An experiment carried out by researchers from the Complutense University of Madrid (UCM) and the Pablo de Olavide University (UPO) in Seville (Spain) shows that performance-based habitat selection can also drive the adaptation process.

“Our study reveals that performance-based habitat selection allows organisms to actively choose the environment in which their traits, such as beak size, fit best. That is, they choose the environment where they perform best,” explains Gabriel Munar Delgado, a UCM researcher at the time of the study and currently at the Centro de Investigação em Biodiversidade e Recursos Genéticos in Portugal.

“When animals choose their habitat based on their characteristics, they are able, to a certain extent, to avoid natural selection. For populations to adapt, it is not always necessary that only the fittest individuals survive and reproduce. If individuals simply choose their optimal habitat, populations can also adapt,” Munar-Delgado emphasizes.

The work, recently published in the journal Current Biology, was carried out in the “Encinar de San Pedro de la Casa de Campo” ornithological reserve in Madrid during the years 2021 and 2022. There, UCM researchers have been monitoring the population of tree sparrows for a decade by checking the nest boxes installed in the area.

To carry out the experiment, the researchers equipped the sparrows with a small plastic ring on one of their legs containing a microchip, similar to that used to chip pets, with a unique identification code for each one.

In autumn of 2021, the researchers installed smart electronic feeders in two different areas within the study area. These feeders, which normally remained closed, opened automatically upon detecting certain microchips. They were programmed in such a way that in one of the areas only half of the selected sparrows could access the seeds, while in the other area access was restricted to the other half of the sparrows. In addition, nest boxes were also placed in these two areas and equipped with microchip readers to record where the sparrows were breeding.

Next, the sparrows explored the areas and discovered where they could obtain seeds from the feeders, using them until their breeding season in spring-summer 2022. During this time, the researchers reviewed the data from the nest box readers and observed in which area the sparrows had bred.

“The results were very clear: the vast majority of the sparrows chose to breed in the area where they had access to seeds. In this way, they managed to have 30% more chicks. This demonstrates their ability to assess to which habitat they were best adapted and move towards those areas to reproduce,” Munar-Delgado highlights.

This observation confirms that performance-dependent habitat selection influences the distribution of these birds. In addition, it was found that almost all the sparrows paired up and reproduced with other sparrows that also had access to seeds in the same area.

“When individuals with similar characteristics choose to live in the same places to which they are adapted, as a consequence they stop pairing with those with different characteristics. These movements and pairings then cause these groups of individuals and their descendants to adapt to different environments. This is the same outcome as for natural selection – only here it is not the environment that selects the organisms, it is the organisms that select the environment,” says Pim Edelaar, professor at the UPO and principal investigator of the project.

The results of this study are expected to have a great impact on how the process of biological adaptation is understood and studied in the scientific world. Likewise, the results of this study could have a long-term influence on environmental policies, ecosystem management, pest control and biodiversity conservation. “Understanding how animals at an individual level can, or even need to, choose their habitat based on their own traits will make it easier to understand the adaptation process and create more effective conservation strategies,” the researchers conclude.

Bibliographic reference:

Munar-Delgado et al., “Performance-based habitat choice can drive rapid adaptive divergence and reproductive isolation”, Current Biology (2024), https://doi.org/10.1016/j.cub.2024.10.006.