Mono-dimensional and multi-dìmensional niches in a Mediterrane an seabirds community

Fasola M. & Saino N.

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The overlaps in the food and in tbe habitat niche components, between 8 species of sympatrically breeding gulls and terns, were inversely correlated. The indexes of the multidimensional (food and habitat) niche were compared witb the estimates generated by summation (L) and by product (lt) of the monodimensional parameters. Although the results may not be applied quantitatively to otber cases, tbey show that monodimensional approaches only describe tbe selection of single resources by the consumers, without in any way offering inference about the absolute amount of complete ecological overlap. Overlap values between species, obtained by tbe Land the lt methods, are subject to very large errors; contrary to previous suggestions, the lt metbod approximates the complete niche better than does the L metbod, even when tbe use of differing resources is dependent Both Land lt metbods in most cases estimated correctly tbe rank, but not the absolute value, of niche breadtb. The rank of complete overlap between species was correctly estimated only when the average overlap of one species witb alI tbe otber species in the community was considered.