4.2 Paleo-distributions and habitat stability
The nature of the intervening habitat surrounding rainforest refugia
during the Pleistocene has been widely debated. Some authors have argued
that much of the Central African rainforest was replaced by savannas
(DeMenocal, 2004; Maley, 1996; Maley & Brenac, 1998), while others have
emphasized the possibility of more subtle shifts in forest composition
(i.e., from wet to dry forest; Colinvaux et al., 1996, 2001; White,
1981). Toxicodryas species are generally characterized as
arboreal across rainforest and woodland habitats and the two species
exhibit widely overlapping distributions in West and Central Africa
(Chippaux & Jackson, 2019). Our paleo-distribution modeling suggested
that no substantial contraction of suitable climate occurred for either
species during the LGM (Fig. 7a), and our habitat stability mapping
suggested that core ranges of both species have remained stable for the
past 22,000 years (Fig. 7c). The greatest potential for habitat
expansion in this species appears to be to the south into today’s
northern Angola and the southern DRC (Fig. 7).
Similar paleo-distribution studies on frogs have suggested substantial
habitat contraction in Central Africa during the Pleistocene (Leaché et
al., 2019; Portik et al., 2017). In contrast, our inferred widespread
habitat stability in Toxicodryas may be due to the relatively
reduced dependence of arboreal snakes on moist habitats, as reflected by
their distribution in both woodland and rainforest. The stability ofToxicodryas habitat through the Pleistocene supports the
hypothesis that rainforest composition shifted to dryer woodlands
surrounding rainforest refugia, instead of a more dramatic shift to
strict savannah habitat. Southward shifts in species suitability may
correspond with predicted forest distribution shifts of White (1981),
suggesting a replacement of lowland rainforest with montane forest
habitat.