Could the environment limit dispersal between Sunda and Sahul?

• Published in: Journal of vegetation science Vol. 32; no. 1
• Main Authors: Trethowan, Liam A., Bello, Francesco
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.01.2021
• Subjects: Archipelagoes; Biogeography; Dispersal; dispersal limitation; Dispersion; Drought; Filtration; Grime's CSR theory; Heavy metals; Janzen's seasonality hypothesis; Phylogeny; Sea currents; Soil contamination; southeast Asia; Wallacea; Wallacea
• ISSN: 1100-9233; 1654-1103
• DOI: 10.1111/jvs.12978

Summary Dispersal limitation is cited as the driver of biogeography in archipelagic southeast Asia. Could environmental filtering play an equally important role? From west to east across the archipelago there are three bioregions: Sunda, Wallacea and Sahul. Historic spatial separation of Sunda and Sahul is thought to limit species exchange. Here, I hypothesise that the Wallacean environment may be too stressful for many lineages originating from Sunda and Sahul — limiting dispersal between these two regions. I highlight that Wallacea has: (a) proportionally less lowland habitat; (b) more phytotoxic, heavy metal‐rich ultramafic soils; (c) sea currents flowing toward drought‐prone seasonal areas; and (d) forests that may be shorter with a different biotic environment. Preliminary results show that genera previously identified as originating from Sunda (using fossil and phylogenetic data) are shorter in stature (an indicator of stress tolerance), are more likely to be found in the smaller lowland areas and seasonal habitat of Wallacea and occupy islands further east. Shorter genera originating from Sahul are more likely to occupy ultramafic‐rich areas of Wallacea and to be found further west. Incorporating species strategies, such as stress tolerance, into future work should clarify environmental filtering's influence upon southeast Asian biogeography. At the centre of Southeast Asia, islands have less lowlands and more ultramafic soils and drought prone seasonal areas (see photo of dry riverbed surrounded by forests in Sumbawa) and possibly shorter forests than surrounding islands. This should influence Southeast Asian biogeography. I suggest that species strategies allowing them to cope with these conditions should be noticeable in the flora.