SLU news

Fish eat frogs, birds eat fish, all need water, all need food

Published: 27 April 2023
Bird on a stone.

SLU has assessed the suitability of constructed wetlands for the biodiversity of birds, amphibians and fish. Although there was some variation, the results suggest that birds and amphibians can live together in the created environments. However, separate wetland creation with different objectives may be required to benefit both bird and fish communities.

Walking through a beautiful wetland, the sun is shining and you start to notice the nature around you when some Eurasian teals start to quack. You also notice a fisherman trying to catch a northern pike. The man is very patient and does not seem bothered that there is no catch on the hook. The temperature is pleasant and you decide to dip your feet into the water. As the water stops rippling and calms down, you notice a great crested newt swimming around, minding its own business. You begin to wonder how all these very different species can co-exist.

Ecosystem services and biodiversity

Wetlands provide a wide range of ecosystem services that benefit humans, and are important habitats for many species of birds, amphibians and fish. However, wetlands are also under threat from human activities such as land-use change and pollution, which have led to a decline in aquatic biodiversity in many parts of the world. To counteract this trend, there has been an increase in wetland conservation initiatives over the last few decades, and wetland creation has become a popular tool for restoring or enhancing wetland habitats.

Created wetlands

Ineta Kačergytė and her colleagues at SLU have studied 52 created wetlands. They investigated the species associations that may influence the outcome of wetland creation efforts. What is perhaps interesting about the method of this study is that, as well as conducting field surveys of birds, they also used new molecular tools called environmental DNA metabarcoding to assess the presence of species in these wetlands.

“Birds and amphibians were positively associated, while bird-fish associations appeared to be negative. Therefore the society may need to create separate wetlands with different objectives to benefit both bird and fish communities,” says Ineta Kačergytė.

Positive and negative associations

A positive association mean that the species are occurring together more often than you would expect by chance. Sometimes species encounters benefit each other, it could be, for example, that some birds may use other birds for good habitat indication. Negative associations are when they co-occur less often than expected by chance, for example due to avoidance, predation or competition.

The positive associations between birds and amphibians suggest that wetland creation can benefit multiple taxa at the same time, which is good news for the overall conservation of wetland biodiversity.

Potential conflicts 

“Wetland creation is an important conservation tool that can contribute to the restoration and enhancement of habitats for a wide range of species. However, potential conflicts between different species may need to be carefully considered when planning these initiatives,” says Ineta Kačergytė.

Of course, it is important to note that the researchers did not look at how the presence of birds affected the ability of amphibians to reproduce and the likelihood of amphibian juveniles reaching adulthood. Whether we can find similar positive relationships for other wetland taxa, such as wetland insects and plants, remains unknown, but would be very important information for achieving the national environmental objective of 'thriving wetlands'.

Mix of different wetlands?

To address this, it may be necessary to create a mix of different wetland types to benefit specific species groups, or specific wetlands for biodiversity hotspots.

“By considering how wetland taxa interact, we can design more effective and targeted conservation strategies that benefit multiple species and promote the long-term sustainability of wetland ecosystems,” says Ineta Kačergytė.

Scientific article

Community associations of birds with amphibians and fish in wetlands created for biodiversity, Biological Conservation, Ineta Kačergytė et al