Better understanding the tradeoffs presented by different bioplastics should help elucidate which options, if any, are viable replacements over the long run.
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Edited by Jonathan B. Losos, Washington University in St. Louis, St. Louis, MO, and approved May 6, 2019 (received for review October 22, 2018)
Significance
The island species–area relationship (ISAR) is a fundamental diversity pattern, best described by the power model. Biogeographic theory assumes predictable variation in power model parameters in relation principally to system isolation, but these assumptions are only weakly supported by previous work, which has been limited in considering the two parameters separately and oversimplistically. By developing and testing a hierarchical (structural equation) model of factors influencing ISAR form, we show that island species diversity patterns are shaped by intra-archipelago processes more strongly than by isolation from mainland source pools. These findings point to a need to quantify the role of differing scales of isolation in influencing propagule exchange among insular systems to develop improved predictive diversity models.
Abstract
The increase in species richness with island area (ISAR) is a well-established global pattern, commonly described by the power model, the parameters of which are hypothesized to vary with system isolation and to be indicative of ecological process regimes. We tested a structural equation model of ISAR parameter variation as a function of taxon, isolation, and archipelago configuration, using a globally distributed dataset of 151 ISARs encompassing a range of taxa and archipelago types. The resulting models revealed a negative relationship between ISAR intercept and slope as a function of archipelago species richness, in turn shaped by taxon differences and by the amount and disposition of archipelago area. These results suggest that local-scale (intra-archipelago) processes have a substantial role in determining ISAR form, obscuring the diversity patterns predicted by island theory as a function of archipelago isolation. These findings have implications for the use and interpretation of ISARs as a tool within biogeography, ecology, and conservation.
Footnotes
- ↵1To whom correspondence may be addressed. Email: robert.whittaker{at}ouce.ox.ac.uk.
Author contributions: T.J.M., F.R., K.A.T., and R.J.W. designed research; T.J.M., F.R., K.A.T., and R.J.W. performed research; T.J.M., F.R., K.A.T., and R.J.W. analyzed data; and T.J.M., F.R., K.A.T., and R.J.W. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1818190116/-/DCSupplemental.
Published under the PNAS license.
A global model of island species–area relationships
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- Ecology
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