·         In 1859, Charles Darwin published the book “On the Origin of Species”, where he states that invading species with a high degree of evolutionary closeness to the invaded community (phylogenetic relationship), would be less likely to become established, because “struggle for survival” would be more intense between related species. However, experiments conducted by Dr Sergio Castro, researcher at the Faculty of Chemistry and Biology and CEDENNA, have shown something different.

“Many people have accepted Darwin’s hypotheses as incontrovertible facts due to his recognized status in science. However, many of these hypotheses lie on mechanisms that have not been evaluated. This is a common situation in science development: usually the observations made are tested afterwards,” Dr Sergio A. Castro, researcher at the Laboratory of Ecology and Biodiversity of Universidad de Santiago, says.

In order to test Darwin’s hypothesis, Dr Castro and his research team developed a Fondecyt project. In this context, their paper “Evaluating Darwin’s Naturalization Hypothesis in Experimental Plant Assemblages: Phylogenetic Relationships Do Not Determine Colonization Success” was published by the renowned journal PLOS ONE, currently the largest scientific journal in the world, with a high impact factor (Q1) for its citations.

“Different species can be introduced in an area and several of them can finally establish themselves as populations, as if they were native species, without depending on human action. These are considered naturalized species. In our experiment, we observed a colonizing plant in different vegetal communities. These communities had different degrees of phylogenetic relatedness with the invading species. If Darwin was right, a trend towards the establishment of the invading species would have been recorded, depending on the evolutionary relatedness. However, after three years, we evaluated the results and they did not support Darwin’s hypothesis,” Dr Castro says.

The experiment was conducted in Batuco (a place close to Santiago) and 15 species were selected. One of them, the native lettuce Lactuca, was used as a colonizing or invading species, while the other 14, like chamomile, broad bean, arugula, among others, were used as experimental assemblage communities. With these plants, five treatments were organized according to their different phylogenetic relatedness with respect to Lactuca. They showed that colonization did not depend on phylogenetic relatedness. 

“En nuestro estudio todas las plantas pudieron convivir, independiente de sus parentescos. Por esto, los resultados manifiestan que la hipótesis de Darwin no tiene un respaldo tan sólido o por lo menos no es tan general como él lo planteaba”, indica Castro.

“In our study, all plants were able to coexist, regardless of their relatedness. Therefore, the results show that Darwin’s hypothesis does not have a strong base or, at least, the hypothesis is not as generalized as he stated,” Dr Castro says.

The researcher has also evaluated Darwin’s naturalization hypothesis by analyzing the composition of Chilean flora and introduced exotic plants. This work not only disproved the hypothesis, but it yielded opposite results.

“We found that species from other environments can be introduced in Chile’s central zone and find relatives that survive well in this climate. These relatives can provide pollinators and seed dispersers, making naturalization more likely to happen, contrary to what is expected in Darwin’s hypothesis,” he says.

Having an impact on global change

In the past few decades, people have become more interested in knowing how the different human activities affect the environment. The focal point has been climate change, passing over other factors, like introducing foreign species, flora or fauna, in other places. These factors are considered as part of global change.

“Chile is a biogeographic island. It is surrounded by a mountain chain, a desert and an ocean; therefore its flora has evolved isolated for more than 180 years. However, in the past centuries some species have been introduced that are risky to native species,” he explains.

Chile’s central zone biogeography is so particular that it is considered one of the 35 biodiversity hotspots of the world. These places are characterized by a high level of species endemism, but at the same time, their preservation is in danger as a result of human impact.

“An introduced species can produce the extinction of a native one, damaging our biodiversity. Nowadays, our variety of exotic plants is wide if compared with the variety of our native flora. But, what can we do to prevent this situation? There is little we can do in a globalization context, but we can generate diagnosis to prevent some species from entering and becoming naturalized,” Dr Castro says.

Translated by Marcela Contreras