The Indonesian island of Sulawesi is comprised of a mosaic of soil types
including the largest ultramafic outcrops in the tropics (ultramafic soils are
macronutrient low and phytotoxic heavy metal rich). The island’s ontogeny is also
distinctive, whereby it has formed only recently < 2 million years ago via
agglomeration from a number of proto-islands. How the island’s phytogeography
is influenced by the dual impact of edaphic heterogeneity and island ontogeny is
unknown. Equally, how the numerous metal elements influence plant-soil
interactions scale up to determine phytogeography is not well understood.
I show here that tree communities in Sulawesi are both influenced by
dynamics of island formation and edaphic chemistry. I identify the effect of soils
upon foliar metal concentrations of tree communities. This manifests as many
species existing within a similar/core stoichiometric niche space (defined by leaf
metal axes) irrespective of soil chemistry, but on heavy metal rich soils, species
also occupy distinctive niche space far from most other members of the
community. As such, I find that soil metals drive the differences in niche space
occupied by communities rather than plant macronutrients. I also find that species
found across both different soil types and regions in Sulawesi tend to occupy a
broader stoichiometric niche than those species restricted to a region and or soil
type. Conversely, clades that are overrepresented across different soil types and
regions do not show greater niche breadth than those overrepresented on a single
soil type and or region, indicating that occupying both a conserved and broad
niche can promote dispersal.
This work provides evidence for the interacting roles of island ontogeny
and edaphic heterogeneity upon biogeography and the interrelationship with the
plant stoichiometric niche
