Facilitative and competitive interaction components among New England salt marsh plants

Authors: BRUNO, JOHN - University Of North Carolina; Rand, Tatyana; EMERY, NANCY - University Of Colorado; BERTNESS, MARK - University Of Colorado

Submitted to: PeerJ
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2017
Publication Date: 11/29/2017
Citation: Bruno, J.F., Rand, T.A., Emery, N.C., Bertness, M.D. 2017. Facilitative and competitive interaction components among New England salt marsh plants. PeerJ. 5:e4049. https://doi.org/10.7717/peerj.4049.
DOI: https://doi.org/10.7717/peerj.4049

Interpretive Summary: The interactions between plants can be broken down into positive and negative components. The net interaction between two species is simply the sum of these counteracting forces. Disentangling the positive and negative components of species interactions is a critical step in advancing our understanding of how the interaction shift along gradients, such as soil type or moisture, and whether different species have similar or very different effects on their neighbors. Virtually no information currently exist to address these issues. In this study we carried out a manipulative field experiment to disentangle the positive and negative interaction components between dominant matrix forming grasses and rushes, and a perennial broadleaf plant, Aster tenuifolius, in New England salt marshes. Specifically we asked whether positive and negative interaction components: (1) Are similar or different for three matrix forming grass and rush species (Juncus gerardi, Distichlis spicata, and Spartina patens), and (2) Change across Aster life stages (seedling, young plant vs adult). The strength of the positive component of the matrix-broadleaf interaction was stronger than the negative component for all three matrix species, resulting in a strong positive net interaction. Although there was little difference among matrix species in their net effects, the negative component of the interaction varied slightly; the competitive effect of J. gerardi was negligible while D. spicata had a pronounced negative interaction component. We found little difference in the effects of J. geradi on Aster at different later history stages; interaction component strengths did not differ between juveniles and adults. However, mortality of seedlings in neighbor removal plots was 100%, indicating a particularly strong and critical facilitative effect of matrix species on this forb during the earliest life stages. Overall our results suggest that matrix forming grasses and rushes play a critical and largely redundant role in facilitating Aster across all life history stages.

Technical Abstract: Intra- and interspecific interactions can be broken down into facilitative and competitive components. The net interaction between two organisms is simply the sum of these counteracting elements. Disentangling the positive and negative components of species interactions is a critical step in advancing our understanding of how the interaction between organisms shift along physical and biotic gradients, and whether component interactions are unique or redundant across species in natural communities. Virtually no data currently exist to address these issues. In this study we carried out a manipulative field experiment to disentangle the positive and negative interaction components between dominant matrix forming grasses and rushes, and a perennial forb, Aster tenuifolius, in New England salt marshes. Specifically we asked whether positive and negative interaction components: (1) Are unique or redundant across three matrix forming grass and rush species (Juncus gerardi, Distichlis spicata, and Spartina patens), and (2) Change across Aster life stages (seedling, juvenile vs adult). The strength of the positive component of the matrix-forb interaction was stronger than the negative component for all three matrix species, resulting in a strong positive net interaction. Although there was little variation among matrix species in their net effects, the negative component of the interaction varied slightly; the competitive effect of J. gerardi was negligible while D. spicata had a pronounced negative interaction component. We found little difference in the effects of J. geradi on Aster at different later history stages; interaction component strengths did not differ between juveniles and adults. However, mortality of seedlings in neighbor removal plots was 100%, indicating a particularly strong and critical facilitative effect of matrix species on this forb during the earliest life stages. Overall our results suggest that matrix forming grasses and rushes play a critical and largely redundant role in facilitating Aster across all life history stages.