From streams to forests: ecology in the natural world

Much of our research uses mathematical models and controlled microbial experiments to isolate ecological mechanisms, but an equally important question is whether those ideas help us understand the much greater complexity of natural ecosystems. We often work with collaborators to bridge the gap between controlled experiments and the complexity of natural systems. This work has ranged across a broad collection of natural systems: geothermally heated streams in Iceland, Sphagnum peatlands, forests and grasslands, urban bird communities, freshwater fishes, and ecological patterns measured across entire countries and continents. These studies connect recurring themes—functional diversity, species interactions, environmental responses and stability—to ecosystems in which the environment cannot be held constant.

A quick tour of the systems

Ecosystem or system	Organisms / properties	Question	Example work
Geothermally heated streams, Iceland	Ciliate microbial communities	How does natural warming alter freshwater communities?	Plebani et al. 2015 [1]
Forest landscapes	Trees and their functional traits	Can functional diversity be measured remotely?	Schneider et al. 2017 [2]
Switzerland	Carbon regulation, erosion prevention, air quality and recreation	Can ecosystem services and their trade-offs be monitored from Earth observation?	Braun et al. 2018 [3]
Urban ecosystems worldwide	Birds	How does urbanisation change the functional diversity of animal communities?	Hagen et al. 2017 [4]
British and North American landscapes	Birds	How do traits, climate and spatial synchrony influence community dynamics?	Hordley et al. 2021 [5]
Temperate terrestrial and freshwater ecosystems	1,246 bird and 580 fish communities	How do temperature and biodiversity influence ecological stability in nature?	Ghosh et al. 2024 [6]
Sphagnum peatlands	Microbial food webs	Do richness or trophic interactions better explain ecosystem functioning?	Jassey et al. 2023 [7]
Northern peatlands	Photosynthetic microorganisms and carbon cycling	Can microbial photosynthesis modify the response of peatland carbon cycling to warming?	Hamard et al. 2025 [8]
Global mountains, islands and deltas	Multiple ecosystem services	How are services bundled together across contrasting landscapes?	Reader et al. 2022, 2024 [9]
Biodiversity experiments and natural-system datasets	Plants and other communities	How general are relationships among biodiversity, productivity and environmental conditions?	Parreño et al. 2021; Hong et al. 2022 [10]

Iceland’s naturally heated streams

One direct way to investigate climate warming is to find ecosystems in which nature has already created a temperature experiment. In Iceland, geothermal activity produces neighbouring streams that are similar in many respects but differ substantially in temperature. Plebani and colleagues studied ciliate communities in 13 such streams spanning mean temperatures of approximately 5–20°C [1]. The same naturally warmed streams have also been used to test how well the architecture of entire food webs can be predicted as temperatures rise, extending the question from single communities to whole networks of feeding interactions. Their results also showed why field ecology can complicate simple expectations from laboratory experiments: on submerged rocks, ciliate biomass and local diversity declined as temperature increased, whereas on sandy substrates community composition showed no comparable temperature dependence. The effect of temperature therefore depended on the physical environment in which the organisms lived, with flow, resources, disturbance and exposure to grazers all potentially modifying how warming affected the microbial community. Natural experiments such as these occupy a useful middle ground between laboratory and observational ecology, because environmental variation is naturally generated but occurs across comparable ecosystems in the field.

Measuring forests and ecosystem services from above

Natural ecosystems also present a problem of scale. Traits can be measured carefully on individual plants, but ecological questions often concern entire forests and landscapes. Schneider and colleagues addressed this using a combination of airborne laser scanning and imaging spectroscopy to map morphological and physiological variation among trees [2]. The resulting maps estimated functional diversity continuously across a forest landscape rather than assigning a single diversity value to an individual vegetation plot. The remotely sensed estimates agreed reasonably with leaf measurements and forest inventory data collected on the ground, while also revealing relationships between functional diversity, topography and soil conditions [2]. This work connects directly to the earlier research on functional diversity: the question moves from how should functional diversity be measured? to can we actually observe it across real landscapes?

Remote sensing also makes it possible to move beyond biodiversity itself and investigate what landscapes provide. Braun and colleagues combined Earth observation with ecosystem-service models to examine changes across Switzerland between 2004 and 2014 [3], considering services including carbon dioxide regulation, soil erosion prevention, air-quality regulation and recreational hiking. Rather than all services changing together, their relationships depended on both location and spatial scale, with some services showing synergies and others trade-offs. Related work has extended this perspective internationally, asking how suites of ecosystem services are associated with human modification across major delta systems and how recurring ecosystem-service bundles emerge across mountains, islands and deltas. The ecological unit has therefore expanded dramatically, from individual organisms and communities to landscapes whose ecological properties also affect human societies.

Birds, cities and changing climates

Birds have provided another important bridge between functional-diversity theory and large-scale natural communities. Hagen and colleagues compared 529 bird species across 25 urban areas worldwide, using 27 functional traits associated with resource use and comparing urban communities with paired non-urban communities [4]. The results were not a simple story of cities having uniformly lower functional diversity. After accounting for differences in species richness, urban assemblages could have relatively high functional diversity, while characteristics including vegetation, population density and city size were associated with the patterns observed. Other work with long-running bird monitoring data has considered the distinction between response traits—characteristics associated with how species respond to environmental change—and effect traits, which describe how species contribute to ecological functioning [5], a distinction explored further in Predicting ecosystem functioning. This allows natural bird communities to be viewed not simply as lists of species but as distributions of ecological strategies, linking changes in community composition to potential changes in ecosystem functioning.

Long-term biodiversity monitoring also makes it possible to test ecological stability theory at much larger scales. Ghosh, Matthews and Petchey analysed 1,246 bird communities and 580 fish communities from temperate regions, asking how biodiversity and different aspects of temperature were related to community stability [6]. Temperature was not represented by a single mean value: the study distinguished its median, variability, long-term trend and extremes and examined how these components related to diversity, synchrony and stability. The results differed between birds and fishes. In fish communities, variation among species in responses to changing median temperature was associated with the diversity–synchrony–stability relationship, whereas in birds there was evidence for a role of temperature extremes [6]. This provides an important test of ideas developed in the response-diversity work: stability in natural communities depends not only on how many species are present, but also on whether their populations respond to environmental variation in similar or different ways.

Peatlands: tiny organisms in a major carbon store

Some of the smallest organisms studied by the group occur in ecosystems of global significance. Peatlands contain large stores of carbon, and their future under climate change depends partly on the microorganisms responsible for photosynthesis, decomposition and nutrient cycling. In a Sphagnum-dominated peatland, Jassey and colleagues investigated microbial food-web structure and ecosystem functions including decomposition and enzyme activity [7]. Taxonomic richness itself did not directly explain variation in the measured functions. Instead, food-web properties—including trophic interactions, connectance, biomass and energy transfer—were more informative, shifting attention from how many microbial taxa occur in a peatland towards how energy moves among them.

More recently, Hamard and colleagues investigated another easily overlooked component of peatland ecology: photosynthesis by microorganisms [8]. Their work shows that microbial photosynthesis can mitigate carbon loss from northern peatlands under warming, adding an important biological process to our understanding of peatland carbon cycling. Together, these studies illustrate a recurring feature of this research: ecosystem-scale processes can emerge from interactions among organisms that are individually microscopic. Understanding peatland responses to environmental change therefore requires attention not only to the plants that dominate the visible landscape but also to the microbial communities and food webs associated with them.

Field systems as tests of ecological ideas

These natural-system studies span very different organisms and environments, but several common questions recur: does biodiversity stabilise ecological communities, does it matter which traits species possess, do species respond independently or synchronously to environmental change, and are ecosystem processes better predicted by species richness, functional differences or interactions among organisms? Field studies make these questions harder because temperature covaries with other environmental conditions, species interact with many other organisms, landscapes have histories, disturbances occur unexpectedly, and human activities alter both ecosystems and the services obtained from them. But that complexity is precisely why natural ecosystems matter. Laboratory experiments allow ecological mechanisms to be isolated and mathematical models make their assumptions explicit; natural experiments and long-term observations then ask whether those mechanisms remain useful when confronted with the full complexity of ecological systems. Across streams, forests, peatlands, cities and continental monitoring networks, the underlying goal remains much the same: to understand how differences among organisms, their interactions and their responses to environmental change scale up to determine how ecosystems function and persist.

References

1. Plebani, M., Fussmann, K.E., Hansen, D.M., O’Gorman, E.J., Stewart, R.I.A., Woodward, G. & Petchey, O.L. (2015). Substratum-dependent responses of ciliate assemblages to temperature: a natural experiment in Icelandic streams. Freshwater Biology, 60, 1561–1570. DOI: 10.1111/fwb.12588
2. Schneider, F.D., Morsdorf, F., Schmid, B., Petchey, O.L., Hueni, A., Schimel, D.S. & Schaepman, M.E. (2017). Mapping functional diversity from remotely sensed morphological and physiological forest traits. Nature Communications, 8. DOI: 10.1038/s41467-017-01530-3
3. Braun, D., Damm, A., Hein, L., Petchey, O.L. & Schaepman, M.E. (2018). Spatio-temporal trends and trade-offs in ecosystem services: An Earth observation based assessment for Switzerland between 2004 and 2014. Ecological Indicators. DOI: 10.1016/j.ecolind.2017.10.016
4. Hagen, O., Ibáñez-Álamo, J.D., Petchey, O.L. & Evans, K.L. (2017). Impacts of Urban Areas and Their Characteristics on Avian Functional Diversity. Frontiers in Ecology and Evolution, 5, 84. DOI: 10.3389/fevo.2017.00084
5. Hordley, L.A., Gillings, S., Petchey, O.L., Tobias, J.A. & Oliver, T.H. (2021). Diversity of response and effect traits provides complementary information about avian community dynamics linked to ecological function. Functional Ecology, 35, 1938–1950. DOI: 10.1111/1365-2435.13865
6. Ghosh, S., Matthews, B. & Petchey, O.L. (2024). Temperature and biodiversity influence community stability differently in birds and fishes. Nature Ecology & Evolution, 8, 1835–1846. DOI: 10.1038/s41559-024-02493-7
7. Jassey, V.E.J., Petchey, O.L., Binet, P., Buttler, A., Chiapusio, G., Delarue, F., et al. (2023). Food web structure and energy flux dynamics, but not taxonomic richness, influence microbial ecosystem functions in a Sphagnum-dominated peatland. European Journal of Soil Biology, 118, 103532. DOI: 10.1016/j.ejsobi.2023.103532
8. Hamard, S., Planchenault, S., Walcker, R., Sytiuk, A., Le Geay, M., Küttim, M., et al. (2025). Microbial photosynthesis mitigates carbon loss from northern peatlands under warming. Nature Climate Change, 15, 436–443. DOI: 10.1038/s41558-025-02271-8
9. Reader, M.O., Eppinga, M.B., de Boer, H.J., Damm, A., Petchey, O.L. & Santos, M.J. (2022). The relationship between ecosystem services and human modification displays decoupling across global delta systems. Communications Earth & Environment, 3. Reader, M.O., Eppinga, M.B., de Boer, H.J., Petchey, O.L. & Santos, M.J. (2024). Consistent ecosystem service bundles emerge across global mountain, island and delta systems. Ecosystem Services, 66, 101593.
10. Parreño, M.A., Schmid, B. & Petchey, O.L. (2021). Comparative study of the most tested hypotheses on relationships between biodiversity, productivity, light and nutrients. Basic and Applied Ecology, 53, 175–190. Hong, P., Schmid, B., De Laender, F., Eisenhauer, N., Zhang, X., Chen, H., et al. (2022). Biodiversity promotes ecosystem functioning despite environmental change. Ecology Letters, 25, 555–569.