Birds’ nesting success may vary significantly between years. Ample evidence exists that this variation is caused by temporal fluctuations in rodent populations, as rodents are important components in the diets of nest predators. The alternative prey hypothesis supposes that generalist predators switch to alternative prey (bird nests) when their main prey (rodents) is lacking, thus causing increased nest predation. According to the shared predation hypothesis, by contrast, predator density is enhanced at rodent population peaks and results in simultaneous increase in main and alternative prey predation. To evaluate these hypotheses, nest predation rate dynamics were examined using artificial nests (n = 560) and rodent abundance (2240 traps) during four breeding seasons in Central European (the Czech Republic) secondary forests. Although rodent abundance increased at the population peak by almost seven times compared to the baseline and nest predation rate also showed significant inter-year variation, the data support neither the alternative prey nor shared predation hypotheses. In rich ecosystems with complex trophic levels, predators can use many resources as alternative prey. Therefore, bird nest predation risk does not increase or decrease in periods of low rodent abundance.
Coccinellids are effective predators and a key component of the predator guild in rice ecosystems. In order to enhance their efficacy, a study was undertaken to assess the seasonal movement of coccinellids into rice fields and the role of the surrounding flora on their colonization. The seasonal abundance of coccinellids and their prey was recorded on the rice crop and the surrounding flora at fortnightly intervals from 2012 to 2015. Coccinellid prey range was assessed using PAGE electrophoresis. The herbivorous insects associated with weeds were Aphis gossypii Glover, Aphis craccivora (Koch), Cicadulina bipunctata (Melichar), Schizaphis graminum (Rondani), Sitobion sp., Thaia oryzivora Ghauri and Zygina maculifrons Matsumura. Of the species of coccinellids recorded in rice fields, Harmonia octomaculata (Fabricius), Micraspis discolor (F.), Propylea dissecta (Mulsant), Coccinella transversalis Fabricius, Cheilomenes sexmaculata (Fabricius), Scymnus nubilus Mulsant and Brumoides suturalis (Fabricius) were also recorded on weeds. The esterase profiles indicated that the leafhoppers and aphids on the weeds were the prey of the coccinellids before they colonized the rice fields. The coccinellids recorded on the weeds showed bands corresponding to the insects present on the weeds. Beetles collected from rice fields had different bands, some of which corresponded to the green leafhopper (GLH) Nephotettix virescens Distant, the brown planthopper (BPH) Nilaparvata lugens Stal and white backed planthopper (WBPH) Sogatella furcifera Hovarth infesting rice. In addition, some bands corresponded to hoppers and aphids that were present on the surrounding flora. The results indicate the importance of surrounding flora in the conservation and colonization of rice fields by coccinellids., Chitra Shanker, Lydia Chintagunta, Sampathkumar Muthusamy, Sunil Vailla, Amudhan Srinivasan, Gururaj Katti., and Obsahuje bibliografii