Community assembly in Nothobranchius annual fishes: Nested patterns, environmental niche and biogeographic history

Abstract

The assembly of local communities from regional species pools is shaped by historical aspects of distribution, environmental conditions, and biotic interactions. We studied local community assembly patterns in African annual killifishes of the genus Nothobranchius (Cyprinodontiformes), investigating data from 168 communities across the entire range of regionally co-existing species. Nothobranchius are small fishes associated with annually desiccating pools. We detected a nested pattern of local communities in one region (Southern Mozambique, with Nothobranchius furzeri as the core and dominant species), but no nestedness was found in the second region (Central Mozambique, with Nothobranchius orthonotus being the dominant species). A checkerboard pattern of local Nothobranchius community assembly was demonstrated in both regions. Multivariate environmental niche modeling revealed moderate differences in environmental niche occupancy between three monophyletic clades that largely co-occurred geographically and greater differences between strictly allopatric species within the clades. Most variation among species was observed along an altitudinal gradient; N. furzeri and Nothobranchius kadleci were absent from coastal plains, Nothobranchius pienaari, Nothobranchius rachovii, and Nothobranchius krysanovi were associated with lower altitude and N. orthonotus was intermediate and geographically most widespread species. We discuss implications for ecological and evolutionary research in this taxon.

Keywords: Africa; altitudinal gradient; checkerboard pattern; dispersal; ephemeral pools; temporary water body.

Figure 1

Adult males of all study species

Figure 2

Distribution maps of three study clades and species co‐existence. The presence of (a) Nothobranchius furzeri (yellow) an Nothobranchius kadleci (dark red), (b) Nothobranchius orthonotus (violet), and (c) Nothobranchius pienaari (black), Nothobranchius rachovii (blue) and Nothobranchius krysanovi (red) populations at particular sites. Small empty points represent sampled sites where population of a given clade was absent. (d) A combined dataset illustrating geographic aspect of species co‐occurrence in local Nothobranchius communities, where sites with single, two and three co‐existing species are illustrated. An inset details the region with a parapatric distribution of N. rachovii and N. pienaari. The maps were created in R environment (R Core Team 2015) [packages sp (Bivand, Pebesma, & Gomez‐Rubio, 2013), rgdal (Bivand, Keitt, & Rowlingson, 2016), maps (Becker, Wilks, Brownrigg, Minka, & Deckmyn, 2016) and GIStools (Brunsdon & Chen, 2014)]. The altitudinal gradient for Mozambique was downloaded from http://www.diva-gis.org/gdata

Figure 3

Quantification of species co‐existence in local Nothobranchius communities. Venn diagrams visualizing proportional species co‐occurrence (a) within Nothobranchius furzeri range, (b) within Nothobranchius kadleci range and (c) outside the range of F‐clade. Diagrams were constructed using Venny 2.0.2 (Oliveros, 2007–2015)

Figure 4

Relative species abundance. Quantitative estimates of relative species abundance were calculated as relative proportion of individuals of a particular species in a Nothobranchius community for a given site. Co‐existence between (a) Nothobranchius furzeri and its congeners, (b) Nothobranchius kadleci and congeners, and (c) Nothobranchius orthonotus and Nothobranchius pienaari are illustrated. Mean values with 95% confidence intervals were calculated from a set of all separate species ratios. The number of communities used for quantitative estimates is given for each combination

Figure 5

Niche similarity among and within clades. Two‐dimensional visualization of niches along environmental gradient detected by the principle component analysis (PCA). (a–c) clade‐specific niches with (d) correlation of environmental predictors with PCA axes, and species‐specific niches for (e) Nothobranchius furzeri, (f) Nothobranchius kadleci, (g) Nothobranchius pienaari, (h) Nothobranchius rachovii and (i) Nothobranchius krysanovi. Gray shading indicates density of occurrence along two PCA gradients. The solid and dashed contours indicate 100% and 50% of available environment, respectively

Figure 6

Univariate responses of species presence to altitudinal gradient. The response curves were constructed using general additive models, with three knots fixed to account for second‐order polynomial fit. Mean smoother estimates visualize the probability of particular species presence along altitudinal gradients, with 95% confidence intervals