Books & Articles
  • Fauchald, P., Skov, H., Skern-Mauritzen, M., Johns, D. & Tveraa, T. (2011) "Wasp-Waist Interactions in the North Sea Ecosystem" PLoS ONE 6(7): e22729
  • Fauchald, P. (2009) "Spatial interaction between seabirds and prey: review and synthesis" Mar. Ecol. Prog. Ser. 391:139-151
    [notes] The Ideal Free Distribution theory predicts a close spatial match between predators and prey. Studies have shown that seabird and prey distribution seldom conforms with this prediction. In this study, I review recent theoretical advances in spatial predator-prey interactions and relate these with studies of seabirds and pelagic schooling fish and crustaceans. Studies on seabirds and prey have generally assumed that prey are nonresponsive. Predator-prey interactions should, however, be viewed as a 2-way spatial game where seabirds track concentrations of prey while prey move away from areas with high risk of predation. The outcome of the game depends on how seabirds and prey are spatially constrained. Constraints include the spatial distribution of resources, interspecific competition, the location of spawning and breeding areas, and limitations on diving depth. Although game theoretic models can explain some general aspects of the spatial interaction, the spatial distribution of seabirds and prey is generally much more aggregated and elusive than can be expected from the game theoretic equilibrium. This is because spatial pattern is formed through self-organizing behavior that includes schooling, local enhancement and area-restricted search (ARS). Schooling and local enhancement are processes with strong positive density dependence that destabilize the predator-prey interaction locally. However, the unstable local dynamics might be stabilized by spatial constraints and the effects of ARS processes at large scales. KEY WORDS: Game model, Schooling, Local enhancement, Area-restricted search, Euphausia superba, Mallotus villosus, Clupea spp., Diomedea spp., Uria spp., Rissa tridactyla
  • Fauchald, P. & Tveraa, T. (2006) "Hierarchical patch dynamics and animal movement pattern" Oecologia 149:383-395
    [notes] In hierarchical patch systems, small-scale patches of high density are nested within large-scale patches of low density. The organization of multiple-scale hierarchical systems makes non-random strategies for dispersal and movement particularly important. Here, we apply a new method based on first-passage time on the pathway of a foraging seabird, the Antarctic petrel (Thalassoica antarctica), to quantify its foraging pattern and the spatial dynamics of its foraging areas. Our results suggest that Antarctic petrels used a nested search strategy to track a highly dynamic hierarchical patch system where small-scale patches were congregated within patches at larger scales. The birds searched for large-scale patches by traveling fast and over long distances. Once within a large-scale patch, the birds concentrated their search to find smaller scale patches. By comparing the pathway of different birds we were able to quantify the spatial scale and turnover of their foraging areas. On the largest scale we found foraging areas with a characteristic scale of about 400 km. Nested within these areas we found foraging areas with a characteristic scale of about 100 km. The large-scale areas disappeared or moved within a time frame of weeks while the nested small-scale areas disappeared or moved within days. Antarctic krill (Euphausia superba) is the dominant food item of Antarctic petrels and we suggest that our findings reflect the spatial dynamics of krill in the area. Keywords: Area-restricted search, First-passage time, Hierarchical foraging, Random walk, Satellite telemetry
  • Fauchald, P. & Tveraa, T. (2003) "Using first-passage time in the analysis of area-restricted search and habitat selection" Ecology 84(2):282-288
    [notes] How animals change their movement patterns in relation to the environment is a central topic in a wide area of ecology, including foraging ecology, habitat selection, and spatial population ecology. To understand the underlying behavioral mechanisms involved, there is a need for methods to measure changes in movement patterns along a pathway through the landscape. We used simulated pathways and satellite tracking of a long-ranging seabird to explore the properties of first- passage time as a measure of search effort along a path. The first-passage time is defined as the time required for an animal to cross a circle with a given radius. It is a measure of how much time an animal uses within a given area. First-passage time is scale dependent, and a plot of variance in first-passage time vs. spatial scale reveals the spatial scale at which the animal concentrates its search effort. By averaging the first-passage time on a geographical grid, it is possible to relate first-passage time to environmental variables and the search pattern of other individuals. Keywords: animal movement; Antarctic Petrel; dispersal; first-passage time; hierarchical foraging; radio tracking; random walk; satellite telemetry; scale; search pattern; Thalassoica antarctica[0282:UFPTIT]2.0.CO;2
  • Fauchald, P., Erikstad, K.E. & Skarsfjord, H. (2000) "Scale dependent predator-prey interactions: the hierarchical spatial distribution of seabirds and prey" Ecology 81(3):773-783
    [notes] It has been suggested that the spatial distribution of many marine pelagic organisms can be described by a hierarchical patch structure. Here, we present evidence for a hierarchical spatial distribution of murres (Uria spp.) foraging on capelin (Mallotus villosus) in the Barents Sea. We found three distinct levels of patchiness. At the largest level we found spatial structures with a characteristic scale of >300 km, and a spatial overlap between murre and capelin. Within the large-scale structures, we found medium-scale patches with a characteristic scale of ~50 km, and an overlap between the patches of murre and capelin. Within the medium-scale patches we found small-scale patches with a characteristic scale of ~3 km. At the smallest scale there was no overlap between patches of capelin and murre. Our results indicate that murres actively track the spatial distribution of capelin at several scales. We suggest that murres use a strategy where the search pattern reflects the hierarchical properties of the prey system. Under this hypothesis the predator searches for large-scale patches by using long travel distances and low turning frequency. Once within a large- scale patch, the predator starts searching for smaller scale patches by using shorter travel distances and higher turning frequencies. Such a search pattern will minimize the area to be searched by the predator and move the predator upward in the hierarchical prey system in a stepwise fashion. Keywords: Barents Sea; capelin; foraging; hierarchical patch structure; Mallotus villosus; murre; predator-prey; scale; seabird; spatial distribution; Uria.[0773:SDPPIT]2.0.CO;2

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