Taxon Cycles in Neotropical Mangroves

Abstract

The concept of the taxon cycle involves successive range expansions and contractions over time, through which a species can indefinitely maintain its core distribution. Otherwise, it becomes extinct. Taxon cycles have been defined mostly for tropical island faunas; examples from continental areas are scarce, and similar case studies for plants remain unknown. Most taxon cycles have been identified on the basis of phylogeographic studies, and straightforward empirical evidence from fossils is lacking. Here, empirical fossil evidence is provided for the recurrent Eocene to the present expansion/contraction cycles in a mangrove taxon (Pelliciera) after a Neotropical-wide study of the available pollen records. This recurrent behavior is compatible with the concept of the taxon cycle from biogeographical, chronological and ecological perspectives. The biotic and abiotic drivers potentially involved in the initiation and maintenance of the Pelliciera expansion/contraction cycles are analyzed, and the ecological and evolutionary implications are discussed. Whether this could be a trend toward extinction is considered under the predictions of the taxon cycle theory. The recurrent expansion and contraction cycles identified for Pelliciera have strong potential for being the first empirically and unequivocally documented taxon cycles and likely the only taxon cycles documented to date for plants.

Keywords: Neotropical mangroves; Pelliciera; Rhizophora; expansion/contraction cycles; fossil pollen; range shifts; relict distribution; taxon cycles.

Figure 2

Present distribution of Pelliciera species. (A) Map of the Americas with the distribution area of Pelliciera highlighted by a red box. (B) Close up of the occurrence patterns of the two Pelliciera species (modified from Ref. [38]). The Colombian Chocó region is highlighted because it is one of the most humid regions of the world, with precipitation values up to 13,000 mm y⁻¹ [46].

Figure 1

The taxon cycle and its fossil expression. (A) Variations in geographical extent and intraspecific differentiation along the stages of the taxon cycle (redrawn from Ref. [5]). (B) Variations in the geographical area of fossils according to the asymmetric model [7]. The stages represented in the fossil record (gray area) and the condensed phase (CP), which is apparently unrecorded, are indicated. FAD, first appearance datum; LAD, last appearance datum.

Figure 3

Graphical display of the results from Table S1 (Supplementary Material). Present Pelliciera localities were taken from Figure 2. Countries: B, Brazil; Bz, Belize; C, Colombia; CR, Costa Rica; Cu, Cuba; E, Ecuador; ES, El Salvador; FG, French Guiana; G, Guatemala; Gy, Guyana; H, Honduras; Hp, Hispaniola (Haiti and Santo Domingo); J, Jamacia; M, Mexico; N, Nicaragua; P, Panama; Pe, Peru; PR, Puerto Rico; S, Surinam; T, Trinidad and Tobago; V, Venezuela.

Figure 4

Pelliciera range shifts between the Eocene and the present subdivided into four chronological phases. (A) Phase I, thinning expansion (Eocene-Oligocene). (B) Phase II, displacement (Oligocene-Miocene). (C) Phase III, contraction (Miocene-Pliocene). (D) Phase IV, reorganization (Pliocene-Present).

Figure 5

Diagram of the Pelliciera biographical loop with indication of the ranges of abundance of its fossil pollen in each geological epoch. PPR, present Pelliciera range.

Figure 6

The Eocene expansion–contraction Pelliciera loop. (A) Eocene localities (Figure 3) subdivided into Early, Middle and Late Eocene ages (Table S1 of the Supplementary Material). Countries: C, Colombia; J, Jamaica; P, Panama; V, Venezuela. (B) Early to Middle Eocene expansion. (C) Middle to Late Eocene contraction. The initial Early Eocene range (A) is indicated by a broken line.