Albertine C. Ellis-Adam

Future prospects for the rare, late-flowering Gentianella germanica and Gentianopsis ciliata in Dutch nutrient-poor calcareous grasslands

We discuss the population biology of two calcareous grassland gentians, Gentianella germanica and Gentianopsis ciliata, in relation to the habitat management currently practiced in The Netherlands. There, at the margin of their range, both species are rare. Gentianella germanica persists on six remaining locations, whereas Gentianopsis ciliata, with two populations, is nearly extinct. Gentianella germanica is a strict biennial, Gentianopsis ciliata an iteroparous perennial. Both species depend on insects for seed production and su!er from low insect visitation. Pollination experiments in one Dutch population demonstrated that Gentianopsis ciliata is self-compatible, but hardly sets any seed under natural conditions due to pollen limitation. The low reproductive success of both species is partly due to the low pollinator densities at their late flowering time, partly caused by the small population size of the gentians themselves, and partly a result of mowing too early. The latter has destroyed the seed crop of several subsequent years in one population of Gentianopsis ciliata and some of Gentianella germanica. In Gentianella germanica, the early mowing and low insect visitation seems to have resulted in selection of less herkogamous and consequently more autofertile individuals. The perspectives for Gentianopsis ciliata are currently extremely poor in The Netherlands. Under the present circumstances, extinction will most likely occur within 10‐20 years. Population reinforcement (seeding, artificial cross-pollination with nearby populations) should be considered if we want to conserve this species. For both gentians, but also of other flagship species of nutrient-poor calcareous grasslands, the total grassland area needs to be enlarged and must constitute an interconnected network of reserves. The traditional management method, sheep grazing, is to be preferred over mowing, but only if the flock visits each grassland patch or reserve for only a short time of less than a day, and with intervals of more than 2 weeks between visits. If mowing is preferred for other reasons, it should be done rotationally, and not before October. # 2002 Elsevier Science Ltd. All rights reserved.

Variable herkogamy and autofertility in marginal populations ofGentianella germanica in the Netherlands

Gentianella germanica(Willd.) Börner, a rare plant species, occurs at the margin of its distribution area in the Netherlands. It is found only in isolated patches of chalk grassland surrounded by intensively-used agricultural land. In 1997 and 1998, we investigated the spatial and temporal separation of anthers and stigma in relation to autofertility. We performed our experiments in one large and two small populations to investigate the possible selection against herkogamy and for increased autofertility in marginal populations with pollination limitation. Dichogamy appeared to be very weak and varied within individuals. Homogamous and protandrous flowers were most frequent. Dichogamy is apparently no effective barrier against self-fertilization in this species. Herkogamy varied significantly between individuals and between populations, and plant and flower size were not correlated with anther-stigma separation. Both observations suggest a genetic basis for herkogamy. Autofertility was generally high in all three populations. Only in one small population was a correlation between autofertility and herkogamy found. In this population, most plants had the stigma positioned above the anthers (mean herkogamy +0.8 mm), while in the other two populations the stigma was positioned mainly in between or below the anthers (mean herkogamy −0.55 mm). In comparison with earlier data from 1991 and 1992, plants in the large population were less herkogamous and more self-fertile in 1998. Since 1993 this population was mown each year one month earlier than usual, leading to dramatic reductions (bottlenecks) in population size. In addition, the early mowing time may have caused a further reduction of the already scarce visitation by pollinating insects. We hypothesize that both adverse conditions may have caused a selection of plants with smaller anther-stigma separation and higher autofertility and thus showing that human influence can have profound effects on the reproductive success and evolution of rare plant species, even if it occurs in the context of nature conservation.

Oviposition and Post-Embryonic Development of the Watermite Piona Alpicola (Neuman, 1880)

Some aspects of the biology of the watermite Piona alpicola were studied. The food was composed of Cladocera and chironomid larvae. The eggs were laid in oblong rows, that usually contained 5 to 20 eggs. While laying the eggs the female moves backwards. The process of egg laying is described. Hibernating females under laboratory conditions, began to lay eggs in March and April. The period of egg laying can last for more than a month. The maximum number of eggs counted per female was approximately 340. Laboratory-bred females began laying 14, 18 or 20 days after copulation. The larvae appeared to parasitize upon the imagines of Chironomus plumosus and C. tentans. The larvae attach themselves to the intersegmentalia of the abdomen of the chironomid. The length of the various developmental phases was determined. We concluded that two, possibly even three generations appear per year.

Matrix population models from 20 studies of perennial plant populations

Demographic transition matrices are among the most commonly applied population models for both basic and applied ecological research. The relatively simple framework of these models and simple, easily interpretable summary statistics they produce have prompted the wide use of these models across an exceptionally broad range of taxa. Here, we provide annual transition matrices and observed stage structures/population sizes for 20 perennial plant species which have been the focal species for long-term demographic monitoring. These data were assembled as part of the “Testing Matrix Models” working group through the National Center for Ecological Analysis and Synthesis (NCEAS). The data represent 82 populations with >460 total population-years of observations. It is our hope that making these data available will help promote and improve our ability to monitor and understand plant population dynamics. The complete data sets corresponding to abstracts published in the Data Papers section of the journal are publ...