Competitive behaviour of umbilicate lichens - an experimental approach

Area of Science:

• Ecology
• Botany
• Lichenology

Background:

• Lichens Lasallia pustulata and Umbilicaria spodochroa inhabit coastal cliffs in southern Scandinavia.
• These lichens exhibit shield-shaped thalli attached by a central holdfast, leading to competition for light and space through overlapping growth.

Purpose of the Study:

• To investigate the interaction dynamics between Lasallia pustulata and Umbilicaria spodochroa.
• To determine the behavioral mechanisms driving differential overlapping patterns in response to environmental stimuli, specifically precipitation.

Main Methods:

• Matched pair experiments were conducted in a laboratory setting.
• Field observations of interacting lichen pairs were performed in their natural habitat.

Main Results:

• Different responses to precipitation between U. spodochroa and L. pustulata lead to consistent overlapping, with U. spodochroa typically positioning itself above L. pustulata.
• This differential overlapping is attributed to varying water absorption capacities in the upper and lower cortices of the two species.
• Overlapping by U. spodochroa significantly reduces light transmission, inhibiting growth and causing mortality in the shaded L. pustulata.

Conclusions:

• The study reveals a competitive exclusion mechanism driven by differential hydration responses in lichens.
• U. spodochroa's ability to consistently overlap L. pustulata results in a competitive advantage, impacting community structure on coastal cliffs.