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Testing the potential benefits of small fields for biocontrol needs a landscape perspective
Full text linkRelationship between grazing intensity, vegetation structure and survival of nests in semi-natural grasslands
No full textOne of the causes of decline of farmland birds in Europe is the loss of broods. Here, we investigated if region, cattle grazing intensity, habitat edges and vegetation structure around artificial nests influence predation, the major cause of broods’ loss. We placed artificial open ground nests (N = 304) resembling the nests of Skylark (Alauda arvensis), baited by one plasticine and one Quail egg in inside and edge habitats of extensively and intensively grazed grasslands in three regions in Hungary in 2003. Interestingly, none of the three factors (region, grazing intensity, edge effect) had significant effects on brood loss according to the generalised linear mixed model, however, interactions between region and management and among region, management and edge effect were significant. This suggests that the effect of management is not the same in different regions, and edge effect depends on both region and management. We also found that nest predation rate is lower if nests are placed in tall grass and greater vegetation cover. This pattern indirectly supports the negative effects of intensive grazing, which can remove most of the vegetation. Therefore, we suggest that extensive grazing should be favoured to conserve ground nesting birds, however, it is essential to avoid duplicating management regimes from one region to another, due to regional differences in the pattern of survival probability
Relationship between grazing intensity, vegetation structure and survival of nests in semi-natural grasslands
No full textOne of the causes of decline of farmland birds in Europe is the loss of broods. Here, we investigated if region, cattle grazing intensity, habitat edges and vegetation structure around artificial nests influence predation, the major cause of broods’ loss. We placed artificial open ground nests (N = 304) resembling the nests of Skylark (Alauda arvensis), baited by one plasticine and one Quail egg in inside and edge habitats of extensively and intensively grazed grasslands in three regions in Hungary in 2003. Interestingly, none of the three factors (region, grazing intensity, edge effect) had significant effects on brood loss according to the generalised linear mixed model, however, interactions between region and management and among region, management and edge effect were significant. This suggests that the effect of management is not the same in different regions, and edge effect depends on both region and management. We also found that nest predation rate is lower if nests are placed in tall grass and greater vegetation cover. This pattern indirectly supports the negative effects of intensive grazing, which can remove most of the vegetation. Therefore, we suggest that extensive grazing should be favoured to conserve ground nesting birds, however, it is essential to avoid duplicating management regimes from one region to another, due to regional differences in the pattern of survival probability
Egg distribution of the southern festoon (Zerynthia polyxena) (Lepidoptera, Papilionidae)
No full textWe investigated environmental factors grouped along hierarchical spatial scales influencing the egg density of a monophagous papilionid, the southern festoon (Zerynthia polyxena) on its food-plant, the birthwort (Aristolochia clematitis). Two patch level variables were considered: habitat type (black locust plantation, clearing and hummock) and food-plant patch size. We measured several plant variables at the egg-bearing shoots. We counted the number and measured the mean height of birthworts within the microenvironment of the egg-bearing shoots. We also measured the height and counted the leaves of each egg-bearing shoot itself. Plant apparency was defined as the height difference between egg-bearing shoots and the surrounding ones. Two variables were measured on the egg-bearing shoots (hence at food-plant scale): number of leaves and position of eggs on the leaf-storeys. Habitat type affected the distribution of eggs; black locust plantations and hummocks were preferred against clearings. At a smaller scale, neither shoot density, nor food-plant apparency affected egg distribution. At the plant level, the number of eggs increased with the number of leaves, and the position of eggs also co-varied with egg density, having fewer eggs in clusters positioned higher on shoots. We conclude that spatially correlated data on butterfly egg distribution should be analysed considering the intrinsically hierarchical structure of environmental factors
Arthropod functional traits shaped by landscape-scale field size, local agri-environment schemes and edge effects
Full text linkAgri-environment scheme (AES) approaches can be classified according to whether they prescribe management in non-productive areas, such as field boundaries and wildflower strips, or in productive areas, such as arable crops. Here we tested the ecological effectiveness of two popular AESs in Germany: wildflower strips next to winter wheat fields as off-field management and organic farming on winter wheat fields as on-field management. We selected ten landscapes along a field size gradient with three focal wheat fields, one conventional field with flower strip, one organic field and one conventional field without flower strip as a control. We sampled arthropods with pitfall traps at field edges and field interiors. We selected three ecological traits for spiders and carabids (body size, feeding trait, dispersal ability). We calculated community weighted mean values (CWM), and we used linear mixed effects models to test the effect of management type and transect position on CWM values. We found pronounced edge effects on most traits, and weaker effects of field size and AES in shaping functional traits. Smaller spiders, spiders with higher ballooning propensity and more web-builders were in the field interior than at the field edge, whereas carnivore carabids preferred field interiors. We also found a strong effect of landscape configuration, i.e. mean field size, as larger field size was positively related to more web-building spiders and more carnivore beetles. Flower strips enhanced populations of web-building spiders. Our results suggest that small-scale agriculture leading to high landscape-scale edge density has a major effect in shaping functional traits and potential ecosystems services in agricultural landscapes. Spider and carabid communities exhibit very different responses to edge vs. interior sites, and, based on the landscape-scale field size gradient emphasize the importance of landscape configuration in shaping the heterogeneity of the arthropods’ traits and presumably ecosystem services in agricultural landscapes
DO DIFFERENT PLASTICINE EGGS IN ARTIFICIAL GROUND NESTS INFLUENCE NEST SURVIVAL?
No full textIn order to understand the role of plasticine eggs in nest predation studies, altogether 78 ground nests were monitored in a large wheat field near to Pecs (southern Hungary) in June 2006. Two eggs were placed in each of the artificial nests, comprising, in an alternating sequence, quail + quail, quail + natural colour plasticine, and quail + white lime coloured plasticine eggs. During one week 65.4% of the artificial nests were depredated. When the damage or disappearance of any of the eggs was considered as a predation event, the daily survival rates of nest containing only two quail eggs was higher than of nests with quail and natural plasticine eggs and significantly higher than of nests with quail and white coloured plasticine eggs. When considering predation to real eggs only, the results remained similar, however, the significant difference in survival rates of the two nest types with different plasticine eggs disappeared. Simultaneously with the nest predation experiments, 78 small mammal live traps were set up in the wheat field and operated for 7 nights. The capture success of traps baited with quail egg was 9.9%, with natural plasticine egg 15.4%, and with white coloured plasticine egg 23.1%, but only a marginal significant difference was found between daily survival rates of quail vs. white coloured plasticine eggs. Natural, but especially white coloured plasticine eggs resulted in an increased predation rate, therefore we suggest that in artificial ground nest experiments nest should be considered to be predated only when the real egg is damaged or disappeared.Boly Inc.; 1.5 subprogram of the NKFP [3A/061/2004
Egg distribution of the southern festoon (Zerynthia polyxena) (Lepidoptera, Papilionidae)
No full textWe investigated environmental factors grouped along hierarchical spatial scales influencing the egg density of a monophagous papilionid, the southern festoon (Zerynthia polyxena) on its food-plant, the birthwort (Aristolochia clematitis). Two patch level variables were considered: habitat type (black locust plantation, clearing and hummock) and food-plant patch size. We measured several plant variables at the egg-bearing shoots. We counted the number and measured the mean height of birthworts within the microenvironment of the egg-bearing shoots. We also measured the height and counted the leaves of each egg-bearing shoot itself. Plant apparency was defined as the height difference between egg-bearing shoots and the surrounding ones. Two variables were measured on the egg-bearing shoots (hence at food-plant scale): number of leaves and position of eggs on the leaf-storeys. Habitat type affected the distribution of eggs; black locust plantations and hummocks were preferred against clearings. At a smaller scale, neither shoot density, nor food-plant apparency affected egg distribution. At the plant level, the number of eggs increased with the number of leaves, and the position of eggs also co-varied with egg density, having fewer eggs in clusters positioned higher on shoots. We conclude that spatially correlated data on butterfly egg distribution should be analysed considering the intrinsically hierarchical structure of environmental factors
DO DIFFERENT PLASTICINE EGGS IN ARTIFICIAL GROUND NESTS INFLUENCE NEST SURVIVAL?
No full textIn order to understand the role of plasticine eggs in nest predation studies, altogether 78 ground nests were monitored in a large wheat field near to Pecs (southern Hungary) in June 2006. Two eggs were placed in each of the artificial nests, comprising, in an alternating sequence, quail + quail, quail + natural colour plasticine, and quail + white lime coloured plasticine eggs. During one week 65.4% of the artificial nests were depredated. When the damage or disappearance of any of the eggs was considered as a predation event, the daily survival rates of nest containing only two quail eggs was higher than of nests with quail and natural plasticine eggs and significantly higher than of nests with quail and white coloured plasticine eggs. When considering predation to real eggs only, the results remained similar, however, the significant difference in survival rates of the two nest types with different plasticine eggs disappeared. Simultaneously with the nest predation experiments, 78 small mammal live traps were set up in the wheat field and operated for 7 nights. The capture success of traps baited with quail egg was 9.9%, with natural plasticine egg 15.4%, and with white coloured plasticine egg 23.1%, but only a marginal significant difference was found between daily survival rates of quail vs. white coloured plasticine eggs. Natural, but especially white coloured plasticine eggs resulted in an increased predation rate, therefore we suggest that in artificial ground nest experiments nest should be considered to be predated only when the real egg is damaged or disappeared.Boly Inc.; 1.5 subprogram of the NKFP [3A/061/2004
Management effects on carabid beetles and spiders in Central Hungarian grasslands and cereal fields
No full textModern agriculture is one of the main anthropogenic threats to biodiversity. To explore the effects of agricultural intensification we investigated carabids and spiders in two studies; in 2003 in grasslands and two years later in cereal fields in the same region. Both aimed to study the effect of management on arthropod diversity and composition at local and landscape scales. In 2003, we used a paired design for grasslands (extensively vs. intensively grazed). In 2005, a gradient design was applied with a total of seven land-use intensity categories. In both studies, sampling was carried out using funnel traps with the same sampling effort. Linear mixed models showed that high grazing intensity in grasslands had a positive effect on carabid species richness and abundance, but no effect on spiders. Landscape diversity had a positive effect only on carabid abundance. In the case of cereal fields, the management intensity (nitrogen fertiliser kg/ha) had a negative effect on spider richness and no effect on carabids. After variance partitioning, both local and landscape characteristics seem to be important for both cereal and grassland arthropod communities. Based on our results, we think that current and future agri-environmental schemes should be concentrated on cropland extensification. Low intensity croplands could act as a buffer zone around the semi-natural grasslands, at least in this biogeographic region
Effects of three flower field types on bumblebees and their pollen diets
No full textAgri-environment schemes, like flower fields, have been implemented in the EU to counteract the dramatic decline of farmland biodiversity. Farmers in Lower Saxony, Germany, may receive payments for three flower field types: annual, perennial (five years old), and mixed flower fields composed of yearly alternating annual and biannual parts. We assessed the effectiveness of these flower field types in providing bumblebee foraging habitat compared to control cereal fields. We sampled bumblebees with transect walks and assessed the richness of exploited pollen plants using DNA meta-barcoding and direct observations. All flower field types enhanced bumblebee abundance and species richness compared to control fields but attracted mostly three generalist species. Although we expected highest benefits from the more heterogeneous mixed flower fields, abundance was highest in annual, only intermediate in mixed, and lowest in perennial flower fields. Bumblebee species richness did not differ between flower field types. Overall, the proportion of sown plants in pollen loads was surprisingly low (< 50%). Bombus pascuorum, but not B. terrestris agg., exploited 10% of the sown plant species in perennial, 36% in annual and 45% in mixed flower fields, respectively. Compared to direct observations, pollen samples revealed 4.5 times more visited plant species and thus assessed floral resource use more reliably. Plant species richness in pollen loads decreased with local flowering plant species richness and increased with proportion of annual crops in the landscape, potentially due to the exploitation of more diverse and scattered resources, including flowering crops, in homogenized landscapes to fulfil dietary requirements. Our results indicate that under the current management, both annual and mixed flower fields provide the most attractive food resources, while perennial flower fields offered the poorest foraging habitats. Conclusively, flower fields seem important but resources from the surrounding landscape are still needed to sustain bumblebees in agricultural landscapes
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