For fruit seeds, humans are modern dinosaurs
By physically managing their environment, megafauna as dinosaurs have slowed down the size of fruit seeds – a role that can now be fulfilled by humans
What do humans have in common with the dinosaurs who have trampled through the old forests? It turns out that the two can have a surprising impact on the size of the seeds in the fruits that grow around them. When the researchers have mapped the evolution of the size of the seeds on that of terrestrial animals, they observed that when the land became larger, fruit seeds – with some disproportionate exceptions. A recent study in Paleontology Illustrate how, during natural history, gigantic megafauna such as dinosaurs have slowed down the growth of the size of the seeds by physically modifying the ecosystem, influencing the levels of forest light. Today, this role can be fulfilled by a much smaller species: humans.
The idea that terrestrial animals can modify their environment is “quite simple and well supported in a variety of scales”, explains Clive G. Jones, environmentalist at the Cary Institute of Ecosystetal Studies in Millbrook, NY, which was not involved in the new study. For example, savannah elephants push the trees and tear themselves off from shrubs, transforming the landscape of plants. But even this elephantin influence is minor compared to that of prehistoric creatures.
The new model of researchers suggests that dinosaurs have caused a level of destruction that has eliminated an evolving trend in growing seeds, explains the main author of the study Christopher E. Doughty, scientist of the earth system at the Northern Arizona University. Larger seeds tend to attract larger animals for dispersion and germinating larger plants, explains Doughty; The two factors can give plants better access to the sun in overcrowded conditions. But this was generally not the case when there were “big reversing wood dinosaurs, opening the environment” and slimming the forests, says Doughty.
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After the dinosaurs have turned off, the forestry has become about 20% darker. This change “resets the slate” for plants and other animals, says Doughty. And “meanwhile, the canopy has become more closed,” notes Brian Atkinson, a paleobotanist from the University of Kansas not involved in the study. This growth would have imposed evolutionary pressure on the seeds to grow again, says Atkinson, which is also reflected in fossil data. Another drop in the size of the seeds occurred with the emergence of early giant mammals and persisted until they go out.
But even if we are far from the megafauna, the influence of humans on forests – in particular via forest exploitation – recovers that of these giants that have been extracted for a long time, says Doughty. If we continue at this rate, our effect on fruit seeds could one day compete with that of dinosaurs.
Jones notes that humans also influence plant life in many ways. “Agriculture [is] An obvious example, “he says, as well as” the introduction of exotic species, cleaning forests to make a suburb, cities, etc. ».
This complexity is one of the reasons why it could be difficult for the model to predict future sizes of fruit seeds, says Doughty. Another important factor to consider is the rapid pace to which human technology tends to develop in areas such as agriculture. Although the model provides a good analytical comparison of the alterations of forest density by megafauna and by humans, developments such as agriculture mean that “normal ecological rules no longer really apply”.
