Breeding success and several breeding parameters were studied at 5 feral pigeon colonies. We found that density and the age of breeding pairs affect reproduction, with also the age of the nest significantly influencing reproductive indicators and success. Hatching, fledging and breeding success were higher in colonies with lower breeding pair densities. These indicators were also higher for experienced pairs compared to first time breeders. The number of nests in a pair’s territory had little effect on breeding performance. Among all the breeding parameters studied (timing of breeding, length of the breeding season, number of broods per year) only the latter was positively correlated with the density of birds. Breeding pairs had significantly more broods during a year in highly dense colonies compared with those of low density. The remaining factors studied were similar in all breeding colonies regardless of their density. Breeding parameters were primarily dependent on breeding pair age – experienced pairs began breeding earlier, ended later, conducted a longer breeding season and, as a result, produced more broods per year. The age of a nest also influenced the breeding season. Many factors were found to cause egg and nestling loss. Mechanical damage to eggs, eggs and nestlings falling out of nests, embryo death, jackdaw predation, competition among fledglings, and nestling disease were dependent on the level of pigeons’ reproductive activity, especially in overly dense colonies.
Stocked and wild trout diet was assessed in two north-eastern Portugal headstreams during the summer season of three successive years (2000 to 2002). Significant differences were detected in the diet composition between stocked (age 1+) trout and distinct size-class of wild trout. Stocked fish showed preference, almost exclusively, for food items captured near the surface (primarily terrestrial adult insects), emergent pupae and subimagos. In contrast, young-of-year (YOY) wild trout fed predominantly on the most available aquatic prey taxa such as Chironomidae (Diptera) larvae and Baetidae (Ephemeroptera) nymphs; however, Trichoptera larvae were not taken. Wild trout preference changed from benthic aquatic invertebrates to terrestrial origin organisms and this ratio increased with size, suggesting an ontogenetic diet variation. Significant diet overlap was only detected between stocked and dominant wild trout, which were not displaced from the energetically profitable areas. Therefore, this study showed the absence of an evident competition for food in both streams, even when trout density was largely augmented by stocking activity. However, since no obvious benefits on space and time were obtained, stocking must be carefully evaluated and alternative approaches considered, like habitat improvement and adequate fisheries management, in order to increase the natural productivity of these systems.
Functional responses at each developmental stage of predators and intraspecific competition associated with direct interactions among them provide insights into developing biological control strategies for pests. The functional responses of Harmonia axyridis (Pallas) at each developmental stage of Melanaphis sacchari (Zehntner) and intraspecific competition among predators were evaluated under laboratory conditions. The results showed that all stages of H. axyridis displayed a type II functional response to M. sacchari. Based on Holling's disc equation, the instantaneous searching rates were highest (a) and handling time was shortest (Th) of fourth instar larvae (a = 0.8818; Th = 3.9 min) and female adults (a = 0.9881; Th = 3.0 min) at larval and adult stages, respectively. The coefficients of mutual interference (m) assessed by the intraspecific competition equation were higher for fourth instar larvae (m = 0.4764) and female adults (m = 0.4183). The present study indicates that fourth instar and female adult were more effective stages of H. axyridis in the context of biological control but suitable predator densities need to be considered before natural enemy release., Pengxiang Wu, Jing Zhang, Muhammad Haseeb, Shuo Yan, Lambert Kanga, Runzhi Zhang., and Obsahuje bibliografii
Unfavourable growth conditions significantly determine the yield of crop plants. Intraspecific competition is a condition in which plants compete with each other for environmental resources. An excessive density contributes to increased competition within species, which results in disruption of photosynthesis process. According to this idea, experiments were conducted to investigate the photosynthetic response of potato (Solanum tuberosum) plants to excessive congestion. Two potato varieties of different earliness classes (Vineta and Satina) were used to evaluate the efficiency of the photosynthetic apparatus based on chlorophyll (Chl) fluorescence measurements under stress conditions. Changes in Chl contents of the tested plants were also analysed. In relation to intraspecific competition, we can conclude that the Vineta variety was less sensitive to this stress factor. In contrast, the photosynthetic apparatus of the Satina variety showed less efficient functioning under these conditions. In this study, the application of Chl fluorescence was presented for the first time in order to analyse the effects of intraspecific competition in plants., J. Olechowicz, C. Chomontowski, P. Olechowicz, S. Pietkiewicz, A. Jajoo, M. H. Kalaji., and Obsahuje bibliografii