Life history strategy in herbaceous perennials: inferring demographic patterns from the aboveground dynamics of a primarily subterranean, myco-heterotrophic orchid

Authors


R. P. Shefferson, Univ. of Georgia, Odum School of Ecology, 140 E. Green St, Athens, GA 30601, USA. E-mail: dormancy@uga.edu

Abstract

Myco-heterotrophs are non-photosynthetic plants that parasitize mycorrhizal fungi for their nutritional requirements, especially carbon. Because green plants sprout both to photosynthesize and to reproduce, the lack of photosynthesis in myco-heterotrophs suggests that these plants need only to sprout to reproduce. Further, they may be long-lived, with fitness favoring high, stable survival over frequent reproduction and leading to size-biased reproduction. We hypothesized that sprouting would be rare and would always lead to flowering in a ten-year monitoring study of a myco-heterotrophic plant, the autumn coral root Corallorhiza odontorhiza. We also postulated that these plants would exhibit strong size-based flowering patterns. We tested these hypotheses by parameterizing a variety of mark–recapture models of survival, fecundity, and demographic transitions among two life history stages: flowering and non-sprouting (vegetatively dormant). We further developed and tested novel models estimating the influence of reproduction on demographic transitions one, two, and three years after flowering. Our results suggested that this population is typically subterranean, with only a small proportion of living plants actually sprouting in any given year. Plants typically flowered and fruited when they sprouted (flowering frequency > 0.99), supporting our first hypothesis that sprouting occurs only in concert with reproduction. We also found that reproduction was associated with long-term reproductive demographic impacts – plants that flowered more in the past three years were more likely to continue doing so than those that flowered only once. Our use of ‘memory’ mark–recapture models, in which transitions across years are allowed to vary with demographic events occurring across several previous years, proved a powerful means of testing for their long-term impacts of reproductive events.

Ancillary