Environmental factors and nutritional utilization patterns affect niche overlap indices between Aspergillus ochraceus and other spoilage fungi

The total number, and the type of C source utilized in common by an ochrato xin producing strain of Aspergillus ochraceus and six other spoilage fungi varied with the range used (95, Biolog GN plates, or 18 major C sources fou nd in maize). The niche size and niche overlap index (NOI) were markedly in fluenced by water availability (water activity, a(w)) and temperature. With freely available water (0.995 a(w)) there was ecological similarity betwee n A, ochraceus, A. alternata, A. candidus and A. flavus, all exploiting the same sources at both 18 and 30 degrees C. However, under water stress, A. ochraceus had a low NOI compared with A. niger, A. flavus and A. candidus, and Eurotium spp., suggesting that there was very little niche overlap in u tilization of different C sources. The NOIs were not directly related to gr owth rates. Niche overlap between species was shown to be in a state of flu x and significantly influenced by environmental factors. This may have impo rtant implications in understanding ecological interactions, and dominance by species in a community, and for pre-emptive exclusion of specific specie s.