Lombardo P. & M. Mjelde, 2014.  Quantifying interspecific spatial overlap in aquatic macrophyte communities.  Hydrobiologia 737: 25-43 (Special Issue: Plants in Hydrosystems).


Abstract—  Levins's asymmetrical α (alpha) index quantifies between species overlap over resources more realistically than similar-purpose single-value indices.  The associated community-wide mean-α index expresses the degree of "species packing".  Both indices were formulated upon competing animal (i.e., mobile) organisms and are independent of population densities.  However, overlap over resources for nonmobile organisms such as plants may have an impact even below carrying capacity.  The proposed α-hat (alpha-hat) index, based on Levins's α index, quantifies spatial overlap for plants integrating information on species spatial distribution and crowding conditions.  The α-hat index is specifically designed for plant distribution data collected in discrete plots with density expressed as percent coverage (%cover) of substratum.  We also propose a community-wide α-hatc index, conceptually analogous to mean-α, but furnished with a measure of dispersion [SE(α-hatc)].  Species importance within the community is inferred from comparisons of pairwise α-hat's with α-hatc.  The α-hat and α-hatc indices correlate closely and exponentially with plant density, and correct apparent over- and underestimations of interaction intensity at low and very high crowding by Levins's α and mean-α, respectively.  Index application to aquatic plant communities gave results consistent with within-community and general ecological patterns, suggesting a high potential of the proposed α-hat and α-hatc indices in basic and applied macrophyte ecological studies and management.

© Springer Science+Business Media Dordrecht 2013, reprinted with permission of the publisher.

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