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Selected AbstractsVariability in survival and mortality of Acacia drepanolobium Sjøstedt following prescribed burning at Olpejeta Conservancy, KenyaAFRICAN JOURNAL OF ECOLOGY, Issue 3 2010Geoffrey M. Wahungu Abstract Mortalities to Acacia drepanolobium, a main item in the diet of the eastern black rhino (Diceros bicornis Michaeli) in Olpejeta conservancy, Kenya, are caused by three main factors: drought, browsers and fire. The effect of controlled fires on A. drepanolobium was examined by monitoring survival and growth in experimental plots before and after fire episodes between 2003 and 2007. Density, survival and growth in A. drepanolobium trees were compared eighteen months before and after burning. Tall trees were more likely to die from fire compared to short trees (R2 = 0.575; df = 6; P = 0.048), while seedling densities increased after fire (,2 = 36.57; df = 1; P = 0.001). Even with increased seedling densities, burned areas attracted large numbers of seedling predators, lowering the possibility of seedling recruitment into adult, as mean seedling heights reduced significantly (ANOVA, F = 204.42; df = 1; P = 0.036). Fires also significantly lowered flowering (F = 346; df = 1; P < 0.05) in A. drepanolobium, thereby affecting fruit production. Although fires caused mortalities to adult A. drepanolobium, the most significant effect was tree reversals into seedling height class as trees resprouted. Although fire may increase browse biomass of A. drepanolobium available for black rhino, it is not an appropriate black rhino habitat management tool because burnt areas attract many seedling predators that lower seedling recruitment into adult trees. Résumé La mortalité d'Acacia drepanolobium dans l'aire de conservation d'Olpejeta, au Kenya, est causée par trois facteurs principaux, la sécheresse, les herbivores et les feux. On a examiné l'effet des feux contrôlés sur A. drepanolobium en suivant la survie et la croissance dans des parcelles expérimentales 18 mois avant et après les feux, entre 2003 et 2007. On a comparé la densité, la survie et la croissance d'A. drepanolobium 18 mois avant et après les feux. Les grands arbres étaient plus susceptibles de mourir à cause des feux que les petits (R² = 0,575; ddl = 6; P = 0,048) alors que la densité des jeunes plants augmentait après les feux (,² = 36,57; ddl = 1; P = 0,001). Même si la densité de jeunes plants était accrue, les zones brûlées attiraient de grands nombres de prédateurs de ces plants, diminuant ainsi la possibilité de recrutement vers l'âge adulte, parce que la hauteur moyenne des jeunes plants était significativement réduite (Anova, F = 204,42; ddl = 1; P =0,036). Les feux réduisaient aussi significativement la floraison (F = 346; ddl = 1; P < 0,05) chez A. drepanolobium, affectant dès lors la production de fruits. Même si les feux causaient une certaine mortalité chez les A. drepanolobium adultes, l'effet le plus significatif était le retour des arbres dans des classes de hauteur des jeunes plants lorsque les arbres rejetaient. Même si les feux peuvent augmenter la biomasse de brout d'A. drepanolobium disponible pour les rhinos noirs, ils ne sont pas un outil de gestion approprié pour l'habitat des rhinos parce que les zones brûlées peuvent attirer des nombreux prédateurs des jeunes plants qui réduisent le recrutement de ceux-ci vers l'âge adulte. [source] Influence of temporal fluctuations in seed abundance on the diet of harvester ants (Pogonomyrmex spp.) in the central Monte desert, ArgentinaAUSTRAL ECOLOGY, Issue 8 2009GABRIELA I. PIRK Abstract Harvester ants usually go through temporal fluctuations in environmental seed abundance and composition which could influence their behaviour and ecology. The aim of this study was to evaluate how these fluctuations influence the diet of Pogonomyrmex rastratus, P. pronotalis and P. inermis (Hymenoptera, Formicidae) in the central Monte desert during three consecutive growing seasons. Although seeds were the main item in the diet, these ants turned more generalist when seed abundance of the most consumed species (grasses Aristida spp., Trichloris crinita, Pappophorum spp., Digitaria californica and Stipa ichu) was low. Accordingly, diversity of items in the diet decreased with seed abundance in a logarithmical fashion, showing higher foraging efficiency for seeds at higher seed abundance. Seed diversity, however, was not related to seed abundance as ants always included several species in their diet, with alternating prevalence. The proportion of the most consumed species increased logarithmically in the diet of P. rastratus and P. pronotalis along with their abundance in the environment probably as a consequence of diet switching (from forb and shrub seeds to grass seeds) and by an increase in foraging efficiency at higher seed densities. In contrast, foraging activity of P. inermis was very low at low seed abundance and its diet included only the five grasses. Among the most consumed species, proportion in the diet was not associated with relative abundance in the environment. Aristida spp., Pappophorum spp. and D. californica were overall highly selected. However, the flexibility in the diet of P. pronotalis and P. rastratus and the low foraging activity of P. inermis during periods of low resource abundance could attenuate potential top-down effects in the central Monte desert. This study shows that bottom-up effects are important in ant-seed interactions and should be considered when predicting and evaluating ants' effects on seed resources. [source] Feeding habits and trophic morphology of inshore lizardfish (Synodus foetens) on the central continental shelf off Veracruz, Gulf of MexicoJOURNAL OF APPLIED ICHTHYOLOGY, Issue 6 2005V. H. Cruz-Escalona Summary The inshore lizardfish, Synodus foetens, is one of the most common coastal demersal predators on the continental shelf of the Gulf of Mexico (GOM), but the biology and feeding ecology of this species is virtually unknown. Between November 2001 and January 2003 (10 collections), 603 individuals of S. foetens ranging from 112 to 420 mm standard length (SL) and 13 to 630 g (wet weight) were collected from the continental shelf of Alvarado, Veracruz, Mexico. About 60% of the individuals had empty stomachs with the stomach fullness of the remaining individuals being distributed as follows: 5% full (24.8%), 50,75% full (13.5%), and completely full (1.7%). The mean (± SD) wet weight of stomach contents was 12.1 ± 10.8 g during the rainy season, and 19.0 ± 13.0 g during the nortes season. Seventeen prey items were identified, with the majority thereof being fish. The most important prey items were Upeneus parvus, Loligo pealei, Engyophrys senta, Trachurus lathami, and Anchoa hepsetus. Seasonal changes in the diet were observed, with U. parvus and L. pealei being the most important prey during the nortes season, whereas E. senta and L. pealei were the main items during the rainy season. Prey size selection was evident among size classes of S. foetens, although no trophic overlap was observed among size classes (Cik , 0.004). High trophic level values were determined for all size classes by season (rainy season = 4.67, nortes season = 4.84), and indicated this species belongs to the piscivorous trophic guild that preys upon both demersal and pelagic species. [source] THE NEW MODEL OF THE RAILWAY INDUSTRY IN SPAIN WITHIN THE EUROPEAN FRAMEWORKANNALS OF PUBLIC AND COOPERATIVE ECONOMICS, Issue 3 2007J. BAREA ABSTRACT,:,This study identifies the strengths and weaknesses of the the new regulatory framework for railways in Spain. We offer a description of the present situation of the railway industry in Spain, following the coming into force of the new Railway Industry Law in January 2005. We also analyse the international experience in light of the principles underlying the liberalization of the railway industry in Europe and, in particular, the cases of the United Kingdom and France. These two models are suitable for our purposes based on these main items: the degree of effective competition, the similarity to the Spanish case, the rail market growth and the geographical location. Our conclusions are that Spain has overcome some mistakes made by the countries mentioned above, like leaving infrastructure investment or security aspects in the hands of the private sector, however others have been committed, such as the excessive influence of the government on the basic actors of the industry or defining a complex system without well defined responsibilities. [source] | ||||||||||