Roadside Populations Research Articles

Germination attributes of metsulfuron-resistant and metsulfuron-susceptible tropical ageratum (Ageratum conyzoides) populations under various environmental conditions

Abstract Tropical ageratum (Ageratum conyzoides L.) is a problematic weed frequently observed in association with commercially important crops in Australian agroecosystems. Knowledge of the germination response of A. conyzoides is crucial for proactively managing this weed species, especially when herbicide resistance is involved. Herbicide screening and metsulfuron dose–response experiments were conducted on two separate populations of A. conyzoides (referred to as Sugarcane and Roadside) in an open environment to identify a metsulfuron-resistant population. Based on the survival percentage in the metsulfuron dose–response experiment, the Sugarcane population was found to be 54 times more resistant compared with the metsulfuron-susceptible population (Roadside). Subsequent laboratory experiments were performed to investigate the differential germination response of the two populations. No germination or emergence difference was observed between the Sugarcane and Roadside populations under various thermal regimes (15/5 to 35/25 C with a 12/12-h photoperiod), salinity levels (0 to 320 mM), osmotic potentials (0 to −1.6 MPa), and burial depths (1 to 4 cm). However, different environmental conditions significantly impacted the germination and emergence of A. conyzoides. Ageratum conyzoides germinated over a wide range of temperatures, with the highest germination rate (>90%) occurring at 30/20 C. With increasing levels of salinity, osmotic potential, and burial depth, the germination/emergence of A. conyzoides declined and was completely inhibited at 300 mM salinity, −0.8 MPa osmotic potential, and a 1-cm burial depth. The data generated from this study will be useful in developing a model-based approach to predict the occurrence of this weed species and thus aid in designing ecologically sustainable integrated weed management protocols.

Population origin and heritable effects mediate road salt toxicity and thermal stress in an amphibian

Human impacts on wild populations are numerous and extensive, degrading habitats and causing population declines across taxa. Though these impacts are often studied individually, wild populations typically face suites of stressors acting concomitantly, compromising the fitness of individuals and populations in ways poorly understood and not easily predicted by the effects of any single stressor. Developing understanding of the effects of multiple stressors and their potential interactions remains a critical challenge in environmental biology. Here, we focus on assessing the impacts of two prominent stressors associated with anthropogenic activities that affect many organisms across the planet – elevated salinity (e.g., from road de-icing salt) and temperature (e.g. from climate change). We examined a suite of physiological traits and components of fitness across populations of wood frogs originating from ponds that differ in their proximity to roads and thus their legacy of exposure to pollution from road salt. When experimentally exposed to road salt, wood frogs showed reduced survival (especially those from ponds adjacent to roads), divergent developmental rates, and reduced longevity. Family-level effects mediated these outcomes, but high salinity generally eroded family-level variance. When combined, exposure to both temperature and salt resulted in very low survival, and this effect was strongest in roadside populations. Taken together, these results suggest that temperature is an important stressor capable of exacerbating impacts from a prominent contaminant confronting many freshwater organisms in salinized habitats. More broadly, it appears likely that toxicity might often be underestimated in the absence of multi-stressor approaches.

Glycolytic modulations and antioxidant capacity in Amazonian fish, Bryconops giacopinii (Characiformes: Iguanodectidae), living at high temperature

Abstract Temperature is projected to continue increasing in the upcoming years. The effects of temperature warming in deforested stream populations have not been addressed yet and are a promising area to understand the consequences of increased temperature on fish physiology. Therefore, the aims of this study were to determine the manner in which Bryconops giacopinii from deforested habitat modulates the LDH kinetics in response to warming and whether the antioxidant system is able to withstand thermal stress. We collected individuals from two roadside streams (deforested) and one forested stream and measured the LDH kinetics parameters (Vmax and Km) for pyruvate and lactate, measured the total ROS production, and measured the activity of antioxidant enzymes and the oxidative stress biomarker. Our results showed lower affinity and higher LDH activity for lactate oxidation in road-side populations, suggesting that populations living in high temperatures use lactate as aerobic fuel. Besides, there was an increase in ROS production, and CAT and GSH levels in road-side populations, but not LPO levels, suggesting that B. giacopinni is able to neutralize the ROS production with the antioxidant systems. Our results bring important findings in the adaptation of this specie to a warm environment.

Invasive success of star weed (Parthenium hysterophorus L.) through alteration in structural and functional peculiarities.

Parthenium weed poses significant threats to cropping systems, socioeconomic structures, and native ecosystems. The pronounced impact is primarily attributed to its rapid and efficient invasion mechanism. Despite that the detrimental effects of Parthenium weed are widely acknowledged, an in-depth scientific comprehension of its invasion mechanism, particularly regarding modifications in structural and functional attributes under natural conditions, is still lacking. To bridge this knowledge gap and formulate effective strategies for alleviating the adverse consequences of Parthenium weed, a study was conducted in the more cultivated and densely populated areas of Punjab, Pakistan. This study was focused on fifteen distinct populations of the star weed (Parthenium hysterophorus L.) to investigate the factors contributing to its widespread distribution in diverse environmental conditions. The results revealed significant variations in growth performance, physiological traits, and internal structures among populations from different habitats. The populations from wastelands exhibited superior growth, with higher accumulation of soluble proteins (TSP) and chlorophyll content (Chl a&b, TChl, Car, and Chl a/b). These populations displayed increased root and stem area, storage parenchyma, vascular bundle area, metaxylem area, and phloem area. Significant leaf modifications included thicker leaves, sclarification around vascular bundles, and widened metaxylem vessels. Roadside populations possessed larger leaf area, enhanced antioxidant activity, increased thickness of leaves in terms of midrib and lamina, and a higher cortical proportion. Populations found in agricultural fields depicted enhanced shoot biomass production, higher levels of chlorophyll b, and an increased total chlorophyll/carotenoid ratio. Additionally, they exhibited increased phloem area in their roots, stems, and leaves, with a thick epidermis only in the stem. All these outcomes of the study revealed explicit structural and functional modifications among P. hysterophorus populations collected from different habitats. These variations were attributed to the environmental variability and could contribute to the widespread distribution of this species. Notably, these findings hold practical significance for agronomists and ecologists, offering valuable insights for the future management of Parthenium weed in novel environments and contributing to the stability of ecosystems.

Survival tactics of an endangered species Withania coagulans (Stocks) Dunal to arid environments.

Withania coagulans is a valuable medicinal plant with high demand, but its wild growth and local usage pose a threat to its natural habitat. This study aims to understand the plant's growth, anatomy, and physiology in different environmental conditions to aid in conservation and re-vegetation efforts. Fifteen differently adapted populations of Withania coagulans were collected from diverse ecological regions, viz., (i) along the roadside, (ii) hilly areas, (iii) barren land, and (iv) wasteland to unravel the adaptive mechanisms that are responsible for their ecological success across heterogenic environments of Punjab, Pakistan. The roadside populations had high values of photosynthetic pigments, total soluble proteins, root endodermis thickness, stem and leaf cortical thickness, and its cell area. The populations growing in hilly areas showed better growth performance such as vigorous growth and biomass production. Additionally, there was enhanced accumulation of organic osmolytes (glycine betaine and proline), chlorophyll content (chl a/b), and enlarged epidermal cells, cortical cells, vascular bundles, metaxylem vessels, and phloem region in roots. In case of stem area, epidermal thickness, cortical thickness, vascular bundle, and pith area showed improved growth. However, the barren land population showed significant increase in carotenoid contents, vascular bundle area, and metaxylem area in roots, and xylem vessels and phloem area in stems and leaves. The wasteland population surpassed the rest of the populations in having greater root dry weight, higher shoot ionic contents, increased root area, thick cortical, and vascular bundle area in roots. Likewise, cortical thickness and its cell area, and pith area in stems, whereas large vascular bundles, phloem region, and high stomatal density were recorded in leaves. Subsequently, natural populations showed the utmost behavior related to tissue organization and physiology in response to varied environmental conditions that would increase the distribution and survival of species.

Phenology and Population Differentiation in Reproductive Plasticity in Feathertop Rhodes Grass (Chloris virgata Sw.)

An understanding of phenology and reproductive plasticity of a weed species can provide valuable information to manage it precisely. This study evaluated the phenotypic plasticity of feathertop Rhodes grass (Chloris virgata Sw.) where cohorts of four different populations (two from cropping and two from roadside situations) were initiated in early spring (4 September), late spring (4 November), mid-summer (4 January), and early autumn (4 March) in southern New South Wales (NSW), Australia. The team grew individual plants in the absence of competition under natural conditions. Life-history and fitness-related traits of both phenology and morphology were measured, and dry biomass of vegetative and reproductive parts were determined at physiological maturity. Among the four sowing times, the late-spring sowing treatment took the longest time from emergence to the first seed head emergence (70–110 days), while it had the shortest seed maturity period (8–16 days). Length of reproductive and total life period of the four populations differed across the four sowing-time treatments. The plants that emerged in mid-summer had the longest reproductive period (30 days) whereas the early-autumn emerging plants died before the reproductive stage because of the cold temperatures during winter. The mid-summer cohort required slightly longer time (63–85 days) to achieve seed head formation and less time (19–24 days) for seed maturity than those plants that emerged in early or late spring. All the reproductive features were varied by sowing times and population. The number of seed heads (12–15 per plant) and spikelets (12–13 per seed head), as well as the seed head biomass, re-productive biomass allocation pattern, and seed production, generally increased in the mid-summer-emerged cohort. Seed production in the mid-summer (9942 seeds/plant) cohort was 10% and 70% higher than the late spring (8000 seeds/plant) and early spring (3240 seeds/plant) cohorts, respectively. The ratio of reproductive biomass to vegetative biomass increased in the mid-summer sowing times in all populations, and this species displayed true plasticity in reproductive allocation. Additionally, the four populations of feathertop Rhodes grass differed significantly in phenological, vegetative, and reproductive traits, depending on the sowing time. The reproductive fitness of the four populations varied, with the two roadside populations (FELT 04/20 and STURT/16–17) appearing to be better adapted than the two cropping populations (PARK 01/20 and GLEN 03/18). The results from our study could help construct a basic framework for a variety of weed-management tactics to achieve successful control.

Road salt is more toxic to wood frog embryos from polluted ponds

Organisms that rely on aquatic habitats in roaded landscapes face a growing array of consequences from pollution, especially due to freshwater salinization. Critically, these consequences can vary from population to population depending on exposure histories and evolutionary responses. Prior studies using transplant and common garden experiments have found that aquatic-stage wood frogs (Rana sylvatica) from roadside populations are less fit in the wild and more sensitive to road salt than their counterparts from woodland populations away from roads. While this pattern is consistent with local maladaptation, unresolved insights into the timing and duration of these effects leave open the possibility that negative outcomes are countered during development. Here, we asked whether the survival disadvantage of roadside wood frogs is stage-specific, and whether this disadvantage reverses before metamorphosis. We used a common garden road salt exposure experiment and a field-based reciprocal transplant experiment to examine differences in survival across life-history stage and with respect to population type. In each experimental context, roadside embryos showed a survival disadvantage relative to woodland embryos, and this disadvantage was not reversed prior to metamorphosis. We also found that salt exposure delayed metamorphosis more strongly for roadside than woodland populations. Together, these results suggest that local maladaptation in aquatic-stage wood frogs is driven by embryonic sensitivity to salt and that roadside populations are further compromised by delayed developmental rates. Future studies should consider which embryonic traits fail to adapt to salt toxicity, and how those traits might correlate with terrestrial trait variation.

The Influence of Environmental Factors on Seed Germination of Polygonum perfoliatum L.: Implications for Management

Polygonum perfoliatum L. is an aggressive vine, currently invading the Black Sea region, Turkey. However, information about the seed germination biology of this species is scanty. The objective of the current study was to determine the seed germination biology of three naturalized populations of this species. Chemical scarification with 98% sulfuric acid for 30 min followed by cold-wet stratification at 4 °C for 4 weeks effectively released seed dormancy in tested populations. Seeds of all populations required a 12 h photoperiod for the highest germination, while germination under continuous dark and light remained similar. The seeds were able to germinate under a wide range of constant (5–40 °C) and alternating temperatures, pH (3–11), osmotic potential (0 to −1.4 MPa) and salinity (0–500 mM NaCl). However, the peak germination was observed under 20 °C constant and 20/15 °C alternating day/night temperature, and pH 6.8. Seeds of all populations were able to withstand 200 mM salinity and −0.6 MPa osmotic potential. Increasing seed burial depth initially stimulated seedling emergence and then a sharp decline was observed for the seeds buried below >2 cm depth. More than 90% of the seeds were unable to emerge when buried >6 cm depth. Polygonum perfoliatum has a large potential for range expansion; therefore, immediate management of the naturalized populations is warranted. This weed species in agricultural fields can be managed by burying the seeds in deeper soil layers (6 cm), while post-emergence management strategies need to be developed for roadside populations.

Rapid continental spread of a salt-tolerant plant along the European road network

The spread of alien species with the expansion of road networks and increasing traffic is a well-known phenomenon globally. Besides their corridor effects, road maintenance practices, such as the use of de-icing salts during winter facilitate the spread of halophyte (salt tolerant) species along roads. A good example is Plantago coronopus, a mainly coastal halophyte which has started spreading inland from the Atlantic and Mediterranean coastal habitats, recently reaching even Central European countries (e.g. Hungary). Here we studied the spread of this halophyte and tried to identify factors explaining its successful dispersion along roads, while also comparing native and non-native roadside occurrences with regard to altitude of the localities, size of roadside populations and frequency of roadside occurrences. We completed a comprehensive literature review and collected more than 200 reports of occurrence from roadsides spanning a total of 38 years. During systematic sampling the frequency of the species along roads was significantly higher in the Mediterranean (native area), than along Hungarian (non-native area) roads, however the average number of individuals at the sampling localities were very similar, and no significant difference could be detected. Using a germination experiment, we demonstrate that although the species is able to germinate even at high salt concentrations, salt is not required for germination. Indeed salt significantly decreases germination probability of the seeds. The successful spread of the species could most likely be explained by its remarkably high seed production, or some special characteristics (e.g. seed dimorphism) and its ability to adapt to a wide range of environmental conditions. Considering the recent and rapid eastward spread of P. coronopus, occurrences in other countries where it has not been reported yet can be predicted in coming years.

Water conservation strategies through anatomical traits in the endangered arid zone species Salvadora oleoides Decne.

Salvadora oleoides Decne. (Salvadoraceae) is a facultative and mesomorphic xerophyte, well adapted to arid and semi-arid regions. Twelve populations were selected from different ecological regions of Punjab to investigate structural modifications that are essential for water conservation, by either improving water-storing capacity or preventing water loss from the plant body, hence, enabling this species to cope with environmental extremities. We observed significant plasticity in structural features, which ensures ecological success in a variety of environmental conditions. Huge variation was seen in various tissue systems, i.e., epidermis and epidermal appendages, collenchyma, size of internal oil glands, storage parenchyma, shape, size and arrangement of vascular tissue, intensity of sclerification, and stomatal size, shape and orientation. The desert populations showed additional parenchymatous layer under multilayered epidermis, xylem completely surrounded by phloem, broad metaxylem vessels, intensive sclerification in and outside vascular tissue, and numerous and small sized stomata on abaxial leaf surface. Population from salt-affected areas showed greater stem cross-sectional area, enlarge palisade parenchymatous cells, multilayered epidermis, large storage parenchyma, and sclerified vascular bundles. Roadside populations possessed sclerified vascular bundles and dense hairiness on leaf surface.

Bilateral Asymmetry and Shape of Lamina Plantago major L

The aim of the work was to answer the question whether pollution by vehicles and the geographical location of populations affect the asymmetry and shape of the leaf plate Plantago major. The Generalized Procrustes Analysis was provided and the difference in the variance of paired landmarks was indicated. Based on vector coordinates, the symmetry and asymmetry covariance matrices of two types were created, and canonical covariance analysis was performed. The difference was found using the distances between the centers of the coordinate sets, the so-called Mahalanobis distances. The overall pool of leaves showed the presence of fluctuating asymmetry at the level of leaf blades in roadside populations. In the control, a mixture of two types of asymmetry: fluctuating and directional was traced. Canonical variation analysis showed the difference between the center of sets (p <0.0001). A correlation was obtained between the symmetric and asymmetric components of the shape. An allometric ratio of size/asymmetry and size/shape of the sheet plate were not obtained. The decrease in the number of landmarks from 52 to 26 did not affect the results. Thus motor transport, as shown by most of the samples (4 out of 6), had a significant impact on both the shape and asymmetry of the leaf blades. The geographical difference also affected both type of variability, as the difference in the asymmetry and shape of the plantain leaf blades increased over the geographical extent from Vladimir to Moscow on a distance about 200km.

About the asymmetry structure of the leaf blade Common plantain

Using the method of geometric morphometrics the contour of the image of the leaf blade of the Common plantain (Plantago major) was aligned along the axis of symmetry to answer the question of whether the asymmetry and shape were influenced by environmental pollution by vehicles and climatic conditions. Procrustes distances showed that fluctuating asymmetry was higher in roadside populations in 2019. In the control populations, a mixture of two types of asymmetry, fluctuating and directional, was obtained. In 2020 with high precipitation (47% more than in 2019), asymmetry was represented by higher directional asymmetry (p &lt;0.0001), although the overall asymmetry remained the same. The nonparametric Kruskal-Wallis test showed the influence on the shape only climatic environments of the year (p &lt;0.001). The geographical location of the populations and the combined effect of the factors year and the place of leaves gathering did not affect the shape of the leaf blade. In 2020, no data were obtained on the excess of asymmetry in roadside populations compared to the control, therefore authors conclude about the weak bioindicative properties of the Common plantain in response to traffic pollution.

Motorway age is linked to larger body size, but not song carrier frequency, in male grasshoppers from roadside populations

Producing calls with increased minimum carrier frequency is well documented in sound communicating species confronted with noise pollution, possibly helping them to avoid acoustic masking of low-frequency signals. However, the lack of studies on invertebrates limits our understanding of the potentially adverse effects of anthropogenic noise on natural populations. While males of the grasshopper Chorthippus biguttulus are known to produce courtship signals with elevated low-frequency local maxima (LFLM) in roadside populations, previous studies provided no insight into morphological traits underlying LFLM shifts. Although developmental plasticity was identified as one main factor accounting for elevated LFLM, an additional role for a more hard-wired trait architecture was proposed, possibly as a result of adaptation to traffic noise. Our current study therefore aims to assess (1) whether the position of LFLM is related to male body size, (2) whether body size is correlated with motorway age, and (3) whether the position of LFLM is correlated with motorway age in C. biguttulus males from roadside populations. In addition to substantial variation in LFLM among C. biguttulus males, we found that larger males produced signals with lower LFLM, suggesting a potential role in female choice as a predictor of male quality. While we found no significant correlation between LFLM and motorway age, C. biguttulus males were larger near older motorway sections. This positive correlation may be due to several reasons, including: (1) higher nutrient concentration and availability in plant tissues due to eutrophication of roadside habitats; (2) temporal succession of male size phenotypes during colonization processes; and/or (3) selection for larger body size in roadside populations. Our results highlight the multifaceted and often complex nature of the relationships between morphology, signal traits and anthropogenic pressures on sound communication in invertebrates.

The Demography of Gentiana autumnalis in Populations Under Varying Management Regimes in New Jersey

Gentiana autumnalis (pine barren gentian) is a rare, fall-flowering perennial that is endemic to pine barren habitat from New Jersey to South Carolina. This disturbance-adapted, early successional species is at risk in New Jersey as a result of human interactions, namely growing season mowing and fire suppression. We used a repeated measures design to compare the differences between managed (mowing and prescribed fire) and unmanaged G. autumnalis populations for density, life stage, mortality, and fecundity. Managed populations had a greater gentian density, proportion of reproductive individuals, and seedlings compared to unmanaged populations. Implementing prescribed burns and mowing at previously unmanaged sites prior to spring growth increased gentian density, flowering, and seed set the same year. Our data support that prescribed burning and mowing can be beneficial management tools for the conservation of G. autumnalis and other disturbance-adapted species that require open early-successional habitat. However, their implementation can have negative consequences if conducted during the growing season, especially for roadside populations that are periodically mowed. Declining rare plant populations have the potential to benefit from management practices that facilitate ideal growing conditions and influence life stage transitions that will best improve population growth rate over time.

Inland populations of Juncus balticus (Juncaceae) in Scotland

Typically considered a coastal species in Great Britain, Juncus balticus Willd. also occurs inland as a native plant beside the Rivers Avon, Dulnain and Findhorn in NE Scotland (and beside the R. Lossie in the 19th Century). Here it is found at median altitude 290 m AOD (inter-quartile range, 249 - 341 m). It also occurs as a native at one inland loch-side, and was found beside another loch in the 19th Century. In total, J. balticus has been recorded beside inland rivers from 14 10 km grid squares. In its inland riverside habitat, J. balticus is overwhelmingly found within communities dominated by native plant taxa, primarily associated with infertile, moist to damp, weakly to moderately acid soils, with high levels of illumination. Few observers are familiar with seeing J. balticus at its inland sites, therefore it is possible that this species has been overlooked along other rivers and burns in NE Scotland, and perhaps elsewhere. The first record of J. balticus beside a road was in 1907, long before roads were widely treated with salt in the winter, but it was not until 1979 that a second roadside population was discovered. Roadside and trackside populations have now been found in 19 10 km grid squares. At most of these sites it is likely to be an accidental introduction. It is now more widespread on roadsides than along inland riversides. The isolated nature of the roadside populations indicates that there have been multiple independent colonisations. It is highly likely that additional roadside populations await discovery, and that further colonisation events will occur.

Seed germination niche for common ragweed (Ambrosia artemisiifolia L.) populations naturalized in Turkey

Common ragweed (Ambrosia artemisiifolia L.) is an invasive species, and is currently spread in different habitats over several regions in Turkey. However, no information exists on the seed germination biology of Turkish populations. Therefore, the seed germination niche (upper and lower limits of environmental conditions for seed germination) was determined for common ragweed populations in two climatic regions (Thrace and Black Sea) of Turkey. Seed germination was evaluated under different photoperiods, constant temperatures and levels of water stress, salinity and pH. Seedling emergence was recorded from various seed burial depths. Significant differences were observed among populations for the seed germination niche and seedling emergence. Seed germination niche helps explain the occurrence of the species in the diverse environmental conditions found across Turkey. Seeds from the Thrace populations were more tolerant to water and salinity stress and germinated under relatively higher pH levels than those from the Black Sea populations. Further, seeds from the Thrace region germinated to higher percentages at all temperatures than those from the Black Sea populations. Seeds from all populations germinated to higher percentages in light/dark than in dark. Seedling emergence was significantly retarded by a seed burial depth >4 cm. The results suggest that the species has extensive range expansion potential in the country and that immediate management of the naturalized populations is needed. In agricultural habitats, the species can be managed by shallow tillage and subsequent management of emerging seedlings to reduce the soil seed bank. Management strategies such as appropriate mowing time and mowing frequency need to be developed for control of roadside populations.

Fitter frogs from polluted ponds: The complex impacts of human-altered environments.

Human‐modified habitats rarely yield outcomes that are aligned with conservation ideals. Landscapes that are subdivided by roads are no exception, precipitating negative impacts on populations due to fragmentation, pollution, and road kill. Although many populations in human‐modified habitats show evidence for local adaptation, rarely does environmental change yield outright benefits for populations of conservation interest. Contrary to expectations, we report surprising benefits experienced by amphibian populations breeding and dwelling in proximity to roads. We show that roadside populations of the wood frog, Rana sylvatica, exhibit better locomotor performance and higher measures of traits related to fitness compared with frogs from less disturbed environments located further away from roads. These results contrast previous evidence for maladaptation in roadside populations of wood frogs studied elsewhere. Our results indicate that altered habitats might not be unequivocally detrimental and at times might contribute to metapopulation success. While the frequency of such beneficial outcomes remains unknown, their occurrence underscores the complexity of inferring consequences of environmental change.

Do roads act as a barrier to gene flow of subterranean small mammals? A case study with Ctenomys minutus

Road-barrier effects can lead to population isolation, with consequent negative outcomes for individuals and populations. Small mammals have been identified as particularly vulnerable to barrier effects, yet few studies have focused on subterranean species. Given the burrowing habit of these species, we hypothesized that roads block their movement and therefore the gene flow between roadside populations. The tiny tuco-tuco (Ctenomys minutus), a small subterranean rodent that inhabits the coastal plains of southern Brazil, was used as a model species to test this hypothesis. We used 14 microsatellites to genotype 80 individuals from four colonies (n = 20 per colony). We compared the population differentiation (FST, G″ST and DEST) and population structuring (STRUCTURE and GENELAND, and discriminant analysis of principal components) of two colony pairs, one pair divided by a road, and the other with no road or other potential barrier between the colonies (control). The results indicated higher genetic differentiation and structuring between the roadside colonies than in the control sites, although less evident than initially predicted. We concluded that the road reduced but did not halt the gene flow of C. minutus. Nevertheless, in view of the rapid economic development of the region, measures to ensure long-term gene flow, i.e., installation or retrofitting of crossing structures, should be considered. This study complements previous analyses of road-barrier effects on small mammals, suggesting that subterranean species such as C. minutus can cope with these barriers, at least in conditions similar to our study area.

How traffic facilitates population expansion of invasive species along roads: The case of common ragweed in Germany

Abstract Because common ragweed (Ambrosia artemisiifolia L., henceforth Ambrosia) has negative effects on human health, it is a common focus for management, which would benefit from a better understanding of the underlying mechanisms by which the species spreads. Road systems are known to be invasion corridors, but the conduit function of vehicles for the rapid spread of Ambrosia along roads and for population extension along roadside verges has not yet been demonstrated convincingly. To quantify the effect of different traffic volumes on the dispersal and population extension of Ambrosia, we used two approaches: First, by combining field experiments along roads with records of the seed rain around single plants, we simulated a combined dispersal kernel that revealed the interactions between primary dispersal and traffic‐mediated secondary dispersal. Second, we recorded the seedling recruitment around isolated roadside populations over 2 years to determine how traffic‐related parameters affect population extension. The longest traffic‐mediated dispersal distances exceeded those of primary dispersal by about one order of magnitude. Traffic volume had a significant positive effect on dispersal distances and on the lateral deposition of seeds on the road verge. Seedling recruitment around isolated roadside populations was significantly higher in the driving direction than against, but only at the distance where the major seed rain of traffic‐mediated dispersal is to be expected according to the combined dispersal kernel (3–15 m). Synthesis and applications. This study isolates the effects of road traffic from confounding mechanisms (e.g. mowing machinery, propagule pressure from infested fields) on common ragweed (Ambrosia artemisiifolia L.) invasions. Results demonstrate the traffic‐mediated dispersal in Ambrosia invasions as a routine and predictable process that facilitates population extension in the direction of traffic along roadsides, depending on traffic volume. This highlights the importance of prioritizing mowing along high use roads and mowing of isolated populations to prevent seed abscission and further spread of common ragweed.

Time to cut: population models reveal how to mow invasive common ragweed cost-effectively

Roadsides are an important habitat for invasive common ragweed, Ambrosiaartemisiifolia L., by facilitating seed dispersal. Reducing the size of roadside populations is therefore essential for confining this highly allergenic species. Here, we aim to determine the cost-effectiveness of mowing regimes varying in frequency and timing, by analysing population-level effects and underlying demographic processes. We constructed population models of A.artemisiifolia parameterised by demographic data for four unmanaged reference populations across Europe in two years. We integrated the effects of four experimental mowing regimes along Austrian road sides on plant performance traits of five years and experimental data on seed viability after cutting. All four experimental regimes reduced the projected intrinsic population growth rates (r) compared to the unmanaged controls by reducing plant height and seed viability, thereby counteracting increased size-dependent fecundity. The prevailing 2-cut regime in Austria (cutting during vegetative growth, here in June and just before seed ripening, here in September) performed least well and the reduction in r was mainly due to reduced seed viability after the second cut. The efficacy of the two best experimental regimes (alternative schemes for 2 or 3 cuts) was mainly due to cutting just before female flowering (here in August) by decreasing final adult plant height dramatically and thereby reducing seed numbers. Patterns were consistent across reference populations and years. Whether regimes reduced r below replacement level, however, varied per population, year and the survival rate of the seeds in the soil bank. Our model allowed projecting effects of five theoretical mowing regimes with untested combinations of cuts on r. By plotting r-cost relationships for all regimes, we identified the most cost-effective schemes for each cutting frequency (1–3 cuts). They all included the cut just before female flowering, highlighting the importance of cutting at this moment (here in August). Our work features i) the suitability of a modelling approach for the demography of an annual species with a seed bank, ii) the importance of seed viability in assessing mowing effects, iii) the use of population models in designing cost-effective mowing regimes.