The island rule explains consistent patterns of body size evolution in terrestrial vertebrates

Area of Science:

• Evolutionary Biology
• Island Biogeography
• Vertebrate Zoology

Background:

• Island ecosystems often exhibit unique evolutionary patterns, notably the 'island rule' where small species grow larger (gigantism) and large species grow smaller (dwarfism).
• The general applicability and underlying drivers of the island rule across diverse vertebrate groups and global island systems remain debated.

Purpose of the Study:

• To conduct a phylogenetic meta-analysis to evaluate the prevalence and drivers of body size evolution in terrestrial vertebrates on islands compared to mainlands.
• To investigate how factors like climate, island size, and isolation modulate the 'island rule' effects across different vertebrate classes.

Main Methods:

• Phylogenetic meta-analysis of paired island-mainland populations of terrestrial vertebrates.
• Statistical assessment of body size evolution patterns, including gigantism and dwarfism.
• Analysis of environmental and geographical factors (climate, island size, isolation) influencing body size changes.

Main Results:

• The 'island rule' is a widespread phenomenon in island mammals, birds, and reptiles, with amphibians showing a tendency towards gigantism.
• The magnitude of insular dwarfism and gigantism is significantly influenced by climatic conditions, island size, and degree of isolation.
• Smaller and more isolated islands exhibit more pronounced body size changes in mammals and reptiles.

Conclusions:

• The island rule is a pervasive evolutionary pattern across vertebrates, but its manifestation is complex and context-dependent.
• Ecological pressures and environmental conditions on islands critically shape vertebrate body size evolution, leading to nuanced outcomes beyond simple gigantism or dwarfism.