James G. Sanderson

Nested species subsets, gaps, and discrepancy

Abstract The nested-subset hypothesis of Patterson and Atmar states that species composition on islands with less species richness is a proper subset of those on islands with greater species richness. The sum of species absences, referred to as gaps, was suggested as a metric for nestedness, and null models have been used to test whether or not island species exhibited nestedness. Simberloff and Martin stated that finding examples of non-nested faunas was difficult. We revisit previous analyses of nested faunas and introduce a new metric we call “discrepancy” which we recommend as a measure for nestedness. We also recommend that the sample spaces conserve both row sums (number of species per site) and column sums (number of sites per species) derived from the incidence matrix. We compare our results to previous analyses.

Null matrices and the analysis of species co-occurrences

Abstract Patterns in species occurrences on islands have been analyzed by several authors. At issue is the number of non-occurring pairs of species (also known as checkerboards). Previous authors have suggested that if the number of checkerboards differs from what is expected by chance, then island communities might have been structured by competition. Investigators have pursued this problem by first generating random (or null) matrices and then testing a metric derived from the collection of null matrices against the metric calculated from the actual species co-occurrence matrix. The random matrices were constrained by requiring the number of species on each island, and the number of islands on which each species occurred to be equal to their observed values. We show that results from previous studies are generally flawed. We present a fast, efficient algorithm to generate null matrices for any set of fixed row and column sums, and propose a modification of a previously proposed metric as a test statistic. We evaluated the efficacy of our construction method for null creation and our metric using incidence matrices from the avifauna of Vanuatu (formerly New Hebrides).

Wildlife Issues in a Changing World

Introduction Wildlife Laws Examples of Wildlife Issues What is Wildlife? Genetic Diversity Origin and Distribution of Biodiversity The Evil Quartet Evil Quartet 1: Overexploitation Evil Quartet 2: Habitat Fragmentation and Destruction Evil Quartet 3: Introduced Species Evil Quartet 4: Chains of Extinctions Harvesting of Wildlife Remembering History: The Eastern U.S. Experience- A History of Wildlife Issues in Florida, New Jersey, Maine and Pennsylvania From Exploitation to Reintroduction: Wildlife in the Western U.S.-California, Arizona, Colorado, New Mexico Global Perspectives of Wildlife Issues Oceanic International Issues An In-Depth Study of Irian Jaya An In-Depth Case Study of Gorillas Can Humans Manage Wildlife? Novel Solutions Epilogue