Notícias
Study reveals that extinction of large mammals alters leaf damage caused by pathogens
A groundbreaking scientific article has been published in the Journal of Ecology - one of the world's leading ecology journals - investigating the complex relationships between large herbivorous mammals, phylogenetic diversity and natural enemies of plants and the subsequent impact on tropical forest ecosystems.
The research, conducted by Brazilian and Spanish scientists in tropical forests in Brazil, explored the crucial role of natural enemies in plant leaf damage. These natural enemies range from large mammalian ungulates to microscopic pathogens. The study tested the largely unexplored consequences of local extinctions of large herbivorous mammals on interactions between plants and their natural enemies, especially in relation to herbivorous insects and pathogens that attack leaves in the understory of the forests.
The basis was a long-term defaunation experiment conducted in four protected areas of the Atlantic Forest. In these areas, permanent exclusion plots for large herbivorous mammals such as peccaries, tapirs, agoutis, pacas and cattleya deer were installed, where the dynamics of the vegetation have been monitored since 2015 by the research group of Prof. Mauro Galetti, from UNESP in Rio Claro, mainly by researchers Sergio Nazareth and Valesca Ziparro, co-authors of the study.
When investigating how the loss of large animals affects leaf damage caused by herbivorous insects and pathogens, the researchers found a significant reduction (9%) in the leaf damage of 10,050 leaves from 3,350 understory plants. This decrease was mainly due to a notable reduction (up to 29%) in damage caused by leaf pathogens - and not by insect herbivory, in the closed plots - where large animals were excluded. The authors also found a positive correlation between leaf damage, defaunation and the evolutionary distinctiveness of plants, revealing a previously unknown cascading effect of the extinction of large herbivores in forest ecosystems.
The study concludes that the extinction of large herbivorous mammals has an indirect effect on leaf damage caused by pathogens. These indirect effects may decrease the potential of plants to dilute pathogen damage by decreasing plant species richness, reinforcing their role as top-down regulators in forest dynamics. These findings have significant implications for plant fitness and, ultimately, for the maintenance and generation of biodiversity in some of the most diverse ecosystems on the planet.
Researcher Carine Emer, from the Rio de Janeiro Botanical Garden Research Institute, first author of the article, reports that they did not expect these results: "Initially, we thought that the absence of large mammals would result in a cascading effect on insect herbivory, but only pathogens were affected by defaunation and this correlates with the evolutionary characteristics of plant communities. These unexpected results show that we know very little about the dynamics of multitrophic interactions in tropical forests and highlight the importance of observing 'invisible' enemies, which are fundamental to maintaining the balance of nature and regulating the ecosystem services it provides."
In an interview with Pesquisa Fapesp magazine, Emer explains why reducing the damage caused by pathogens can affect the ecological balance, biodiversity and evolution of plants in these areas: "Plants have been interacting with their natural enemies for thousands of years, in an arms race of defense and attack. To do this, they develop defenses, both physical and chemical. In turn, the natural enemies, such as pathogens, create new forms of attack, in which the plants create new defenses. This is an important factor in maintaining and generating biodiversity, since new species of both plants and the organisms that interact with them can emerge in this process," explains Emer,
Another member of the team, researcher Nacho Villar, currently at the Netherlands Institute of Ecology, highlights the robustness of the results: "Although the experiment was carried out in four different forests, with different compositions and densities of plants and large mammals, we found cascading effects of large mammals on pathogenic leaf damage in all of them. Even in forest where the largest mammals, such as tapirs and peccaries, are absent, the extinction of medium-sized mammals, such as deer, pacas and agoutis, has comparable cascading effects. This is remarkable and clearly suggests that these cascading effects may be present in other forests with different species compositions of large mammals, almost certainly in other humid tropical forests. Obviously, our study is a first step, so the generality of our findings needs to be confirmed with experiments in other types of forests".
This groundbreaking research opens up new avenues for understanding the complex networks of interactions between different natural plant enemies and their consequences for the overall health and diversity of forest ecosystems.