1. Parasites are one of the main actors in host-parasite interactions. Still, their role as a prey and the related consequences for such interactions and in other respects, such as food webs, are frequently overlooked.2. This paper analyses predation pressure on a ubiquitous avian ectoparasitic fly, Carnus hemapterus, identifies their main natural enemies and quantifies their relative effect on the abundance of the parasite. Also, the effect of nest-site type on their main enemies' predation pressure was analysed.3. Several ant species were found in the nest boxes of the host species, the European roller (Coracias garrulus), during the breeding season and preyed upon adult and larval stages of Carnus.4. Ants were also the putative predators of carnid pupae after the breeding season, when significant reduction (on average, by half) in the abundance of carnid pupae occurred in 75% of nest boxes within few months.5. Carnid pupae are also reported here, for the first time, to be parasitised by the parasitoid wasp Chartocerus conjugalis, whose prevalence was around 21%.6. Nest-site type had no clear effect on the predation rate of carnid pupae after the breeding season.7. It was concluded that predation is an important factor regulating the abundance of ectoparasites, and thus, it may influence the outcome of host-parasite relationships.
This study assesses the effects of environmental traits and landscape management on the biodiversity of saproxylic beetles from “dehesas” located in Sierra Morena Mountains (Córdoba, Southern Iberian Peninsula). The dehesa is an open savanna-like landscape with mature/old trees scattered on a pasture cover where both living and dead wood are of great importance for the maintenance of macroinvertebrate fauna. The study was carried out in five plots, with different environmental features and management. A total of 137 branches belonging to the four main tree species present in the area were collected, classified, and kept under four different thermal conditions. From January to June 2019, the adult emergences were followed. A total of 466 saproxylic specimens of 31 species were obtained, 5 of them included in red lists of protected fauna. Two Bostrichidae species (Lichenophanes numida Lesne and Scobicia pustulata Fab.) and two Cerambycidae (Chlorophorus ruficornis Oliv. and Trichoferus fasciculatus Faldermann) are included in the “European Red List of Saproxylic Beetles”; and the Clerid Tillus ibericus Bahillo de la Puebla, López–Colón and García–Paris, is included in the “Red Book of Invertebrate of Andalucía”. Differences were observed regarding the diversity and abundance among the plots and among the tree species from which the beetles emerged. Simple regression analyses revealed negative relationships between tree density/Buprestidae, livestock/Bostrichidae, and land use/Cerambycidae. Multivariant logistic regression analysis did not find significant relationships among environmental traits and saproxylic diversity. Results confirmed that dry wood was a main resource for the maintenance dehesas’ biodiversity because it constitutes an ecological niche exploited by a significant set of saproxylic beetles belonging to the Bostrichidae, Buprestidae, and Cerambycidae families, in addition to other guilds of species, mainly Carabidae and Cleridae, which feed on the above-mentioned groups. Our results also support that increasing environmental temperature accelerates the development of Buprestidae, but this effect was not evident for the Bostrichidae species.
Context dependence arises when ecological relationships vary with the conditions under which they are observed. Context dependence of interactions involving parasites is poorly known, even if it is key to understanding host–parasite relationships and food web dynamics. This paper investigates to which extent predation pressure on an avian ectoparasite (Carnus hemapterus) is context‐dependent. Based on a predator‐exclusion experiment, predation pressure on C. hemapterus pupae in the host's nest for 3 years, and its variation between habitat types are quantified. Variation in precipitation and normalized difference vegetation index (NDVI) is also explored as a likely cause of context dependency. We hypothesize that predation pressure should fluctuate with such surrogates of food availability, so that inter‐annual and intra‐annual differences may emerge. The number of nests with significant reduction of pupae varied widely among years ranging from 24% to 75%. However, average pupae reduction in nests where a significant reduction occurred did not vary between years. No differences in predation rates between habitat types were detected. Precipitation and NDVI varied widely between years and NDVI was consistently lower around nests on cliffs than around nests on trees and farmhouses. Parallels were found between variation in predation pressure and precipitation/NDVI at a wide scale (highest predation the driest year, and much lower the 2 rainier ones), but not at the nest scale. This paper shows clear context‐dependent insect predation pressure on an ectoparasite under natural conditions, and that such interaction changes in signs rather than magnitude between years. The causes for these variations require longer‐term studies and/or well‐designed, large‐scale experiments.
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