What do we study?

Post-fire dispersal of lichen propagules and algal symbionts

Lichens are a diverse and important component of California’s chaparral ecosystems, yet we know little about processes driving colonization and succession in these communities. Colonization by lichen epiphytes depends on the dispersal of both lichen symbionts from source populations, the availability of suitable substrates and environmental conditions that permit lichen development and growth. While substrate availability and environmental suitability are thought to be the primary limiting factors for the establishment of most lichen species, particularly early after a disturbance that removes woody substrates, the role of dispersal limitation has thus far remained understudied. The large-scale burning of chaparral habitats at Quail Ridge during the 2020 Hennessey fire, provides a unique opportunity to study colonization and secondary succession in lichen communities. We are quantifying potential dispersal limitation in lichens by establishing long-term spore traps in burned areas at varying distances from source populations. Using these data, in conjunction with initial surveys of unburned source populations and annual visual surveys of burned areas, we can determine (1) when propagules of lichen-forming fungi and photobionts first arrive in burned areas, (2) when macroscopic lichen thalli first establish on woody substrates and (3) whether the timing of dispersal and establishment is related to source population size and species-specific traits (such as reproductive mode, propagule size and growth form). This project is in collaboration with Jesse Miller.

Functional consequences of lichen traits

We and many others are working toward a general theory describing how physical traits of lichens predict species’ distributions by causing differential fitness of lichen symbionts across environments. This involves linking symbiont diversity to performance and linking physical traits to their effect on three primary functional axes: water-use strategy, growth-defense tradeoffs, and dispersal-colonization tradeoffs. The development of a general and robust theory of lichen functional traits requires demonstrating these linkages across a broad suite of species and habitats, through a mixture of lab-based measurements, field sampling and transplantation experiments. 

Broad-scale ecology and biogeography of North American lichens

How do species’ broad-scale distributions reflect trait-mediated environmental constraints on fitness? Water availability is a primary constraint on lichen physiology. Large-scale geographic distributions may reflect water-use traits that allow species to utilize rain, dew or humid air. We are leveraging large lichen collection data sets that span North America to evaluate whether species’ distributions reflect their functional traits and continental patterns of water-availability.

We are also analyzing spatial patterns of lichen biodiversity across multiple data sets to determine whether ecological conclusions differ among survey data that were originally collected for different purposes and which utilize different methods.

Host-symbiont interactions in environmentally-structured meta-communities

How do environmental constraints on mutualistic symbionts affect the structure of host communities? The answer should depend on which species interact (i.e. the association network), how strongly the environment limits persistence, and the degree to which interactions facilitate survival. We are developing a general simulation model that investigates the effects of host-symbiont interaction networks on biodiversity patterns along environmental gradients and are currently exploring the effect of association network structure on the model’s theoretical predictions.

As a part of this project, we are examining how algal and fungal diversity co-vary in lichen communities from different canopy micro-environments and subsequently whether diversity patterns can be used to infer environmental constraints. We are actively seeking additional collaborations with scientists who are interested in using the model to determine whether their empirical biodiversity data indicate environmental limitations on hosts versus symbionts.

Ecology of endolichenic fungi in Oakmoss lichen

Endolichenic fungi are fungi that live inside lichens and we currently know very little about their ecology and what factors constrain their distributions. In collaboration with a research course at Stanford University, we are examining the diverse fungi that live inside Oakmoss lichen (Evernia prunastri), a common lichen in California. We are particularly interested in the effect of environment, landscape spatial structure, and lichen host traits on endolichenic fungal diversity and the distributions of particular fungal species.