Variability of resource partitioning in sympatric tropical boobies

Abstract

Inter-and intraspecific competition can lead to resource partitioning in sympatric species, processes likely affected by environmental productivity and population size. We investigated the foraging behaviour and diet of masked (Sula dactylatra) and red-footed (S. sula) boobies at Tromelin Island, western Indian Ocean, to examine the role of resource partitioning in the foraging strategies of these sympatric species in an extreme oligotrophic environment. We compared our results to published studies with differing environmental conditions or population sizes. We used GPS loggers and Argos transmitters to track foraging movements and used time-depth recorders to estimate dive depths. Masked boobies travelled further and at faster rates than redfooted boobies, and sexes did not differ in foraging behaviour. Based on randomization tests, the foraging range of each species (95% utilization distribution; UD) overlapped significantly. However, at core foraging areas (50% and 25% UD), interspecific segregation was greater than expected by chance alone. No intraspecific spatial segregation was detected between sexes. Environmental characteristics of area-restricted search zones differed between species, but not sexes; masked boobies utilized warmer, deeper, and less windy oceanic environments than red-footed boobies. Masked boobies attained greater diving depths than red-footed boobies and consumed primarily flying fish, whereas red-footed boobies consumed mostly squid. Red-footed and masked boobies breeding in the extreme oligotrophic environment near Tromelin demonstrated greater dietary partitioning differences in foraging ranges compared to a less oligotrophic environment. This suggests that environmental productivity may play a role in processes of resource partitioning in these sympatric species.KEY WORDS: Resource partitioning · GPS · Satellite tracking · Area-restricted search · Diet · Sula dactylatra · Sula sula Resale or republication not permitted without written consent of the publisher

Seasonal shifts in foraging distribution due to individual flexibility in a tropical pelagic forager, the Ascension frigatebird

“…Tropical seabirds frequently exploit all marine areas within a species' flight range, leading to a dispersed distribution around islands (Kappes et al 2011, Hennicke & Weimerskirch 2014, Oppel et al 2015. This dispersed distribution could occur by individuals consistently travelling to a certain location, with individuals exhibiting differences in their preferred foraging location, thus leading to a dispersed distribution at the population level.…”

Geographical variation in the foraging behaviour of the pantropical red-footed booby

“…RFBs and masked boobies from Palmyra Atoll showed strong differences in their foraging behaviour and ranges, with RFBs being again more pelagic than masked boobies (Young et al 2010). The 2 same species at Tromelin Island (Indian Ocean), surrounded by more oligotrophic waters, demonstrated interspecific segregation at the level of core foraging areas but not at the scale of the whole foraging region (Kappes et al 2011). However, intraand interspecific competition did not explain the higher maximum ranges observed at Tern Island (3000 to 5000 RFB pairs) compared to Palmyra Atoll that hosts 25 000 RFB pairs and 1 more tropical booby species (Young et al 2015).…”

“…Kappes et al 2011, Oppel et al 2015. The wide distribution of RFB populations provides the opportunity to examine the influence of contrasted biotic and abiotic conditions from different breeding sites on foraging behaviour.…”

Individual-level Variation and Higher-level Interpretations of Space Use in Wide-ranging Species: An Albatross Case Study of Sampling Effects

“…The variability among sub-samples should be assessed including maximum and minimum estimates in area occupied, along with the range in geographic locations of those areas. Increasingly, studies are including significance tests for overlap analyses; the proportional area of overlap between specified contours estimated for groups of interest from full datasets are compared with those estimated from randomized iterative sub-samples as a test of whether enough individuals were tracked to make reasonable higher-level inferences of significant spatial segregation (e.g., Breed et al, 2006;Kappes et al, 2011;Cleasby et al, 2015;Orben et al, 2015). This approach, coupled with area saturation curves, can improve confidence in the appropriateness of higher-level extrapolations.…”