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Contrasting species and functional beta diversity in montane ant assemblages

View Article: PubMed Central - PubMed

ABSTRACT

Aim: Beta diversity describes the variation in species composition between sites and can be used to infer why different species occupy different parts of the globe. It can be viewed in a number of ways. First, it can be partitioned into two distinct patterns: turnover and nestedness. Second, it can be investigated from either a species identity or a functional‐trait point of view. We aim to document for the first time how these two aspects of beta diversity vary in response to a large environmental gradient.

Location: Maloti‐Drakensberg Mountains, southern Africa.

Methods: We sampled ant assemblages along an extensive elevational gradient (900–3000 m a.s.l.) twice yearly for 7 years, and collected functional‐trait information related to the species’ dietary and habitat‐structure preferences. We used recently developed methods to partition species and functional beta diversity into their turnover and nestedness components. A series of models were used to test whether the observed beta diversity patterns differed from random expectations.

Results: Species beta diversity was driven by turnover, but functional beta diversity was composed of both turnover and nestedness patterns at different parts of the gradient. Null models revealed that deterministic processes were likely to be responsible for the species patterns but that the functional changes were indistinguishable from stochasticity.

Main conclusions: Different ant species are found with increasing elevation, but they tend to represent an increasingly nested subset of the available functional strategies. This finding is unique and narrows down the list of possible factors that control ant existence across elevation. We conclude that diet and habitat preferences have little role in structuring ant assemblages in montane environments and that some other factor must be driving the non‐random patterns of species turnover. This finding also highlights the importance of distinguishing between different kinds of beta diversity.

No MeSH data available.


Related in: MedlinePlus

Biplot displaying the structure of the morphological space on the first two principal coordinate axes occupied by the ant fauna of the Sani Pass, southern Africa. Each data point is a species. Lower and left hand axes describe the axis scores (synthetic traits) for each species. Upper and right hand axes describe the loadings of each original trait on the principal coordinate axes. The loadings of each original trait are visualized with red labels and arrows (WL, Weber's length; ML, relative mandible length; LL, relative leg length; EP, eye position). For illustration, black dashed lines represent the convex hull of the entire ant fauna. Inner and outer blue dashed lines represent the convex hull of the assemblages at 3000 and 900 m a.s.l., respectively, for the wet season of 2009. These two assemblages display functional nestedness.
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jbi12537-fig-0001: Biplot displaying the structure of the morphological space on the first two principal coordinate axes occupied by the ant fauna of the Sani Pass, southern Africa. Each data point is a species. Lower and left hand axes describe the axis scores (synthetic traits) for each species. Upper and right hand axes describe the loadings of each original trait on the principal coordinate axes. The loadings of each original trait are visualized with red labels and arrows (WL, Weber's length; ML, relative mandible length; LL, relative leg length; EP, eye position). For illustration, black dashed lines represent the convex hull of the entire ant fauna. Inner and outer blue dashed lines represent the convex hull of the assemblages at 3000 and 900 m a.s.l., respectively, for the wet season of 2009. These two assemblages display functional nestedness.

Mentions: The first two PCoA axes captured c. 80% of the variation present in the morphological structure of the ant traits (Table 1). This variation was split nearly evenly between the two axes. Given the loadings of the original traits in the PCoA, we interpret axis 1 as a gradient in predatory specialization (Table 1, Fig. 1): species with traits associated with being predatory specialists (relatively large mandibles, laterally positioned eyes and relatively short legs) had negative scores on axis 1, whereas species with more generalized traits (relatively short mandibles, dorsally positioned eyes and relatively long legs) had positive scores on axis 1. We interpret axis 2 as representing preference for different habitat complexities (Table 1, Fig. 1). Species with traits indicating that they occupy dense, complex habitats (small bodies, relatively short mandibles and short legs) had positive scores on axis 2; species with traits indicating that they occupy open, simple habitats (large bodies, relatively long mandibles and relatively long legs) had negative scores on axis 2. As the first two axes contain most of the variation in the morphological traits, we only use these axes for the interpretation of our results.


Contrasting species and functional beta diversity in montane ant assemblages
Biplot displaying the structure of the morphological space on the first two principal coordinate axes occupied by the ant fauna of the Sani Pass, southern Africa. Each data point is a species. Lower and left hand axes describe the axis scores (synthetic traits) for each species. Upper and right hand axes describe the loadings of each original trait on the principal coordinate axes. The loadings of each original trait are visualized with red labels and arrows (WL, Weber's length; ML, relative mandible length; LL, relative leg length; EP, eye position). For illustration, black dashed lines represent the convex hull of the entire ant fauna. Inner and outer blue dashed lines represent the convex hull of the assemblages at 3000 and 900 m a.s.l., respectively, for the wet season of 2009. These two assemblages display functional nestedness.
© Copyright Policy - creativeCommonsBy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4979679&req=5

jbi12537-fig-0001: Biplot displaying the structure of the morphological space on the first two principal coordinate axes occupied by the ant fauna of the Sani Pass, southern Africa. Each data point is a species. Lower and left hand axes describe the axis scores (synthetic traits) for each species. Upper and right hand axes describe the loadings of each original trait on the principal coordinate axes. The loadings of each original trait are visualized with red labels and arrows (WL, Weber's length; ML, relative mandible length; LL, relative leg length; EP, eye position). For illustration, black dashed lines represent the convex hull of the entire ant fauna. Inner and outer blue dashed lines represent the convex hull of the assemblages at 3000 and 900 m a.s.l., respectively, for the wet season of 2009. These two assemblages display functional nestedness.
Mentions: The first two PCoA axes captured c. 80% of the variation present in the morphological structure of the ant traits (Table 1). This variation was split nearly evenly between the two axes. Given the loadings of the original traits in the PCoA, we interpret axis 1 as a gradient in predatory specialization (Table 1, Fig. 1): species with traits associated with being predatory specialists (relatively large mandibles, laterally positioned eyes and relatively short legs) had negative scores on axis 1, whereas species with more generalized traits (relatively short mandibles, dorsally positioned eyes and relatively long legs) had positive scores on axis 1. We interpret axis 2 as representing preference for different habitat complexities (Table 1, Fig. 1). Species with traits indicating that they occupy dense, complex habitats (small bodies, relatively short mandibles and short legs) had positive scores on axis 2; species with traits indicating that they occupy open, simple habitats (large bodies, relatively long mandibles and relatively long legs) had negative scores on axis 2. As the first two axes contain most of the variation in the morphological traits, we only use these axes for the interpretation of our results.

View Article: PubMed Central - PubMed

ABSTRACT

Aim: Beta diversity describes the variation in species composition between sites and can be used to infer why different species occupy different parts of the globe. It can be viewed in a number of ways. First, it can be partitioned into two distinct patterns: turnover and nestedness. Second, it can be investigated from either a species identity or a functional‐trait point of view. We aim to document for the first time how these two aspects of beta diversity vary in response to a large environmental gradient.

Location: Maloti‐Drakensberg Mountains, southern Africa.

Methods: We sampled ant assemblages along an extensive elevational gradient (900–3000 m a.s.l.) twice yearly for 7 years, and collected functional‐trait information related to the species’ dietary and habitat‐structure preferences. We used recently developed methods to partition species and functional beta diversity into their turnover and nestedness components. A series of models were used to test whether the observed beta diversity patterns differed from random expectations.

Results: Species beta diversity was driven by turnover, but functional beta diversity was composed of both turnover and nestedness patterns at different parts of the gradient. Null models revealed that deterministic processes were likely to be responsible for the species patterns but that the functional changes were indistinguishable from stochasticity.

Main conclusions: Different ant species are found with increasing elevation, but they tend to represent an increasingly nested subset of the available functional strategies. This finding is unique and narrows down the list of possible factors that control ant existence across elevation. We conclude that diet and habitat preferences have little role in structuring ant assemblages in montane environments and that some other factor must be driving the non‐random patterns of species turnover. This finding also highlights the importance of distinguishing between different kinds of beta diversity.

No MeSH data available.


Related in: MedlinePlus