Dormancy in Caladenia: a Bayesian approach to evaluating latency

Abstract

Dormancy is common in many terrestrial orchids in southern Australia and other temperate environments. The difficulty for conservation and management when considering dormancy is ascertaining whether non-emergent plants are dormant or dead. Here we use a multi-state capture–recapture method, undertaken over several seasons, to determine the likelihood of a plant becoming dormant or dying following its annual emergent period and evaluate the frequency of the length of dormancy. We assess the transition probabilities from time series of varying lengths for the following nine terrestrial orchids in the genus Caladenia: C. amoena, C. argocalla, C. clavigera, C. elegans, C. graniticola, C. macroclavia, C. oenochila, C. rosella and C. valida from Victoria, South Australia and Western Australia. We used a Bayesian approach for estimating survivorship, dormancy and the likelihood of death from capture–recapture data. Considering all species together, the probability of surviving from one year to the next was ~86%, whereas the likelihood of observing an individual above ground in two consecutive years was ~74%. All species showed dormancy of predominantly 1 year, whereas dormancy of three or more years was extremely rare (<2%). The results have practical implications for conservation, in that (1) population sizes of Caladenia species are more easily estimated by being able to distinguish the likelihood of an unseen individual being dormant or dead, (2) population dynamics of individuals can be evaluated by using a 1–3-year dormancy period and (3) survey effort is not wasted on monitoring individuals that have not emerged for many years.

Using vital statistics and core-habitat maps to manage critically endangered orchids in the Western Australian wheatbelt

“…Pfeifer et al (2006) used matrix models to estimate longterm survival probabilities on the basis of rates of transition between life states. Tremblay et al (2009a) used a Bayesian capture-recapture multistate analysis for nine Australian Caladenia species to estimate dormancy and survival probabilities. Only C. graniticola is included in both Tremblay et al (2009a) and the present study, allowing comparisons to be made.…”

“…Tremblay et al (2009a) used a Bayesian capture-recapture multistate analysis for nine Australian Caladenia species to estimate dormancy and survival probabilities. Only C. graniticola is included in both Tremblay et al (2009a) and the present study, allowing comparisons to be made. For this species, most of the parameters estimated by modelling approaches are similar to those measured in the present study, except one, which is different (dormancy for C. graniticola was several years longer in the present study).…”

Optimising conservation translocations of threatened

“…obs), showing that as seedlings they can be completely reliant on their symbiotic fungi for nutrition. Like many Australian terrestrial orchids, C. colorata is annually summer dormant, and is capable of prolonged dormancy of 1-3 years (Tremblay et al 2009). Increased mycorrhizal density in and surrounding adults in the temperate North American orchid Isotria medeoloides is correlated with re-emergence of adult orchids from dormancy (Rock-Blake et al 2017).…”

Landscape Fire, Biodiversity Decline and a Rapidly Changing Milieu: A Microcosm of Global Issues in an Australian Biodiversity Hotspot

“…In the present study area and surrounding region, Quarmby [147] noted that several threatened Caladenia species (spider orchids) were known to survive summer fires, a time coincident with their dormant phase; as a corollary, they are most vulnerable to fire when they are actively growing, especially in autumn and winter, when the tubers are being replaced and mycorrhizal associations are being re-established [147]. For some species at least, bulbs can remain dormant for periods of one to three years [148], so not appearing annually in population monitoring programs [149].…”