Life and Death in a Petersham Cemetery: The Life Histories of Lichens
Lichens are ecosystems, typically formed from an individual fungus, associated photosynthetic partners, and myriad other fungi and bacteria. In October 2005 I began a survey of Xanthoparmelia lichens growing on tombstones of a New England cemetery. Each year I record the births, growth, and deaths of near to 1,000 thalli. I am using data to explore a series of questions, including: is the probability of death equivalent across years, or is death more likely at older ages? Can a lichen be immortal? I am also using genetic data to explore the demographic histories of these species, testing a hypothesis that Xanthoparmelia experienced a massive increase in numbers in the recent past, coincident with the advent of intensive farming across New England and construction of miles of stone walls. Data collected to date suggest the life history patterns of these symbiotic, modular, and indeterminate organisms may be poorly served by traditional demographic models.