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Birds, Bats or Climate? Eucalypt Floral Traits Reflect Pollination Over Abiotic Environment
R E Stephens1,2, H Sauquet2,3, B Laugier4
1School of Natural Sciences Macquarie University Ryde New South Wales Australia.
Ecology and Evolution
|June 12, 2025
Summary
Flower size and color in eucalypts evolved together, driven by pollinators, not climate. The absence of bats strongly predicts larger, colorful flowers, likely to attract birds.
Area of Science:
- Ecology
- Evolutionary Biology
- Botany
Background:
- Floral traits like size and color vary due to environmental factors.
- Eucalypts (Eucalyptus, Corymbia, Angophora) exhibit diverse flower traits, but the drivers of this variation are unclear.
- While larger, colorful flowers are more common in southwest Australia, the contributing environmental factors remain unknown.
Purpose of the Study:
- To investigate the relative influence of pollination and abiotic factors on flower size and color in eucalypts.
- To understand the macroecological patterns of floral trait variation in relation to pollinator availability.
Main Methods:
- Extracted bud size (flower size proxy) and flower color (white-cream vs. colorful) for 798 eucalypt species from online floras.
- Assessed vertebrate pollination environment (bird, marsupial, bat richness/presence) and abiotic factors (temperature, precipitation, soil phosphorus).
Main Results:
- Flower size and color in eucalypts have co-evolved and are not strongly predicted by climate or soil conditions.
- Pollination environment, specifically the absence of flower-visiting bats, was the most significant predictor of flower size and color.
- Larger, colorful flowers are associated with bird pollination in bat-absent areas, while small, white-cream flowers suggest generalist pollination.
Conclusions:
- Continental-scale floral trait variation in eucalypts is shaped by macroecological patterns of pollinator availability.
- The biotic environment, particularly pollinator diversity and presence, plays a crucial role in shaping plant reproductive strategies.
- The findings highlight how pollinator absence can drive the evolution of specific floral menarik traits.
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