Functional Traits in Lichen Ecology: A Review of Challenge and Opportunity

Abstract

Community ecology has experienced a major transition, from a focus on patterns in taxonomic composition, to revealing the processes underlying community assembly through the analysis of species functional traits. The power of the functional trait approach is its generality, predictive capacity such as with respect to environmental change, and, through linkage of response and effect traits, the synthesis of community assembly with ecosystem function and services. Lichens are a potentially rich source of information about how traits govern community structure and function, thereby creating opportunity to better integrate lichens into 'mainstream' ecological studies, while lichen ecology and conservation can also benefit from using the trait approach as an investigative tool. This paper brings together a range of author perspectives to review the use of traits in lichenology, particularly with respect to European ecosystems from the Mediterranean to the Arctic-Alpine. It emphasizes the types of traits that lichenologists have used in their studies, both response and effect, the bundling of traits towards the evolution of life-history strategies, and the critical importance of scale (both spatial and temporal) in functional trait ecology.

Keywords: ecosystem services; effect traits; functional ecology; lichenised-fungi; life-history strategy; response traits; scale; spatial; temporal.

Figure 1

Schematic to show contrasting types of traits that might yield qualitative (shapes) or quantitative (measuring tape) data, and their potential relationship to environmental drivers controlling a species/community response, and/or the effect on ecosystem processes. Arrows show an a priori understanding of linkages between traits (e.g., photobiont type also affects water holding capacity). Note that thallus colour is indirectly related to the environment through associated traits such as photobiont type or secondary compounds. Additionally, that reproductive strategy associates with lichen anatomical traits but is separated out because of its link through to demographic processes that also affect community composition.

Figure 2

A schematic to suggest how lichen response traits, especially those linked to the key physiological parameter of thallus hydrology (growth form, photobiont type), can also affect the physical environment of energy and water balance as a regulating ecosystem service, while also linking to biogeochemistry as a supporting ecosystem service. As regards the effect traits, boxes represent what are routinely categorical and ellipses continuous measurements.

Figure 3

A sample of trait-based lichen studies, comparing the use of temporal and spatial scale (vertical and horizontal axes), when considering the scale of biological organisation (colour) and the environmental factor(s) of interest (numbered) for (a) response traits and (b) effect traits. The plot is supported by the review of studies presented in Supplementary Tables S1 and S2.