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Neighbour Effects (neighbour + effects)

Distribution by Scientific Domains

Life Sciences	50%

Selected Abstracts

Unemployment clusters across Europe's regions and countries

ECONOMIC POLICY, Issue 34 2002
Henry G. Overman
Summary High unemployment and regional inequalities are major concerns for European policy-makers, but so far connections between policies dealing with unemployment and regional inequalities have been few and weak. We think that this should change. This paper documents a regional and transnational dimension to unemployment , i.e., geographical unemployment clusters that do not respect national boundaries. Since the mid 1980s, regions with high or low initial unemployment rates saw little change, while regions with intermediate unemployment moved towards extreme values. During this polarization, nearby regions tended to share similar outcomes due, we argue, to spatially related changes in labour demand. These spatially correlated demand shifts were due in part to initial clustering of low-skilled regions and badly performing industries, but a significant neighbour effect remains even after controlling for these, and the effect is as strong within as it is between nations. We believe this reflects agglomeration effects of economic integration. The new economic geography literature shows how integration fosters employment clusters that need not respect national borders. If regional labour forces do not adjust, regional unemployment polarization with neighbour effects can result. To account for these ,neighbour effects' a cross-regional and transnational dimension should be added to national anti-unemployment policies. Nations should consider policies that encourage regional wage setting, and short distance mobility, and the EU should consider including transnational considerations in its regional policy, since neighbour effects on unemployment mean that an anti-unemployment policy paid for by one region will benefit neighbouring regions. Since local politicians gain no votes or tax revenues from these ,spillovers', they are likely to underestimate the true benefit of the policy and thus tend to undertake too little of it. [source]

Phosphorus uptake, not carbon transfer, explains arbuscular mycorrhizal enhancement of Centaurea maculosa in the presence of native grassland species

FUNCTIONAL ECOLOGY, Issue 6 2002
C. A. Zabinski
Summary 1Previous studies have shown that arbuscular mycorrhizas (AM) enhance the growth of the invasive forb Centaurea maculosa when growing with native grass species. Using 13CO2, we tested the hypothesis that this enhancement is explained by carbon transfer from native species to C. maculosa via mycorrhizal hyphal linkages. 2A C. maculosa plant was paired with one of five native species , three grasses (Festuca idahoensis, Koeleria cristata and Pseudoroegneria spicata) and two forbs (Achillea millefolium and Gaillardia aristata) , in pots that separated the plants with either a mesh barrier (28 µm, excludes fine roots but not hyphae) or a membrane barrier (0·45 µm, excludes roots and hyphae). 313CO2 was added to the atmosphere of either Centaurea or the native species after 20 weeks' growth. A 25 min pulse application was followed by 7 days' growth and subsequent harvest. 4The biomass response of C. maculosa was consistent with previous experiments: C. maculosa was larger when growing in mesh barrier pots, when hyphae were able to access the opposite side of the pot; in mesh barrier pots only, biomass varied with neighbouring species. Native plant biomass did not vary between mesh- vs membrane-barrier pots. 5There was no evidence of carbon transfer, either from the native plant to C. maculosa or in the reverse direction. 6Centaurea maculosa contained significantly more phosphorus in mesh-divided pots, but this depended on the neighbouring plant. The P concentration in C. maculosa was significantly higher in mesh-divided pots when growing with a grass and not a forb. Native species contained more P in mesh-divided pots than membrane-divided pots, and P concentration differed between species (higher in forbs than grasses), but did not vary between mesh- and membrane-divided pots. 7Our study suggests that C. maculosa is able to exploit its mycorrhizal symbiosis more effectively than the native grassland species. The mechanism for this appears to be luxury consumption of P through efficient utilization of extra-radical hyphae, but that effect is dependent on neighbouring species, and occurs when growing with a grass neighbour. 8Although no single study can disprove the carbon-transfer hypothesis, our work suggests that AM-mediated neighbour effects are the result of mycorrhizal networks that increase species' access to P. Whether the synergistic effects of neighbours are due to complementarity of AM fungal symbionts utilized by different plant species, or have to do with the structure of AM networks that develop more extensively with multiple host plants, remains to be investigated. [source]

Advanced snowmelt causes shift towards positive neighbour interactions in a subarctic tundra community

GLOBAL CHANGE BIOLOGY, Issue 8 2006
SONJA WIPF
Abstract Positive and negative species interactions are important factors in structuring vegetation communities. Studies in many ecosystems have focussed on competition; however, facilitation has often been found to outweigh competition under harsh environmental conditions. The balance between positive and negative species interactions is known to shift along spatial, temporal and environmental gradients and thus is likely to be affected by climate change. Winter temperature and precipitation patterns in Interior Alaska are rapidly changing and could lead to warmer winters with a shallow, early melting snow cover in the near future. We conducted snow manipulation and neighbour removal experiments to test whether the relative importance of positive and negative species interactions differs between three winter climate scenarios in a subarctic tundra community. In plots with ambient, manually advanced or delayed snowmelt, we assessed the relative importance of neighbours for survival, phenology, growth and reproduction of two dwarf shrub species. Under ambient conditions and after delayed snowmelt, positive and negative neighbour effects were generally balanced, but when snowmelt was advanced we found overall facilitative neighbour effects on survival, phenology, growth and reproduction of Empetrum nigrum, the earlier developing of the two target species. As earlier snowmelt was correlated with colder spring temperatures and a higher number of frosts, we conclude that plants experienced harsher environmental conditions after early snowmelt and that neighbours could have played an important role in ameliorating the physical environment at the beginning of the growing season. [source]

Herbivore and neighbour effects on tundra plants depend on species identity, nutrient availability and local environmental conditions

JOURNAL OF ECOLOGY, Issue 1 2008
Anu Eskelinen
Summary 1I performed a factorial transplant experiment to test the roles of plant,plant interactions, herbivory by mammal grazers and resource availability for plant performance in two contrasting habitat types in a mountain tundra environment. 2Three perennial dicot herbs, Solidago virgaurea, Erigeron uniflorus and Saussurea alpina, were used as target plants to study the effects of neighbour removal and grazer exclusion, and nutrient enrichment and liming on plant growth, survival and reproductive success. These treatments were replicated in two contrasting habitat types, infertile acidic and fertile non-acidic tundra heaths. 3The effects of plant,plant interactions on Saussurea varied from facilitation in infertile acidic habitats to competition in fertile non-acidic habitats and in nutrient-enriched conditions, while the overall performance of Saussurea was strongly negatively influenced by the presence of grazers, the effects being greater when plants were fertilized and in fertile non-acidic heaths. Erigeron performed better under nutrient-enriched conditions than in unfertilized plots, when neighbours had been removed. Solidago was negatively affected by grazing and this impact was greater in nutrient-enriched plots and in non-acidic heaths than in acidic heaths and for unfertilized controls. There were no interactions between neighbour removal and herbivory in any of the three species, indicating that these processes operated independently. 4Grazer-preferred tall plants are strongly limited by consumption by mammal herbivores in nutrient-enriched conditions and in inherently fertile habitats. By contrast, arctic,alpine specialists and species of low stature experience increased competition with neighbouring vegetation in fertile habitats and in enriched nutrient conditions. 5Synthesis. Overall, the results suggest that the strength and directions of plant,plant and plant,herbivore interactions depend on plant species identity and are modified by soil edaphic factors to govern vegetation processes in tundra plant communities. These findings have important implications for understanding the forces structuring vegetation in barren tundra ecosystems under a changing environment. [source]

Spatial pattern and neighbour effects on Helianthemum squamatum seedlings in a Mediterranean gypsum community

JOURNAL OF VEGETATION SCIENCE, Issue 4 2005
Adrián Escudero
Abstract Question: Do, in a semi-arid gypsum environment, neighbours condition the spatial patterns of emergence, survival and height of Helianthemum squamatum seedlings? Location: Vicinity of Chinchón, province of Madrid, Spain (40°11,N, 3° 35,W, 550 m a.s.l.) Methods: We evaluated the effects of neighbours on the survival and growth of naturally emerging Helianthemum seedlings in a semi-arid area during a two-year period. We followed a two-fold approach based on the use of neighbour models for seedling survival and growth and spatial point pattern analyses for seedling emergence, taking into account the germination date. Results: Seedlings appeared clumped in the vicinity of mature Helianthemum individuals. The neighbour models fitted showed that interactions with neighbours were extremely important for the survival and growth of Helianthemum seedlings. These models also suggest that the effects of neighbours on these variables vary with changes in spatial scale and in the abiotic conditions. Some species exerted negative or positive effects on Helianthemum seedlings only at certain spatial scales, and others exerted negative or positive effects at earlier stages of seedling development, but none later and vice versa. Conclusions: We suggest that the observed patterns are mainly influenced by small-scale modifications in soil conditions and microclimate created by neighbours, which change in time and space. [source]