Human activity affects the interactions between plants and seed-dispersing birds

Publicado em 16 março 2020

Studies carried out in the past few decades have shown how the destruction of forests leads to a decline in biodiversity. A Brazilian research group led by scientists from São Paulo State University (UNESP) has now reported the results of an investigation into how landscape changes through deforestation, habitat loss and fragmentation directly result not only in the loss of species, but also in their species, which are ecological Interactions. The report is published in Biotropica and features on the cover of the magazine. The study was supported by the São Paulo Research Foundation (FAPESP).

“In ecology, we know a lot about species-area relationships, but little or almost nothing about the relationship between species-interactions and land loss. Our study used ecological networks to find out how seed distribution interactions respond to land loss and landscape fragmentation. Shrinking of forest fragments leads to a loss of ecological interactions, which are important for the functioning of forests and the conservation of biological diversity, “said Carine Emer, first author of the article, which was created as a postdoc at the Conservation Biology Laboratory (LABIC)) of the Bioscience Institute ( IB-UNESP) in Rio Claro with funds from FAPESP.

The study was part of the “Ecological Consequences of Defaunation in the Atlantic Rainforest” project supported by FAPESP and led by Mauro Galetti, professor at IB-UNESP.

The researchers compiled data from 16 plant-frugivore interactions in different fragments of the Atlantic rainforest biome that were selected to form a gradient of human disturbances derived from the size of each forest residue. They focused on the interactions between plants and seed-distributing birds, since these animals are considered essential for constant forest regeneration. They came to the conclusion that the smaller the forest fragment, the fewer species live there and the fewer interactions can remain.

Forests and interactions

The largest and best preserved forest in the study was located in the Intervales State Park in the south of the state of São Paulo with 42,000 hectares. It had the highest biodiversity (81 frugivores and 185 fruiting plants) and the most interactions between plants and seeds (1,100 or 3.65 per species).

At the other end of the slope was a six-hectare fragment that has been regenerating in Piracicaba for just over eight years. A much smaller number of frugivorous birds (28 species) interacted with only a few fruit-bearing plant species (6)). Thus 169 seed-dispersant interactions were recorded, which corresponds to only 1.47 per species.

In the former area, a bird species distributed the seeds of three to four plant species. In the latter, it distributed no more than two.

“The first to disappear are the larger birds, which are essential for the distribution of large-seeded plants. This loss is not just numerical. It also works and directly affects the forest regeneration process,” said Emer. “In the medium to long term, plants with large seeds that lose their main distributors will disappear from the landscape and are limited to larger, better-preserved areas. The fragmented forest will become numerically and functionally poorer. The only remaining birds are small species whose functional role is to be found To disperse small seed plants. In other words, we are losing the ecological function of spreading large seeds. This can change our forests forever. “

Another article previously published by the group, also with Emer as the main author, showed that interactions with large species are lost in forest fragments of less than 10,000 hectares. It also highlighted the importance of small generalist bird species that disperse the small seeds of equally generalist plants and maintain connectivity in a fragmented landscape. In other words, Emer noted, “The Atlantic rainforest is currently interacting with generalist birds that disperse plant species that are adapted to disturbed environments.”

In addition to larger species, fragmentation also has a disadvantageous effect on so-called specific interactions. For example, a plant species that is spread by one or only a few bird species is more threatened with extinction than another species whose fruits are eaten by several different bird species.

The research line also includes a study published in the prestigious journal last year Advances in science in which the group estimated millions of years of loss of seed distribution in the Atlantic rainforest due to the disappearance of large birds for evolutionary history.

“The Atlantic rainforest has shrunk to only about 12% of its original area, and most of it is small forest fragments,” said Emer. “There is a wide variety of seed distribution interactions in the fragments we analyzed, most of which occur only in one or two fragments. These interactions correspond to millions of years of evolution. Species with different developmental pathways interact in the present and are increasingly on a limited areas. Overall we have reached a threshold beyond which we can no longer afford losses. Every single fragment of the Atlantic rainforest corresponds to millions of years of unique evolutionary history that must be preserved. ”

More information:

Carine Emer et al., Seed Distribution Networks in Tropical Forest Fragments: Area Effects, Restarts and Interaction Diversity, Biotropica (2019). DOI: 10.1111 / btp.12738

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