Origins and Assembly of Malesian Rainforests

Abstract

Unraveling the origins of Malesia's once vast, hyperdiverse rainforests is a perennial challenge. Major contributions to rainforest assembly came from floristic elements carried on the Indian Plate and montane elementsfrom the Australian Plate (Sahul). The Sahul component is now understood to include substantial two-way exchanges with Sunda inclusive of lowland taxa. Evidence for the relative contributions of the great Asiatic floristic interchanges (GAFIs) with India and Sahul, respectively, to the flora of Malesia comes from contemporary lineage distributions, the fossil record, time-calibrated phylogenies, functional traits, and the spatial structure of genetic diversity. Functional-trait and biome conservatism are noted features of montane austral lineages from Sahul (e.g., diverse Podocarpaceae), whereas the abundance and diversity of lowland lineages, including Syzygium (Myrtaceae) and the Asian dipterocarps (Dipterocarpoideae), reflect a less well understood combination of dispersal, ecology, and adaptive radiations. Thus, Malesian rainforest assembly has been shaped by sharply contrasting evolutionary origins and biogeographic histories.

Museomics for reconstructing historical floristic exchanges: Divergence of stone oaks across Wallacea

“…The forest communities of Asia are unique and distinct from those in Africa and the Neotropics, by being particularly speciose in a number of tree families (e.g. Dipterocarpaceae, Myrtaceae, Lauraceae and others [30]). Not surprisingly perhaps, few families with large seeds [i.e.…”

Evolutionary constraints and adaptation shape the size and colour of rain forest fruits and flowers at continental scale

“…Many of the Australian rain forest angiosperm taxa have origins in Sunda (Southeast Asia), and the allocation of species to groups based on origins (Sunda versus Sahul) was central to the exploration of the selected traits (Kooyman et al, 2019;Yap et al, 2018). In that context, the assembly of the Australian flora from the Miocene onwards includes substantial interaction with Sunda (and the Sunda taxa as invaders being dispersed into Sahul).…”

“…40 Ma), and by the Miocene ( c . 20 Ma) contact between the Sunda and Sahul plates had commenced, and floristic interchanges (that continue to the present) had begun (Hill, ; Kooyman et al, , ).…”

“…Such data sets are rare and allow us to explore questions related to trait variability across gradients of latitude (e.g., Rossetto, Kooyman, et al, ; Wright et al, ), biogeographical history, including the origins (source) of floras, and the outcome of shifts in climate variables (e.g., Yap et al, ). Within the context of our study system (Australian rain forests), we have a clear understanding of the biogeography and history of the rain forest flora (Hill, ; Kooyman et al, , , , ; Rossetto, McPherson, et al, ; Yap et al, ), species distributions (Kooyman, Rossetto, Allen & Cornwell, ), landscape‐level dynamics (van der Merwe et al, ; Rossetto, Crayn, Ford, Mellick, & Sommerville, ), the impact of historical climatic fluctuations (Mellick, Lowe, Allen, Hill, & Rossetto, ; Worth et al, ) and fruit (and seed) dispersal (Rossetto, Kooyman, et al, ). Genetic work in tropical and subtropical Australian rain forest shows strong signals for frugivory‐mediated dispersal being a major force in landscape connectivity (van der Merwe, McPherson, Siow, & Rossetto, ; Rossetto et al, ; Rossetto, Kooyman, Sherwin, & Jones, ; Rossetto, Kooyman, et al, ).…”

“…By the early Eocene, the core area of the Sunda plate, which includes the present-day islands of Borneo, Sumatra, Java and Bali, in addition to the Malay Peninsula, became an elevated and emergent extension of continental Asia (Clements & Hall, 2011). The Sahul plate (Australia-New Guinea) broke from Antarctica in the Eocene (c. 40 Ma), and by the Miocene (c. 20 Ma) contact between the Sunda and Sahul plates had commenced, and floristic interchanges (that continue to the present) had begun (Hill, 1994;Kooyman et al, 2014Kooyman et al, , 2019.…”