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Tropical Highlands (tropical + highland)
Selected AbstractsImpact of the fish Garra on the ecology of reservoirs and the occurrence of Microcystis blooms in semi-arid tropical highlands: an experimental assessment using enclosuresFRESHWATER BIOLOGY, Issue 8 2009TADESSE DEJENIE Summary 1.,Many man-made reservoirs in the semi-arid highlands of Northern Ethiopia (Tigray) are characterised by the occurrence of intensive blooms of cyanobacteria and a dominance of small riverine fishes belonging to the genus Garra. 2.,We carried out enclosure experiments to test for the effect of these small fish on abiotic characteristics, phytoplankton biomass and zooplankton community structure in the pelagic of two reservoirs (Gereb Awso and Tsinkanet). Two experiments were carried out in each of the reservoirs, one at the end of the rainy season (highest water level) and one at the end of the dry season (lowest water level). 3.,The presence of Garra in general increased the amount of suspended matter, nutrient concentrations (total nitrogen and total phosphorus), phytoplankton and Microcystis biomass (including the proportion of Microcystis in the phytoplankton community), and reduced water transparency. The positive effect of the presence of Garra on nutrient concentrations and phytoplankton productivity indicate that Garra has the potential to affect food web functioning indirectly through bottom-up effects, by enhancing nutrient concentrations through sediment resuspension and excretion of nutrients. Indeed, population densities of the cladoceran zooplankton taxa Ceriodaphnia and Diaphanosoma also showed an overall increase in enclosures with Garra. 4.,However, our data also provide some evidence for a potential of Garra to exert top-down control on large bodied daphnids (Daphnia carinata, D. barbata), although such effect varied among experiments. The limited capability of Garra to control zooplankton communities mainly reflects the low efficiency of these small, riverine and benthos-oriented fish in foraging on zooplankton and suggests the existence of an unoccupied niche for zooplanktivorous fish in the majority of the reservoirs. 5.,Although the main effects of Garra on the pelagic food web seemed to be mediated by bottom-up mechanisms, our results also indicate that one of the key variables, the relative abundance of Microcystis, was impacted by Daphnia -mediated trophic cascade effects. [source] Estimates of genetic parameters for Boran, Friesian, and crosses of Friesian and Jersey with the Boran cattle in the tropical highlands of Ethiopia: milk production traits and cow weightJOURNAL OF ANIMAL BREEDING AND GENETICS, Issue 3 2004S. Demeke Summary Breed additive and non-additive effects plus heritabilities and repeatabilities for milk yield per lactation (LMY), milk yield per day (DMY), lactation length (LL), annual milk yield (AMY), annual milk yield per metabolic body weight (AMYBW) and cow weight at calving (BW) were estimated for 5464 lactation records collected from purebred Boran (B), Friesian (F), and crosses of Friesian and Jersey (J) breeds with the Boran breed raised in the tropical highlands of Ethiopia. Single trait analysis was carried out by using two equivalent repeatability animal models. In the first model the genotype was fitted as a fixed group effect, while in the second model the genotype was substituted by breed additive, heterotic and recombination effects fitted as fixed covariates. Both the F and J breed additive effects, measured as a deviation from the B breed were significant (p < 0.01) for all traits, except for BW of the J. The F and J additive contributions were 2774 ± 81 and 1473 ± 362 kg for LMY, 7.1 ± 0.2 and 4.8 ± 0.8 kg for DMY, 152 ± 7 and 146 ± 31 days for LL, 2345 ± 71 and 1238 ± 319 kg for AMY, 20.6 ± 0.9 and 18.9 ± 4.3 kg for AMYBW, and 140 ± 4 and ,21 ± 22 kg (p > 0.05) for BW. The heterotic contributions to the crossbred performance were also positive and significant (p < 0.01) for all traits. The F1 heterosis expressed as a deviation from the mid-parent values were 22 and 66% for LMY, 11 and 20% for DMY, 29 and 29% for LL, 21 and 64% for AMY, 42 and 42% for AMYBW, and 2% (p < 0.05) and 11% for BW for the F × B and J × B crosses, respectively. The recombination effect estimated for the F × B crosses was negative and significant for LMY (,526 ± 192 kg, p < 0.01), DMY (,3.0 ± 0.4 kg, p < 0.001), AMY (,349 ± 174 kg, p < 0.05) and BW (,68 ± 11 kg, p < 0.001). For the J × B crosses the recombination loss was significant and negative only for DMY (,2.2 ± 0.7 kg, p < 0.05) and BW (,33 ± 17 kg, p < 0.05). The direct heritabilities (h2) estimated for LMY, DMY, LL, AMY and AMYBW were 0.24 ± 0.04, 0.19 ± 0.03, 0.13 ± 0.03, 0.23 ± 0.04 and 0.17 ± 0.05, respectively. Based on the genetic parameters estimated, the best breeding strategy to increased milk production under highland Ethiopian conditions is to apply selection on purebred base populations (Boran and Friesian) and then crossing them to produce F1 dairy cows. However, for breeding decision based on total dairy merit, further investigations are needed for traits such as milk quality, reproduction, longevity and survival. Zusammenfassung Additive Rasseneffekte, nicht additive Effekte, Heritabilitäten und Wiederholbarkeiten für Milchmenge pro Laktation (LMY), Milchmenge pro Tag (DMY), Laktationsdauer (LL), jährliche Milchmenge (AMY), jährliche Milchmenge pro metabolischem Körpergewicht (AMYBW) und Kuhgewichte zur Kalbung (BW) wurden anhand von 5464 Laktationsdatensätzen von reinrassigen Boran (B), Friesian (F) und Kreuzungen der Rassen Friesian und Jersey (J) mit der Rasse Boran, die im tropischen Hochland von Äthiopien groß gezogen wurden, geschätzt. Einmerkmalsmodelle wurden mit zwei äquivalenten Wiederholbarkeits-Tiermodellen durchgeführt. Im ersten Modell wurde der Genotyp als fixer Gruppeneffekt berücksichtigt, während im zweiten Modell der Genotyp durch additive Rasseneffekte, Heterosis und Rekombinationseffekte als Kovariable ersetzt wurde. Die additiven Rasseneffekte von F und J, gemessen als Abweichung von der Rasse B, waren für alle Merkmale signifikant (p < 0,01), ausgenommen BW für die Rasse J. Die additiven Rasseneffekte von F und J betrugen 2774 ± 81 und 1473 ± 362 kg für LMY, 7,1 ± 0,2 und 4,8 ± 0,8 kg für DMY, 152 ± 7 und 146 ± 31 Tage für LL, 2345 ± 71 und 1238 ± 319 kg für AMY, 20,6 ± 0,9 und 18,9 ± 4,3 kg für AMYBW und 140 ± 4 und ,21 ± 22 kg (p > 0,05) für BW. Die Heterosis bei den Kreuzungstieren war positiv und signifikant für alle Merkmale (p < 0,01). Die Heterosis der F1 -Tiere, ausgedrückt als Abweichung vom Mittel der beiden Eltern, betrug 22 und 66% für LMY, 11 und 20% für DMY, 29 und 29% für LL, 21 und 64% für AMY, 42% und 42% für AMYBW und 2% (p < 0,05) und 11% für BW für die F × B und J × B Kreuzungen. Der geschätzte Rekombinationseffekt für die F × B Kreuzungen war negativ und signifikant für LMY (,526 ± 192 kg, p < 0,01), DMY (,3,0 ± 0,4 kg, p < 0,001), AMY (,349 ± 174, p < 0,05) und BW (,68 ± 11 kg, p < 0,001). Für die J × B Kreuzungen war der Rekombinationsverlust signifikant und negativ nur für DMY (,2,2 ± 0,7 kg, p < 0,05) und BW (,33 ± 17, p < 0,05). Die geschätzten Heritabilitäten (h2) betrugen für LMY, DMY, LL, AMY und AMYBW 0,24 ± 0,04, 0,19 ± 0,03, 0,13 ± 0,03, 0,23 ± 0,04 und 0,17 ± 0,05. Basierend auf den geschätzten genetischen Parametern erscheint Selektion in den Reinzuchtpopulationen B und F und anschließ end Kreuzung dieser Tiere zur Erstellung von F1 -Milchkühen als günstigste Zuchtstrategie, um die Milchproduktion unter äthiopischen Hochlandbedingungen zu steigern. Für Zuchtentscheidungen, die die gesamte Milchproduktion berücksichtigen, sind weitere Untersuchungen notwendig für Merkmale wie Milchqualität, Reproduktion, Persistenz und Langlebigkeit. [source] Evaluating soil rhizobacteria for their ability to enhance plant growth and tuber yield in potatoANNALS OF APPLIED BIOLOGY, Issue 2 2010A. Oswald The objectives of this study were to identify promising microorganisms to improve potato productivity in low-input systems of tropical highlands and to compare results from in vitro, greenhouse and field experiments to advance the development of a screening method for rhizobacteria and develop an efficient assessment of their effect on plant growth in field conditions. A total of 150 bacterial strains were screened in vitro, in greenhouse and field trials. The series of experiments confirmed the plant growth-promoting ability of a range of rhizobacteria. Although in vitro and greenhouse results were promising, the field experiment showed variability and the results require further verification. The in vitro tests might have limited value for screening as no correlation could be found between in vitro tests and pot trial results. However, trials in controlled conditions produced insights into the mechanisms causing better plant growth in potato, such as early tuberisation, fast development of leaf area and probably greater photosynthetic rates. [source] |