Search results for "BLE"

2021

The social vespid wasps are common insect predators and several species behave in unison in the same biotopes. It is commonly accepted that social wasps are mainly opportunistic generalist predators without differences in prey selection and hence they compete for the same food resources. Trophic positions of six vespid wasp species and their potential prey from four sites in Finland and one in the UK were evaluated using carbon and nitrogen stable isotopes (δ 13 C and δ 15 N). The difference in isotope values indicated different trophic positions among species. In general, Dolichovespula spp. showed higher δ 15 N values than Vespula spp., which suggests that Dolichovespula forage on higher…

Nest defence against avian brood parasites is promoted by egg-removal events in a cowbird–host system

2011

Recent studies of birds have found that the antiparasite behaviour of host species is modified by social learning. We tested whether individual or social learning modifies the nest defence of yellow warblers, Setophaga petechia, against the parasitic brown-headed cowbird, Molothrus ater. Using field experiments, we exposed warblers to simulated events of nest parasitism and predation, or allowed them to observe conspecifics mobbing a cowbird. Intensity of nest defence by yellow warblers was greater after simulated threats at their nest than after they had observed mobbing of cowbirds by conspecifics. Warblers defended their nests more aggressively when they perceived a cowbird as an egg pre…

2021

Hosts of brood parasitic cuckoos often employ mobbing attacks to defend their nests and, when mobbing is costly, hosts are predicted to adjust their mobbing to match parasitism risk. While evidence exists for fine-tuned plasticity, it remains unclear why mobbing does not track larger seasonal changes in parasitism risk. Here we test a possible explanation from parental investment theory: parents should defend their current brood more intensively as the opportunity to replace it declines (re-nesting potential), and therefore “counteract” any apparent seasonal decline to match parasitism risk. We take advantage of mobbing experiments conducted at two sites where reed warblers (Acrocephalus sc…

Periphyton support for littoral secondary production in a highly humic boreal lake

2016

Steep stratification and poor light penetration in highly humic lakes typically restrict oxygenated littoral areas to narrow lake margins. However, in some instances, surrounding floating vegetation mats can sustain highly productive periphyton and more diverse invertebrate communities than pelagic areas. Little is known about how these littoral food webs function or the extent to which the pelagic and littoral food webs are coupled. We added 15N-labeled ammonium nitrate to the floating moss mat surrounding the littoral zone of Mekkojärvi, a small highly humic and fishless lake in southern Finland. Our goal was to increase the δ15N values of periphyton to investigate the diets of littoral i…

Fish introductions and light modulate food web fluxes in tropical streams: a whole-ecosystem experimental approach.

2016

Decades of ecological study have demonstrated the importance of top-down and bottom-up controls on food webs, yet few studies within this context have quantified the magnitude of energy and material fluxes at the whole-ecosystem scale. We examined top-down and bottom-up effects on food web fluxes using a field experiment that manipulated the presence of a consumer, the Trinidadian guppy Poecilia reticulata, and the production of basal resources by thinning the riparian forest canopy to increase incident light. To gauge the effects of these reach-scale manipulations on food web fluxes, we used a nitrogen (15 N) stable isotope tracer to compare basal resource treatments (thinned canopy vs. co…

Defoliation of two-wire vertical trellis: effect on grape quality

2017

ABSTRACTBasal leaves were removed from Cabernet Sauvignon vines trained to a two-wire vertical trellis at fruit set and at veraison. Leaf removal did not modify total soluble solids and titratable acidity at harvest. Defoliation at fruit set of lower cordon recovered the grape anthocyanin composition gap between upper and lower cordons and that produced a positive effect on anthocyanin synthesis. Hence, control of the upper cordon and defoliation of fruit set of the lower cordon treatments showed comparable values of anthocyanins. Defoliation at veraison did not produce any appreciable effect. This study shows that skin anthocyanin composition in a two-wire vertical trellis can be modified …

Airborne-laser-scanning-derived auxiliary information discriminating between broadleaf and conifer trees improves the accuracy of models for predicti…

2020

Managing forests for ecosystem services and biodiversity requires accurate and spatially explicit forest inventory data. A major objective of forest management inventories is to estimate the standing timber volume for certain forest areas. In order to improve the efficiency of an inventory, field based sample-plots can be statistically combined with remote sensing data. Such models usually incorporate auxiliary variables derived from canopy height models. The inclusion of forest type variables, which quantify broadleaf and conifer volume proportions, has been shown to further improve model performance. Currently, the most common way of quantifying broadleaf and conifer forest types is by ca…

Habitat- and density-dependent demography of a colonial raptor in Mediterranean agro-ecosystems

2016

Agricultural intensification is considered the major cause of decline in farmland bird populations, especially in the Mediterranean region. Food shortage increased by the interaction between agricultural intensification and density-dependent mechanisms could influence the population dynamics of colonial birds.Weused demographic data on lesser kestrels (Falco naumanni), a key species of Mediterranean pseudo-steppes, to understand the importance of land-use changes and density-dependent mechanisms in the light of its fluctuating conservation status in the Western Palearctic. Our analysis indicated an important influence of land uses (artichokes, arable and grassland fields) and colony size on…

Comparison of input data with different spatial resolution in landscape pattern analysis – A case study from northern Latvia

2017

A suitable spatial scale needs to be selected in geographical and landscape ecological research, and this requires great consideration as different scales have profound effect on derived landscape spatial patterns. Numerous studies have investigated the effects of different scales on landscape metrics using simulated patterns, but few have been conducted to compare different data sources with variable scale for regional- and landscape-scale assessments. Possibly this has occurred because researchers have been prone to use the best available source, a well-known standard, and easiest to use. This study was conducted to assess the impact of input data resolution on values of landscape pattern…

Differential performance of a specialist and two generalist herbivores and their parasitoids on Plantago lanceolata

2011

The ability to cope with plant defense chemicals differs between specialist and generalist species. In this study, we examined the effects of the concentration of the two main iridoid glycosides (IGs) in Plantago lanceolata, aucubin and catalpol, on the performance of a specialist and two generalist herbivores and their respective endoparasitoids. Development of the specialist herbivore Melitaea cinxia was unaffected by the total leaf IG concentration in its host plant. By contrast, the generalist herbivores Spodoptera exigua and Chrysodeixis chalcites showed delayed larval and pupal development on plant genotypes with high leaf IG concentrations, respectively. This result is in line with t…