| BEN |
| BOTANICAL ELECTRONIC NEWS |
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| ISSN 1188-603X |
| No. 290 June 9, 2002 | aceska@victoria.tc.ca | Victoria, B.C. |
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In early June of 2002, while amateur mycologists pursued the last morels of the season, and found Amanita pantherina flourishing in the woods, the general public woke up to the news that paradise (in the form of Vancouver Island) had been invaded by Cryptococcus neoformans var. gattii. This asexual basidiomycetous yeast (its teleomorph being Filobasidiella neoformans of the Aphyllophorales) has previously been thought to be restricted to tropical areas, especially Australia and New Guinea, where it grows on Eucalyptus trees.
The fungus is an opportunistic parasite of humans, but since everyone presumably inhales its spores at some time, most people must be resistant or immune. Many of those who do become infected remain asymptomatic, but some -- immunocompromised, elderly, smokers, or young children -- may develop lung disease, or in a few cases, brain disease, which is always fatal if left untreated. Initial symptoms include a persistent cough, chest pain, weight loss, night sweats and shortness of breath.
Now the medical authorities tell us that Cryptococcosis, which in the past has cropped up in only one or two people a year on Vancouver Island, has struck over 50 Islanders in the past three years. One woman patient died, and many are on long term antifungal medication. Almost all those infected had visited either Rathtrevor Park near Parksville, or Cathedral Grove east of Port Alberni. It has now been found that the fungus is growing on several common tree species -- Douglas fir, alder, cedar, Garry oak and grand fir -- in this area, and these may be the source of the inoculum.
In addition, during the past two years, vets have reported no fewer than 35 cases in animals, from dogs and cats to llamas and four wild dolphins (which died). This again is a large increase over the usual 2-3 cases per year.
The sudden increase in incidence remains unexplained, though the possibility that climate change has something to do with it, in permitting the gattii variety to become established here, has been raised. The authorities do not suggest that people avoid the parks in question, noting that none of the park staff have developed the disease, and that it is more dangerous to drive there than to camp there. They also point out that the disease is curable. Another encouraging feature of this mycosis is that it is not transmitted between people.
After the recent surge in cases of necrotizing fasciitis (the so-called flesh-eating disease), this is just one more thing to think about, possibly designed to take our minds off the extremely painful political affliction that is being visited upon this beautiful Province.
[Check also Bryce Kendrick's "The Fifth Kingdom" on-line at: http://www.mycolog.com/ - AC]
Abstract
A demographic monitoring study and greenhouse experiments conducted from 1991 to 1994 provided information about the population dynamics and biology of Castilleja levisecta, a multi-stemmed hemi-parasitic perennial endemic to the Pacific Northwest. Greenhouse experiments were conducted to examine seed dormancy, germination requirements and host species preference. Empirical data from two study plots were used to construct stage structured transition matrix models to examine population dynamics. Life history stage distributions varied among plots and years. The population is characterized by prolific seed production, a short-lived seed bank, limited seedling recruitment, and the ability for plants to grow quickly or regress within a single season.
Introduction
A rare species that may be "protected" within a preserve may continue to be at risk of extinction, due to demographic or environmental stochastic factors that may limit the resilience or ability of the population to recover. Demographic and environmental stochasticity become increasingly important as population size is reduced (Menges 1986).
The protection and recovery of rare or endangered species require an understanding of the biological status of a population, and the ecological and genetic factors that affect the growth, survival and reproduction of the population (Schemske et al. 1994). The demography of a species can be described in terms of its life cycle, which consists of transitions made from one stage to another, such as growth, regression, or stasis (Caswell 1989). Demographic monitoring and stage based transition matrix models can provide information about population growth rates, survival, reproduction and stable stage structure, and can be used to identify critical life history stages and those factors that affect them (Travis & Sutter 1986, Menges 1986). Demographic studies can be used to predict future population changes, and to analyze specific, targeted action that may be needed to increase the likelihood of a species' survival.
In this paper I present a summary of the results a three-year demographic and monitoring study to examine the population dynamics of Castilleja levisecta or Golden Paintbrush, a Pacific Northwest rare endemic and US threatened species. The objectives of the study were to address the following questions:
Study Site and Species
The population of Castilleja levisecta under study was located in a 13-hectare Natural Area Preserve in Thurston County, Washington. The preserve is managed by the Washington State Department of Natural Resources, and is one of the last remnants of a native Puget Trough prairie community.
Castilleja levisecta Greenm. is a multi-stemmed perennial in the family Scrophulariaceae. Plants frequently have 3-15 unbranched stems. Non-flowering stems can be as tall as 22 cm, but are typically somewhere around 6 cm tall. Flowering plants have been found to have as many as 8 inflorescences that can reach up to 33 cm in height (Wentworth, 1994). It is easily identified by its showy inflorescences consisting of whorls of conspicuous golden-yellow leaf bracts surrounding less conspicuous greenish flowers. Plants emerge in early March and flower from April through July.
An endemic to the PNW, Castilleja levisecta occupies low elevation grasslands typically associated with Festuca idahoensis and F. rubra, and a variety of other vascular plant species. Historically Castilleja levisecta had been reported from over 30 sites ranging from the Willamette Valley in Oregon, north to Vancouver Island in BC. Its earliest collection was in 1875 in Victoria BC, and it was described by Greenman in 1898, with other earlier collections from Mill Plain, in 1880, Roy, in 1889 and Pt. Ludlow in 1890. C. levisecta had been on WA State's list of endangered species since the first list was published in 1981. The continued conversion of open grasslands to agricultural and other human uses, and the encroachment of trees, shrubs and invasive species have taken their toll. Today C. levisecta is believed to be extinct in Oregon, and the remaining 10 populations of varying sizes struggle to survive in Washington and BC. Castilleja levisecta was a candidate for listing under the federal ESA in 1991. Knowledge of C. levisecta at that time came from the collective fieldwork of Sheehan and Sprague (1984) and Evans, Schuller & Augenstein (1984).
Methods
In a three-year demographic monitoring study conducted from 1991-1994, I followed the fates of over 800 C. levisecta individuals in two study plots. Plants were mapped, tagged and classified into one of four life history stages based on a combination of size and reproductive status. Seedlings were rarely distinguishable in the field, therefore I selected plants that were <= 4cm tall for the Small stage classification. Medium plants were those >4cm, Small Reproductives were those having 1-2 inflorescences, and Large Reproductives were those with 3 or more inflorescences (Wentworth 1994).
In order to better understand the biology of C. levisecta, I also conducted preliminary field and greenhouse experiments to examine pollination requirements, seed dormancy characteristics and plant parasitism or host preference.
Summary & Results
Results from the pollinator exclusion experiments in which fruit set was compared between bagged and unbagged inflorescences indicated that fruit set was almost 5 times greater in unbagged inflorescences. The seeds are less than 1 mm long, are covered by a reticulating membrane and do not appear to have any specialized dispersal mechanisms. Cold stratification was required for germination in the lab. In field and laboratory trials, germination was found to be greater in the first year than in the 2nd, and no germination occurred in the third year.
Like many species within the family Scrophulariaceae and particularly with the genus Castilleja (Heckard 1962, Kuijt 1969), C. levisecta is considered to be a facultative root parasite. Greenhouse experiments in which Castilleja seedlings were grown in pots with and without three selected suspected or possible host plants -- Fragaria virginiana, Chrysanthemum leucanthemum, and Festuca idahoensis, indicated that C. levisecta did not require a host to survive and flower. Plants appeared to produce haustorial parasitic connections in pots with or without host plants. The presence alone of haustoria, however, does not necessarily indicate functional parasitism (Kuijt, personal communication). This suggests that C. levisecta may be a facultative root parasite at best.
Results from following the fates of over 800 C. levisecta individuals over 3 years indicated a less than simple life cycle in which plants have the ability to grow quickly or regress within a single season. Regression was greater than growth in many cases and was particularly high (60-80%) in Large Reproductives. Regression, or the tendency for a plant to fall back into a smaller or non-reproductive stage, can complicate the assessment of demographic trends in that a more obvious reproductive plant in one year can become less obvious in subsequent years and more likely to be overlooked. It also suggests a reduction in reproductive potential in mature plants in one year that may not reliably produce flowers in the next year.
The analysis of the demographic data indicated spatial and temporal variation between study plots and stage class densities from year to year. Demographic analysis conducted through the use of Ramas Stage software indicated that population growth rates also varied by plot and by year. Population growth rate is represented by Lambda, Lambda <1 indicates the population is decreasing, Lambda = 1 indicates it is stable, and Lambda > 1 indicates it is increasing. Elasticity, or the proportional contribution made by each stage class to population growth was greatest in the Medium stage class, suggesting that conservation efforts should include a focus on this often overlooked stage.
Conclusions
Castilleja levisecta was listed as a Threatened species under the Federal Endangered Species Act in 1997. While the loss of suitable habitat due to conversion was likely a leading factor responsible for the initial demise of all but 10 remaining populations, it is not the only or current threat to the survival of this rare species. Although my study population occupies a natural area preserve that is relatively protected and supports a greater diversity of native prairie species than many of the remaining sites, recovery efforts in general are faced with the challenges of invasive non-native, species such as Hieracium pilosella (mouse-ear hawkweed, a Class B noxious weed), Cytisus scoparius (Scot's broom, a class B-noxious weed), and Chrysanthemum leucanthemum (ox-eye daisy, a class C noxious weed). There are also the challenges of encroachment by native species like Pseudotsuga menziesii (Douglas fir), Pteridium aquilinum (bracken fern), Rubus ursinus (Pacific blackberry) and Symphoricarpos albus (snowberry).
These and other threats such as herbivory by rabbits or deer, and trampling could lead to the loss of this species without continued, diligent and sometimes seemingly controversial management efforts. Management efforts should continue to include long term monitoring and the restoration of existing habitat. More research and data are needed about recruitment rates, host preference with implications for re-introductions, and minimum viable population size to provide a basis for sound conservation and management strategies.
References