Density-dependent switches in diet:a likely mechanism for negative feedbacks on goose population increase?

Goose grazing on arctic tundra vegetation has shown both positive and negative effects on subsequent foraging conditions. To understand the potential of a density-dependent feedback on herbivore population size, the relation between grazing pressure and future foraging conditions is essential. We studied the effect of increasing grazing pressure of barnacle geese (Branta leucopsis) on Spitsbergen. During the establishment of a breeding colony in the period 1992-2004, the proportion of graminoids decreased in the diet of wild geese, while the percentage of mosses increased. Grazing trials with captive geese in an unexploited area showed a similar shift in diet composition. High-quality food plants were depleted within years and over years. Intake rate declined too and as consequence, metabolisable energy intake rate (MEIR) decreased rapidly with increasing grazing pressure. During three successive years of experimental grazing, MEIR decreased at all levels of grazing pressure and declined below minimal energetic requirements when grazing exceeded natural levels of grazing pressure. This suggests that foraging conditions rapidly decline with increasing grazing pressure in these low-productive habitats. The potential for density-dependent feedbacks on local population increase is discussed

Behavioral response of naïve and non-naïve deer to wolf urine

Large carnivores are recolonizing many regions in Europe, where their ungulate prey have lived without them for >150 years. Whether the returning large carnivores will modify ungulate behavior and indirectly affect lower trophic levels, depends on the ability of ungulates to recognize risk based on past encounters and cues indicating carnivore presence. In two case studies, we tested, by means of camera trapping, the behavioral response of deer to wolf urine. The first case study was in the Netherlands where deer (still) live in absence of wolves, and the second in Poland with long-term wolf presence. As controls we used water (no scent) and all-purpose soap (unfamiliar scent). Deer vigilance level on control plots was 20% in both case studies indicating that wolf occupancy per se does not lead to a consistent difference in behavior. Placing wolf urine did not significantly affect deer behavior in either the wolf-absent or the wolf-present area. More intense cues, or a combination of cues, are likely needed to affect deer behavior. Moreover, we found an unexpected reaction of deer towards all-purpose soap of reduced foraging (and tendency for increased vigilance) in the wolf-present area, whereas it did not affect deer behavior in the wolf-absent area. We hypothesize that deer associate all-purpose soap with human presence, causing no response in human-dominated landscapes (the Netherlands), but triggering a behavioral reaction in more remote areas (Poland). This illustrates attention should be paid to controls used in scent experiments as they may be associated differently than intended

Wolves and tree logs:Landscape-scale and fine-scale risk factors interactively influence tree regeneration

Large carnivores can reduce ungulate numbers by predation and via induced risk effects alter ungulate behavior, indirectly affecting lower trophic levels. However, predator-induced risk effects probably act at different spatial scales, which have often been ignored in trophic cascade studies. We studied how a fine-scale risk factor (distance from tree logs) affects ungulate browsing intensity and how this is modified over a landscape-scale risk gradient (distance from human settlements to wolf core) in the Białowieża forest, Poland. We found that landscape-and fine-scale risk factors strongly interacted in determining the strength and magnitude of carnivore-induced risk effects on lower trophic levels. In low-risk areas, tree logs reduced browsing intensity in small patches (approx. 4–6 m from logs), whereas in high-risk areas browsing intensity was reduced up to at least 16 m from tree logs. Moreover, the magnitude of these effects changed, with the strongest reduction in browsing intensity around tree logs in high-risk areas (up to 37%) and the smallest in low-risk areas (< 20%). Overall, the results of this study indicate that perceived risk factors act at different spatial scales, where impediments (objects blocking view and escape routes) act as a risk factor at a fine scale and carnivore distribution shapes perceived risk at the landscape scale. Moreover, these risk factors strongly interact, thereby determining the functional role of large carnivores in affecting ecosystem processes. These interactive effects should be incorporated in predator-induced trophic cascade studies to understand patterns of tree regeneration in ecosystems where large carnivores and herbivores live together

Small herbivoers losing control: Plant-herbivore interactions along a natural productivity gradient

Different theories have been postulated about how plant-herbivore interactions will change along gradients of plant productivity. They lead to different predictions on the importance of top-down and bottom-up effects in structuring communities. The classical exploitation theory predicts increasing top-down control along a gradient of primary productivity. At intermediate levels of productivity, herbivores will be regulated plant biomass, whereas at high levels of productivity herbivores will be regulated by carnivores. In contrast, the quality treshold theory predicts that bottum-up effects become of more importance at high productivity. Decreasing plant quality will result in decreasing herbivore numbers. Both theories predict that herbivores will have the strongest impact on the vegetation at intermediate levels of productivity. ... Zie: Summary

Small herbivores losing control : plant-herbivore interactions along a natural productivity gradient

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(Table 2) Protein and fibre content of important food plants of barnacle geese (Branta leucopsis) in Adventdalen

Goose grazing on arctic tundra vegetation has shown both positive and negative effects on subsequent foraging conditions. To understand the potential of a density-dependent feedback on herbivore population size, the relation between grazing pressure and future foraging conditions is essential. We studied the effect of increasing grazing pressure of barnacle geese (Branta leucopsis) on Spitsbergen. During the establishment of a breeding colony in the period 1992-2004, the proportion of graminoids decreased in the diet of wild geese, while the percentage of mosses increased. Grazing trials with captive geese in an unexploited area showed a similar shift in diet composition. High-quality food plants were depleted within years and over years. Intake rate declined too and as consequence, metabolisable energy intake rate (MEIR) decreased rapidly with increasing grazing pressure. During three successive years of experimental grazing, MEIR decreased at all levels of grazing pressure and declined below minimal energetic requirements when grazing exceeded natural levels of grazing pressure. This suggests that foraging conditions rapidly decline with increasing grazing pressure in these low-productive habitats. The potential for density-dependent feedbacks on local population increase is discussed

Replication Data for: Wolves and tree logs: Landscape-scale and fine-scale risk factors interactively influence tree regeneration

This dataset contains all data used for the paper Van Ginkel et al, 2018, Ecosystems, and is organised in three zipped folders. The metadata file describes all abbreviations used in the data files: Van-Ginkel-etal_2018_Ecosystems_RAW_Data Van-Ginkel-etal_2018_Ecosystems_PROCESSED_Data Van-Ginkel-etal_2018_Ecosystems_txt-files_R-scripts Van-Ginkel-etal_2018_Ecosystems_Metadata.txt If you have questions regarding this dataset or are interested in using our data, please contact one of the authors indicated

(Table 2) Protein and fibre content of important food plants of barnacle geese (Branta leucopsis) in Adventdalen

Abstract: Goose grazing on arctic tundra vegetation has shown both positive and negative effects on subsequent foraging conditions. To understand the potential of a density-dependent feedback on herbivore population size, the relation between grazing pressure and future foraging conditions is essential. We studied the effect of increasing grazing pressure of barnacle geese (Branta leucopsis) on Spitsbergen. During the establishment of a breeding colony in the period 1992-2004, the proportion of graminoids decreased in the diet of wild geese, while the percentage of mosses increased. Grazing trials with captive geese in an unexploited area showed a similar shift in diet composition. High-quality food plants were depleted within years and over years. Intake rate declined too and as consequence, metabolisable energy intake rate (MEIR) decreased rapidly with increasing grazing pressure. During three successive years of experimental grazing, MEIR decreased at all levels of grazing pressure and declined below minimal energetic requirements when grazing exceeded natural levels of grazing pressure. This suggests that foraging conditions rapidly decline with increasing grazing pressure in these low-productive habitats. The potential for density-dependent feedbacks on local population increase is discussed. Category: geoscientificInformation Source: Supplement to: Kuijper, Dries Pieter Jan; Ubels, R; Loonen, Maarten J J E (2009): Density-dependent switches in diet: a likely mechanism for negative feedbacks on goose population increase? Polar Biology, 32(12), 1789-1803, https://doi.org/10.1007/s00300-009-0678-2 Supplemental Information: During sampling, selective grazing by geese was mimicked by selecting only live leaf tips of every encountered plant or fresh tops of mosses. Data extracted in the frame of a joint ICSTI/PANGAEA IPY effort, see http://doi.pangaea.de/10.1594/PANGAEA.150150 Coverage: EVENT LABEL: * LATITUDE: 78.200000 * LONGITUDE: 16.700000 * LOCATION: Spitsbergen, Svalbard * METHOD/DEVICE: Biological sampl

Replication Data for: Wolves and tree logs: Landscape-scale and fine-scale risk factors interactively influence tree regeneration

This dataset contains all data used for the paper Van Ginkel et al, 2018, Ecosystems, and is organised in three zipped folders. The metadata file describes all abbreviations used in the data files: Van-Ginkel-etal_2018_Ecosystems_RAW_Data Van-Ginkel-etal_2018_Ecosystems_PROCESSED_Data Van-Ginkel-etal_2018_Ecosystems_txt-files_R-scripts Van-Ginkel-etal_2018_Ecosystems_Metadata.txt If you have questions regarding this dataset or are interested in using our data, please contact one of the authors indicated