Home Sciences Gulls disperse seeds of invasive plants in cities

Gulls disperse seeds of invasive plants in cities

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Gulls disperse about 30% of plant seeds, both native and invasivein urban green areas, as shown by a study led by the Institute of Marine Sciences (ICM-CSIC) and the Doñana Biological Station (EBD-CSIC).

The results have implications for the management of urban green spaces. It has been carried out in the city of Barcelona analyzing the movements of GPS-tagged seagulls and the detection of seeds found in their diet.

«Birds can play a fundamental role in the dispersal of plants, including exotic species», the EBD-CSIC researcher has summed up explains Víctor Martín. Martín has detailed that the birds can ingest the seeds directly or ingest other smaller birds that have previously ingested them. Those seeds are then deposited elsewhere as they pass through the digestive tract.

“If this dispersion occurs in cities, it can cause ecological and economic problems related to the management of green urban areas. Especially when the plants that are dispersed are invasive species. This affects the local biodiversity of urban ecosystems», the researcher warned.

Most of the seeds found in the study did not present fleshy fruits and had a reduced size. This indicates that the gulls acquire them through the consumption of other smaller species, such as pigeons and Argentine parrots, which are mainly granivorous.

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They also found other species of plants with larger seeds and fleshy fruit that would be consumed directly by the seagulls.

Gulls are opportunistic seabirds

The study, published in the journal ‘Science of the Total Environment’, focused on the yellow-legged gull (larus michahellis). It is an opportunistic seabird that has stable populations in Barcelona and is adapted to exploiting urban resources.

Researchers from the Barcelona Public Health Agency (ASPB), the Catalan Institute of Ornithology (ICO) and the Center for Ecological Studies of Hungary. The biologists analyzed the movements made between 2018 and 2019 by 20 yellow-legged gulls tagged with GPS devices.

«Understanding dispersion and spatial patterns can help the knowledge of exotic species within urban green areas», has highlighted Tomás Montalvo, ASPB researcher.

Fig tree, kiwi, palm tree… are some of the exotic species

In the study they have identified seven exotic species that are dispersed by seagulls. Some of them are fig, tooth grass, nightshade, trompillo, kiwi, Mexican fan palm and dodder.

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Depending on the job, more than 1,000 seeds a day are dispersed by seagulls inside and outside the limits of the city of Barcelona.

95% of the seeds are transported within the city itself over distances of around 700 meters. The remaining 5% can be moved up to 35 kilometers beyond the city limits.

Of the seeds that are dispersed within the city, about 30% are deposited in urban green areas, suitable for the seeds to establish (bushy areas, green parks and urban pastures).

In this sense, Raül Aymí, a researcher at the ICO, pointed out that “the results of the study suggest that seagulls would be important dispersal vectors between urban green areas.” They also open the door to other studies “on how birds can contribute to the expansion of exotic species in cities.”

The ICM-CSIC researcher Joan Navarro has concluded that “this work provides very valuable information for understanding urban marine ecology. Especially about the interactions with human interests and the possible ecosystem services of the resident population of seagulls in Barcelona».

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