Will we be able to rely on the ecosystem services streams provide under future drought scenarios?

ACEMS investigator Dr Catherine Leigh has combined efforts with a team of collaborators in the UK and Australia to find out how repeated drought in streams affects biodiversity.

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Image of the stream mesocosms (courtesy: Mark E Ledger)

The team used a combination of mini ‘replica’ streams known as mesocosms (see image), cutting-edge null modelling methods and biodiversity-partitioning methods to show how stream drying changes the community of freshwater animals that live in them through time.

It turns out that the different species that made up stream communities changed a lot – but this happened in the streams that kept flowing for the whole two years of the experiment, as well as in the streams that were dried up for a few days each month.

The story was very different when it came to the traits of the community – things like the animals’ different ways of feeding, their sizes, life durations, reproduction rates, etc. In the streams that flowed all year round, the composition of traits in the community remained stable. But in the streams that repeatedly dried up, the trait composition changed more and more.

Why is this important and what could it mean?

We rely on animals living in streams – creatures like mayflies, dragonflies, snails, worms – to perform important processes and functions that help keep water clean and breakdown organic material like leaves to make the nutrients in them available. For example, many stream caddisflies feed on leaves, shredding them up into little bits in the process. So processes like these are related to the traits that stream animals possess.

The benefits we derive from these processes are called ecosystem services. So, if the trait composition of stream communities start getting more variable through time, in response to repeated drying events, then the ecosystem services we derive from streams might become more transient (less stable and reliable).

Current rates of biodiversity loss are a major concern, especially for freshwater species. This research reminds us that biodiversity is not just about species, but also their functions, and that we need to know about both in order to understand the implications of biodiversity change.

Link to publicationhttps://onlinelibrary.wiley.com/doi/10.1111/jbi.13638

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