. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 446 Bulletin Museum of Comparative Zoology, Vol. 147, No. 10 chrysocr colopteru. CINEREUM SPECIES GROUP DRY Figure 5a. Figure 5. Hypothesized patterns of speciation within the cinereum (5a) and sylvia (5b) species groups in Todirostrum. Isolation of ancestral populations (shaded areas) during two dry periods and their directions of dispersal from initial refuge sites are diagrammed. During dry periods populations of cinereum and sylvia dispersed through regions of open vegetation (solid arrows). Dashed lines outline h
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 446 Bulletin Museum of Comparative Zoology, Vol. 147, No. 10 chrysocr colopteru. CINEREUM SPECIES GROUP DRY Figure 5a. Figure 5. Hypothesized patterns of speciation within the cinereum (5a) and sylvia (5b) species groups in Todirostrum. Isolation of ancestral populations (shaded areas) during two dry periods and their directions of dispersal from initial refuge sites are diagrammed. During dry periods populations of cinereum and sylvia dispersed through regions of open vegetation (solid arrows). Dashed lines outline hypothesized distribu- tions of these species during a recent dry period. The distribution of cinereum was restricted during a pre- vious humid period, when the central Amazonian forest had returned. This range contraction (see dashed arrows away from Amazonia in 5a) resulted in the isolation of a population in southeastern Brazil, which be- came T. poliocephalum. During humid periods ancestral populations of the modern forest-inhabiting species dispersed (dashed arrows), but contracted again during a recent dry period (upper right diagrams in 5a and 5b). Todirostrum maculatum might not have been fully restricted to a refugium during the recent dry phase given its current preference for mangroves and streamside vegetation, and the ancestral distribution shown here (heavily dotted region in 5a, with question mark) is speculative. have been widespread on the continent during the dry phases. With each climatic cycle, a new magni- tude of complexity is naturally added to the distribution patterns in any phyletic group. 1 fence precise ranges of forms existing prior to two or three cycles would be impossible to determine from modern distribution data. For this reason, the following re- construction begins subsequent to the iso- lation of three species group precursors from the single Todirostrum Please note that these images are extracted from scanned page images that may
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