Models based on individual level movement predict spatial patterns of genetic relatedness for two Australian forest birds

Fine-scale landscape change can alter dispersal patterns of animals, thus influencing connectivity or gene flow within a population. Furthermore, dispersal patterns of different species may be influenced by the landscape in varying ways. Our research first aimed to examine whether the spatial genetic structure within populations of closely related bird species differs in response to the same landscape. Second, we examined whether individual-level movement characteristics are a mechanistic driver of these differences. We generated a priori predictions of how landscape features will influence dispersal (particularly the response of individuals to habitat boundaries both natural and human-induced) based on a movement model developed by Fahrig (Funct Ecol 21:1003–1015, 2007). This model allowed us to predict genetic relatedness patterns in populations of two passerine bird species with different life-history traits from Queensland, Australia (yellow-throated scrubwren Sericornis citreogularis, a habitat specialist; white-browed scrubwren Sericornis frontalis, a habitat generalist). We quantified our predictions using cost-distance modelling and compared these to observed pairwise genetic distances (a _r ) between individuals as calculated from microsatellite markers. Mantel tests showed that our a priori models correlated with genetic distance. Euclidean distance was most closely correlated to genetic distance for the generalist species (r = 0.093, P = 0.002), and landscape models that included the avoidance of unsuitable habitat were best for the specialist species (r = 0.107, P = 0.001). Our study showed that predictable movement characteristics may be the mechanism driving differences in genetic relatedness patterns within populations of different bird species.     

Wetland hydrology,area, and isolation influence occupancy and spatial turnover of the painted turtle, <Emphasis Type="Italic">Chrysemys picta</Emphasis>

Habitat area and isolation have been useful predictors of species occupancy and turnover in highly fragmented systems. However, habitat quality also can influence occupancy dynamics, especially in patchy systems where habitat selection can be as important as stochastic demographic processes. We studied the spatial population dynamics of Chrysemys picta (painted turtle) in a network of 90 wetlands in Illinois, USA from 2007 to 2009. We first evaluated the relative influence of metapopulation factors (area, isolation) and habitat quality of focal patches on occupancy and turnover. Next, we tested the effect of habitat quality of source patches on occupancy and turnover at focal patches. Turnover was common with colonizations (n = 16) outnumbering extinctions (n = 10) between the first 2 years, and extinctions (n = 16) outnumbering colonizations (n = 3) between the second 2 years. Both metapopulation and habitat quality factors influenced C. picta occupancy dynamics. Colonization probability was related positively to spatial connectivity, wetland area, and habitat quality (wetland inundation, emergent vegetation cover). Extinction probability was related negatively to wetland area and emergent vegetation cover. Habitat quality of source patches strongly influenced initial occupancy but not turnover patterns. Because habitat quality for freshwater turtles is related to wetland hydrology, a change from drought to wet conditions during our study likely influenced distributional shifts. Thus, effects of habitat quality of source and focal patches on occupancy can vary in space and time. Both metapopulation and habitat quality factors may be needed to understand occupancy dynamics, even for species exhibiting patchy population structures.     

Assessment of the mating system of Camellia sinensis in biclonal seed orchards based on PCR markers

Summary

The mating system parameters of tea (Camellia sinensis) were determined in four isolated biclonal seed orchards using two PCR-based marker technologies, Randomly Amplified Polymorphic DNA (RAPD) and Inter-Simple Sequence Repeats (ISSR), in an open-pollinated array of 180 progeny from six genotypes. The genotypes consisted of the three cultivated varieties of tea, namely China, Assam and Cambod, with 60 progeny of each. High-value multi-locus (t_m = 0.995 ± 0.094) and single-locus (t_s = 0.971 ± 0.011) estimates of out-crossing rates indicated predominant out-crossing and suggested maintenance of adequate genetic variability within families. The t_m estimated from RAPD markers (0.988 ± 0.051) was higher than that estimated based on ISSR markers (0.936 ± 0.022). The difference between t_m – t_s (0.024 ± 0.094) was low, indicating negligible biparental in-breeding. Likewise, the estimated correlation of paternity (r_p = 0.070) was low, indicating that many of the offspring did not share the same paternal genitor, despite the isolation of the two putative parents, which is an indication of high pollen contamination rate and long-distance mating. These results suggest that a review of the current isolation distances between orchards is necessary, to increase the pollination efficiency between two isolated breeding cultivars.     

Matrix quality and habitat configuration interactively determine functional connectivity in a widespread bush cricket at a small spatial scale

Unlike rare or specialised species, widespread abundant species have often been neglected when studying effects of habitat fragmentation. However, recently, it was shown that in the widespread abundant bush cricket Pholidoptera griseoaptera gene flow becomes restricted when the share of suitable habitat dropped below a threshold of 20% at the landscape scale. Here, using the same highly fragmented landscape, we studied the impact of habitat configuration and matrix quality on genetic variation and population differentiation of P. griseoaptera at a small spatial scale. We investigated four clusters of three populations that were either disconnected or connected and had either low quality (arable land) or high quality (grassland) matrix. The number of alleles was significantly lower in disconnected than in connected clusters, irrespective of matrix quality. Genetic differentiation was equally high in the two disconnected clusters and in the connected cluster with low quality matrix (G _ST ≥ 0.030; D ≥ 0.082), whereas it was significantly reduced when connected habitats were embedded in a high quality grassland matrix (G _ST = 0.004; D = 0.011). Analyses of least-cost paths showed that grassy landscape elements in fact represent high quality matrix, but that linear grassy margins are costly for dispersal. The effect of habitat configuration on genetic diversity may be explained by lower effective population sizes in disconnected habitats. The fact that only the connected populations in high quality matrix were not differentiated indicates that landscape management should simultaneously consider habitat configuration and matrix quality to effectively promote small and dispersal-limited species, also at small spatial scales.     

Landscape resistance and American marten gene flow

Landscape heterogeneity can influence animal dispersal by causing a directional bias in dispersal rate, as certain landscape configurations might promote, impede, or prevent movement and gene flow. In forested landscapes, logging operations often contribute to heterogeneity that can reduce functional connectivity for some species. American martens (Martes americana) are one such species, as they are considered specialists of late-seral coniferous forests. We assessed marten gene flow to test the hypothesis that habitat management has maintained landscape connectivity for martens in the managed forests of Ontario, Canada. We genotyped 653 martens at 12 microsatellite loci, sampled from 29 sites across Ontario. We expected that if forest management has an effect on marten gene flow, we would see a correlation between effective resistance, estimated by circuit theory, and genetic distance, estimated by population graphs. Although we found a positive relationship between effective resistance and genetic distance (Mantel r = 0.249, P < 0.001), marten gene flow was better described by isolation by Euclidean distance (Mantel r = 0.410, P < 0.001). Our results suggest that managed forests in Ontario are well connected for marten and neither impede nor promote marten gene flow at the provincial scale.     

Isolation and characteristics of eight novel polymorphic microsatellite loci from the genome of garlic (Allium sativum L.)

Here we characterized eight novel polymorphic SSR markers, developed from an enriched genomic library of garlic (Allium sativum L.). These SSRs produced a total of 64 alleles across 90 garlic accessions, with an average of 8 alleles per locus. Values for observed (H_O) and expected (H_E) heterozygosity ranged from 0.16 to 0.77 (mean = 0.44) and from 0.22 to 0.86 (mean = 0.65), respectively. Six loci deviated significantly (P < 0.05) from Hardy–Weinberg equilibrium (HWE). The averages of gene diversity and PIC values were 0.65 and 0.62, respectively. The mean genetic similarity coefficient was 0.4380, indicating that among garlic accessions existed wide genetic variation. Based on 64 alleles obtained by 8 SSRs, a phenogram was constructed to understand the relationships among the 90 accessions. These newly developed SSRs should prove very useful tools for genotypes identification, assessment of genetic diversity and population structure in garlic.     

Open areas in a landscape enhance pollen-mediated gene flow of a tree species: evidence from northern Switzerland

Habitat fragmentation often has negative consequences for genetic diversity, and thereby for the viability of populations. However, these negative consequences might be counteracted by gene flow as the latter provides functional connectivity between apparently isolated habitat fragments. Gene flow is itself influenced by landscape structure and composition, and it is therefore important to understand the relationship between gene flow and landscape structure and composition. We used linear LAD regression models to investigate the relationship between contemporary gene flow by pollen in the rare, insect-pollinated forest tree Sorbus domestica and several landscape features. None of the landscape components—which included closed forest, deep valleys, open land and settlements—proved to be an impermeable barrier to gene flow by pollen. We found evidence that settlements, large open areas, and a pronounced topography increased long-distance gene flow in the landscape as compared to a random model including all possible gene flow trajectories. These results are encouraging from a conservation view, as gene flow in species pollinated by generalist insects seems to provide functional connectivity and may help to maintain genetic diversity in rare plant species in fragmented landscapes.     

The size distribution metrics and kinetic energy of raindrops above and below an isolated tree canopy in urban environment

Raindrop impact on bare soils is the initial phase of rainfall-induced soil erosion which is altered under any type of vegetation due to the interactions of rainfall with the canopies. This study examines the drop size distribution (DSD) and kinetic energy (KE) of raindrops above and below the birch tree (Betula pendula Roth.) canopy in a research plot in the city of Ljubljana, Slovenia using a one-year observation of 63 rainfall events and the effect of meteorological variables under moderate continental climate. Simultaneous measurement of the microstructures of open rainfall and throughfall was carried out using an optical disdrometer. The result of our analysis revealed that throughfall DSD showed two distinct major peaks (bimodal) occurring primarily on smaller drop sizes while open rainfall has only one. The cumulative drop number, median drop-volume diameter (D₅₀), and drop fall velocity of throughfall were 16.4%, 26.6%, and 5.0% lower than those of open rainfall, respectively. Also, the relative volume percentage of raindrops > 1.5 mm is 1.5 times higher than those observed in throughfall drops which indicates that the presence of the canopy caused the fractionation of larger drops into smaller droplets. These reductions significantly differ depending on the phenoseasons of the canopy with the leafed state being higher than the leafless state. Similarly, the Kruskal-Wallis H test result revealed that birch tree elicits a statistically significant change in the kinetic energy of open rainfall, thus weakening the mean rainfall KE by 33.7%. On the other hand, KE is positively affected by the phenological condition of the canopy with higher attenuation being observed during its leafed state. Also, the correlation analysis demonstrated that vapor pressure deficit, air temperature, and relative humidity have stronger associations with throughfall kinetic energy among meteorological variables considered. These findings underscore the necessity of an optimized selection of tree species for afforestation programs.     

Historical processes and landscape context influence genetic structure in peripheral populations of the collared lizard (<Emphasis Type="Italic">Crotaphytus collaris</Emphasis>)

Populations at the periphery of a species’ range often show reduced genetic variability within populations and increased genetic divergence among populations compared to those at the core, but the mechanisms that give rise to this core-periphery pattern in genetic structure can be multifaceted. Peripheral population characteristics may be a product of historical processes, such as founder effects or population expansion, or due to the contemporary influence of landscape context on gene flow. We sampled collared lizards (Crotaphytus collaris) at four locations within the northern Flint Hills of Kansas, which is at the northern periphery of their range, to determine the genetic variability and extent of genetic divergence among populations for ten microsatellite loci (n = 229). We found low genetic variability (average allelic richness = 3.37 ± 0.23 SE; average heterozygosity = 0.54 ± 0.05 SE) and moderate population divergence (average F_ST = 0.08 ± 0.01 SE) among our sample sites relative to estimates reported in the literature at the core of the species’ range in Texas. We also identified differences in dispersal rates among sampling locations. Gene flow within the Flint Hills was thus greater than for other peripheral populations of collared lizards, such as the Missouri glade system where most of the mesic grasslands have been converted to forest since the last glacial retreat, which appears to have greatly impeded gene flow among populations. Our findings signify the importance of considering landscape context when evaluating core-peripheral trends in genetic diversity and population structure.     

Modeling individual leaf area of ginger (Zingiber officinale Roscoe) using leaf length and width

Leaf area estimation is an important biometrical observation one has to do for comparing plant growth in field and pot experiments. In this study, a leaf area estimation model was developed for ginger (Zingiber officinale Roscoe), using linear measurements of leaf length (L) and maximum width (W). Leaves from five ginger varieties (Varada, Rejatha, Mahima, Maran and Himachal) were used to develop the model in 2006–2007. The actual leaf area (LA) was measured with a leaf area meter (LI-3100, LI-COR, Lincoln, NE, USA) and taken as reference LA. The linear measurements were used to build linear (LA = a + b × L × W) and power models (LA = α × (L × W)^β) for each variety, as the modeling among variety were not different from each other, data for all five varieties have been pooled and compared with earlier models by graphical procedures and statistical criteria such as Mean Square Error (MSE), Root Mean Square Error (RMSE) and Chi-square (χ²). The selected model was validated during 2007–2008. The validation data set was used to produce a validation model for each variety by re-estimating the model parameters to develop the estimation model and the models were compared for consistency. The predicted LA (PLA) was compared with observed LA (OLA) by graphical procedures and lack of agreement was evaluated by calculating the relative bias, estimated by the mean of differences (d) and the standard deviation (SD) of the differences. Normality test was carried out by Spearman's rank correlation coefficient (r_s) and residuals were normally distributed. Finally, the proposed model for leaf area estimation of ginger is LA = −0.0146 + 0.6621 × L × W, R² = 0.997. This model can be reliably used for estimating leaf area of ginger non-destructively. The same equation can be extrapolated to all varieties and land races of ginger as it is vegetatively propagated crop with narrow genetic variability.     

Capability of the ‘Ball-Berry’ model for predicting stomatal conductance and water use efficiency of potato leaves under different irrigation regimes

The capability of the ‘Ball-Berry’ model (BB-model) in predicting stomatal conductance (g_s) and water use efficiency (WUE) of potato (Solanum tuberosum L.) leaves under different irrigation regimes was tested using data from two independent pot experiments in 2004 and 2007. Data obtained from 2004 was used for model parameterization, where measurements of midday leaf gas exchange of potted potatoes were done during progressive soil drying for 2 weeks at tuber initiation and earlier bulking stages. The measured photosynthetic rate (A_n) was used as an input for the model. To account for the effects of soil water deficits on g_s, a simple equation modifying the slope (m) based on the mean soil water potential (Ψ_s) in the soil columns was incorporated into the original BB-model. Compared with the original BB-model, the modified BB-model showed better predictability for both g_s and WUE of potato leaves on the parameterization data set. The models were then tested using the data from 2007 where plants were subjected to four irrigation regimes: non-irrigation (NI), full irrigation (FI), partial root-zone drying (PRD), and deficit irrigation (DI) for 3 weeks during tuber initiation and earlier bulking stages. The simulation results showed that the modified BB-model better simulated g_s for the NI and DI treatments than the original BB-model, whilst the two models performed equally well for predicting g_s of the FI and PRD treatments. Although both models had poor predictability for WUE (0.47 < r² < 0.71) of potato leaves, the modified BB-model was able to distinguish the effects of the irrigation regimes on WUE being that the WUE was generally greater for PRD than for FI and DI plants. Conclusively, the modified BB-model is capable of predicting g_s and of accounting for the differential effects of irrigation regimes on WUE of potato leaves. This information is valuable for further simulating potato water use thereby optimizing WUE under field conditions.     

Genetic diversity in mainland and island populations of the endangered Pancratium maritimum L. (Amaryllidaceae) in Tunisia

Tunisian Pancratium maritimum L. populations are at present endangered and represented by scattered individuals as a result of coastal habitat destruction caused by urbanization and overharvesting for its significant ornamental interest. Nineteen populations growing in mainland and island habitats were sampled for allozyme diversity to assess their genetic diversity and structuration using seven isozymes revealed by starch gel electrophoresis. The species exhibited relatively high levels of genetic diversity (the mean A_p = 1.37, P = 37.4%, and H_e = 0.100), indicates a preferentially outcrossing mating system.     

Aspen persistence near the National Elk Refuge and Gros Ventre Valley elk feedgrounds of Wyoming, USA

We investigated aspen (Populus tremuloides)regeneration in the Gros Ventre River Valley, the National Elk Refuge and a small part of Grand Teton National Park, Wyoming, USA to see if elk (Cervus elaphus) browsing was as damaging as previously thought. We conducted a landscape-scale survey to assess aspen regeneration across gradients of wintering elk concentrations using 68 randomly selected aspen stands in the 1090 km² study area. Forty-four percent of the stands sampled supported some newer regeneration that had reached the canopy. There were no significant differences of regeneration across elk winter range classification (p=0.25) or distance from feedgrounds (p=0.96). However, a multiple linear regression found that the concentration of elk was one of several important predictors of successful aspen regeneration (p=0.005, R ²=0.36). Our results suggest that stand-replacing regeneration occurs across the landscape at a variety of elk densities despite some trends of reduced regeneration under greater elk concentrations. We propose that high spatial and temporal variation and scattered patches of successful aspen regeneration characterize aspen persistence between periods of episodic regeneration and recruitment.     

Unmanned aerial systems for modelling air pollution removal by urban greenery

Urban greenery plays an important role in reducing air pollution, being one of the often-used, nature-based measures in sustainable and climate-resilient urban development. However, when modelling its effect on air pollution removal by dry deposition, coarse and time-limited data on vegetation properties are often included, disregarding the high spatial and temporal heterogeneity in urban forest canopies. Here, we present a detailed, physics-based approach for modelling particulate matter (PM₁₀) and tropospheric ozone (O₃) removal by urban greenery on a small scale that eliminates these constraints. Our procedure combines a dense network of low-cost optical and electrochemical air pollution sensors, and a remote sensing method for greenery structure monitoring derived from Unmanned aerial systems (UAS) imagery processed by the Structure from Motion (SfM) algorithm. This approach enabled the quantification of species- and individual-specific air pollution removal rates by woody plants throughout the growing season, exploring the high spatial and temporal variability of modelled removal rates within an urban forest. The total PM₁₀ and O₃ removal rates ranged from 7.6 g m^-2 (PM₁₀) and 12.6 g m^-2 (O₃) for mature trees of Acer pseudoplatanus to 0.1 g m^-2 and 0.1 g m^-2 for newly planted tree saplings of Salix daphnoides. The present study demonstrates that UAS-SfM can detect differences in structures among and within canopies and by involving these characteristics, they can shift the modelling of air pollution removal towards a level of individual woody plants and beyond, enabling more realistic and accurate quantification of air pollution removal. Moreover, this approach can be similarly applied when modelling other ecosystem services provided by urban greenery.     

Functional connectivity defined through cost-distance and genetic analyses: a case study for the rock-dwelling mountain vizcacha (<Emphasis Type="Italic">Lagidium viscacia</Emphasis>) in Patagonia,Argentina

Landscape connectivity can have profound consequences for distribution and persistence of populations and metapopulations. Evaluating functional connectivity of a landscape for a species requires a measure of dispersal rates through landscape elements at a spatial scale sufficient to encompass movement capabilities of individuals over the entire landscape. We evaluated functional connectivity for a rock-dwelling mammal, the mountain vizcacha (Lagidium viscacia), in northern Patagonia. Because of the strict association of mountain vizcachas with rocks, we hypothesized that connectivity for this species would be influenced by geology. We used molecular genetic estimates of gene flow to test spatially explicit models of connectivity created with GIS cost-distance analysis of landscape resistance to movement. We analyzed the spatial arrangement of cliffs with join counts and local k-function analyses. We did not capture and genotype individuals, but sampled at the population level through non-invasive collection of feces of mountain vizcachas. The model of landscape connectivity for mountain vizcachas based on geology was corroborated by the pattern of genetic structure, supporting the hypothesis that functional connectivity for mountain vizcachas is influenced by geology, particularly by the distribution of appropriate volcanic rocks. Analysis of spatial arrangement of cliffs indicated that occupied cliffs are clustered and confirmed that rivers act as barriers to dispersal for mountain vizcachas. Our methods could be used, within certain constraints, to study functional landscape connectivity in other organisms, and may be particularly useful for cryptic or endangered species, or those that are difficult or expensive to capture.     

Estimation of broad-leaved canopy growth in the urban forested area using multi-temporal airborne LiDAR datasets

Inter-annual canopy growth is one of the key indicators for assessing forest conditions, but the measurements require laborious field surveys. Up-to-date LiDAR remote sensing provides sufficient three-dimensional morphological information of the ground to monitor canopy heights on a broad scale. Thus, we attempted to use multi-temporal airborne LiDAR datasets in the estimation of vertical canopy growth, across various types of broad-leaved trees in a large urban park.The growth of broad-leaved canopies in the EXPO '70 urban forest in Osaka, Japan was assessed with 19 plots at the stand level and 39 selected trees at the individual-tree level. Airborne LiDAR campaigns repeatedly observed the park in the summers of 2004, 2008, and 2010. We acquired canopy height models (CHMs) for each year from the height values of the uppermost laser returns at every 0.5 m grid. The annual canopy growth was calculated by the differences in CHMs and validated with the annual changes in field-measured basal areas and tree heights.LiDAR estimations revealed that the average annual canopy growth from 2004 to 2010 was 0.26 ± 0.11 m m⁻² yr⁻¹ at the plot level and 0.26 ± 0.10 m m⁻² yr⁻¹ at the individual-tree level. This result showed that growing trends were consistent at different scales through 2004 to 2010 despite uncertainty in estimating short-term growth for small crown areas at the individual-tree level. This LiDAR-estimated canopy growth shows a moderate relation to field-measured increase of basal areas and average heights. The estimation uncertainties seem to result from the complex canopy structure and irregular crown shape of broad-leaved trees. Challenges still remain on how to incorporate the growth of understory trees, growth in the lateral direction, and gap dynamics inside the canopy, particularly in applying multi-temporal LiDAR datasets to the large-scale growth assessment.     

Comparison of non-destructive LAI determination methods and optimization of sampling schemes in an open Populus euphratica ecosystem

Populus euphratica (P. euphratica) grows in the water-limited Tarim River Basin in spatially heterogeneous open ecosystems; thus, efforts to quantify the leaf area index (LAI) with optical instruments developed for homogeneous closed canopies have a high probability of failure. In this study, we explored methods for designing an acceptable sampling scheme to quantify the tree LAI for open P. euphratica canopies in arid areas. Field data were collected from three 30 m × 30 m plots and one 100 m × 100 m plot. We compared three indirect methods, i.e. i) allometry, ii) LAI-2000 canopy analyser, iii) Tracing Radiation and Architecture of Canopies (TRAC), and a new semi-direct method combining leaf density and crown volume (SDDV) method for quantifying the isolated tree and canopy LAI of a P. euphratica forest. We also analysed the effects of random and grid sampling designs on the accuracy of the LAI estimates obtained with the LAI-2000. The results showed that the allometric method is applicable to isolated trees with regular shapes; however, because the LAI of P. euphratica was calculated from an allometric equation based on the basal area (at 1.3 m), the allometric equation is prone to failure if the basal area is beyond a specific range. Because there are no significant differences in the plot size between the allometric and the SDDV method predictions, the proposed SDDV method can be used as an alternative for field measurements. The combination of LAI-2000 and TRAC is found to be more reliable than TRAC only, and the field view of the LAI-2000 sensor and the clumping index are important factors for sparse vegetation LAI retrieval. The results from sampling optimization showed that for the LAI-2000 instrument, the best sampling method is grid sampling, and the sampling interval should not be less than 20 m. For random sampling scheme, the number of sampling points in a 100 m × 100 m plot should be greater than 86 with a coefficients of variation of 15% and an allowable error (AE) of 0.15 m² m⁻², respectively.     

Measuring landscape connectivity: On the importance of within-patch connectivity

Context

Many connectivity metrics have been used to measure the connectivity of a landscape and to evaluate the effects of land-use changes and potential mitigation measures. However, there are still gaps in our understanding of how to accurately quantify landscape connectivity.

Objectives

A number of metrics only measure between-patch connectivity, i.e. the connectivity between different habitat patches, which can produce misleading results. This paper demonstrates that the inclusion of within-patch connectivity is important for accurate results.

Methods

The behavior of two metrics is compared: the Connectance Index (CONNECT), which measures only between-patch connectivity, and the effective mesh size (m_eff), which includes both within-patch and between-patch connectivity. The connectivity values of both metrics were calculated on a set of simulated landscapes. Twenty cities were then added to these landscapes to calculate the resulting changes in connectivity.

Results

We found that when using CONNECT counter-intuitive results occurred due to not including within-patch connectivity, such as scenarios where connectivity increased with increasing habitat loss and fragmentation. These counter-intuitive results were resolved when using m_eff. For example, landscapes with low habitat amount may be particularly sensitive to urban development, but this is not reflected by CONNECT.

Conclusions

Applying misleading results from metrics like CONNECT can have detrimental effects on natural ecosystems, because reductions in within-patch connectivity by human activities are neglected. Therefore, this paper provides evidence for the crucial need to consider the balance between within-patch connectivity and between-patch connectivity when calculating the connectivity of landscapes.

     

Multi-scale effects of landscape complexity and crop management on pollen beetle parasitism rate

Improving our understanding about how natural enemies respond to semi-natural habitats and crop management scattered in the landscape may contribute to the development of ecologically based pest management strategies maximising biological control services. We investigated how soil tillage and semi-natural habitats influenced the parasitism rates of pollen beetle (Meligethes aeneus F.) larvae at 8 different spatial scales (from 250 to 2000 m radius circular sectors) in 42 oilseed rape (OSR) fields. We used multimodel inference approaches to identify and rank the influence of soil tillage and semi-natural habitats on parasitism rates, and to quantify the importance of each scale. Parasitism rates were due to three univoltine parasitoid species (Tersilochus heterocerus, Phradis morionellus and P. interstitialis) and varied from 0 to 98%. We found that both fine and large scales contributed to explain significantly parasitism rates, indicating that biological control of pollen beetle is a multi-scale process. At the 250 m scale, parasitism rates of T. heterocerus were positively related to the proportion of semi-natural habitats and the proximity to previous year OSR fields. At large scales (1500 to 2000 m), parasitism rates of T. heterocerus were positively related to semi-natural habitats and negatively related to the proportion of previous year OSR fields with conventional soil tillage. Parasitism rates of Phradis spp. were only positively related to the proportion of semi-natural habitats at the 1250 and 1500 m scales. These multi-scale effects are discussed in relation to the influence of semi-natural habitats and soil tillage on parasitoid populations and their movement behaviours within the landscape.     

Water transport through the roots of ornamental shrub cuttings

Summary

The use of leafy cuttings to propagate ornamental shrubs such as Corylus maxima cv. Purpurea is often hampered by “weaning” problems. These arise when the rooted cuttings are removed from the supportive environment designed to promote rooting and are transferred to a more natural, but relatively stressful, environment. The shrivelling of leaves which ensues points to some failure of normal plant water relations, which may be caused either by excessive water loss from the leaves, or an inadequate water supply from the roots, or a combination of these factors. To understand this problem more fully, the root hydraulic conductance of C. maxima cv. Purpurea cuttings was investigated, and compared with that of Weigela florida cv. Variegata, a shrub which does not exhibit weaning problems. The root hydraulic conductance for both species increased with the size of the root system, and root fresh weight was shown to provide a useful basis for relative measurements of root conductance. On this basis, cuttings of W. florida exhibited a higher root hydraulic conductance than comparable C. maxima cuttings (1.5 × 10^?4 and 9.7 × 10^?5 g s^?1 MPa^?1 g_root^?1 respectively), but the difference was not sufficiently large to account for the differences in weaning of these two species. It is suggested that the adventitious root system of C. maxima is functioning normally, but that it cannot supply enough water to balance uncontrolled water loss from the leaves.