Linking Darwin’s naturalisation hypothesis and Elton’s diversity–invasibility hypothesis in experimental grassland communities

TLDR: This study explicitly demonstrates for the first time how the mechanisms underlying the two classical invasion hypotheses interact in driving invasion success in grassland communities.

Abstract: Darwin's naturalisation hypothesis posing that phylogenetic distance of alien species to native residents predicts invasion success, and Elton's diversity-invasibility hypothesis posing that diversity of native communities confers resistance to invasion , are both rooted in ideas of species coexistence. Because the two hypotheses are inherently linked, the mechanisms underlying them may interact in driving the invasion success. Even so, these links and interactions have not been explicitly disentangled in one experimental study before. To disentangle the links between the two hypotheses, we used 36 native grassland herbs to create greenhouse mesocosms with 90 grassland communities of different diversities, and introduced each of five herbaceous alien species as seeds and seedlings. We used phylogeny and four functional traits (plant height, specific leaf area, leaf size, and seed mass) to calculate different measures of phy-logenetic and functional distance and diversity. Specifically, we tested how the alien-native distance (phylogenetic or functional) and the native diversity (phylo-genetic or functional) affected each other in their effects on germination, seedling survival, growth, and reproduction of the aliens. Overall, our results supported both hypotheses. Multivariate functional distance based on four traits jointly had stronger positive effects than phylogenetic distance and the univariate ones based on each trait separately. Moreover, the aliens were more successful if they were more competitive by being taller and having larger leaves with a lower SLA than the native residents. Univariate functional diversity based on each trait separately had stronger negative effects than phyloge-netic and multivariate functional diversity. Most importantly, we found that the effects of alien-native phylogenetic and multivariate functional distance became stronger as diversity increased. Our analyses with single traits also showed that the strength of the effects of both alien-native hierarchical functional distances (indicative of competitive inequalities) and absolute functional distances (indica-tive of niche differences) increased at higher diversities, where competition is more severe. Synthesis. Our study explicitly demonstrates for the first time how the mechanisms underlying the two classical invasion hypotheses interact in driving invasion success in grassland communities. This may help to explain some of the puzzling results of studies testing either of the two hypotheses.

Figures

Fig. 1 Contour plots illustrating the effects of: a-d) phylogenetic distance between alien species and residents (PDist), phylogenetic diversity of 659 native communities (PDiv), and their interaction (PDist × PDiv), and e-h) multivariate functional distance between alien species and residents 660 (FDist) and multivariate functional diversity of native communities (FDiv), based on all four functional traits (height, SLA, leaf size and seed mass) 661 jointly, and their interaction (FDist × FDiv), on germination rate, seedling survival rate, biomass and reproduction (number of reproductive units) of 662 alien species. For the statistical results, see Tables 1 and 2. Significance of the main effects (PDist, PDiv, FDist, FDiv) and the interactions (PDiv × 663 PDist , FDist × FDiv) is indicated as ns (i.e. non-significant, P≥0.05), * (P < 0.05), ** (P < 0.01), *** (P < 0.001) in the upper right corner of each plot. 664 The column right to each plot indicates values of the respective response variable. 665

Fig. 2 Contour plots illustrating the effects of either univariate hierarchical functional distance (hFDist) or univariate absolute functional distance 668 (aFDist) between alien species and residents, univariate functional diversity of native communities (FDiv), based on each single functional trait 669 (height, SLA, leaf size and seed mass) separately, and their interaction (hFDist / aFDist × FDiv), on a.1-a.8) germination rate, b.1-b.8) seedling 670 survival rate, c.1-c.8) biomass, and d.1-d.8) reproduction (number of reproductive units) of alien species. For the statistical results, see Table 3. 671 Significance of the main effects (hFDist, aFDist, FDiv) and the interactions (hFDist × FDiv, aFDist × FDiv) is indicated as ns (i.e. non-significant, 672 P≥0.05), * (P < 0.05), ** (P < 0.01), *** (P < 0.001) in the upper right corner of each plot. The column right to each plot indicates values of the 673 respective response variable. 674

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Linking Darwin’s naturalisation hypothesis and Elton’s
diversity-invasibility hypothesis in experimental
grassland communities
Yanhao Feng, Timothée Fouqueray, Mark van Kleunen
To cite this version:
Yanhao Feng, Timothée Fouqueray, Mark van Kleunen. Linking Darwin’s naturalisation hypoth-
esis and Elton’s diversity-invasibility hypothesis in experimental grassland communities. Journal of
Ecology, Wiley, 2018, Ecological Succession in a Changing World, 107 (2), pp.794-805. �10.1111/1365-
2745.13061�. �hal-02457011�

1
Linking Darwin's naturalisation hypothesis and Elton’s diversity-invasibility
1
hypothesis in experimental grassland communities
2
Yanhao Feng*
1,2,3
, Timothée Donatien Fouqueray
1,4
& Mark van Kleunen
1,5
3
1
Ecology, Department of Biology, University of Konstanz, Universitätsstrasse 10, Konstanz,
4
78464, Germany
5
2
Department for Physiological Diversity, Helmholtz Centre for Environmental Research - UFZ,
6
Permoserstraße 15, 04318 Leipzig, Germany
7
3
Department for Physiological Diversity, German Center for Integrative Biodiversity Research
8
(iDiv), Deutscher Platz 5e, 04103 Leipzig, Germany
9
4
Department of Biology, Ecole Normale Supérieure de Lyon, 15 parvis René Descartes,
10
69007 Lyon, France
11
5
Zhejiang Provincial Key Laboratory of Plant Evolutionary Ecology and Conservation,
12
Taizhou University, Taizhou 318000, China
13
14
Author of correspondence:
15
Yanhao Feng
16
Phone: +49 (0) 341-97-33230
17
*Email: yanhao.feng@idiv.de
18

2
Abstract
19
1. Darwin's naturalisation hypothesis posing that phylogenetic distance of alien species
20
to native residents predicts invasion success, and Elton’s diversity-invasibility
21
hypothesis posing that diversity of native communities confers resistance to invasion,
22
are both rooted in ideas of species coexistence. Because the two hypotheses are
23
inherently linked, the mechanisms underlying them may interact in driving the
24
invasion success. Even so, these have not been explicitly disentangled in one
25
experimental study before.
26
2. To disentan g le the potential links and interactions, we created greenhouse
27
mesocosms with 90 native grassland communities of different diversities with 36
28
herbaceous native species and introduced each of five herbaceous alien species as
29
seeds and seedlings. Specifically, we tested how the alien-native (phylogenetic or
30
functional) distance and the native diversity affected each other in their effects on
31
germination, seedling survival, growth and reproduction of the aliens. To disentangle
32
the underlying mechanisms of the interactions, we used phylogeny and four
33
functional traits (plant height, specific leaf area, leaf size, seed mass) to calculate
34
different measures of phylogenetic and functional distance and diversity.
35
3. Overall, our results supported both hypotheses. Multivariate functional distance
36
based on four traits jointly had stronger positive effects than phylogenetic distance
37
and the univariate ones based on each trait separately. Moreover, the aliens were
38
more successful if they are more competitive by being taller and having larger leaves
39
with a lower SLA than the native residents. Univariate functional diversity based on
40

3
each trait separately had stronger negative effects than phylogenetic and multivariate
41
functional diversity. More importantly, we found that the effects of alien-native
42
phylogenetic and multivariate functional distance strengthened as diversity increased.
43
Our analyses with single traits also showed that the strength of the effects of both
44
alien-native hierarchical functional distances (indicative of competitive inequalities)
45
and absolute functional distances (indicative of niche differences) reinforced at higher
46
diversities where competition is more severe.
47
4. Synthesis. Our study explicitly demonstrates for the first time how the mechanisms
48
underlying the two classical invasion hypotheses interact in driving invasion success
49
in grassland communities. This may help to explain some of the puzzling results of
50
studies testing either of the two hypotheses.
51
Keywords
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Darwin's naturalisation conundrum, biotic resistance, modern coexistence theory, niche
53
differences, competitive inequality, competitive exclusion, invasion ecology
54

4
Introduction
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A major quest in ecology is to understand the mechanisms driving the success of alien
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species in native communities. While numerous invasion hypotheses have been proposed, it
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is suggested that the mechanisms associated with some of them may be implicitly interlinked
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(Catford, Jansson & Nilsson 2009; Jeschke 2014). In essence, whether or not alien species
59
invade native communities is a question of coexistence between alien species and native
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residents. Classical invasion hypotheses, which are often rooted in ideas of species
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coexistence (Levine & D'Antonio 1999; MacDougall, Gilbert & Levine 2009), have long
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focused on identifying the characteristics predisposing alien species to become invasive and
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the properties that render native communities invasible (Richardson & Pyšek 2006). Darwin
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(1859) posited that alien species will be more successful in a native community if they are
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phylogenetically distantly related to native residents (Darwin’s naturalisation hypothesis),
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because phylogenetic distance may indicate niche differences favouring coexistence (Violle
67
et al. 2011). Elton (1958) proposed that alien species will be less successful in more diverse
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native communities (Elton’s diversity-invasibility hypothesis), where fewer unoccupied niches
69
are available for newcomers (Herbold & Moyle 1986).
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Numerous studies have tested Darwin’s naturalisation hypothesis, but the results are
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mixed (Duncan & Williams 2002; Strauss, Webb & Salamin 2006; Diez et al. 2008; Jiang,
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Tan & Pu 2010; Li et al. 2015a; Feng & van Kleunen 2016; Yannelli et al. 2017). Potential
73
explanations are that the studies differ in the spatial and phylogenetic scales considered
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(Thuiller et al. 2010) and stages of invasions (Li et al. 2015b; Cadotte et al. 2018), and are
75

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