HABITAT AVAILABILITY CAUSES THE SPECIES ABUNDANCE-DISTRIBUTION RELATIONSHIP

The objective of this study was to examine the effect of different amo unts of available habitat on the relationship between the distribution and abundance of species using a spatially explicit, stochastic, indi vidual-based simulation model. We define abundance as the mean abundan ce of a species in occupied breeding habitat sites and distribution as the proportion of breeding habitat sites that are occupied by that sp ecies. We hypothesized that on a patchy landscape, more available bree ding habitat will result in both higher abundance and wider distributi on because of an increased number of successful dispersers. Therefore, a positive relationship between distribution and abundance is expecte d for a group of species in a landscape if individual species have dif ferences in habitat use and therefore different amounts of habitat are available to them on the same landscape. In the simulation experiment the amount of breeding habitat was varied to examine the effects on a bundance and distribution. We found a positive correlation between (1) abundance and the number of breeding habitat cells on the simulation landscape (2) distribution and the number of breeding habitat cells on the landscape and, (3) abundance and distribution. These results sugg est that differences in amount of available habitat could account for a positive relationship between abundance and distribution.