The island rule-like patterns of plant size variation in a young
land-bridge archipelago: roles of environmental circumstance and biotic
competition
Abstract
The island rule- a general pattern of dwarfism in large species to
gigantism in small species on islands relative to mainland- is typically
seen as a macroevolutionary phenomenon. However, it remains unknown
whether the ecological processes associated with abiotic and biotic
factors generate a pattern of plant size variation similar to the island
rule. Through measuring plant height for 29623 individuals of 50 common
woody species in the Zhoushan Archipelago (8500 years old and yet to
undergo major evolutionary adaptation) and the adjacent mainlands in
Eastern China, we examined whether island area and remoteness, resource
availability, environmental stress, plant-plant competition and insect
herbivory can explain the pattern of plant size variation. We found
pronounced variations in plant height, similar to those of the island
rule. Further analyses revealed that islands with low resource
availability, such as low soil organic matter content and low
precipitation, had a high degree of dwarfism; islands experiencing high
environmental stress, such as high soil pH, had a high degree of
dwarfism; and islands experiencing less plant-plant competition had a
high degree of gigantism. The magnitude of plant dwarfism was also
higher on small and remote islands than on larger and nearer islands.
These results highlight the importance of ecological processes
associated with abiotic and biotic conditions in shaping the island
rule-like patterns of plant size variation. Our study therefore suggests
that the island rule can be caused by both ecological and evolutionary
processes. Given that the age of our studied archipelago is too young to
undergo major evolution, our results evidenced that ecological processes
likely played a prominent role for generating the island rule-like
patterns. Future studies on the island rule need to perform experiments
to disentangle evolutionary from ecological mechanisms.