Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

The Theory of Island Biogeography

Entropies such as the Shannon–Wiener and Gini–Simpson indices are not themselves diversities. Conversion of these to effective number of species is the key to a unified and intuitive interpretation of diversity. Effective numbers of species derived from standard diversity indices share a common set of intuitive mathematical properties and behave as one would expect of a diversity, while raw indices do not. Contrary to Keylock, the lack of concavity of effective numbers of species is irrelevant as long as they are used as transformations of concave alpha, beta, and gamma entropies. The practical importance of this transformation is demonstrated by applying it to a popular community similarity measure based on raw diversity indices or entropies. The standard similarity measure based on untransformed indices is shown to give misleading results, but transforming the indices or entropies to effective numbers of species produces a stable, easily interpreted, sensitive general similarity measure. General overlap measures derived from this transformed similarity measure yield the Jaccard index, Sorensen index, Horn index of overlap, and the Morisita–Horn index as special cases.

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Entropy and diversity

A the many human activities that cause habitat loss (Czech et al. 2000), urban development produces some of the greatest local extinction rates and frequently eliminates the large majority of native species (Vale and Vale 1976, Luniak 1994, Kowarik 1995, Marzluff 2001). Also, urbanization is often more lasting than other types of habitat loss. Throughout much of New England, for example, ecological succession is restoring forest habitat lost from farming and logging, whereas most urbanized areas in that region not only persist but continue to expand and threaten other local ecosystems (Stein et al. 2000). Another great conservation challenge of urban growth is that it replaces the native species that are lost with widespread “weedy” nonnative species. This replacement constitutes the process of biotic homogenization that threatens to reduce the biological uniqueness of local ecosystems (Blair 2001). Urban-gradient studies show that, for many taxa, for example, plants (Kowarik 1995) and birds and butterflies (Blair and Launer 1997), the number of nonnative species increases toward centers of urbanization, while the number of native species decreases. The final conservation challenge of sprawl is its current and growing geographical extent (Benfield et al. 1999). A review by Czech and colleagues (2000) finds that urbanization endangers more species and is more geographically ubiquitous in the mainland United States than any other human activity. Species threatened by urbanization also tend to be threatened by agriculture, recreation, roads, and many other human impacts, emphasizing the uniquely far-reaching transformations that accompany urban sprawl. About 50% of the US population lives in the suburbs, with another 30% living in cities (USCB 2001). Over 5% of the total surface area of the United States is covered by urban and other built-up areas (USCB 2001). This is more land than is covered by the combined total of national and state parks and areas preserved by the Nature Conservancy. More ominously, the growth rate of urban land use is accelerating faster than land preserved as parks or conservation areas by the Conservancy (figure 1). Much of this growth is from the spread of suburban housing. It is estimated, for example, that residential yards occupy 135,000 acres in the state of Missouri (MDC 2002). This residential landscape represents nearly 1% of the total area of Missouri and is nearly three times the area occupied by Missouri state parks. Here I review the growing literature that documents how urban (and suburban) expansion harms native ecosystems. This knowledge can aid conservation efforts in two major ways. One is through the use of ecological principles—such as preserving remnant natural habitat and restoring modified habitats to promote native species conservation—to reduce the impacts of urbanization on native ecosystems. Rare and endangered species sometimes occur in urbanized habitats (Kendle and Forbes 1997, Godefroid 2001) and thus could be conserved there. Managing the large amount of residential vegetation (1% of the state area, as noted above) in ways that promote native plants and animals could also make a significant contribution to conservation.

https://bioone.org/journals/BioScience/volume-52/issue-10/0006-3568(2002)052[0883:UBAC]2.0.CO;2/Urbanization-Biodiversity-and-Conservation/10.1641/0006-3568(2002)052[0883:UBAC]2.0.CO;2.pdf

Urbanization, Biodiversity, and Conservation

Aim Beta diversity (variation of the species composition of assemblages) may reflect two different phenomena, spatial species turnover and nestedness of assemblages, which result from two antithetic processes, namely species replacement and species loss, respectively. The aim of this paper is to provide a unified framework for the assessment of beta diversity, disentangling the contribution of spatial turnover and nestedness to beta-diversity patterns.

Innovation  I derive an additive partitioning of beta diversity that provides the two separate components of spatial turnover and nestedness underlying the total amount of beta diversity. I propose two families of measures of beta diversity for pairwise and multiple-site situations. Each family comprises one measure accounting for all aspects of beta diversity, which is additively decomposed into two measures accounting for the pure spatial turnover and nestedness components, respectively. Finally, I provide a case study using European longhorn beetles to exemplify the relevance of disentangling spatial turnover and nestedness patterns.

Main conclusion  Assigning the different beta-diversity patterns to their respective biological phenomena is essential for analysing the causality of the processes underlying biodiversity. Thus, the differentiation of the spatial turnover and nestedness components of beta diversity is crucial for our understanding of central biogeographic, ecological and conservation issues.

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Partitioning the turnover and nestedness components of beta diversity

A recent increase in studies of β diversity has yielded a confusing array of concepts, measures and methods. Here, we provide a roadmap of the most widely used and ecologically relevant approaches for analysis through a series of mission statements. We distinguish two types of β diversity: directional turnover along a gradient vs. non-directional variation. Different measures emphasize different properties of ecological data. Such properties include the degree of emphasis on presence/absence vs. relative abundance information and the inclusion vs. exclusion of joint absences. Judicious use of multiple measures in concert can uncover the underlying nature of patterns in β diversity for a given dataset. A case study of Indonesian coral assemblages shows the utility of a multi-faceted approach. We advocate careful consideration of relevant questions, matched by appropriate analyses. The rigorous application of null models will also help to reveal potential processes driving observed patterns in β diversity.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1461-0248.2010.01552.x

Navigating the multiple meanings of β diversity: a roadmap for the practicing ecologist

Species diversity may be additively partitioned within and among samples (alpha and beta diversity) from hierarchically scaled studies to assess the proportion of the total diversity (gamma) found in different habitats, landscapes, or regions. We developed a statistical approach for testing null hypotheses that observed partitions of species richness or diversity indices differed from those expected by chance, and we illustrate these tests using data from a hierarchical study of forest-canopy beetles. Two null hypotheses were implemented using individual- and sample-based randomization tests to generate null distributions for alpha and beta components of diversity at multiple sampling scales. The two tests differed in their null distributions and power to detect statistically significant diversity components. Individual-based randomization was more powerful at all hierarchical levels and was sensitive to departures between observed and null partitions due to intraspecific aggregation of individuals. Sample-based randomization had less power but still may be useful for determining whether different habitats show a higher degree of differentiation in species diversity compared with random samples from the landscape. Null hypothesis tests provide a basis for inferences on partitions of species richness or diversity indices at multiple sampling levels, thereby increasing our understanding of how alpha and beta diversity change across spatial scales.

https://www.jstor.org/stable/10.1086/378901

Partitioning Species Diversity across Landscapes and Regions: A Hierarchical Analysis of α, β, and γ Diversity

Ecologists have traditionally viewed the total species diversity within a set of communities as the product of the average diversity within a community (alpha) and the diversity among the communities (beta). This multiplicative concept of species diversity contrasts with the lesser known idea that α- and β-diversities sum to give the total diversity. This additive partitioning of species diversity is nearly as old as the multiplicative concept, yet ecologists are just now beginning to use additive partitioning to examine patterns of species diversity. In this review we discuss why additive partitioning remained “hidden” until just a few years ago. The rediscovery of additive partitioning has expanded the way in which ecologists define and measure β-diversity. Beta diversity is no longer relegated to describing change only along an environmental gradient. Through additive partitioning, β-diversity is explicitly an average amount of diversity just as is α-diversity. We believe that the additive partitioning of diversity into α and β components will continue to become more widely used because it allows for a direct comparison of α- and β-diversities. It also has particular relevance for testing ecological theory concerned with the determinants of species diversity at multiple spatial scales and potential applications in conservation biology.

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The additive partitioning of species diversity: recent revival of an old idea

Ecologists and conservation biologists are keenly interested in how patterns of species diversity change across spatial scales. We examined how additive partitioning can be used to statistically evaluate spa- tial patterns of species diversity and develop conservation strategies. We applied additive partitioning to data on arboreal beetle diversity (richness, Shannon, Simpson) collected from a nested design consisting of four hi- erarchical levels—trees, forest stands, sites, and ecoregions—that corresponded to increasingly broader spa- tial scales within the eastern deciduous forest of Ohio and Indiana ( U.S.A.). A significant percentage (relative to that of randomization tests) of total species richness and Shannon and Simpson diversity was attributed to beta diversity between ecoregions and, to a lesser extent, among sites (parks and nature preserves) within ecoregions. Hierarchical cluster analysis corroborated these findings. We also found differences between rare species ( � 0.05% of total abundance) and common species ( � 0.5% of total abundance) in the overall per- centage of richness explained by each spatial scale. Rare species accounted for the majority (45%) of the 583 total beetle species in our study and were strongly influenced by broad spatial scales (i.e., ecoregions), whereas the richness of common species was significantly greater than expected across the range of spatial scales ( from trees to ecoregions). Our results suggest that the most effective way to preserve beetle diversity in the eastern deciduous forest of the United States is to acquire and protect multiple sites within different ecoregions. More generally, we advocate the use of diversity partitioning because it complements existing models in conserva- tion biology and provides a unique approach to understanding species diversity across spatial scales.

Additive Partitioning of Species Diversity across Multiple Spatial Scales: Implications for Regional Conservation of Biodiversity

Urbanization - the anthropogenic conversion of natural ecosystems into human-dominated ecosystems - has occurred on global scales. The human-dominated landscape presents particular challenges to researchers because the effects of urbanization on ecological processes are not well understood. We investigated the influence of urbanization on predation by conducting an artificial nest experiment along an urban gradient of six sites ranging from natural to urbanized ecosystems. Previous hypotheses suggest that predation pressures in urban environments will either 1) increase because of the high abundance of exotic species which act as predators or 2) decrease due to the lack of natural predators. To determine relative predation pressures among sites along the urban gradient, we monitored the fates of 16 artificial avian nests at each of the six sites for a total of 96 nests in each year (1996, 1997). We analyzed the dependency of nest fate (depredated or undisturbed) on intensity of urbanization (sites along the urban gradient), nest height (ground, above-ground), and year using loglinear models. The frequency of nest predation was strongly dependent on site along the urban gradient, indicating that urbanization intensity was an important determinant of nest fate. Predation pressure exhibited an overall decline from natural to urban sites in both years, suggesting that urban environments have low predation pressures relative to natural areas. The predatory relaxation in urban environments may partially explain the greater abundance of some species in urban environments, particularly urban exploiters such as european starlings Sturnis vulgaris. house sparrows Passer domesticus. and rock doves Columba livia.

Predation on artificial bird nests along an urban gradient: predatory risk or relaxation in urban environments?

Ecologists frequently regress local species richness on regional species richness to draw inferences about the processes that structure local communities. A more promising approach is to quantify the contributions of alpha and beta diversity to regional diversity (the ABR approach) using additive partitioning. We applied this approach to four local– regional relationships based on data from 583 arboreal beetle species collected in a hierarchically nested sampling design. All four local–regional relationships exhibited proportional sampling, yet the ABR approach indicated that each was produced by a different combination of alpha and beta richness. Using the results of the ABR analysis, we also analysed the scale dependence of alpha and beta using a hierarchical linear model. Alpha diversity contributed less than expected to regional diversity at the finest spatial scale and more than expected at the broadest spatial scale. A switch in relative dominance from beta to alpha diversity with increasing spatial scale suggested scale transitions in ecological processes. Analysing the scale dependence of diversity components using the ABR approach furthers our understanding about the additivity of species diversity in biological communities.

The alpha–beta–regional relationship: providing new insights into local–regional patterns of species richness and scale dependence of diversity components

Jon C. Gering

Papers

Partitioning Species Diversity across Landscapes and Regions: A Hierarchical Analysis of α, β, and γ Diversity

The additive partitioning of species diversity: recent revival of an old idea

Additive Partitioning of Species Diversity across Multiple Spatial Scales: Implications for Regional Conservation of Biodiversity

Predation on artificial bird nests along an urban gradient: predatory risk or relaxation in urban environments?

The alpha–beta–regional relationship: providing new insights into local–regional patterns of species richness and scale dependence of diversity components