Secondary foundation species enhance biodiversity


It has long been recognized that primary foundation species (FS), such as trees and seagrasses, enhance biodiversity. Among the species facilitated are secondary FS, including mistletoes and epiphytes. Case studies have demonstrated that secondary FS can further modify habitat-associated organisms (‘inhabitants’), but their net effects remain unknown. Here we assess how inhabitants, globally, are affected by secondary FS. We extracted and calculated 2,187 abundance and 397 richness Hedges’ g effect sizes from 91 and 50 publications, respectively. A weighted meta-analysis revealed that secondary FS significantly enhanced the abundance and richness of inhabitants compared to the primary FS alone. This indirect facilitation arising through sequential habitat formation was consistent across environmental and experimental conditions. Complementary unweighted analyses on log response ratios revealed that the magnitude of these effects was similar to the global average strength of direct facilitation from primary foundation species and greater than the average strength of trophic cascades, a widely recognized type of indirect facilitation arising through sequential consumption. The finding that secondary FS enhance the abundance and richness of inhabitants has important implications for understanding the mechanisms that regulate biodiversity. Integrating secondary FS into conservation practice will improve our ability to protect biodiversity and ecosystem function.

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Fig. 1: Primary and secondary foundation species and their inhabitants: definitions and examples.
Fig. 2: Effects of secondary FS on abundance and taxonomic richness of inhabitants.


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M.S.T. and D.R.S. were supported by the Marsden Fund of the Royal Society of New Zealand and the Coasts and Oceans programme of The National Institute of Water and Atmospheric Research. T.W. and P.E.G. were supported by funding from the Australian Research Council. C.A. was supported by National Science Foundation (NSF) DEB 1546638. P.M.S. is supported by the Cawthron Institute. The authors acknowledge financial support from the Centre of Integrative Ecology, School of Biological Sciences, University of Canterbury, for the workshop ‘Facilitation cascades across ecosystems’.

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M.S.T. identified relevant literature, extracted all data and calculated effect sizes. M.S.T. and Q.H. analysed the data. All authors contributed to the development of the experimental design, data interpretation and manuscript.

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Correspondence to Mads S. Thomsen.

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Supplementary information

Supplementary Information

Supplementary Methods, Supplementary Figures 1–2, Supplementary References, Supplementary Results.

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Supplementary Table 1

List of studies and foundation species analysed

Supplementary Data 1

List of all analysed effect sizes and test variables

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Thomsen, M.S., Altieri, A.H., Angelini, C. et al. Secondary foundation species enhance biodiversity. Nat Ecol Evol 2, 634–639 (2018).

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