Extinction and morphospace occupation: A critical review

Abstract

Processes of extinction, especially selectivity, can be studied using the distribution of species in morphospace. Random extinction reduces the number of species but has little effect on the range of morphologies or ecological roles in a fauna or flora. In contrast, selective extinction culls species based on their functional relationship to the altered environment and, therefore, to their position within a morphospace. Analysis of the distribution of extinctions within morphospaces can thus help understand whether the drivers of the extinction are linked to functional traits. Current approaches include measuring changes in disparity, mean morphology, or evenness between pre- and post-extinction morphologies. Not all measurements are straightforward, however, because morphospaces may be non-metric or non-linear in ways that can mislead interpretation. Dimension-reduction techniques like principal component analysis – commonly used with highly multivariate geometric morphometric data sets – have properties that can make the center of morphospace falsely appear to be densely populated, can make selective extinctions appear randomly distributed, or can make a group of non-specialized morphologies appear to be extreme outliers. Applying fully multivariate metrics and statistical tests will prevent most misinterpretations, as will making explicit functional connections between morphology and the underlying extinction processes.

A Cybertaxonomic Revision of the “Crocidura pergrisea” Species Complex with a Special Focus on Endemic Rocky Shrews: Crocidura armenica and Crocidura arispa (Soricidae)

“…The key sample comprises three species from the “pergrisea” group: C. armenica , C. arispa , and C. serezkyensis , which came from type localities ( Figure 3 ). The main concept of the morphological comparison in the current study is the morphospace estimation approach [ 33 , 36 ]; therefore, there were 13 species added into the analysis for the multidimensional morphospace building. These species were chosen as they had the following characteristics: (i) a geographic position relatively close to the key group within Central and East Asia: C. suaveolens , C. caspica , C. gueldenstaedtii , C. leucodon , and C. zarudnyi ( Table S3 ); (ii) membership in a certain phylogenetic group [ 16 ]: the C. leucodon clade ( C. leucodon ) or the C. suaveolens clade ( C. gueldenstaedtii , C. caspica , C. shantungensis , C. sibirica , C. suaveolens , and C. zarudnyi ); (iii) presence in previously studied three-dimensional datasets [ 20 ]: the East Palearctic shrew, C. lasiura , along with three species from the East Asian clade: C. phanluongi , C. sapaensis , and C. zaitsevi .…”

“…The recent paper of Polly [ 33 ] discusses possible misinterpretations of morphospace analysis results. Because our main approach to the interspecies analysis is a morphospace assessment [ 20 , 29 , 30 , 31 , 32 ], we should take into account Polly’s main statement: consequences of ignoring the full dimensionality of morphospace can potentially mislead an investigator [ 33 ].…”

“…The recent paper of Polly [ 33 ] discusses possible misinterpretations of morphospace analysis results. Because our main approach to the interspecies analysis is a morphospace assessment [ 20 , 29 , 30 , 31 , 32 ], we should take into account Polly’s main statement: consequences of ignoring the full dimensionality of morphospace can potentially mislead an investigator [ 33 ]. In the present study, to avoid potentially misleading conclusions, we used (a) the Jackson algorithm (see above) for choosing loaded axes that include “biological information” about the shape variation; and (b) cluster analysis (UPGMA) based on Euclidean distances of the Procrustes coordinates.…”

“…According to the difficulties of the integrative approach that are described above, we assume that there are three main benefits of CTtax as follows: (a) Cybertypes are freely accessible via existing digital repositories (e.g., MorphoBank), and each 3D model of a cybertype and additional specimens (hypodigm) is accompanied by morphological descriptions and two-dimensional images, which will contribute to comprehensibility of the description. (b) 3D datasets of particular morphological complexes (e.g., a hemimandible and isolated tooth) are obtained as raw data for a multivariate analysis, including a morphospace analysis [ 20 , 30 , 32 ] (regarding this approach, see the recent paper by Polly [ 33 ]). The morphospace analysis by means of 3D datasets is a powerful and sensitive tool for describing morphological variety and for comparisons at different levels, and is at least more sensitive than linear-data-based morphometry, which is important for rare and damaged material.…”

Morphospace dynamics and intraspecies variety of Sorex araneus and S. tundrensis according to recent and fossil data

“…The components located above the "broken-stick" were chosen for the analysis. This approach allows us avoid possible misinterpretations of the morphospace analysis on the basis of PCA, which were discussed in the recent paper of Polly (2023).…”