships between species are important and under what circumstances they are not so relevant. Understanding the forces that allow or not expand populations of living beings is crucial to understand the ecological and evolutionary dynamics ”.
The researchers’ next step is to apply their experimental method to other ecosystems and geographic areas. Dan Doak, a professor at the University of Colorado at Boulder and a co-author of the study, reiterates the value of his findings.
” Now, with climate change, figuring out why there are limitations to the proliferation of species is even more urgent than before . Our work shows the various forces that shape the environments where plants or animals live and that sometimes the triggering mechanisms for these effects are not what we biologists had assumed. “
