Niche differentiation, competition or habitat filtering? Mechanisms explaining co-occurrence of plant species on wet meadows of high conservation value

Prepared by Patryk Czortek, Anna Orczewska & Marcin K. Dyderski

Semi-natural grasslands are regarded as ecosystems highly endangered in Europe. Among them, the purple-moor grass (Molinia) meadows are considered to have the highest conservation value. Due to the diverse abiotic conditions and early-autumn, manual mowing practised once per few years, these ecosystems are known due to their high diversity of plant species of contrasting ecological requirements. In this context, plant species typical of Molinia meadows can be considered as extremely specialised. For these reasons, the recognition of ecological mechanisms that shape their co-occurrence is very difficult.

Our study covered 58 vegetation plots established in well-developed Molinia meadows, located in the Natura 2000 Special Area of Conservation “Łąki Dąbrowskie” (S Poland). This area has a high diversity of plant species typical of Molinia communities, which are relatively well preserved (see photo above). Using a set of vegetation traits and components of functional diversity, we demonstrated how different ecological mechanisms (niche differentiation, interspecific competition and habitat filtering) influence the occurrence of the entire group of plant species, as well as individual species typical of Molinia meadows. We consider niche differentiation as the mechanism by which the species use environmental resources differently, allowing them to coexist and preventing from interspecific competition. Habitat filtering, in turn, refers to the survival of species with respect to more extreme environmental conditions

We identified high niche differentiation (and low habitat filtering) as the main mechanism determining the occurrence of the entire group of species typical of Molinia meadows. High importance of this mechanism may also indicate the high variability of different ways of the environmental resources usage demonstrated by single species. Moreover, a low level of interspecific competition could be regarded as an important mechanism positively influencing their occurrence.

Therefore, the detailed insights on how single plant species co-occur in a community may become a useful approach in the attempts of maintenance or successful restoration of species-rich meadow ecosystems. In light of this finding, the conservation of well-developed Molinia meadows should predominantly focus on the community level and maintain a complex of specific microhabitat conditions. Also, examining the performance of individual species may become useful when attempts are made to assess whether a species existence is endangered. It may also help to formulate their conservation priorities in small, isolated patches of Molinia meadows scattered in a transformed, human-dominated landscape.

This is a plain language summary for the paper of Czortek et al. published in the Journal of Vegetation Science (https://doi.org/10.1111/jvs.12983).