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Darwin's naturalization conundrum can be explained by spatial scale.

ABSTRACT: Darwin proposed two seemingly contradictory hypotheses regarding factors influencing the outcome of biological invasions. He initially posited that nonnative species closely related to native species would be more likely to successfully establish, because they might share adaptations to the local environment (preadaptation hypothesis). However, based on observations that the majority of naturalized plant species in the United States belonged to nonnative genera, he concluded that the lack of competitive exclusion would facilitate the establishment of alien invaders phylogenetically distinct from the native flora (competition-relatedness hypothesis). To date, no consensus has been reached regarding these opposing hypotheses. Here, following Darwin, we use the flora of the United States to examine patterns of taxonomic and phylogenetic relatedness between native and nonnative taxa across thousands of nested locations ranging in size and extent, from local to regional scales. We find that the probability of observing the signature of environmental filtering over that of competition increases with spatial scale. Further, native and nonnative species tended to be less related in warm, humid environments. Our work provides an empirical assessment of the role of observation scale and climate in biological invasions and demonstrates that Darwin's two opposing hypotheses need not be mutually exclusive.

SUBMITTER: Park DS

PROVIDER: S-EPMC7245080 | biostudies-literature | 2020 May

REPOSITORIES: biostudies-literature

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Darwin's naturalization conundrum can be explained by spatial scale.

Park Daniel S DS Feng Xiao X Maitner Brian S BS Ernst Kacey C KC Enquist Brian J BJ

Proceedings of the National Academy of Sciences of the United States of America 20200504 20

Darwin proposed two seemingly contradictory hypotheses regarding factors influencing the outcome of biological invasions. He initially posited that nonnative species closely related to native species would be more likely to successfully establish, because they might share adaptations to the local environment (preadaptation hypothesis). However, based on observations that the majority of naturalized plant species in the United States belonged to nonnative genera, he concluded that the lack of com ...[more]

PMID: 32366659

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Project description:Background:Despite numerous tests of Darwin's naturalization hypothesis (DNH) evidence for its support or rejection is still contradictory. We tested a DNH derived prediction stating that nonnative species (NNS) without native congeneric relatives (NCR) will spread to a greater number of localities than species with close relatives in the new range. This test controlled the effect of residence time (Rt) on the spread of NNS and used naturalized species beyond their lag phase to avoid the effect of stochastic events in the establishment and the lag phases that could obscure the NCR effects on NNS. Methods:We compared the number of localities (spread) occupied by NNS with and without NCR using 13,977 herbarium records for 305 NNS of weeds. We regressed the number of localities occupied by NNS versus Rt to determine the effect of time on the spread of NNS. Then, we selected the species with Rt greater than the expected span of the lag phase, whose residuals were above and below the regression confidence limits; these NNS were classified as widespread (those occupying more localities than expected by Rt) and limited-spread (those occupying fewer localities than expected). These sets were again subclassified into two groups: NNS with and without NCR at the genus level. The number of NNS with and without NCR was compared using ?2 tests and Spearman correlations between the residuals and the number of relatives. Then, we grouped the NNS using 34 biological attributes and five usages to identify the groups' possible associations with spread and to test DNH. To identify species groups, we performed a nonmetric multidimensional scaling (NMDS) analysis and evaluated the influences of the number of relatives, localities, herbarium specimens, Rt, and residuals of regression. The Spearman correlation and the Mann-Whitney U test were used to determine if the DNH prediction was met. Additionally, we used the clustering objects on subsets of attributes (COSA) method to identify possible syndromes (sets of biological attributes and usages) associated to four groups of NNS useful to test DNH (those with and without NCR and those in more and fewer localities than expected by Rt). Results:Residence time explained 33% of the variation in localities occupied by nonnative trees and shrubs and 46% of the variation for herbs and subshrubs. The residuals of the regression for NNS were not associated with the number or presence of NCR. In each of the NMDS groups, the number of localities occupied by NNS with and without NCR did not significantly differ. The COSA analysis detected that only NNS with NCR in more and fewer localities than expected share biological attributes and usages, but they differ in their relative importance. Discussion:Our results suggest that DNH does not explain the spread of naturalized species in a highly heterogeneous country. Thus, the presence of NCR is not a useful characteristic in risk analyses for naturalized NNS.

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Darwin's naturalization conundrum can be explained by spatial scale.

Publications

Darwin's naturalization conundrum can be explained by spatial scale.

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