Comparative analyses of avian population fluctuations have shown large interspecific differences in population variability that have been difficult to relate to variation in general ecological characteristics. Here we show that interspecific variation in demographic stochasticity, caused by random variation among individuals in their fitness contributions, can be predicted from a knowledge of the species' position along a "slow-fast" gradient of life-history variation, ranging from high reproductive species with short life expectancy at one end to species that often produce a single offspring but survive well at the other end of the continuum. The demographic stochasticity decreased with adult survival rate, age at maturity, and generation time or the position of the species toward the slow end of the slow-fast life-history gradient. This relationship between life-history characteristics and demographic stochasticity was related to interspecific differences in the variation among females in recruitment as well as to differences in the individual variation in survival. Because reproductive decisions in birds are often subject to strong natural selection, our results provide strong evidence for adaptive modifications of reproductive investment through life-history evolution of the influence of stochastic variation on avian population dynamics.

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The spatial integrity of a habitat or landscape is determined by the occurrence of habitat fragments and of perforations inside them. A landscape is said to have less spatial integrity with increasing numbers of fragments and perforations. The Euler number (epsilon) is a numerical measure of spatial integrity, based upon the difference (nf-np) between the number of fragments (nf) and the number of perforations (np). In this contribution, epsilon is evaluated, and an improvement is presented as a new index epsilon*, which is a combination of two metrics (epsilon j, epsilon d) based on nf and np. The term epsilon j quantifies the intensity of perforation and/or fragmentation. The term epsilon d measures the extent to which fragmentation predominates perforation, and vice versa. The intensity and dominance measures are combined into an Euclidean distance measure, generating the new ensemble value epsilon*, calculated as epsilon* = (nf + np)-1 square root of [1 + nf2]. Use, sensitivity, and application of epsilon*, epsilon j, and epsilon d are illustrated using percolation maps. Application of the new metrics by environmental scientists is encouraged because (1) no negative values can be generated with epsilon*, epsilon j, and epsilon d; (2) the range of epsilon*, epsilon j, and epsilon d is fixed; (3) process dominance and intensity are both assessed; (4) epsilon*, epsilon j, and epsilon d are easy to calculate and to interpret; and (5) epsilon* is not only based upon (nf - np), as epsilon is. Guidelines for practical use by means of a biplot of epsilon j and epsilon d are given.