Short-term studies underestimate 30-generation changes in a butterfly metapopulation

Most studies of rare and endangered species are based on work carried out within one generation, or over one to a few generations of the study organism. We report the results of a study that spans 30 generations (years) of the entire natural range of a butterfly race that is endemic to 35 km2 of north Wales, UK. Short-term studies (surveys in single years and dynamics over 4 years) of this system led to the prediction that the regional distribution would be quite stable, and that colonization and extinction dynamics would be relatively unimportant. However, a longer-term study revealed unexpectedly high levels of population turnover (local extinction and colonization), affecting 18 out of the 20 patches that were occupied at any time during the period. Modelling the system (using the 'incidence function model' (IFM) for metapopulations) also showed higher levels of colonization and extinction with increasing duration of the study. The longer-term dynamics observed in this system can be compared, at a metapopulation level, with the increased levels of variation observed with increasing time that have been observed in single populations. Long-term changes may arise from local changes in the environment that make individual patches more or less suitable for the butterfly, or from unusual colonization or extinction events that take metapopulations into alternative states. One implication is that metapopulation and population viability analyses based on studies that cover only a few animal or plant generations may underestimate extinction threats

Reduced Population Control of an Insect Pest in Managed Willow Monocultures

BACKGROUND: There is a general belief that insect outbreak risk is higher in plant monocultures than in natural and more diverse habitats, although empirical studies investigating this relationship are lacking. In this study, using density data collected over seven years at 40 study sites, we compare the temporal population variability of the leaf beetle Phratora vulgatissima between willow plantations and natural willow habitats. METHODOLOGY/PRINCIPAL FINDINGS: The study was conducted in 1999-2005. The density of adult P. vulgatissima was estimated in the spring every year by a knock-down sampling technique. We used two measures of population variability, CV and PV, to compare temporal variations in leaf beetle density between plantation and natural habitat. Relationships between density and variability were also analyzed to discern potential underlying processes behind stability in the two systems. The results showed that the leaf beetle P. vulgatissima had a greater temporal population variability and outbreak risk in willow plantations than in natural willow habitats. We hypothesize that the greater population stability observed in the natural habitat was due to two separate processes operating at different levels of beetle density. First, stable low population equilibrium can be achieved by the relatively high density of generalist predators observed in natural stands. Second, stable equilibrium can also be imposed at higher beetle density due to competition, which occurs through depletion of resources (plant foliage) in the natural habitat. In willow plantations, competition is reduced mainly because plants grow close enough for beetle larvae to move to another plant when foliage is consumed. CONCLUSION/SIGNIFICANCE: To our knowledge, this is the first empirical study confirming that insect pest outbreak risk is higher in monocultures. The study suggests that comparative studies of insect population dynamics in different habitats may improve our ability to predict insect pest outbreaks and could facilitate the development of sustainable pest control in managed systems

EXPERIMENTAL AND THEORETICAL WORK OF DOUBLY CHARGED MOLECULAR IONS: N22+N^{2+}_{2} AND CO2+CO^{2+}

$^{1}$ B.J. Olsson, G. Kindvall and M. Larsson, J. Chem. Phys. (in press).Author Institution: Research Institute of Physics, Frescativagen 24Only a few doubly charged molecular ions are known to possess emission spectra. The $^{1}\Sigma^{+}_{u}-x^{1}\Sigma^{+}_{g}$ transition of $N^{2+}_{2}$ was rotationally analyzed by Carroll already 1958 and more recently by Cossart and coworkers. We have used the high frequency deflection technique to perform the first direct vibrationally resolved measurement of a fluorescence lifetime of a doubly charged molecular $ion^{1}$. Furthermore, we have used the complete active space SCF (CASSCF) method to calculate the electronic transition moment function of the D-X transition. The contracted CI (CCI) method was used to improve the potential curves obtained at the CASSCF level and the radiative lifetime was obtained with help of these potential curves and the electronic transition moment function. The experimental and theoretical lifetimes, 6.010.5 and 8.0 ns respectively, are in good agrecement. No emission from the $CO^{2+}$ ion has yet been observed. The CASSCF and CCI methods have been used to obtain potential curves of low lying triplet states of $CO^{2+}$.With these curves as guidance, emission from $CO^{2+}$ following electron impact on jet cooled CO have been searched for. We also plan to search for a laser induced predissociation spectnm of $CO^{2+}$ with the fast ion beam laser technique