Pollinators are declining rapidly, largely due to land conversion and intensification of agriculture. To mitigate their crisis, low-disturbance habitats, such as sown wildflower plantings (commonly known forms are wildflower strips at the edges of arable fields), could promote pollinators by restoration of their resources (food, sheltering and nesting habitats). However, comprehensive knowledge is lacking on how landscape context, spatial configuration and age of wildflower plantings, seasonality and flower composition affect pollinator communities, especially from East-Central Europe.
To understand these effects, researchers from the HUN-REN Centre for Ecological Research established diverse native wildflower plantings within heterogeneous and homogeneous agricultural landscapes, by two spatial configurations: one large field or three smaller strips. Floral resources and wild pollinator insects (wild bees, hoverflies, butterflies) were sampled, in early and mid-summer, for two years after establishment (2020-21).
Flower resources of the sown plant species increased continuously, and were complemented at high rate by flowering plant species from the soil seed bank, especially in the first year. Both flower abundance and diversity increased the abundance of pollinators, highlighting the important role of using diverse seed mixtures. Wild bee abundance and species richness increased year by year and season by season, while butterfly abundance also demonstrated a yearly increase after establishment. Hoverfly abundance and species richness, however, showed an opposite trend, possibly due to the inter-annual variation. Wild bee and butterfly abundance was higher in the heterogeneous than in the homogeneous landscapes. Researchers did not observe any significant local effects of spatial configuration itself on pollinator populations.
Field-work photos from the transect walk method and the flower resources assessment from the four years of the study Photos: Borbála Bihaly (top left, buttom right) and Áron Bihaly (buttom left, middle and top right)
Our results emphasize that to support pollinators effectively, future wildflower plantings should be maintained for multiple years, in order to maximize floral diversity and ensure continuously available flower resources throughout the entire season.
Further results from the upcoming years and similar long-term and landscape-scale experimental studies are needed to understand all the benefits and ecological processes of diverse native wildflower plantings especially in understudied European regions.
The diverse floral resource of wildflower plantings in the second and third years and the pollinator insects visiting the flowers Photos: Viktor Szigeti (top left and middle left) and Borbála Bihaly (bottom row, top right and middle right)
Researchers at the HUN-REN Centre for Ecological Research (HUN-REN CER) are continuously studying the effects of changing environment on ecosystems, caused by human activity and climate change, and how animals respond to it. They recently showed that the increase of salinity of ponds can drive the evolution of planktonic organisms, and this process can be observed in the Daphnia (water flea) populations in the sodic water of World War II bomb craters in Hungary. The paper presenting their latest discoveries has been published in the flagship biological journal of the Royal Society, Proceedings of the Royal Society B.
Natural ecosystems are exposed to a multitude of stressors including climate change, urbanisation, or the rising salinity of aquatic habitats. These stressors change the environmental conditions, which determine the success of organisms. The emerging spatial variation in environmental factors is called a gradient. The Plankton Ecology Research Group at HUN-REN CER, led by research fellow Csaba Vad, studies the effects of environmental change on the functioning, species composition, and evolution of planktonic communities.
“Organisms have to adapt to environmental stress, otherwise they go extinct,” the researcher says. “Sensitive species can be replaced by other more stress-tolerant species, or the resident populations can also adapt to the changing environment. In other words, an evolutionary adaptation occurs in the population, and this provides an opportunity to survive in the habitat.”
Salinisation, the increasing salinity levels of aquatic ecosystems, is a global threat. The salinity of large lakes is rising as well, but the change can be much more dramatic in shallow temporary ponds. Salinisation is caused by many factors, but one of the most important drivers is increasing evaporation (as a result of warming). Meanwhile, pollution from mining or other industrial activities, or the environmental effects of urbanisation can also lead to salinisation.
Soda pan in the Seewinkel area, Austria (Oberer Stinkersee, photo: Horváth Zsófia)
Soda pans are naturally saline habitats in the lowlands of Carpathian Basin. The researchers studied the plankton communities and salinity of these soda pans and compared them to the communities of ~80-year-old sodic bomb crater ponds in the Great Plains of Hungary. Their exact origin is somewhat uncertain, but some sources suggest that during World War II, American bombers bombed the plains instead of the nearby airport, creating more than 100 explosion craters in an 800 m diameter circle. These craters were filled with sodic water and have since become very useful model systems for ecological research.
The salinity of the bomb crater ponds varies widely, so ecologists were able to compare their Daphnia populations and find out whether they are adapted to this environmental factor. Water fleas, such as the object of this study, Daphnia magna, are large-bodied zooplankton species, which are common model organisms in ecological and evolutionary research, because they play important roles in aquatic communities and can be kept easily in laboratories. “We wanted to find out whether the salinity tolerance of Daphnia originating from ponds with low and high salinity levels is different”, tells Csaba Vad. “We also studied soda pans, which are also sodic and hold similar zooplankton communities to the bomb craters. Both types of these habitats are naturally saline, and can be used as model systems, because their clusters consist of several ponds with different salinity levels in close proximity to each other.”
If local adaptation occurs, the salinity tolerance of the populations is matching with the salinity levels of their home ponds. This means that water fleas from more saline ponds will have a higher salinity tolerance compared to the Daphnia from less saline waters. In theory, local adaptation could be more prominent in more isolated habitats (in ponds more distant in space), because the mixing of their populations with others is less likely in the case of more distant habitats. The soda pans are kilometres apart, while bomb crater ponds are only a few metres away from each other. So, based on merely the position of ponds, more intense evolutionary patterns could be expected to be found in soda pans. But this was not the case.
Local adaptation (adaptation to the local salinity concentrations) was only found in the bomb crater ponds, which are very close to each other in space. There are some possible reasons underlying this observation. For example, salinity levels in soda pans are usually higher and more variable within and across years than in the bomb crater ponds. Soda pans are also shallower and larger, while bomb craters are deeper and smaller in diameter. When soda pans dry up, the resting eggs of water fleas can be easily blown to another pond by the wind. In contrast, bomb craters dry up more rarely (only in years with extreme weather conditions), their salinity level fluctuates less, and during the explosion, a prominent rim was created along their edges. Thus, Daphnia eggs cannot be as easily transported among the neighbouring ponds, and the more stable salinity levels allow for local adaptation to this stressor.
The researchers found adaptation to salinity in the soda pans as well, but this occurred on a regional level. Soda pans have a higher average salinity level than bomb craters, therefore the water flea populations from soda pans have higher overall salinity tolerance than those from the bomb crater ponds.
“Despite soda pans being more distant from each other, because of their more frequent drying-up, the gene flow among their Daphnia populations is more intense,” argues Csaba Vad. “Furthermore, many waterbirds visit soda pans, which transport several aquatic organisms from one pond to another. These circumstances overall reduce the possibility for local adaptation in this habitat type. In contrast, we found strong local adaptation in bomb crater ponds, which are sometimes only a few metres apart. Our results show that the response of aquatic communities to salinity may be influenced by several factors.”
Opening image: The model organism of the study, the water flea Daphnia magna Photo: Zsófia Horváth
Nowadays we hear a lot about climate change impacts in general, however, we still lack in-depth knowledge about how climate change might modify the processes determining the ecological status of lakes and the structure and functioning of aquatic communities. This is largely because these processes are intertwined in a complex manner, making any estimation regarding these changes challenging. In their latest study, researchers of the HUN-REN CER Institute of Aquatic Ecology used model simulations to analyse warming effects on phytoplankton dynamics based on field and experimental observations.
Although numerous lakes around the world have been showing an increase in annual mean temperature over the last few decades, it still remains difficult to assess long-term warming-related impacts in water bodies with various physical and chemical properties and diverse communities. Exploring these impacts is crucial not only for fishes, macroinvertebrates or aquatic macrophytes, but also for planktonic organisms, which form the basis of the aquatic food web and have a substantial influence on material cycles. Despite the broad range of sophisticated techniques developed to study this important group, elucidating how interrelated environmental factors drive plankton functioning is still a hard task due to the typically rapid dynamics of these communities. Monitoring based on regular field work is a crucial part of research on aquatic systems, but it is also time-consuming and lab-intensive, making any sampling effort limited in both space and time. In a sense, this is like following a streaming series with several seasons by only looking at a few snapshots from each episode, trying to guess what the actual story is.
We need complementary approaches to improve our ability to assess, estimate or forecast the ecological effects of climate change.Numerical models are promising candidates for this role, gradually gaining importance in ecological research. Generally speaking, such models describe fundamental relationships in the form of mathematical equations based on current data and scientific knowledge. Such relationships include e.g. species growth as a function of food item availability or the dependence of plant photosynthetic activity on light intensity. The strength of modelling lies in the possibility to create computer-generated simulations about changes in a population, community or ecosystem and their environment through space and/or time, helping to find causality behind natural phenomena. Thus, while field and experimental observations provide data about a series of temporary states and conditions, modelling aims at the processes that induce temporal change in those states and conditions.
In a Hungarian-Greek collaboration, Károly Pálffy, researcher of the institute’s Plankton Ecology Group, studied the dynamics of planktonic algae (phytoplankton, major primary producers of aquatic habitats) using an ecological modelling approach. While analysing a data series on Lake Balaton, Hungary in his previous study he found that the long-term rise in annual mean water temperature was accompanied by increasing seasonal fluctuations in phytoplankton composition (increasing seasonal variability), which might suggest a decline in ecosystem stability. He and his colleagues also managed to demonstrate something highly similar in a mesocosm experiment, raising the question of whether there is a more general connection between warming and the dynamics of planktonic algae.
A typical graphical output of a model simulation of one year run under different seasonal temperature scenarios (daily temperature values characteristic at present and increased with 1, 2 or 3˚C). Curves with different colours represent seasonal changes in the abundance of different species of algae. The modelling of temporal dynamics in multiple randomly assembled phytoplankton communities under different nutrient load and temperature combinations added up to more than 100,000 simulations. The study focussed on both short-term (one year) and long-term (30 years) changes and impacts.
The newly developed model made it possible to simulate changes in phytoplankton on the species level under various temperature scenarios. The output of the simulations was in agreement with the previous observations, elevated mean temperature caused more pronounced seasonal changes in phytoplankton composition, but the degree of this impact was also highly dependent on how the communities received inorganic nutrients essential for their growth. Accordingly, the ratio of the two most important ones, nitrogen and phosphorus as well as the temporal fluctuations in nutrient supply had significant influence on the effect of warming. This is in close agreement with recent studies that suggest the importance of considering nutrient load conditions (the so-called trophic state of a water body) when assessing the effect of climate change on aquatic ecosystems. Besides nutrients, initial species richness of the simulated communities also affected their response to warming. From a methodological point of view, this is an important finding, since it suggests that choosing an adequate number of species can be crucial in the planning of community-scale climate change experiments.
The recent paper published in Limnology and Oceanography also sheds light on what long-term consequences an increase in the seasonal variability of phytoplankton can have in terms of stability. At higher mean temperatures, seasonal extremes in community composition became more prominent, shifting the communities toward lower overall evenness. On a longer time scale, elevated temperatures also increased the probability of species loss, providing a mathematical explanation for the role of warming in reducing plankton community stability and thus modifying aquatic ecosystem functioning. The research group has plans for further extending the model, facilitating the simulation of climate change impacts in a spatial context as well as on the level of the planktonic food web.
Numerical models nowadays have an increasingly important role in the interpretation of field observations
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