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Functional redundancy patterns reveal non-random assembly rules in a species-rich marine assemblage.

Guillemot N, Kulbicki M, Chabanet P, Vigliola L - PLoS ONE (2011)

Bottom Line: First, we found that the relationship between functional and species diversity displayed a non-asymptotic power-shaped curve, implying that rare functions and species mainly occur in highly diverse assemblages.Last, we found little effect of habitat on the shape of the functional-species diversity relationship and on the redundancy of functions, although habitat is known to largely determine assemblage characteristics such as species composition, biomass, and abundance.Our study shows that low functional redundancy is characteristic of this highly diverse fish assemblage, and, therefore, that even species-rich ecosystems such as coral reefs may be vulnerable to the removal of a few keystone species.

View Article: PubMed Central - PubMed

Affiliation: UR-CoRéUs, Institut de Recherche pour le Développement, Noumea, New Caledonia. nicolas.guillemot@gmail.com

ABSTRACT
The relationship between species and the functional diversity of assemblages is fundamental in ecology because it contains key information on functional redundancy, and functionally redundant ecosystems are thought to be more resilient, resistant and stable. However, this relationship is poorly understood and undocumented for species-rich coastal marine ecosystems. Here, we used underwater visual censuses to examine the patterns of functional redundancy for one of the most diverse vertebrate assemblages, the coral reef fishes of New Caledonia, South Pacific. First, we found that the relationship between functional and species diversity displayed a non-asymptotic power-shaped curve, implying that rare functions and species mainly occur in highly diverse assemblages. Second, we showed that the distribution of species amongst possible functions was significantly different from a random distribution up to a threshold of ∼90 species/transect. Redundancy patterns for each function further revealed that some functions displayed fast rates of increase in redundancy at low species diversity, whereas others were only becoming redundant past a certain threshold. This suggested non-random assembly rules and the existence of some primordial functions that would need to be fulfilled in priority so that coral reef fish assemblages can gain a basic ecological structure. Last, we found little effect of habitat on the shape of the functional-species diversity relationship and on the redundancy of functions, although habitat is known to largely determine assemblage characteristics such as species composition, biomass, and abundance. Our study shows that low functional redundancy is characteristic of this highly diverse fish assemblage, and, therefore, that even species-rich ecosystems such as coral reefs may be vulnerable to the removal of a few keystone species.

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Relationship between taxonomic diversity and functional diversity: schematic scenarios (redrawn from [16]).
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pone-0026735-g001: Relationship between taxonomic diversity and functional diversity: schematic scenarios (redrawn from [16]).

Mentions: The relationship between taxonomic and functional diversity is necessarily increasing and going through the origin of the graph. Indeed, adding new species to an assemblage can only increase the number of functions or the redundancy of existing functions. A steep slope in the relationship indicates the fast emergence of new functions, whereas a gentle slope implies a greater redundancy of existing functions. Based on this, [16] proposed four schematic relationships between taxonomic and functional diversity (Figure 1). In the first scenario (A1), each species plays a unique functional role, resulting in a 1∶1 linear relationship between the two types of diversity. All other scenarios assume that multiple species can perform similar functions, i.e. some redundancy exists. The second scenario (A2) is a linear relationship with a <1 slope. It implies that a new function can emerge at a constant incremental rate in species diversity. The third scenario (B) describes ecosystems where functional diversity increases rapidly at low species diversity and subsequently increases at declining rates as and when the number of functions represented in the assemblage becomes important. The last scenario (C) assumes that the relationship between species and functional diversity varies with environmental conditions or habitats. Whereas only a few species sharing a limited set of functional traits can coexist in a simple environment, transition towards a new, more complex environment would be characterised by an abrupt increase in both species and functional diversity. The relationship would then stabilise at values that are characteristic of the second environment/habitat. Typically, this S-shaped scenario would occur when an ecosystem recovers from a disturbance. Both curvilinear scenarios (B and C) may or may not reach an asymptote. If past a given number of species all functional roles are represented, then the relationship between taxonomic and functional diversity will become flat [18]. In this case, it would be critical for both ecology and conservation to determine at what level of diversity this asymptote may occur. Alternatively, a non-asymptotic relationship would imply that only high levels of taxonomic diversity can allow the regular installation of new species with unique and probably rare functions [19], [20]. In this case, a small level of environmental degradation on a large scale may quickly make these species endangered.


Functional redundancy patterns reveal non-random assembly rules in a species-rich marine assemblage.

Guillemot N, Kulbicki M, Chabanet P, Vigliola L - PLoS ONE (2011)

Relationship between taxonomic diversity and functional diversity: schematic scenarios (redrawn from [16]).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3198825&req=5

pone-0026735-g001: Relationship between taxonomic diversity and functional diversity: schematic scenarios (redrawn from [16]).
Mentions: The relationship between taxonomic and functional diversity is necessarily increasing and going through the origin of the graph. Indeed, adding new species to an assemblage can only increase the number of functions or the redundancy of existing functions. A steep slope in the relationship indicates the fast emergence of new functions, whereas a gentle slope implies a greater redundancy of existing functions. Based on this, [16] proposed four schematic relationships between taxonomic and functional diversity (Figure 1). In the first scenario (A1), each species plays a unique functional role, resulting in a 1∶1 linear relationship between the two types of diversity. All other scenarios assume that multiple species can perform similar functions, i.e. some redundancy exists. The second scenario (A2) is a linear relationship with a <1 slope. It implies that a new function can emerge at a constant incremental rate in species diversity. The third scenario (B) describes ecosystems where functional diversity increases rapidly at low species diversity and subsequently increases at declining rates as and when the number of functions represented in the assemblage becomes important. The last scenario (C) assumes that the relationship between species and functional diversity varies with environmental conditions or habitats. Whereas only a few species sharing a limited set of functional traits can coexist in a simple environment, transition towards a new, more complex environment would be characterised by an abrupt increase in both species and functional diversity. The relationship would then stabilise at values that are characteristic of the second environment/habitat. Typically, this S-shaped scenario would occur when an ecosystem recovers from a disturbance. Both curvilinear scenarios (B and C) may or may not reach an asymptote. If past a given number of species all functional roles are represented, then the relationship between taxonomic and functional diversity will become flat [18]. In this case, it would be critical for both ecology and conservation to determine at what level of diversity this asymptote may occur. Alternatively, a non-asymptotic relationship would imply that only high levels of taxonomic diversity can allow the regular installation of new species with unique and probably rare functions [19], [20]. In this case, a small level of environmental degradation on a large scale may quickly make these species endangered.

Bottom Line: First, we found that the relationship between functional and species diversity displayed a non-asymptotic power-shaped curve, implying that rare functions and species mainly occur in highly diverse assemblages.Last, we found little effect of habitat on the shape of the functional-species diversity relationship and on the redundancy of functions, although habitat is known to largely determine assemblage characteristics such as species composition, biomass, and abundance.Our study shows that low functional redundancy is characteristic of this highly diverse fish assemblage, and, therefore, that even species-rich ecosystems such as coral reefs may be vulnerable to the removal of a few keystone species.

View Article: PubMed Central - PubMed

Affiliation: UR-CoRéUs, Institut de Recherche pour le Développement, Noumea, New Caledonia. nicolas.guillemot@gmail.com

ABSTRACT
The relationship between species and the functional diversity of assemblages is fundamental in ecology because it contains key information on functional redundancy, and functionally redundant ecosystems are thought to be more resilient, resistant and stable. However, this relationship is poorly understood and undocumented for species-rich coastal marine ecosystems. Here, we used underwater visual censuses to examine the patterns of functional redundancy for one of the most diverse vertebrate assemblages, the coral reef fishes of New Caledonia, South Pacific. First, we found that the relationship between functional and species diversity displayed a non-asymptotic power-shaped curve, implying that rare functions and species mainly occur in highly diverse assemblages. Second, we showed that the distribution of species amongst possible functions was significantly different from a random distribution up to a threshold of ∼90 species/transect. Redundancy patterns for each function further revealed that some functions displayed fast rates of increase in redundancy at low species diversity, whereas others were only becoming redundant past a certain threshold. This suggested non-random assembly rules and the existence of some primordial functions that would need to be fulfilled in priority so that coral reef fish assemblages can gain a basic ecological structure. Last, we found little effect of habitat on the shape of the functional-species diversity relationship and on the redundancy of functions, although habitat is known to largely determine assemblage characteristics such as species composition, biomass, and abundance. Our study shows that low functional redundancy is characteristic of this highly diverse fish assemblage, and, therefore, that even species-rich ecosystems such as coral reefs may be vulnerable to the removal of a few keystone species.

Show MeSH