Geometric morphometrics meets metacommunity ecology: environment and lineage distribution affects spatial variation in shape

Abstract

Patterns of univariate trait variation across metacommunities are widely explored, as are searches for their underlying causes. Surprisingly, patterns of multivariate shape remain unknown, and the search for drivers of functional traits of communities often neglect the biogeographical distribution of phylogenetic clades. Our aim was to investigate multivariate shape distribution across metacommunities and to determine the main environmental drivers of shape beyond/taking into account the phylogenetic distribution of lineages. We obtained mean skull and mandible shape for 228 species of Neotropical sigmodontine rodents through geometric morphometrics (GM), and then calculated mean shapes for 1°  1° cells across the Neotropics based on the incidence of sigmodontines. We investigated the effects of lineage distribution on mean trait variation by using phylogenetic fuzzy weighting to calculate principal coordinates of phylogenetic structure (PCPS). Effects of environmental variables on shape variation incorporating phylogenetic composition were realized through redundancy analysis. We found that the different distributions of major lineages throughout the Neotropics were responsible for much of the mean shape variation. The association of landscape features with tribal groupings (Oryzomyini with Amazonia and Phyllotini and Abrotrichini with the Andes) were standouts. Environmental variables and lineage distribution explain the same (i.e. shared) portion of shape variation, suggesting phylogenetic niche conservatism at the metacommunity level. Seasonality in temperature and land cover were the best environmental predictors of mean shape: larger tympanic bullae, incisive foramina, and check teeth are all associated with highly seasonal and less vegetated areas. Our new approach of using GM shape across metacommunities was demonstrably useful in understanding largescale biogeographical patterns of shape variation and identifying its underlying causes. The overlap between environmental variables and phylogenetic lineage distribution suggests that a process of niche conservatism is likely: the phenotype-environment correlation is mediated by the differential biogeographical distribution of the main clades.

Using phylogenetic clade composition to understand biogeographical variation in functional traits

“…This is a spatial legacy intrinsic to nature, and should be interpreted instead of corrected for (Hawkins 2012). Full details on the methods can be found in Maestri et al (2016aMaestri et al ( , 2017a. The predictor variables were taken as follows.…”

“…Moreover, size and shape variation can be linked to different sets of predictors Elton 2009, Maestri et al 2016c), suggesting that an analysis of both traits is necessary. Exploration of assemblage-level patterns of variation in size and shape was useful for detection of unknown patterns of trait variation, and to elucidate the role of historical biogeography and macroecological adaptation in the diversification of sigmodontine traits (Maestri et al 2016a(Maestri et al , 2017a.…”

“…However, this approach makes it difficult to investigate how much of the CWM is explained jointly by environmental variables and the phylogenetic distribution of lineages (the portion of variation corresponding to phylogenetic niche conservatism at the metacommunity level; see Pillar and Duarte 2010). Since the distribution of species belonging to distinct phylogenetic lineages across geographical space determines which species are present in a community, and by extension, the CWM, explicit consideration of the distribution of these lineages across an array of metacommunities may be important (Maestri et al 2016a(Maestri et al , 2017a. Failure to account for this distribution may lead to the detection of a spurious correlation between CWM and environmental factors, which could arise simply due to different spatial distributions of the ancestors that gave rise to entire clades (assuming clades with shared traits), distributed in allopatry across space (Lawing et al 2016, Polly et al 2017.…”

“…Maestri (2017) and Maestri et al (2016aMaestri et al ( , 2017a aimed to investigate how the phylogenetic distributions of lineages interact with environmental variables to explain mean trait distribution across metacommunities. CWM was calculated using univariate body size (Maestri et al 2016a) and, for the first time, using multivariate shape (Maestri et al 2017a).…”

“…CWM was calculated using univariate body size (Maestri et al 2016a) and, for the first time, using multivariate shape (Maestri et al 2017a). I analyzed the data using a variance-partitioning analysis framework, whereby the effects of environmental variables and clade composition, both singly and jointly, can be teased apart (Fig.…”