Spatial Patterns in European Rabbit Abundance After a Population Collapse

Assessing the associations between spatial patterns in population abundance and environmental heterogeneity is critical for understanding various population processes and for managing species and communities. This study evaluates responses in the abundance of the European rabbit (Oryctolagus cuniculus), an important prey for predators of conservation concern in Mediterranean ecosystems, to environmental heterogeneity at different spatial scales. Multi-scale habitat models of rabbit abundance in three areas of Doñana, south-western Spain, were developed using a spatially extensive dataset of faecal pellet counts as an abundance index. The best models included habitat variables at the three spatial scales examined: distance from lagoons (broad scale), mean landscape shrub coverage and interspersion of pastures (home-range scale), and shrub and pasture cover (microhabitat scale). These variables may well have been related to the availability of food and refuge for the species at the different scales. However, the models’ fit to data and their predictive accuracy for an independent sample varied among the study regions. Accurate predictions in some areas showed that the combination of variables at various spatial scales can provide a reliable method for assessing the abundance of ecologically complex species such as the European rabbit over large areas. On the other hand, the models failed to identify abundance patterns in a population that suffered the strongest demographic collapse after viral epidemics, underlining the difficulty of generalizing this approach. In the latter case, factors difficult to implement in static models such as disease history and prevalence, predator regulation and others may underlie the lack of association. Habitat models can provide useful guidelines for the management of landscape attributes relevant to rabbits and help improve the conservation of Mediterranean communities. However, other influential factors not obviously related to environmental heterogeneity should also be analyzed in more detail.     

Nesting Success of a Songbird in a Complex Floodplain Forest Landscape in llinois, USA: Local Fragmentation vs. Vegetation Structure

Measuring edge effects in complex landscapes is often confounded by the presence of different kinds of natural and anthropogenic edges, each of which may act differently on organisms inhabiting habitat patches. In such landscapes, proportions of different habitats surrounding nests within patches often vary and may affect nesting success independently of distance to edges. We developed methods to measure and study the effects of multiple edges and varying habitat composition around nests on the breeding success of the Acadian flycatcher (Empidonax virescens), an understory, open-cup nesting songbird. The Kaskaskia River in Southwestern Illinois was our study area and consists of wide (>1000-m) floodplain corridors embedded in an agricultural matrix with a variety of natural (wide rivers, backwater swamps, and oxbow lakes) and anthropogenic (internal openings, and agricultural) habitats. We also measured vegetation structure around each nest. Nest survival increased with increasing nest concealment, and probabilities of brood parasitism increased with increasing distances from anthropogenic and natural water-related openings surrounding nests. The magnitude of these effects was small, probably because the landscape is saturated with nest predators and brood parasites. These results illustrate the importance of considering both larger landscape context and details of natural and anthropogenic disturbances when studying the effects of habitat fragmentation on wildlife.     

Post-storm surveys reveal large-scale spatial patterns and influences of site factors,forest structure and diversity in endemic bark-beetle populations

The storm that struck France on december 26^th and 28^th 1999 felled 140 million m³ of timber and had a high economic, social and landscape impact. This event offered the opportunity to study large-scale patterns in populations of forest insect pests that would benefit from the abundant breeding material. A large-scale survey was carried out in France in 2000 to sample the most frequently observed species developing on spruce (Ips typographus, Pityogene schalcographus) and pine (Tomicus piniperda, Ips sexdentatus) in 898 locations distributed throughout wind-damaged areas. The local abundance of each species scored on a 0 to 5 scale was analysed using geostatistical estimators to explore the extent and intensity of spatial autocorrelation, and was related to site, stand, and neighbourhood landscape metrics of the forest cover (in particular the interconnection with broadleaf forest patches) found within dispersal distance. All species but I. sexdentatus, which was much less abundant, displayed large-scale spatial dependence and regional variations in abundance. Lower infestation levels per tree (windfalls and standing trees) were observed in stands with a high proportion of wind-damaged trees, which was interpreted as the result of beetles distributing themselves among the available breeding material. More infestations were observed in wind-broken trees as compared to wind-felled trees. More importantly, populations showed significant relationships with the structure of coniferous stands (in particular with the number of coniferous patches). T. piniperda population levels were negatively correlated to the amount of coniferous edge shared with broadleaf forest patches, possibly because of the disruptive effect of non-host volatiles on host-finding processes at the landscape-scale. The differences observed between species regarding patterns and relationships to site, stand, and forest cover characteristics are discussed in relation to the ecological characteristics of each species.     

Effects of thermoperiodicity and plant population density on stem and flower elongation, leaf development, and specific fresh weight in single stemmed rose (Rosa hybrida L.) plants

Thermoperiodicity, i.e. growth in the alternating temperature regime with the same diurnal mean compared with growth at the constant temperature at which optimal growth occurs, was studied at three plant population densities in four cultivars of Rosa hybrida L. Single-node cuttings with five-leaflet leaves were excised and grown as single-stemmed rose plants at an average photosynthetic photon flux density of about 260 μmol m⁻² s⁻¹ and supplied with carbon dioxide at about 1000 μmol mol⁻¹. The optimal constant temperature regime was 22 °C day (20 h)/22 °C night (4 h); alternating temperatures were 23 °C day (20 h)/18 °C night (4 h). The plant population densities were 100, 131 and 178 plants m⁻² of bench area. Thermoperiodicity was absent, or could not be detected, in the parameters related to the growth period, the formation of fresh biomass, the bloom quality, and most parameters related to shoot elongation. However, classic thermoperiodic effects of alternating regime were significant in the cultivars Red Velvet and Sonia, with shoot elongation promoted (7.1 and 10.5%, respectively) in the growth phase from onset of axillary bud growth until the flower bud became visible. Compared with the other two cultivars, plants of Red Velvet and Sonia tended to develop longer internodes. The results, obtained concurrently at three different plant population densities, suggest that thermoperiodicity can affect (single-stemmed) plant growth and development in R. hybrida. Increased plant population density also increased plant height at visible flower bud, but the bloom quality, expressed as specific fresh weight, and the flower height at anthesis was decreased at the highest density. Increased plant population density increased the number of five-leaflet leaves developed in Red Velvet, but had no effect on leaf number in Texas and Sonia, while, in Lambada the leaf number was decreased at the highest density.     

Spatial spread of an alien tree species in a heterogeneous forest landscape: a spatially realistic simulation model

The effect of environmental heterogeneity on spatial spread of invasive species has received little attention in the literature. Altering landscape heterogeneity may be a suitable strategy to control invaders in man-made landscapes. We use a population-based, spatially realistic matrix model to explore mechanisms underlying the observed invasion patterns of an alien tree species, Prunus serotina Ehrh., in a heterogeneous managed forest. By altering several parameters in the simulation, we test for various hypotheses regarding the role of several mechanisms on invasion dynamics, including spatial heterogeneity, seed dispersers, site of first introduction, large-scale natural disturbances, and forest management. We observe that landscape heterogeneity makes the invasion highly directional resulting from two mechanisms: (1) irregular jumps, which occur rarely via long-distance dispersers and create new founder populations in distant suitable areas, and (2) regular, continuous diffusion toward adjacent cells via short- and mid-distance vectors. At the landscape scale, spatial heterogeneity increases the invasion speed but decreases the final invasion extent. Hence, natural disturbances (such as severe storms) appear to facilitate invasion spread, while forest management can have contrasting effects such as decreasing invasibility at the stand scale by increasing the proportion of light interception at the canopy level. The site of initial introduction influences the invasion process but without altering the final outcome. Our model represents the real landscape and incorporates the range of dispersal modes, making it a powerful tool to explore the interactions between environmental heterogeneity and invasion dynamics, as well as for managing plant invaders. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Street tree survival rates: Meta-analysis of previous studies and application to a field survey in Philadelphia, PA, USA

Low street tree survival rates and the resulting short lifespans are frequently discussed but inadequately quantified in urban forestry literature. This study addresses street tree survival rates with a meta-analysis of previous literature and a case study assessment of street trees in Philadelphia, USA 2–10 years after planting. Reported survivorship rates from 16 previous studies were compiled. Estimated annual survival rates for individual past studies were mostly above 91.0%. To estimate the annual street tree survival rate across multiple studies, a subset of previous studies was pooled for regression analysis of ln transformed cumulative survivorship vs. time since planting. Lifespan metrics were estimated using the annual survival rates determined from regression analysis. Based on the meta-analysis, we estimated that street tree annual survival rates ranged from 94.9 to 96.5%, and street tree population half-life ranged from 13 to 20 years. Estimated mean life expectancy ranged from 19 to 28 years, which is considerably longer than the 7- or 13-year street tree average lifespan reported in previous studies. Estimated annual survival rates and lifespan metrics were similar in the Philadelphia case study. Urban forest researchers are encouraged to use demographic concepts and analyses in the study of tree survival and mortality, and to monitor tree survival at repeated time intervals every few years.     

Effects of explant type, culture media and growth regulators on callus induction and plant regeneration of Chinese jiaotou (Allium chinense)

To establish an efficient protocol of shoot regeneration from callus, effects of explant type, culture media and plant growth regulators on callus induction and shoot regeneration of Chinese jiaotou (Allium chinense) were evaluated. The results showed that basal plate was the best explant for callus induction (47.5%) when cultured on B5 medium supplemented with 0.1 mg l⁻¹ 6-benzylaminopurine (BA) and 1.0 mg l⁻¹ 2,4-dichlorophenoxyacetic acid (2,4-D), and B5 was the best medium to induce callus formation with 49.3% of the explants forming callus. The highest callus induction (65.2%) was achieved culturing basal plate on B5 medium supplemented with 0.1 mg l⁻¹ BA and 1.0 mg l⁻¹ 2,4-D after 8 weeks of culture. The best callus proliferation was observed on B5 medium with 1.5 mg l⁻¹ 2,4-D. Shoots regenerated at the highest frequency of 58.8% with 4.5 shoots when calli were cultured on B5 medium with 0.1 mg l⁻¹ BA and 1.0 mg l⁻¹ a-naphthaleneacetic acid (NAA). This protocol provides a basis for future studies on genetic improvement and could be applied to large-scale multiplication systems for commercial nurseries of Allium chinense.