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Experimental Years (experimental + year)
Selected AbstractsEarly life history of the Mediterranean gorgonian Paramuricea clavata: implications for population dynamicsINVERTEBRATE BIOLOGY, Issue 1 2008Cristina Linares Abstract. Knowledge about early stages of marine sessile invertebrates dispersing by means of free-swimming propagules is fundamental toward understanding their population biology. In this study, we describe and quantify survivorship of early stages of the gorgonian Paramuricea clavata to contribute to the understanding of their implications on population dynamics of this emblematic species of the Mediterranean hard-bottom communities. Spawning was recorded in June for the 3 years studied (2001,2003). High levels of fertilization rate were observed during the main spawning in 2001 and 2002 (62,69%). This appears to be related to the surface brooding mode of development, synchronous spawning, and high fecundity of the species. The timing of development of the blastulae was ,24 h and the planulae appeared after 48,72 h. In the laboratory, metamorphosis into polyp started between 8 and 25 d, but this timing may have been delayed by lack of unknown appropriate cues for settlement. The behavior of first developed planulae exhibited a marked negative phototaxis that may be a strategy to avoid competition with fast-growing algae on photophilous habitats. Despite the high fertilization rate in P. clavata, laboratory and field experiences indicate that survivorship through the planulae and polyp stages was very low, given that none of the settled polyps survived for >7 months in both experimental years. The low survival of the early stages may help explain the low recruitment rates observed in the field in addition to indicating major limitations for colonization of new areas and for persistence of the local population under disturbances. [source] Life history and fitness consequences of ectoparasitesJOURNAL OF ANIMAL ECOLOGY, Issue 2 2004Patrick S. Fitze Summary 1For iteroparous organisms life-history theory predicts a trade-off between current and future reproduction, and therefore the evolution of host responses to current parasite infestation that will maximize lifetime reproductive success. The parasite-induced variation in reproductive success is thus not the net result of parasite infestation alone, but the parasite-mediated outcome of optimal resource allocation among current and future reproductive events. Understanding the importance of parasites for the evolution of host life history therefore requires an experimental investigation of the effects of parasites over the host's life span. Such studies are currently scant. 2We manipulated the load of an ectoparasite, the hen flea (Ceratophyllus gallinae), in the nests of its most common host, the great tit (Parus major), over a period of 4 years and recorded, the components of current and future reproductive success including survival, divorce, breeding dispersal and various reproductive parameters. Finally we assessed, for females only as paternity of males was unknown, the lifetime reproductive success as a close correlate of Darwinian fitness. 3For current reproduction, our experiment demonstrates that parasites reduce current reproductive success via an increase in the probability of nest failure during incubation and the nestling period. In the presence of fleas, clutch size and the number of fledglings were reduced while the incubation and the nestling period were prolonged. Thus parasitism led to an increase in parental effort but nevertheless reduced current reproductive success. 4For future reproduction, the experiment shows that females breeding in infested nests dispersed over longer distances between breeding attempts. The divorce rate following infestation, the probability of breeding locally in the future and residual reproductive success were not affected significantly by ectoparasites. The study thus suggests that hen fleas play a minor role in shaping the trade-off between current and future reproduction. 5Lifetime reproductive success of females, measured as the total number of locally recruiting offspring over the 4 experimental years, was reduced significantly by ectoparasites. The negative effect of parasites arose by a reduction of the number of fledglings per breeding attempt rather than by a reduction of the number of breeding attempts. [source] Variable but predictable prey availability affects predator breeding success: natural versus experimental evidenceJOURNAL OF ZOOLOGY, Issue 4 2008A. Millon Abstract Food supply is a major source of variation in breeding success for predators, and to what extent individuals are able to cope with temporal variability in food availability remains an outstanding question in life-history studies. We confronted the natural variation in clutch size and breeding success with results from a food supplementation experiment during egg formation, conducted over several contrasted years of natural food supply in an avian specialist predator, the Montagu's harrier Circus pygargus. This raptor mainly preys on common vole Microtus arvalis a cyclic microtine under temperate latitudes. Vole abundance together with timing of breeding accounted for most of the variance in clutch size and number of fledglings. Results from empirical and experimental data were overall in agreement. Fed pairs consistently increased clutch size compared with controls in all experimental years, whereas no effect of food supplementation on egg volume was detected. Supplemented pairs, however, did not fledge significantly more chicks than controls. The costs entailed by the increase in clutch size appear nevertheless to be limited compared with previous studies. Food supply seemed therefore to display sufficient predictability throughout a breeding season to afford individuals the opportunity to adjust their breeding effort to an optimal number of offspring, in agreement with Lack's anticipation hypothesis. [source] The effects of differentiated water supply after anthesis and nitrogen fertilization on ,15N of wheat grainRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 3 2010Ivana Raimanová The ,15N signature of plants integrates various processes in soil and plant. In this study, the effect of different water regimes applied during the period of grain growth of winter wheat on grain ,15N was examined in a 4-year field experiment. The treatments comprised water shortage (S), an ample water supply (W), and rain-fed crop (R). Zero fertilization (N0) and 200,kg,N.ha,1 in mineral fertilizer (N1) treatments were studied. The grain 15N was determined during grain growth and at maturity. The water regime, nitrogen application and year had a significant effect on mature grain ,15N (p,<,0.001). Water and nitrogen explained 54.6% of the variability of ,15N in the experiment, the year accounted for 10.7% and the interactions for another 19.6% of the total variability. The analysis of non-mature grain ,15N showed significant effects of N and year but not of water. Nitrogen fertilization reduced the ,15N of mature grain in years by 0.7,6.3, in comparison with N0 plants; the reduction was more pronounced under stress (average reduction by 4.1,) than under rain-fed (2.4,) and ample water supply (2.2,). Water stress decreased the grain ,15N in fertilized wheat, by 0.1,2.1, and 0.6,3.6, in experimental years, on average by 1.30, and 1.79, in comparison with the R and W water supply, respectively. The effect of water supply was not significant in non-fertilized wheat. A significant negative linear relationship between grain N concentration and ,15N in maturity or during the grain growth (R2,=,0.83, R2,=,0.76, respectively) was found. The observed sources of grain ,15N variability should be taken into consideration when analyzing and interpreting the data on the ,15N signature of plant material from field conditions. Copyright © 2010 John Wiley & Sons, Ltd. [source] Effects of herbage intake on goat performance in the mediterranean type natural pasturesANIMAL SCIENCE JOURNAL, Issue 1 2009Basri H. HAKYEMEZ ABSTRACT This study aimed at identifying changes in natural pastures during the grazing season and investigating the effects of these changes on pasture feeding potential for high yielding dairy goats. During the study, 12 dairy goats were grazed on a 1.5 ha natural pasture for three months from April to June in 2003, 2004 and 2005. The goats were fed 0.5 kg/day of concentrate as a supplement during the grazing season. Botanical composition, herbage production and intake, crude protein (CP), neutral detergent fiber (NDF) and acid detergent fiber (ADF) contents of the pasture were determined. Live weight, milk yield, milk dry matter (DM) and fat content of the goats were monitored. The data were analyzed using a linear model, which evaluated the effects of grazing seasons in each year. Based on the three-year average, 87% of pasture was herbaceous plants and the remaining was shrubs in DM basis with Cistus creticus, Quercus ithaburensis, Pistacia atlantica and Asparagus acutifolius being the major shrub species. The herbage yield in June was significantly lower than in other months in all years (P = 0.001). In all experimental years, the CP content of the pasture decreased but the structural carbohydrates increased as the grazing season proceeded. While live weight was not affected by grazing periods except for 2004 (P = 0.001), milk yield significantly decreased with advancing grazing period (P = 0.001). The results of the present study indicate that natural pasture has a supportive effect in April and May on the milk yield of lactating goats which are in mid-lactation, and suggested that supplementary feeding is required in consecutive grazing periods. [source] | ||||||||||