American Society of Naturalists

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“A meta-analysis of plant interaction networks reveals competitive hierarchies as well as facilitation and intransitivity”

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Nicole L. Kinlock (Nov 2019)

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Kinlock combined network structure across plant communities and found competition and hierarchies, but some stabilizing forces

The nature of interactions in plant communities poses problems with classical roots and modern controversy, many of which remain unresolved. In this paper, N. L. Kinlock combines network approaches with meta-analysis methods to investigate major questions in plant community ecology, including the intensity of competition and/or facilitation, the reciprocity of interactions (asymmetry), and the degree to which species in communities can be ranked in a hierarchy (transitivity). She used plant community interaction data from the literature, as well as data from her own fieldwork of an invaded woody plant community, and analyzed communities as networks of interactions. She then combined network metrics using meta-analysis, incorporating variation at the interaction level, to generalize structure across communities.

On the whole, plant communities were competitive, interactions between species were not reciprocal, and communities were hierarchical (transitive), similar to what has been reported in isolated studies and narrative reviews. However, there were instances of facilitation, symmetric interactions, and intransitivity in individual networks. Also, community structure differed between networks based on study design, habitat type, plant habit (woody or herbaceous), and plant age. This paper quantifies the nature of plant interactions in a systematic and unbiased way, finding some support for classic conceptions of plant community structure, while also bringing to light previously undescribed structural characteristics.

This paper is a part of Kinlock’s Ph.D. dissertation at Stony Brook University, where she is studying how plant community structure influences invasion.


The extent to which competitive interactions and niche differentiation structure communities has been highly controversial. To quantify evidence for key features of plant community structure, I recharacterized published data from interaction experiments as networks of competitive and facilitative interactions. I measured the network structure of 31 woody and herbaceous communities, including the intensity, distribution, and diversity of interactions at the species-pair and community level to determine the generality of competition, winner-loser relationships, and unequal interaction allocation. I developed novel methodology using meta-analysis to incorporate interaction uncertainty into estimates of structural metrics among independent networks. Plant communities were competitive, but intraspecific interactions were sometimes more intense than interspecific interactions. On the whole, interactions were imbalanced and communities were transitive. However, facilitation, balanced interactions, and intransitivity were common in individual communities. Synthesizing network metrics using meta-analysis is an original approach with which to generalize community structure in a systematic way.