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Food Resource Availability (food + resource_availability)
Selected AbstractsSize-related and temporal variation in the diet of the round sardinella, Sardinella aurita (Valenciennes, 1847), in the central Mediterranean SeaJOURNAL OF APPLIED ICHTHYOLOGY, Issue 5 2008S. Lomiri Summary Feeding habits of the round sardinella Sardinella aurita (Valenciennes, 1847) were studied in the central Mediterranean Sea from a sampling of 254 specimens caught seasonally from April 2004 to January 2005. Stomach content analysis showed a zooplankton diet mainly composed of crustaceans, mostly copepods, but also of a large variety of prey categories. The relationship among dietary descriptors pointed to some feeding variation in its diet, which was also confirmed by corresponding analysis. Correlation analysis and analysis of variance of the sample (fish) scores indicated size-related and temporal variations in the round sardinella diet. Small S. aurita fed on smaller sized prey categories, compared to larger fish in which larger zooplankters frequently occurred. While size related variations in the diet seemed likely correlated to changes in the gill arch structure, temporal variations could be due to seasonal food resource availability. Given the few studies carried out on S. aurita in the Mediterranean Sea, these results contribute to improving knowledge on the feeding habits of this species, which is progressively extending its distribution northward in the area. [source] The predatory impact of the freshwater invader Dikerogammarus villosus on native Gammarus pulex (Crustacea: Amphipoda); influences of differential microdistribution and food resourcesJOURNAL OF ZOOLOGY, Issue 1 2005Calum MacNeil Abstract Predation between invading and native species can produce patterns of exclusion and coexistence. Dikerogammarus villosus, a Ponto-Caspian amphipod species, has invaded many central European freshwaters in the past decade, replacing native Gammarus amphipod species. For instance, the arrival of D. villosus in Holland has been accompanied by the decline of Gammarus duebeni and G. tigrinus populations within invaded systems. This study examined what may happen when D. villosus eventually encounters native Dutch populations of Gammarus pulex, and how factors such as microhabitat and food resource availability could contribute to a future species replacement or coexistence. A laboratory simulation of a lake/pooled area of river indicated that G. pulex and D. villosus differed in distribution within the same habitat, and showed that although the distribution of the native differed in the presence of the invader, the presence of the native had no effect on the distribution of the invader. Gammarus pulex suffered severe intraguild predation (IGP) from D. villosus in mixed species treatments with no reciprocal predation of D. villosus by G. pulex. This IGP occurred regardless of whether no alternative food resource was available (91% of the G. pulex population eliminated after 7 days), or alternative foods/prey were available to excess, such as leaf material (85%), chironomids (77%) or fish food flakes (74%). We conclude that although differential microdistribution of the two species could promote coexistence, the presence of alternative foods/prey resources, merely slow the rate of IGP and replacement of the native by the invader. Our study joins one of an increasing number emphasizing the potential damaging impacts of D. villosus on native communities. [source] Variations in bark-stripping by red deer Cervus elaphus across EuropeMAMMAL REVIEW, Issue 3 2006HÉLÈNE VERHEYDEN ABSTRACT 1The literature on bark-stripping by red deer Cervus elaphus in Europe is reviewed to reveal quantitative variation in this behaviour and relate it to deer density and local characteristics such as dominant tree species, occurrence of artificial feeding, altitude, region and size of the study site. We also review the importance of bark in red deer diets over the seasons and discuss the causes of bark-stripping, focusing on the significance of bark as food. 2Over the 36 sites examined, the rate of bark-stripping was highly variable (from 0 to 84% of susceptible trees debarked), with less damage in Scotland than in other European sites for which bark-stripping rates were higher at high red deer density. Altitude, the size of the study site, the number of dominant tree species and the occurrence of artificial feeding do not significantly relate to the rate of bark-stripping. 3Bark sometimes made up a large proportion of red deer diet (> 10%), especially in areas with severe winters (high levels of snow), whereas in study sites with mild winters, bark was practically not eaten at all. 4These results suggest that severe bark-stripping could be related to a reduction in food resource availability. This food availability hypothesis needs to be better documented, dealing particularly with the possible interaction between food availability and red deer density. [source] The influence of increasing population size and vegetation productivity on elephant distribution in the Kruger National ParkAUSTRAL ECOLOGY, Issue 3 2009KIM D. YOUNG Abstract Decisions to reduce the impacts of large herbivores on biodiversity in protected areas are often based on controlling their numbers. However, numbers per se may not be the foremost consideration when managing impacts. This is because density-related changes in distribution can also affect habitat utilization and hence, impact. In this study we tested whether changes in the distribution of African elephants are associated with increasing population size. We used spatially explicit count data collected during the dry seasons from 1998 to 2004 in South Africa's Kruger National Park. We did this at five spatial scales and in landscapes defined by vegetation, geology, climate and soils. We then investigated whether observed distributions and grid-cell-specific densities were associated with the remotely sensed Normalized Difference Vegetation Index (NDVI) as a measure of productivity and therefore food resource availability at the landscape scale. Consistent with density mediated changes, we found that elephant grid-cell occupancy increased with population size, while grid-cell-specific density became less variable. In addition, the combined distribution of bull groups and breeding herds became less clumped with increasing population size. We further found that within landscapes elephants were present on grid-cells with higher NDVI values, but that the influence of NDVI during the dry season on densities among landscapes may be weak. These results suggest that NDVI was more indicative of structural habitat choices such as woody vegetation than food availability per se. Our study highlights the need to consider factors other than population size alone when formulating management decisions to reduce large herbivore impacts on biodiversity in protected areas. [source] | ||||||||||