Prey density affects predator foraging strategy in an Antarctic ecosystem.

Karl M Busdieker,Alice M Trevail,Samantha C Patrick,Sébastien Descamps

doi:10.1002/ece3.5899

Karl M Busdieker, Alice M Trevail + Show 2 more

Open Access

https://doi.org/10.1002/ece3.5899

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Abstract

Studying the effects of prey distribution on predator behavior is complex in systems where there are multiple prey species. The role of prey density in predator behavior is rarely studied in closed ecosystems of one predator species and one prey species, despite these being an ideal opportunity to test these hypotheses. In this study, we investigate the effect of prey density on the foraging behavior of a predatory species in an isolated Antarctic ecosystem of effectively a single predatory species and a single prey species. We use resource selection models to compare prey density in areas utilized by predators (obtained from fine‐scale GPS telemetry data) to prey density at randomly generated points (pseudoabsences) throughout the available area. We demonstrate that prey density of breeding Antarctic petrels (Thalassoica antarctica) is negatively associated with the probability of habitat use in its only predator, the south polar skua (Catharacta maccormicki). Skuas are less likely to utilize habitats with higher petrel densities, reducing predation in these areas, but these effects are present during chick rearing only and not during incubation. We suggest that this might be caused by successful group defense strategies employed by petrel chicks, primarily spitting oil at predators.

Highlights

This study was conducted during the 2012/2013 breeding season at Svarthamaren (Dronning Maud Land, Antarctica 71°53′S, 5°10′E) in a seabird colony dominated by Antarctic petrels (Descamps et al, 2016; Mehlum et al, 1988; Varpe & Tveraa, 2005)
Snow petrels are few in number at Svarthamaren, and breed in rock crevasses that are relatively inaccessible to south polar skuas, and as such are insignificant within the scope of this study
Our study demonstrates a clear association between south polar skua habitat use and the density of their sole prey species during the breeding season, Antarctic petrels

Summary

| METHODS

This study was conducted during the 2012/2013 breeding season at Svarthamaren (Dronning Maud Land, Antarctica 71°53′S, 5°10′E) in a seabird colony dominated by Antarctic petrels (approx. 200,000 pairs of Antarctic petrels, 1,000 pairs of snow petrels and 150 pairs of south polar skuas) (Descamps et al, 2016; Mehlum et al, 1988; Varpe & Tveraa, 2005). To determine Antarctic petrel density, nests were surveyed using a grid of approximately 200 monitoring plot locations distributed at approximately 30 m intervals throughout the petrel colony, and the number of active nests (i.e., nests with an incubating bird) within an approximately 10 m2 area (1.78 m radius) of each monitoring point was recorded in early December (Figure 2, see Lorentsen, Røv, & Bangjord, 1993 for details on the protocol). These numbers were used to estimate petrel density in the whole colony at the beginning of the breeding season to understand whether prey density was a determinant of predator behavior and had not been reduced by predation activity throughout the season.

Findings

| DISCUSSION

| CONCLUSION