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In this study, we addressed how frequently a non-traplining animal should visit food patches. More specifically, we investigate if non-traplining animals engage in a behavior called "defense by exploitation", which is characterized by an increase in visitation rates with increased intra-specific competition. We ran four tests with two gerbil species in the Negev Desert. Firstly, we measured patch use of Gerbillus pyramidum and Gerbillus andersoni allenbyi. We assumed that activity and competition would decrease through the night and that patch use would decrease with number of visits. Secondly, we measured how the number of visits to resource patches increased with the addition of individuals. Thirdly, we repeated this experiment, but instead removed individuals. Lastly, we conducted a simulation to compare these results against theoretical expectations. In the first test, we found support for defense by exploitation in G. pyramidum. The second and third test found no support. The fourth test found support for this increase visitation, but only if costs of locomotion are relatively small., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Foraging ecology and the marine regions exploited by Antarctic seabirds outside of breeding strongly influence their exposure to persistent organic pollutants (POPs). However, relationships between them are largely unknown, an important knowledge gap given that many species are capital breeders and POPs may be deleterious to seabirds. This study investigates the relationship between Antarctic seabird foraging ecology (measured by δ 13 C and δ 15 N) and POPs accumulated in their eggs prior to breeding. Organochlorinated pesticides, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and dechlorane plus (DP) were measured in eggs of chinstrap, Adélie, and gentoo penguins (Pygoscelis antarctica, P. adeliae, P. papua), as well as south polar skua (Catharacta maccormicki), sampled on King George Island. Total POP levels were as follows: skua (3210±3330ng/g lipid weight)>chinstrap (338±128ng/g)>Adélie (287±43.3ng/g)>gentoo (252±49.4ng/g). Trophic position and pre-breeding foraging sites were important in explaining POP accumulation patterns across species. The most recalcitrant compounds were preferentially accumulated in skuas, occupying one trophic level above penguins. In contrast, their Antarctic endemism, coupled with influence from cold condensation of pollutants, likely contributed to penguins exhibiting higher concentrations of more volatile compounds (e.g., hexachlorobenzene, PCB-28 and -52) than skuas. Regional differences in penguin pre-breeding foraging areas did not significantly affect their POP burdens, whereas the trans-equatorial migration and foraging sites of skuas were strongly reflected in their pollutant profiles, especially for PBDEs and DPs. Overall, our results provide new insights on migratory birds as biovectors of POPs, including non-globally regulated compounds such as DP, from northern regions to Antarctica., (Copyright © 2016. Published by Elsevier B.V.)