Mark-recapture statistics have rarely been applied to plants, yet they can be useful for estimating plant demographic traits where individuals may be missed or unob- servable. We applied mark-recapture statistics based on an information theory approach to estimate annual probabilities of dormancy in a five-year study of a threatened, perennial plant, the small yellow lady's slipper orchid ( Cypripedium calceolusssp. parviflorum (Sal- isb.) Fernald). The aboveground states of 548 genets in eight patches were monitored over five years. Apparent survival probabilities (f), corrected for dormancy, were calculated. The best-fit model suggested that apparent survival was constant throughout the study for all patches, while dormancy varied additively with time among patches. The mean prob- ability of dormancy was 0.320 6 0.024, with a mean maximum overestimation of 0.067 as calculated using an estimate of the probability of detection. Dormancy typically lasted for no longer than two consecutive years, although dormancy as long as four years was observed. Dormancy displayed a strong covariate relationship with spring frost days, al- though effects of precipitation and mean spring temperature were almost equally strong. Mean apparent survival probabilities were high in each patch ( f5 0.878), but dormancy probabilities varied considerably among patches (d 5 0.188-0.672). Conventional re- sprouting probabilities underestimated apparent survival by a mean difference of 0.288 (range: 0.150-0.589). This novel application of mark-recapture statistics to plant demog- raphy allowed robust survival estimates that accounted for uncertainty due to an unob- servable, dormant life stage.

Estimating dormancy and survival of a rare herbaceous perennial using mark–recapture models

Effects of disturbance on population dynamics of the threatened orchid Prasophyllum correctum D.L. Jones and implications for grassland management in south-eastern Australia

Summary


1
We need to understand how threatened plant species respond to natural or management-induced habitat changes to conserve them successfully. Because long-term demographic studies are not feasible for large numbers of species, there is a clear need for simple short-term methods to assess demographic responses.

2
The population structure of 23 populations of the endangered perennial Salviapratensis was studied in relation to the vegetation and management of dry floodplain grasslands along Dutch rivers. The aims of the study were to (i) evaluate the suitability of single censuses of population stage structures as a tool for quick assessments of the viability of plant populations; (ii) test whether viable populations of S. pratensis indicate sites of higher conservation value; (iii) obtain information on the viability of the remaining populations; and (iv) provide advice for optimal habitat management.

3
Using cluster analysis, we distinguished three different types of populations: (i) ‘dynamic’ populations, characterized by a large proportion of young individuals (seedlings, juveniles and immatures); (ii) ‘normal’ populations, with a relatively higher proportion of adults but still a considerable number of young individuals; and (iii) ‘regressive’ populations, in which adult stages, especially large flowering individuals, dominated and rejuvenation hardly occurred. The three population types differed with respect to population size and total plant density, which were highest in dynamic, intermediate in normal and lowest in regressive populations.

4
Both the structure and composition of the surrounding vegetation were associated with the type of population found. The percentage of bare soil surface (indicating an open vegetation structure) was positively related to recruitment of S. pratensis. The dynamic populations occurred in a species-rich vegetation, comprising species of nutrient-poor soils and characteristic of floodplain grasslands. The regressive populations occurred more often in species-poor vegetation, comprising mainly species of nutrient-rich conditions.

5
Salvia population structure was correlated with management. We observed that those populations with a late mowing regime had higher proportions of young stages and larger population sizes. Although we expected that recently established populations on the young river dunes formed during ecological restoration projects would be dynamic, most sampled plots were of the regressive type, which suggests that either site conditions were not yet optimal or Allee effects limited further expansion of the small founder populations.

6
We conclude that conservation of the remaining populations of S. pratensis in Dutch dry floodplain grasslands will be best achieved by late mowing with hay removal.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1046/j.0021-8901.2001.00679.x

Population structure of Salvia pratensis in relation to vegetation and management of Dutch dry floodplain grasslands

Summary


1. I present an evolutionary ecology interpretation of vegetative dormancy in mature herbaceous perennials. This kind of vegetative dormancy has been noted for at least 40 years, but has only recently become a topic of study.



2. Vegetative dormancy may be considered in a life-history context. Both vegetative dormancy and mortality typically decrease with increasing size. Vegetative dormancy’s relationship to reproduction is more complex, because some species increase flowering and fruiting after dormancy while others do the opposite.



3. If vegetative dormancy is adaptive, then it is most likely a bet-hedging trait. Dormancy-prone plants are often long-lived, and in such organisms, bet-hedging traits should counter the effects of environmental stochasticity on adult survival. This adaptive context may vary by life span, because in shorter-lived plants, fitness is most sensitive to changes in reproduction rather than survival.



4. Vegetative dormancy could evolve if the costs of sprouting ever outweigh the benefits. The benefits of sprouting include: (i) photosynthesis and (ii) the opportunity to flower and reproduce. The costs include: (i) greater chance of herbivory, (ii) greater need for limiting nutrients, and (iii) greater maintenance costs. The many losses of photosynthesis among plants suggest that these benefits may not always outweigh the costs.



5. Vegetative dormancy may be an evolutionary step towards the loss of photosynthesis. Many non-photosynthetic plants acquire carbon from their mycorrhizal fungi. Many autotrophic, dormancy-prone plants also acquire some carbon from their mycorrhizal fungi. Further, non-photosynthetic plants often become dormant to an even greater extent than autotrophic, dormancy-prone plants.



6.Synthesis Vegetative dormancy often occurs in clades with non-photosynthetic, myco-heterotrophic plants, with implications for the evolution of traits involved in carbon nutrition. The links between vegetative dormancy, other life-history traits, mycorrhizas and the loss of photosynthesis should provide exciting directions for further research in plant evolutionary ecology. Particularly needed is an assessment of the physiology of vegetative dormancy, including whether the mycorrhiza is a carbon source in all dormancy-prone plant species. Equally important is a better understanding of the genetic relationships among photosynthesis, myco-heterotrophy and dormancy.

The evolutionary ecology of vegetative dormancy in mature herbaceous perennial plants

Summary


1
Management decisions are increasingly based on matrix models intended to predict the long-term fate of endangered species. However, certain elements of these models, such as life-state transition probabilities (vital rates), are difficult to parameterize and their values may vary depending on external conditions such as weather. Details of how weather might influence population performance are rare, yet necessary to assess the effects of global climate change on a species’ distribution.

2
Based on a 26-year data set of a population of Himantoglossum hircinum in a nature reserve in Germany, variations of life-history traits and vital rates were studied. Matrix analysis was used to identify the most important life-state transitions for population growth. Multiple linear regression was used to quantify the response of population traits and vital rates to changing weather conditions.

3
Population size increased exponentially and density effects could not be observed. Flowering plants and large plants had the highest and second highest reproductive value, respectively. The population's finite rate of increase fluctuated strongly among years; life-history traits varied strongly and were interlinked, thereby violating the assumptions of matrix modelling in a population viability analysis.

4
Some vital rates and the population growth rate showed a trend over the total period. A certain and sometimes large amount of that variability could be attributed to variability of weather conditions, with warmer winter conditions favouring population performance. Prediction of population size was fairly accurate within a time frame of 10 years, but size class structure was not.

5
Synthesis and applications. Matrix modelling proved to be unreliable for predicting long-term population dynamics, despite the long-term data set used for matrix construction. This can be explained by weather-dependent variability of vital rates driving population dynamics. A minimum study period of 4 years is necessary to produce relevant information for model development. Our study emphasizes the need for critical evaluation of management decisions based only on single short-term studies and for studies covering longer time intervals than 2–3 years.

A. Mendoza

Papers

Demographic properties of an outlier population of Orchis militaris L. (Orchidaceae) in England

Demographic properties of an outlier population ofOrchis militarisL. (Orchidaceae) in England