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The shift from plant – plant facilitation to competition under severe water deficit is spatially explicit

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ABSTRACT

The stress‐gradient hypothesis predicts a higher frequency of facilitative interactions as resource limitation increases. Under severe resource limitation, it has been suggested that facilitation may revert to competition, and identifying the presence as well as determining the magnitude of this shift is important for predicting the effect of climate change on biodiversity and plant community dynamics. In this study, we perform a meta‐analysis to compare temporal differences of species diversity and productivity under a nurse plant (Retama sphaerocarpa) with varying annual rainfall quantity to test the effect of water limitation on facilitation. Furthermore, we assess spatial differences in the herbaceous community under nurse plants in situ during a year with below‐average rainfall. We found evidence that severe rainfall deficit reduced species diversity and plant productivity under nurse plants relative to open areas. Our results indicate that the switch from facilitation to competition in response to rainfall quantity is nonlinear. The magnitude of this switch depended on the aspect around the nurse plant. Hotter south aspects under nurse plants resulted in negative effects on beneficiary species, while the north aspect still showed facilitation. Combined, these results emphasize the importance of spatial heterogeneity under nurse plants for mediating species loss under reduced precipitation, as predicted by future climate change scenarios. However, the decreased water availability expected under climate change will likely reduce overall facilitation and limit the role of nurse plants as refugia, amplifying biodiversity loss.

No MeSH data available.


Relative effect of Retama on species richness and productivity. Relative interaction intensity for (a) plant species richness and (b) community productivity as a function of total rainfall from September to March from four different years of sampling near Tabernas, Spain. The black points represent model estimates (95% CI), and the gray points are individual samples. Three of the data sets (2009, 2010, and one from 2015) have been published (Armas et al., 2011; Hortal et al., 2015; Schöb et al., 2013)
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ece32875-fig-0002: Relative effect of Retama on species richness and productivity. Relative interaction intensity for (a) plant species richness and (b) community productivity as a function of total rainfall from September to March from four different years of sampling near Tabernas, Spain. The black points represent model estimates (95% CI), and the gray points are individual samples. Three of the data sets (2009, 2010, and one from 2015) have been published (Armas et al., 2011; Hortal et al., 2015; Schöb et al., 2013)

Mentions: Relative interaction intensity (RII) for both species richness and productivity shifted from positive (i.e., facilitation) to negative (i.e., competition) as total rainfall decreased. However, the significant categorical rainfall variable—fit after the continuous term (Table S2)—indicates that RII did not respond linearly to decreasing rainfall. Therefore, below a distinct rainfall quantity RII became significantly negative (Figure 2a,b). The highest two rainfall years were statistically indistinguishable from each other but had significantly higher RII biomass values than the other 2 years (Figure 2b). Although the lowest rainfall year showed overall negative RII values, there were plots in the north and west aspects under some Retama with positive RII values.


The shift from plant – plant facilitation to competition under severe water deficit is spatially explicit
Relative effect of Retama on species richness and productivity. Relative interaction intensity for (a) plant species richness and (b) community productivity as a function of total rainfall from September to March from four different years of sampling near Tabernas, Spain. The black points represent model estimates (95% CI), and the gray points are individual samples. Three of the data sets (2009, 2010, and one from 2015) have been published (Armas et al., 2011; Hortal et al., 2015; Schöb et al., 2013)
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5383484&req=5

ece32875-fig-0002: Relative effect of Retama on species richness and productivity. Relative interaction intensity for (a) plant species richness and (b) community productivity as a function of total rainfall from September to March from four different years of sampling near Tabernas, Spain. The black points represent model estimates (95% CI), and the gray points are individual samples. Three of the data sets (2009, 2010, and one from 2015) have been published (Armas et al., 2011; Hortal et al., 2015; Schöb et al., 2013)
Mentions: Relative interaction intensity (RII) for both species richness and productivity shifted from positive (i.e., facilitation) to negative (i.e., competition) as total rainfall decreased. However, the significant categorical rainfall variable—fit after the continuous term (Table S2)—indicates that RII did not respond linearly to decreasing rainfall. Therefore, below a distinct rainfall quantity RII became significantly negative (Figure 2a,b). The highest two rainfall years were statistically indistinguishable from each other but had significantly higher RII biomass values than the other 2 years (Figure 2b). Although the lowest rainfall year showed overall negative RII values, there were plots in the north and west aspects under some Retama with positive RII values.

View Article: PubMed Central - PubMed

ABSTRACT

The stress‐gradient hypothesis predicts a higher frequency of facilitative interactions as resource limitation increases. Under severe resource limitation, it has been suggested that facilitation may revert to competition, and identifying the presence as well as determining the magnitude of this shift is important for predicting the effect of climate change on biodiversity and plant community dynamics. In this study, we perform a meta‐analysis to compare temporal differences of species diversity and productivity under a nurse plant (Retama sphaerocarpa) with varying annual rainfall quantity to test the effect of water limitation on facilitation. Furthermore, we assess spatial differences in the herbaceous community under nurse plants in situ during a year with below‐average rainfall. We found evidence that severe rainfall deficit reduced species diversity and plant productivity under nurse plants relative to open areas. Our results indicate that the switch from facilitation to competition in response to rainfall quantity is nonlinear. The magnitude of this switch depended on the aspect around the nurse plant. Hotter south aspects under nurse plants resulted in negative effects on beneficiary species, while the north aspect still showed facilitation. Combined, these results emphasize the importance of spatial heterogeneity under nurse plants for mediating species loss under reduced precipitation, as predicted by future climate change scenarios. However, the decreased water availability expected under climate change will likely reduce overall facilitation and limit the role of nurse plants as refugia, amplifying biodiversity loss.

No MeSH data available.