Daily Population Size Research Articles

A targeted e-learning approach for keeping universities open during the COVID-19 pandemic while reducing student physical interactions.

The COVID-19 pandemic led to widespread closure of universities. Many universities turned to e-learning to provide educational continuity, but they now face the challenge of how to reopen safely and resume in-class learning. This is difficult to achieve without methods for measuring the impact of school policies on student physical interactions. Here, we show that selectively deploying e-learning for larger classes is highly effective at decreasing campus-wide opportunities for student-to-student contact, while allowing most in-class learning to continue uninterrupted. We conducted a natural experiment at a large university that implemented a series of e-learning interventions during the COVID-19 outbreak. The numbers and locations of 24,000 students on campus were measured over a 17-week period by analysing >24 million student connections to the university Wi-Fi network. We show that daily population size can be manipulated by e-learning in a targeted manner according to class size characteristics. Student mixing showed accelerated growth with population size according to a power law distribution. Therefore, a small e-learning dependent decrease in population size resulted in a large reduction in student clustering behaviour. Our results suggest that converting a small number of classes to e-learning can decrease potential for disease transmission while minimising disruption to university operations. Universities should consider targeted e-learning a viable strategy for providing educational continuity during periods of low community disease transmission.

Demography of the endangered butterfly Euphydryas aurinia (Lepidoptera: Nymphalidae): A case study of populations in sub-Mediterranean dry calcareous grasslands

We studied a population of the regionally endangered marsh fritillary butterfly Euphydryas aurinia inhabiting a system of loosely connected dry calcareous grasslands in sub-Mediterranean Slovenia. Our goal was to set the basis for a long-term monitoring of this butterfly in four meadows using mark-release-recapture (MRR). We determined its demographic parameters, dispersal, behaviour and utilization of nectar plants in different quality patches. Total population size was estimated to be approximately 347 males (95% confidence interval: 262-432) and 326 females (95% confidence interval: 250-402), with an unbiased sex ratio. The average lifespans were 6.3 and 8.6 days, respectively. Daily population sizes followed a parabola with marked protandry. Both sexes were relatively highly mobile with both occasionally moving over half a kilometre. The spatial distribution of animals seemed to be associated with patch size, host plant densities and nectar sources, resulting in much higher population densities in the largest patch. Adult behaviour differed between the sexes, with females resting more and flying less than males. Behaviour also changed during daytime and with the progression of the season. Adults were confirmed to be opportunistic feeders, since as many as ten nectar sources were detected. We conclude that demographic parameters differ greatly among regions and habitats, thus conservation aims should be planned accordingly. Although the population studied is apparently in good condition, there are threats that may hamper the long-term persistence of the species in this area: succession, intensification of mowing and overgrazing.

Do Butterfly Activity Data from Mark-Recapture Surveys Reflect Temporal Patterns?

Temporal patterns in butterfly behavior should reflect diurnal, seasonal and population-level changes in mate availability. Investment into mating should peak at times when potential mates are at a maximum; at other times, individuals should save energy and focus on maintenance activities. To explore these assumptions, we re-analyzed mark-recapture data containing records of behavior for each handled individual: 15 species, 21 separate datasets, total of 20,828 activity records (13,223 males and 7605 females). We used ordination analysis, with activity categories as response variables and controls for dataset identity and weather effects. Across species, basking and nectaring were prevailing morning activities, while mating peaked at afternoons. With the progressing season, males switched from maintenance behavior to mating activities, whereas opposite trend applied to females. Density predictors (sex ratio, daily population size) revealed that mating concentrated to high densities of the opposite sex and that female oviposition, resting and nectaring increased under low density of males. Exploring mark-recapture data for studying behavioral patterns proved to be fruitful but cannot replace focused observations or experiments.

Distribution and habitats of Phengaris (Maculinea) butterflies and population ecology of Phengaris teleius in China

Many species of the butterfly genus Phengaris are regarded as endangered in many parts of their distribution. Several species are also widely distributed across northern China. Due to land use change and overgrazing, their habitats are declining and many patches have been lost. This paper investigates the distribution and habitats of the Chinese Phengaris species (of the subgenus Maculinea). Shrub-grassland near forests seem the most frequent habitat for Phengaris, while flat open grasslands are mostly over-grazed and thus survival for Phengaris butterflies there seems difficult. Throughout Europe, P.teleius is an endangered species, while there is still no information on its status in China. To improve the knowledge on the population ecology of P.teleius, its population structure, adult behaviour and movement were studied through mark–release–recapture methods in the Qinling Mountains of Taibai County. Eight grassland patches which were potentially suitable were found in the area in 2013. In total, 480 individuals (274 females) were marked, resulting in an overall recapture rate of 16 %. The average daily population size was 44 butterflies (±23 SD) during the adult flight period. Sixty-seven percent of the females and 38 % of the males moved less than 50 m, and 17 % of recaptured females and 38 % of males moved more than 200 m. The mean movement distance was 107 ± 177 m for males and 182 ± 122 m for females. The majority of the recaptures (86 %) were made within the patches, only a few individuals (14 %) moved between patches. Due to human disturbance and destruction, all of the eight potentially suitable patches are becoming smaller and increasingly isolated, thus these populations of P.teleius may face an increasing risk of extinction, which may well be a tip of the iceberg of habitat loss and fragmentation of P.teleius in Taibai County and possibly beyond. Hence we hope our initial study of P.teleius could have positive impacts on the conservation of Phengaris butterflies in China.

Conserving Europe’s most endangered butterfly: the Macedonian Grayling (Pseudochazara cingovskii)

The Macedonian Grayling is listed as critically endangered in the recent IUCN Red List of European butterflies because of its extreme rarity and habitat loss due to quarrying. This categorisation was, however, based on rather limited knowledge on its actual distribution, popu- lation size and habitat requirements. In 2012, we conducted field surveys to acquire more information. We found the species at six new sites extending its known range of suitable habitat to just under 10 km 2 . The daily population size was estimated using capture-mark-recapture method in the most densely populated part of the Pletvar pass site at more than 650 individuals. Adults proved to be extremely sedentary, not moving far even within the continuous habitat on the same slope. Oviposition was observed on dry plant material and in a rock crevice close to the potential larval host plant Festuca sp. Quarrying is confirmed to be the main threat to the habitat of the Macedonian Grayling with five out of seven populated sites containing active marble quarries. Due to the enlargement of the known area of occupancy, its threat status would now be estimated at endangered. Despite the restricted knowledge about its distribution and trends in the population size, the IUCN criteria proved to be applicable to determine the threat status of a rare and localized butterfly such as Pseudoc- hazara cingovskii. Its original assessment of being called the most threatened butterfly in Europe resulted in imme- diate research project and subsequent actions that will undoubtedly help to conserve it in the future.

Hermaphroditism in the Iridinidae (Bivalvia: Etherioidea)

The predominant reproductive mode for the Unionoida is hypothesised to be dioecy (gonochorism), with hermaphroditism sporadically distributed within the order. However, since the reproductive modes of unionoidean bivalves have been relatively well documented in comparison to the situation within the Etherioidea, additional data on the reproductive patterns of the latter are necessary to test this generality. A summary of the historic works dealing with hermaphroditism in North American and European Unionidae was presented by Van der Schalie. Within the North American fauna, a relatively large number of dioecious species exhibit a low incidence of hermaphroditic individuals, while a smaller number of species are typically hermaphroditic. Of the ca 300 unionoid species in North America, only seven species have been Figure 4. Daily population size estimates based on the modified Lincoln index. Vertical bars give standard errors of population estimates. The dashed horizontal line shows the total number of individuals found (Fig. 3). Estimates could not be calculated for surveys 9 and 10, because no new individuals were found. Figure 3. Cumulative number of individual sea slugs recorded over our ten-day survey. Open circles indicate observations at high tide, filled ones observations at low tide. ACKNOWLEDGEMENTS

Population dynamics of the solitary digger bee Andrena vaga Panzer (Hymenoptera, Andrenidae) studied using mark‐recapture and nest counts

AbstractThe population size of the solitary digger bee Andrena vaga was documented using mark‐recapture methods during 4 consecutive years (1996–1999). Additionally, the numbers of the parasitoids Nomada lathburiana and Bombylius major were estimated. For calculations of the daily population size, the Jolly‐Seber model for open populations with time‐dependent survival and capture rates was used. The mean daily population size corresponded well to the number of nests marked in the aggregation of A. vaga. The method of mark‐recapture achieved the most accurate data when the number of sampling periods and the capture probability was high. The results document a decrease in population size of the investigated A. vaga aggregation during 4 successive years. A population increase of its parasitoids B. major is considered to be one reason for the population decline of A. vaga in 1999. The sex ratio of A. vaga was biased toward females, contrary to the expected higher number of males. Results of the mark‐recapture studies showed that up to 50% of females left the aggregation or died at the beginning of the season. The females probably colonized new aggregations at distances further than 200 m away from their birth aggregation, as no marked females were observed in the environs of the study area. This behavior is interpreted as a parasite avoidance strategy. The bee populations in the study area form a web of interconnected aggregations. Apparently a flux of extinction and recolonization exists between the different aggregations.

Dynamics and foraging behaviour of adult hornet robberflies, Asilus crabroniformis : implications for conservation management

Mark resighting studies of the hornet robberfly, Asilus crabroniformis, were carried out during the flight seasons of 1999 and 2000 on agricultural land on the Chilterns in Oxfordshire, UK. Six patches of land were identified which contained characteristics thought to be attractive to hornet robberflies. One hundred and twenty eight adults were marked in 1999 and 257 in 2000. Marking was carried out on one of the patches, but resighting observations were collected from all six sites. The daily population sizes were estimated using the Jolly-Seber method. The daily population size peaked between 50 and 72 from 23 August until 13 September in 2000. This was very similar to the peak population size of between 50 and 74 estimated for 1999. Adults were found to be capable of living for nearly 5 weeks. The maximum linear distance from the point of marking that any individual moved across the study site was 625 m, but some individuals moved over 400 m in a single day. Unsuitable habitat (suburban gardens and a main road) did not present a barrier to dispersal. Males were more likely than females to loiter in sites peripheral to the breeding site, whilst females seemed to be more tied to the breeding site. Most adults were caught from dung piles, but insects avoided fresh dung and preferred instead dung that was well into the process of drying out. A variety of insect species were taken as prey, including many beetles and flies. The findings of the study are discussed in relation to the management of the landscape to enhance the long-term prospects of the hornet robberfly in the UK, and to achieve the UK Biodiversity Action Plan target for this species.

Metapopulation dynamics of the bog fritillary butterfly: demographic processes in a patchy population

Metapopulation models predicting the persistence of species on the verge of extinction in fragmented landscapes have to include local population dynamics. In this paper, we report on a 9‐yr study in which a patchy population of the bog fritillary was monitored each year, with special focus on quantifying demographic parameters. We parameterised various constrained linear models (CLM) with capture‐mark‐recapture (CMR) data collected in the field each year and we tested the effects of several variables on demographic parameters. Selecting the best CLM, we estimated the mean and the variance of (1) individual parameters (survival and catchability) and (2) population features (population size, sex‐ratio and recruitment). Survival was not related to the age of the individual but decreased continuously during the flight period, which means that lifetime expectancy is conversely related to the delay between the moment of the emergence of a given individual as compared to the emergence of the first adult in the population. Survival was lower in males than in females, as a consequence of male mate‐locating behaviour. Daily population size fits a parabolic distribution in both sexes, males appearing, reaching their abundance peak and dying before females. Yearly variation in the sex‐ratio is the consequence of the between‐sex difference in the recruitment curve. Total adult population size shows large variations between years. Analysis of the relation between growth rate and abundance indicates density dependence, probably related to parasitism of the larval stages. Density at the equilibrium is about 200 adults/ha.

Quantitative Sampling of Fish Populations with a Mobile Rising Net

Abstract A modified pop net (i.e., an inflatable lift net), used to estimate fish population size, was evaluated in a small northern Colorado lake having a stocked population of rainbow trout Oncorhynchus mykiss of known initial size. At the conclusion of pop-net sampling, the lake was treated with rotenone to estimate final fish population size and the instantaneous daily mortality rate. This rate was used to determine the expected fish population size for each day of sampling. A target value for the population estimates based on pop-net samples was defined as the mean of the expected daily population sizes. Seven estimators were used to predict total fish population size from pop-net sampling; 95% confidence intervals for all ratio estimators included the target value. A volume-based stratified ratio estimator best predicted the fish population size in the study lake.

Population structure and recommendations for conservation of the narrowly endemic alpine butterfly, Boloria acrocnema (Lepidoptera: Nymphalidae)

Boloria acrocnema is a glacial relict species, known from two colonies in alpine southwestern Colorado, USA. Mark-recapture techniques were used to analyse its population structure at its type locality, Mt Uncompahgre. Adult activity there is confined largely to about 1 ha in which the larval foodplant, Salix nivalis, is abundant. Mark-recapture data indicate that daily population sizes are low, most adults remain in residence at the colony only a few days, and there are age-specific sexual differences in movement, with older females perhaps leaving the colony site. Survival of B. acrocnema is probably governed by a pattern of local extinctions, counter-balanced by colonizations of new habitat. The autoecology of B. acrocnema is discussed in the light of present conservation needs of this butterfly. Management actions being taken by several agencies are also presented; these include enforcing grazing restrictions, monitoring collecting pressure, and formal listing of this species under federal and state endangered species programmes.