This blog post is provided by Hannah J. White, Joseph J. Bailey and Samuel R. P.-J. Ross and tells the #StoryBehindthePaper for the paper ‘Response trait diversity and species asynchrony underlie the diversity–stability relationship in Romanian bird communities’, which was recently published in Journal of Animal Ecology. 

The number of individuals and what species there are within ecological communities varies through time. This is known as community stability. There is a general idea in ecology that the more diverse communities are, the more stable they are, as different species vary in their response to changes in the environment. Therefore, when one species declines in numbers, another might increase i.e. there is a level of ‘insurance’.

But what is it that makes species respond differently? How does this ‘stability’ influence how these communities work through time, as part of the wider ecosystem? We answer these questions in our recent paper using data on bird communities in Transylvania, Romania. Specifically, we applied a ‘response-and-effect’ framework where we looked at the traits (characteristics) of species that determine how they respond to the environment (response traits), and those that determine their effect on the environment (effect traits). Response traits for birds include, for example, the number of eggs a species lays in a single clutch as this can determine how a species is able to recover following an environmental disturbance. Effect traits for birds include what the bird eats, as, for example, birds that eat seeds and fruit contribute to seed dispersal, and those that eat insects contribute to pest control.

Firstly, we needed to measure the range of responses that different species show to any change in the environment. This is called response diversity, but there is no consensus on how to measure this. So, we decided to use the diversity of so-called ‘response traits’ to give us an idea of the potential variety of responses of species in each bird community.

Next, we needed to measure stability. Community stability is not just the variation through time of the total number of individuals or total biomass within the community which have been often used in stability studies, but also changes in which species are present and their abundances at different times. We therefore looked at the stability of both total numbers of individuals in the community and of species composition.

The final step was to measure whether the ecosystem consistently works—that is, functions—through time. This can be hard to measure, particularly in organisms other than plants (where measures such as ’greenness’ are often used to approximate how well an ecosystem is functioning). We decided to look at the diversity of traits that we know affect the environment and observe how this varied over time.

We combined these steps to investigate the full pathway of possible mechanisms linking from the diversity of response traits to community stability to the variation in the diversity of effect traits through time. Our results supported general ecological theory that bird communities with a diversity of response traits hold species that respond differently to the environment and therefore show changes in composition over time, but the total number of birds in that community remains relatively stable.

We then took this a step further to investigate how this might vary depending on the land use of different areas. The study was carried out in Transylvania, Romania, which is predominantly rural. Agriculture in this area is generally low intensity and has a high nature value, using traditional harvesting methods such as scythe-cutting for hay meadow management. This might explain why we didn’t see much difference in community stability between agricultural and forest areas, however,

with changes in farming practices and agricultural intensification for large scale cash crops, there is a potential threat to the diversity and stability of bird communities in this region.

How did the paper come about?

This paper stemmed from the fact that we all knew each other well and thought it would be fun to work together. Our interests overlapped and we began to realise that whenever we spoke about stability, we were making a big assumption about biodiversity in this context—although the whole ecological theory behind the positive effect of biodiversity on stability relied on differences between species, rarely had the actual characteristics of species, i.e. their traits, been considered. More commonly, the number of different species was related to community stability, usually in terms of the variation in number of individuals over time, but this missed a vital part of the underlying stabilising mechanism(s). We also realised that this stability was often not related to ecosystems and how they function over time, particularly in organisms other than birds. We thought that using traits of birds that we know impact the ecosystem, e.g. what they eat, helps overcome this gap in our knowledge.

So how did the paper come about? Wanting to work with people you like, and whose work you respect. From there, the scientific discussions flow.

Read the full paper

White, H. J., Bailey, J. J., Bogdan, C., & Ross, S.-J. (2023). Response trait diversity and species asynchrony underlie the diversity–stability relationship in Romanian bird communities. Journal of Animal Ecology, 00, 1–14. https://doi.org/10.1111/1365-2656.14010