Are lichens biocompasses? Revisiting an old prediction using new techniques.
B B S Nunes1,2, A Braga3, M E M Marques4
1Programa de Pós-Graduação em Ecologia, Conservação e Biodiversidade, Universidade Federal de Uberlândia, Uberlândia, Minas Gerais, Brazil.
Lichens on tree trunks in the Southern Hemisphere show a clear southward orientation, driven by sunlight patterns. This radial positioning is consistent across different lichen types and unaffected by tree size or height.
Area of Science:
- Ecology
- Botany
- Environmental Science
Background:
- Abiotic factors significantly impact epiphyte distribution, influencing both vertical and radial positioning on tree trunks.
- Solar incidence creates microclimatic variations, with equator-facing sides being hotter and pole-facing sides being shaded and cooler.
- Understanding epiphyte distribution on a radial dimension is crucial for ecological insights, yet remains underexplored for avascular species.
Purpose of the Study:
- To investigate the radial distribution and orientation of crustose and foliose lichens on Syagrus oleracea trunks in the Southern Hemisphere.
- To test hypotheses regarding lichen orientation preferences, differences between lichen types, and the influence of other environmental variables on directional positioning.
- To apply circular statistical methods to analyze directional data in epiphyte distribution.
Main Methods:
- Surveyed 845 lichen thalli (180 crustose, 665 foliose) on concentric tree trunks.
- Utilized circular statistics, including preferred direction tests, between-sample comparisons, and linear-circular regressions.
- Analyzed radial orientation in relation to height, phorophyte size, canopy cover, and compass direction (azimuth).
Main Results:
- Lichens exhibited non-uniform radial distribution, with a significant southward orientation.
- Both crustose and foliose lichens showed similar directional preferences, suggesting microenvironmental factors are primary drivers.
- Lichen orientation was not significantly affected by trunk height, phorophyte size, or canopy cover, confirming azimuth as the main determinant.
Conclusions:
- Abiotic factors, specifically solar incidence patterns, indirectly dictate lichen niche occupation on a fine radial scale of tree trunks.
- Azimuth is the primary determinant of radial lichen orientation, overriding other potential influences.
- The study provides novel insights into the fine-scale ecological strategies of avascular epiphytes in response to environmental gradients.
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