Michal Knapp

Spatio-Temporal Variation in Contrasting Effects of Resident Vegetation on Establishment, Growth and Reproduction of Dry Grassland Plants: Implications for Seed Addition Experiments

Successful establishment of plants is limited by both biotic and abiotic conditions and their interactions. Seedling establishment is also used as a direct measure of habitat suitability, but transient changes in vegetation might provide windows of opportunity allowing plant species to colonize sites which otherwise appear unsuitable. We aimed to study spatio-temporal variability in the effects of resident vegetation on establishment, growth and reproduction of dry grassland species in abandoned arable fields representing potentially suitable habitats. Seeds were sown in disturbed (bare of vegetation and roots) and undisturbed plots in three fields abandoned in the last 20 years. To assess the effects of temporal variation on plant establishment, we initiated our experiments in two years (2007 and 2008). Seventeen out of the 35 sown species flowered within two years after sowing, while three species completely failed to become established. The vegetation in the undisturbed plots facilitated seedling establishment only in the year with low spring precipitation, and the effect did not hold for all species. In contrast, growth and flowering rate were consistently much greater in the disturbed plots, but the effect size differed between the fields and years of sowing. We show that colonization is more successful when site opening by disturbance coincide with other suitable conditions such as weather or soil characteristics. Seasonal variability involved in our study emphasizes the necessity of temporal replication of sowing experiments. Studies assessing habitat suitability by seed sowing should either involve both vegetation removal treatments and untreated plots or follow the gradient of vegetation cover. We strongly recommend following the numbers of established individuals, their sizes and reproductive success when assessing habitat suitability by seed sowing since one can gain completely different results in different phases of plant life cycle.

Preservative fluid and storage conditions alter body mass estimation in a terrestrial insect

Body mass is a frequently used trait in ecological and evolutionary research. In the present study, I demonstrate that sampling and storage conditions affect wet and dry weights in an insect predator, Anchomenus dorsalis (Pontoppidan) (Coleoptera: Carabidae). Live beetles were placed in one of five preservative fluids for 1 month to simulate sampling by pitfall traps. Sodium chloride solution, ethylene glycol, ethylene glycol + detergent, and propylene glycol caused significant increases in both wet and dry weights compared with control (short‐term frozen) specimens, whereas formaldehyde did not. In a separate experiment, four methods of long‐term (6 months) sample storage (freezing, ethanol, propylene glycol, and ethyl acetate vapour) all caused significant changes in wet weight compared with the control treatment. The dry weight of the specimens preserved in ethanol decreased significantly in contrast to the long‐term frozen specimens and those in propylene glycol and ethyl acetate vapour, whose dry weight did not differ significantly from the control specimens. The combination of formaldehyde as the preservative fluid and freezing as the storage method thus appears to be an optimal combination for studies in which the body mass of dead insects is considered.

Even the Smallest Non-Crop Habitat Islands Could Be Beneficial: Distribution of Carabid Beetles and Spiders in Agricultural Landscape

Carabid beetles and ground-dwelling spiders inhabiting agroecosystems are beneficial organisms with a potential to control pest species. Intensification of agricultural management and reduction of areas covered by non-crop vegetation during recent decades in some areas has led to many potentially serious environmental problems including a decline in the diversity and abundance of beneficial arthropods in agricultural landscapes. This study investigated carabid beetle and spider assemblages in non-crop habitat islands of various sizes (50 to 18,000 square metres) within one large field, as well as the arable land within the field, using pitfall traps in two consecutive sampling periods (spring to early summer and peak summer). The non-crop habitat islands situated inside arable land hosted many unique ground-dwelling arthropod species that were not present within the surrounding arable land. Even the smallest non-crop habitat islands with areas of tens of square metres were inhabited by assemblages substantially different from these inhabiting arable land and thus enhanced the biodiversity of agricultural landscapes. The non-crop habitat area substantially affected the activity density, recorded species richness and recorded species composition of carabid and ground-dwelling spider assemblages; however, the effects were weakened when species specialised to non-crop habitats species were analysed separately. Interestingly, recorded species richness of spiders increased with non-crop habitat area, whereas recorded species richness of carabid beetles exhibited an opposite trend. There was substantial temporal variation in the spatial distribution of ground-dwelling arthropods, and contrasting patterns were observed for particular taxa (carabid beetles and spiders). In general, local environmental conditions (i.e., non-crop habitat island tree cover, shrub cover, grass cover and litter depth) were better determinants of arthropod assemblages than non-crop habitat island size, indicating that the creation of quite small but diversified (e.g., differing in vegetation cover) non-crop habitat islands could be the most efficient tool for the maintenance and enhancement of diversity of ground-dwelling carabids and spiders in agricultural landscapes.

Measurement of Body Condition in a Common Carabid Beetle, Poecilus cupreus: A comparison of Fresh Weight, Dry Weight, and Fat Content

Abstract Because of its direct consequences on reproductive success, body condition is an often-studied individual trait in insects. Various studies on insects use disparate methods to assess “body condition.” However, it is doubtful that the results obtained by disparate methods are comparable. In this study, the body conditions of Poecilus cupreus (Linnaeus) (Coleoptera: Carabidae) from eight sites were compared based on the following commonly used variables: (i) fresh weight, (ii) dry weight, and (iii) fat content. All of these variables were corrected for structural body size. Moreover, the effects of using the following ways of assessing structural body size were examined: (a) one size measurement (length of elytron, which is commonly used in beetles), and (b) three size measurements (length of elytron, width of pronotum and length of hind femur). The results obtained using the various estimations of body condition (i, ii, iii) varied significantly. Therefore, studies employing distinct body measurements to assess body condition are not comparable to each other. Using multiple structural size measurements in body condition analyses is better than the common practice of using only one size measurement. However, in the present study, results provided by both methods differ only slightly. A recommendation on the use of terminology in studies on body condition is introduced.

The effects of habitat, density, gender and duration on overwintering success in Bembidion lampros (Coleoptera: Carabidae)

In temperate climates, winter mortality is a key factor influencing insect survival. In Bembidion lampros (Coleoptera: Carabidae), an abundant polyphagous predator in arable farmland, we investigated how habitat, population density, gender and duration of overwintering affect the winter mortality and body condition of survivors. In a field experiment, we introduced beetles at two population densities into isolators placed either in the interior of the field or in the grassy boundary. Half of the isolators were collected in mid‐March, and the remaining half were collected in mid‐April. Across all treatments, 44–92% of the beetles survived until spring. Survival was significantly higher in the field interior than in the boundary. The longevity of individuals starved after overwintering was higher in females than in males and was positively related to the length of time spent at the overwintering site. Population density was positively related to percentage survival but did not affect body condition. Our results suggest that biotic factors such as population density and predation, though little studied, may have a similar significance as abiotic factors. Even ubiquitous carabid species inhabiting agroecosystems have specific requirements for overwintering. Understanding these requirements is useful for developing techniques to support their overwintering success.

Emergence of sexual size dimorphism and stage-specific effects of elevated temperature on growth rate and development rate in Harmonia axyridis

Temperature is considered to be the most important environmental factor influencing the performance of ectotherms because it determines the rate of most biochemical reactions and thus the efficiency of metabolism and its function. Unfortunately, most studies investigate the effects of temperature on individuals exposed to a particular temperature regime during their whole pre‐imaginal development and detailed information on variation of the temperature effects during ontogeny is rare. In the present study, the effects of the timing of exposure to a transient period of elevated temperature during ontogeny on development rate and growth rate are investigated for the ladybird Harmonia axyridis Pallas. Control beetles are reared at a constant temperature of 20 °C, whereas treated beetles are reared at 20 °C but are exposed to 33 °C for 48 h either during the early‐larval stage, third‐larval instar, fourth‐larval instar or the pupal stage. The rate of development and the growth rate are both accelerated because the timing of exposure to elevated temperature occurred later in pre‐imaginal development (i.e. development rate and growth rate are highest in individuals exposed to elevated temperature during the pupal stage). An exception to this pattern is the lowering of development rate in individuals exposed to elevated temperature during the fourth‐larval instar. Female H. axyridis have a significantly higher development rate and growth rate than males. However, the relative difference in growth rate between the sexes is much higher than the difference in development rate between sexes, resulting in a female‐biased size (mass) dimorphism in adult beetles.

Relative Importance of Sex, Pre-Starvation Body Mass and Structural Body Size in the Determination of Exceptional Starvation Resistance of Anchomenus dorsalis (Coleoptera: Carabidae)

In nature, almost all animals have to cope with periods of food shortage during their lifetimes. Starvation risks are especially high for carnivorous predatory species, which often experience long intervals between stochastic prey capturing events. A laboratory experiment using the common predatory carabid beetle Anchomenus dorsalis revealed an exceptional level of starvation resistance in this species: males survived up to 137 days and females up to 218 days without food at 20°C. Individual starvation resistance was strongly positively affected by pre-starvation body mass but only slightly by beetle structural body size per se. Females outperformed males even when the effect of gender was corrected for the effects of structural body size and pre-starvation body mass. The better performance of females compared to males and of beetles with higher relative pre-starvation body mass could be linked to higher fat content and lean dry mass before starvation, followed by a greater decrease in both during starvation. There was also a difference between the sexes in the extent of body mass changes both during ad libitum feeding and following starvation; the body masses of females fluctuated more compared to males. This study stresses the need to distinguish between body mass and structural body size when investigating the ecological and evolutionary consequences of body size. Investigation of the net effects of body size and sex is necessary to disentangle the causes of differences in individual performances in studies of species with significant sexual size dimorphism.

Body size and nutrition intake effects on fecundity and overwintering success in Anchomenus dorsalis (Coleoptera: Carabidae).

Abstract Structural body size and adult feeding conditions seem to be important determinants of fitness in income breeding species. However, little is known about the relative importance of structural body size and nutritional state on fecundity and winter survival in carabids. In this study, two separate experiments were performed. The effects of the structural body size of females (expressed as the length of the elytra and the width of the pronotum) and the effect of starvation on the fecundity of the ground beetle Anchomenus dorsalis (Pontoppidan, 1763) were investigated in the “fecundity experiment.” The influence of structural body size, feeding conditions (full, partial, or no feeding) before the winter, and behavior during the winter (burrowing into the substrate) on winter survival in A. dorsalis females were studied in the “overwintering experiment.” Egg production was positively influenced by both the structural body size of females and adult feeding. The effect of structural body size on the number of eggs laid outweighed the effect of feeding. However, the total fecundity (the number of eggs laid plus the number of mature eggs in ovaries) were more strongly affected by feeding in comparison to the structural body size of females. Interestingly, there was no significant effect of structural body size, feeding before winter, or behavior during winter on the survival of A. dorsalis females during the winter. However, our overwintering results could be affected by extreme weather conditions throughout experimental season and by the experimental design, which is discussed in detail.

Small-scale spatiotemporal variability in body size of two common carabid beetles

Adult body size is one of the most ecologically relevant quantitative traits that underlies many other life-history traits of particular organism. In insects, there is positive intraspecific relationship between body size and female fecundity. In this study small scale temporal and spatial and space variability in structural body size of Poecilus cupreus and Anchomenus dorsalis was investigated. The beetles were collected in four fields near Prague-Suchdol in autumn 2009 and 2010, and in spring 2010, 2011 and 2012. In both species structural body size was significantly affected by sex (females were the larger sex). In A. dorsalis structural body size was also significantly affected by arable field identity, overwintering (post-overwintering individuals collected in spring were larger in comparison to pre-overwintering individuals collected in autumn), sampling year, overwintering by year and arable field by year interactions. Our results suggest that spatiotemporal variation in environmental conditions experienced by A. dorsalis during larval growth resulted in differences in adult structural body size among particular fields and particular sampling years. In addition, mean structural body size in A. dorsalis was affected by overwintering, which was probably caused by size-specific winter mortality. Moreover, effect of overwintering varied among years, probably according to the specific weather conditions during a particular winter.

The role of various meadow margin types in shaping carabid and staphylinid beetle assemblages (Coleoptera: Carabidae, Staphylinidae) in meadow dominated landscapes

Less intensively managed semi-natural habitats, e.g., field and meadow margins like hedgerows, are thought to be crucial landscape components for maintaining biodiversity in highly disturbed and intensively managed agricultural landscapes. In this study, we focused on the effects of three meadow margin types on activity-density, species richness and species composition of carabid and staphylinid beetles recorded by pitfall traps in Central European landscapes dominated by intensively managed meadows. Carabid activity-density was significantly higher in meadows than in meadow margins and within meadow margins their activity-density increased from grassy meadow margins via shrubby ones to woody meadow margins. We found that recorded species richness of both carabid and staphylinid beetles was not significantly affected by habitat identity (meadow margin or neighbouring meadow) and meadow margin type. Recorded species composition of both investigated taxa was significantly affected by habitat identity and interaction between habitat identity and meadow margin type (i.e. it differed between particular meadow margin types). Assemblages inhabiting various meadow margin types were more dissimilar between each other than assemblages from neighbouring meadows. Meadow margins within grassland dominated landscapes maintain local species richness by hosting different species from those living in surrounding meadows. Dissimilarity of carabid and staphylinid assemblages from meadows neighbouring both sides of particular meadow margin did not differ between meadow margin types. Our results indicate that semi-natural habitats play an important role in maintaining biodiversity not only in agricultural landscapes dominated by arable fields, but also in those dominated by meadows.