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

H umans have long been fascinated by the dynamism of free-flowing waters. Yet we have expended great effort to tame rivers for transportation, water supply, flood control, agriculture, and power generation. It is now recognized that harnessing of streams and rivers comes at great cost: Many rivers no longer support socially valued native species or sustain healthy ecosystems that provide important goods and services (Naiman et al. 1995, NRC 1992).

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The Natural Flow Regime

▪ Abstract The focus of most ideas on diversity maintenance is species coexistence, which may be stable or unstable. Stable coexistence can be quantified by the long-term rates at which community members recover from low density. Quantification shows that coexistence mechanisms function in two major ways: They may be (a) equalizing because they tend to minimize average fitness differences between species, or (b) stabilizing because they tend to increase negative intraspecific interactions relative to negative interspecific interactions. Stabilizing mechanisms are essential for species coexistence and include traditional mechanisms such as resource partitioning and frequency-dependent predation, as well as mechanisms that depend on fluctuations in population densities and environmental factors in space and time. Equalizing mechanisms contribute to stable coexistence because they reduce large average fitness inequalities which might negate the effects of stabilizing mechanisms. Models of unstable coexitence...

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Mechanisms of Maintenance of Species Diversity

I. CONTEXT * The Ecosystem Concept * Earth's Climate System * Geology and Soils * II. MECHANISMS * Terrestrial Water and Energy Balance * Carbon Input to Terrestrial Ecosystems * Terrestrial Production Processes * Terrestrial Decomposition * Terrestrial Plant Nutrient Use * Terrestrial Nutrient Cycling * Aquatic Carbon and Nutrient Cycling * Trophic Dynamics * Community Effects on Ecosystem Processes * III. PATTERNS * Temporal Dynamics * Landscape Heterogeneity and Ecosystem Dynamics * IV. INTEGRATION * Global Biogeochemical Cycles * Managing and Sustaining Ecosystem * Abbreviations * Glossary * References

Principles of Terrestrial Ecosystem Ecology

Meta-analysis provides formal statistical techniques for summarizing the results of independent experiments and is increasingly being used in ecology. The response ratio (the ratio of mean outcome in the experimental group to that in the control group) and closely related measures of proportionate change are often used as measures of effect magnitude in ecology. Using these metrics for meta-analysis requires knowledge of their statistical properties, but these have not been previously derived. We give the approximate sampling distribution of the log response ratio, discuss why it is a particularly useful metric for many applications in ecology, and demonstrate how to use it in meta-analysis. The meta-analysis of response-ratio data is illustrated using experimental data on the effects of increased atmospheric CO2 on plant biomass responses.

The meta-analysis of response ratios in experimental ecology

Increasing global concentrations of atmospheric CO2 are predicted to decrease ocean pH, with potentially severe impacts on marine food webs, but empirical data documenting ocean pH over time are limited. In a high-resolution dataset spanning 8 years, pH at a north-temperate coastal site declined with increasing atmospheric CO2 levels and varied substantially in response to biological processes and physical conditions that fluctuate over multiple time scales. Applying a method to link environmental change to species dynamics via multispecies Markov chain models reveals strong links between in situ benthic species dynamics and variation in ocean pH, with calcareous species generally performing more poorly than noncalcareous species in years with low pH. The models project the long-term consequences of these dynamic changes, which predict substantial shifts in the species dominating the habitat as a consequence of both direct effects of reduced calcification and indirect effects arising from the web of species interactions. Our results indicate that pH decline is proceeding at a more rapid rate than previously predicted in some areas, and that this decline has ecological consequences for near shore benthic ecosystems.

https://www.pnas.org/content/pnas/105/48/18848.full.pdf

Dynamic patterns and ecological impacts of declining ocean pH in a high-resolution multi-year dataset.

Determining the strengths of interactions among species in natural com- munities presents a major challenge to ecology. Using an approach combining experimental perturbations and path analysis, I examined the mechanisms by which birds directly and indirectly affected other members of an intertidal community, evaluated alternative causal hypotheses, and predicted whether interactions among other unmanipulated species would be strong or weak. Comparing treatments with t tests indicated that excluding bird predators with cages caused increases in Pollicipes polymerus, and declines in Nucella spp., Mytilus californianus, and Semibalanus cariosus. However, these conclusions provided no insight into the underlying mechanisms causing the differences. Path analysis permitted insight into the causal mechanisms by making a variety of predictions about the strength of direct interactions: (a) Bird predation negatively affects Pollicipes, but not Nucella, Leptasterias, or Mytilus; (b) Pollicipes reduces Semibalanus and Mytilus abundance because of space competition; (c) Mytilus reduces Semibalanus cover through competition for space; and (d) as prey species, Semibalanus and Pollicipes enhance Nucella density, but Nucella pre- dation does not have important effects on Semibalanus or Pollicipes. Based on the estimated strength of direct interactions, the importance of indirect effects among species could also be predicted. In experiments manipulating Nucella, Pollicipes, Semibalanus, and birds independently of one another, I tested 11 of the interactions predicted by the path analysis; all were supported. Path analysis in conjunction with limited experiments may provide an efficient means to predict important direct and indirect interactions among unmanipulated species within ecological communities.

Predicting direct and indirect effects: an integrated approach using experiments and path analysis'

▪ Abstract Understanding and predicting the dynamics of multispecies systems generally require estimates of interaction strength among species. Measuring interaction strength is difficult because of the large number of interactions in any natural system, long-term feedback, multiple pathways of effects between species pairs, and possible nonlinearities in interaction-strength functions. Presently, the few studies that extensively estimate interaction strength suggest that distributions of interaction strength tend to be skewed toward few strong and many weak interactions. Modeling studies indicate that such skewed patterns tend to promote system stability and arise during assembly of persistent communities. Methods for estimating interaction strength efficiently from traits of organisms, such as allometric relationships, show some promise. Methods for estimating community response to environmental perturbations without an estimate of interaction strength may also be of use. Spatial and temporal scale may ...

Measurement of interaction strength in nature

A multitrophic model integrating the effects of flooding disturbance and food web interactions in rivers predicted that removing floods would cause increases of predator-resistant grazing insects, which would divert energy away from the food chain leading to predatory fish. Experimental manipulations of predator-resistant grazers and top predators, and large-scale comparisons of regulated and unregulated rivers, verified the model predictions. Thus, multitrophic models can successfully synthesize a variety of ecological processes, and conservation programs may benefit by taking a food web perspective instead of concentrating on a single species.

https://science.sciencemag.org/content/sci/273/5281/1558.full.pdf

Effects of Disturbance on River Food Webs

Species may indirectly affect populations of other species in two basic ways. Interac- tion chains result from linked direct interactions between species pairs. Interaction modifica- tions, emergent effects of a multispecies assemblage, result when a third species changes how a pair of other species interacts. Experiments and patterns of abundance in the upper zone of a rocky intertidal community provide examples of both types of indirect effects. By consuming limpets (Lottia digitalis), bird predators indirectly enhance acorn barnacle (Balanus glandula) abundance on horizontal rock benches because limpets dislodge or inadvertently consume young acorn barnacles, an example of an interaction chain. Because L. digitalis has a light-colored shell that is similar in color to barnacle shells, barnacles alter the bird-limpet interaction by changing the ability of birds to find limpets, an example of an interaction modification. Distin- guishing between interaction chains and interaction modifications is important because interac- tion chains can be predicted with only a knowledge of pairwise species interactions while de- scriptions of interaction modifications require a knowledge of all species combinations involved, precluding a priori prediction. By classifying empirically determined indirect effects, the degree to which indirect effects can be predicted from a knowledge of pairwise interactions can be determined, and the mechanisms that cause interaction modifications can be identified to aid in future prediction.

J. Timothy Wootton

Papers

Dynamic patterns and ecological impacts of declining ocean pH in a high-resolution multi-year dataset.

Predicting direct and indirect effects: an integrated approach using experiments and path analysis'

Measurement of interaction strength in nature

Effects of Disturbance on River Food Webs

Indirect effects and habitat use in an intertidal community: interaction chains and interaction modifications