Hugo Saiz (Universidad Rey Juan Carlos, Spain) tells us more about his recently published Journal of Ecology article about plant spatial association networks across dryland ecosystems…
Not surprisingly, the use of networks has increased considerably in community ecology in recent years. Network analysis allows studying ecological communities as a whole while providing valuable information about individual species within the community.
These analyses benefit from a large theoretical framework that enables the measurement of the robustness or the stability of the system, and provide eye-catching figures that make studies appealing to readers. However, while trophic, mutualistic and parasitic interactions dominate studies on ecological networks, other interactions such as facilitation or competition between plants have not received much love in the past (while the idea per se is quite old, De Vries, 1954).
In our new paper, we draw attention to the potential applications of networks in plant ecology by creating plant spatial association networks from a global survey of drylands previously published in Maestre et al. (2012).
Spatial associations have been commonly used as a proxy for interactions between plants, and although the use is not exempt of criticism, we wanted to give them a shot and see if we could learn something when studying them in arid plant communities throughout the globe. Furthermore, the use of spatial networks also gave us a chance to explore some particularities of networks that combine positive and negative links (i.e. signed networks), which are commonly used in social sciences but scarcely studied in the natural sciences.
In some Morocco drylands, Stipa tenacissima forms monospecific vegetation patches. This spatial segregation between Stipa and other species can be characterized by a negative link in a plant spatial network. (Photo: Cristina Escolar)
Network analyses revealed that the spatial structure of plant communities in drylands is quite diverse, ranging from communities where spatial segregation rules to others where aggregation dominates. However, we observed generalities like the high presence of spatial relationships between species (significantly higher than expected by chance) and the trend of plants to create differentiated types of vegetation patches commonly formed by the same group of species. Furthermore, this spatial structure seems to be related to the diversity of plant communities, although we do not know why. Nevertheless, all these results suggest that is promising to include network analyses in the toolbox of plant ecologists.
Plant spatial association networks in global drylands are quite variable, but share characteristics such as high linkage density and the presence of balanced blocks.
A whole field of possibilities for study arises from the creation of a network. Plant networks vary across the globe, but why do they change from site to site? They also share common properties independently of their location – is there any reason behind this? Furthermore, network structure has been related to the stability of the system (Rohr et al., 2014), although this idea fits more with a network built based on ‘true’ biotic interactions. Finally, if plant community diversity is linked to its spatial network structure, what are the mechanisms driving this spatial organization? These are just a few of the many questions that could open the gate to develop future experiments.
To move on in the study of plant networks, a first step would be to improve the link between spatial associations and biotic interactions for plants. This would make the ecological implications of network structure much clearer. Second, once plant networks are built based on reliable interactions, the study of the cause and consequences of network structure could provide a stimulating topic for future research. Meanwhile, spatial patterns can be used to characterize the structure of plant communities and identify key species driving that structure, which can have several applications for ecological conservation. Therefore, I am optimistic that the match between plant communities and networks will bring valuable contributions to plant ecology in the future.
Hugo Saiz (Universidad Rey Juan Carlos, Spain)
Read the full paper online: The structure of plant spatial association networks is linked to plant diversity in global drylands
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