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

1. What are Allee effects? 2. Mechanisms for Allee effects 3. Population dynamics: modelling demographic Allee effects 4. Genetics and evolution 5. Conservation and management 6. Conclusions and perspectives

Allee Effects in Ecology and Conservation

1997 marked the sesquicentenary of the publication by Carl Bergmann of the observation that, in general, large-bodied animal species tend to live further north than their small-bodied relatives. This has been dubbed Bergmann's rule in his honour. However, more than 150 years on, we appear to be little closer to a general understanding of the rule, or even to any consensus as to whether it exists. This is due in large part to confusion about the taxonomic level at which the rule is considered to operate, and to the conflation of pattern and mechanism. In this paper, we attempt to resolve this confusion by highlighting its sources, and by providing a definition of Bergmann's rule that is practical and useful, yet that retains the essential features of its original formulation. We conclude by briefly reviewing the mechanisms proposed to explain Bergmann's rule as we define it.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1472-4642.1999.00046.x

Geographic gradients in body size: a clarification of Bergmann's rule

Connectivity is a fundamental concept that is widely utilized in spatial ecology. The majority of connectivity measures used in the recent ecological literature only consider the nearest neighbor patch/population, or patches within a limited neighborhood of the focal patch (a buffer). Meta-analysis suggests that studies using nearest neighbor connectivity measures are much less likely to find statistically significant effects of connectivity than studies that use more complex measures. Here we compare simple connectivity measures in their ability to predict colonization events in two large and good-quality empirical data sets. The nearest neighbor distance to an occupied patch is found to be an inferior measure. Buffer measures do much better, but their performance is found to be sensitive to the estimate of the buffer radius. For highly fragmented habitats, the best and most consistent performance is found for a measure that takes into account the size of the focal patch and the sizes of and distances to all potential source populations. When experimenting with reduced data sets, it was discovered that nearest neighbor measures fail to find a statistically significant effect of connectivity for a large range of data set sizes for which the more complex measures still detect a highly significant effect. We conclude that the simplicity of a nearest neighbor measure is not an adequate compensation for poor performance.

https://www.jstor.org/stable/info/3071919

Simple connectivity measures in spatial ecology

Different components of global environmental change are often studied and managed independently, but mounting evidence points towards complex non-additive interaction effects between drivers of native species decline. Using the example of interactions between land-use change and biotic exchange, we develop an interpretive framework that will enable global change researchers to identify and discriminate between major interaction pathways. We formalise a distinction between numerically mediated versus functionally moderated causal pathways. Despite superficial similarity of their effects, numerical and functional pathways stem from fundamentally different mechanisms of action and have fundamentally different consequences for conservation management. Our framework is a first step toward building a better quantitative understanding of how interactions between drivers might mitigate or exacerbate the net effects of global environmental change on biotic communities in the future.

/pdf/interactive-effects-of-habitat-modification-and-species-5amkvixp4a.pdf

Interactive effects of habitat modification and species invasion on native species decline.

Host-pathogen models are essential for designing strategies for managing disease threats to humans, wild animals and domestic animals. The behaviour of these models is greatly affected by the way in which transmission between infected and susceptible hosts is modelled. Since host-pathogen models were first developed at the beginning of the 20th century, the 'mass action' assumption has almost always been used for transmission. Recently, however, it has been suggested that mass action has often been modelled wrongly. Alternative models of transmission are beginning to appear, as are empirical tests of transmission dynamics.

https://www.cell.com/trends/ecology-evolution/pdf/S0169-5347(01)02144-9.pdf

How should pathogen transmission be modelled

We explore models for the management of invertebrate pests by enhancing the efficacy or local abundance of existing natural enemies. Different aspects of natural enemy biology had different effects on prey density. Enhancement of enemy search rate or prey conversion efficiency showed the greatest potential for reducing prey density, while maximum consumption rate by predators, and parasitoid fecundity, had less effect. The effect on prey density of increased natural enemy longevity depended on its interaction with other parameters. The degree of manipulation needed to achieve a given reduction in prey populations was largely determined by the enemy's potential reproductive rate. Spatial ‘‘attraction’’ of enemies to a target site had an almost linear effect on local prey density. We conclude that successful conservation biological control benefits from a directed approach, targeting the most important aspects of natural enemy ecology, and that there is considerable potential for further research in this area.

The population consequences of natural enemy enhancement, and implications for conservation biological control

A simulation model for the spread of bovine tuberculosis within New Zealand cattle herds

Simple logistic models are used to investigate and compare the effects of continuous control by culling or sterilisation on population density. The models consider populations regulated by density-dependent mortality or density-dependent recruitment, with monogamous or polygamous mating systems, and with one or both sexes sterilised. For the first time, an analytical solution is presented for the effect of sterilisation on density-dependent population growth. The models suggest that the mating system has a considerable effect on the relative efficacy of sterilisation, and that previous models for sterilisation may have overestimated the impact of sterilisation by assuming idealised monogamous mating. In general, and except for populations with monogamous mating or 'harem' systems and both sexes sterilised, culling gives a more rapid reduction in density than does sterilisation. However, the long-term degree of suppression obtained with the same levels of control applied is likely to be similar. Populations with density-dependent mortality will be reduced by sterilisation more quickly than those regulated by density-dependent recruitment, and the effect on the steady-state density of a given proportion that is sterile is greater in the first case than in the second. However, the effect of a given continuous sterilisation rate (e.g. baiting effort) on density is the same in both cases. We compare our model results with those of others and question previous conclusions about the circumstances under which sterilisation is most effective.

/pdf/modelling-the-relative-efficacy-of-culling-and-sterilisation-2ahyzcscax.pdf

Modelling the relative efficacy of culling and sterilisation for controlling populations

1. A model of intermediate complexity is described to predict and understand the reasons for the ultimate impact of Sphecophaga vesparum vesparum (Hymenoptera : Ichneumonidae), introduced as a classical biological control agent of Vespula vulgaris (Hymenoptera : Vespidae) in New Zealand. The model was parameterized as far as possible from independent field data then fitted to the observed performance of the parasitoid over the first 5 years after release. 2. Wasp nest densities monitored over 5 years and seven sites in beech (Nothofagus spp.) forests averaged 12.2 ha -1 , with a maximum of 33 ha -1 . These are among the highest Vespula densities in the world. A Ricker model accounted for changes in nest density from year to year, giving a maximum ratio of increase in nest density of 3.3 per year and overcompensating density dependence at high densities, probably caused by queen competition and nest usurpation in spring. 3. The parasitoid has established at low levels in two sites, one of which has been studied in detail. Here parasitism levels (% autumn nests parasitized) have remained around 5% for 5 years, with a slight suggestion of an upward trend. 4. The model suggests that ultimate parasitism levels depend almost entirely on the parasitoid's effective ratio of increase, R, defined as the maximum number of spring adults produced per spring adult (spanning several intermediate summer generations). Ultimate suppression of wasp nest densities depends on R, the rate of increase in parasitism within a year, and the mortality of parasitized early spring nests. The initial rate of build-up of parasitism additionally depends on the pattern of emergence of parasitoid cocoons, which may extend over 4 years. 5. R for S. vesparum vesparum at the site where it has established appears to be about 1.3-1.6, which is close to the lower limit of 1 for persistence. Such values suggest an ultimate suppression of wasp nest density and level of parasitism of about 10% and 25%, respectively. 6. The low value of R at this site and the parasitoid's limited likely impact, appear to be due to a combination of delayed emergence of overwintering cocoons, low overwintering cocoon survival, and low production of cocoons per parasitized autumn nest. Additionally, a reduced or variable attack rate may contribute to the parasitoid's lack of establishment at other sites, possibly due to poor synchrony between spring emergence of wasp queens and adult parasitoids. 7. A more successful parasitoid species or ecotype would need to have a higher R value, which requires cocoon emergence after 1 year rather than 2 or more, and/or higher values for the above parameters, particularly overwintering survival of cocoons. In addition, it would have to : act after the spring host density dependence ; cause a high (> 80%) mortality of parasitized spring nests ; and ideally also reduce queen output from autumn nests. An alternative to an agent causing mortality to spring nests would be a microbial one which significantly reduced queen fertility without impairing her competitive ability. 8. A 50% reduction in queen output from autumn nests, due to parasitism by S. vesparum vesparum, contributes little to host suppression because of its timing relative to host density dependence. If an alternative agent reduced wasp densities to a greater extent, the additional contribution of reduced queen output would become relatively more significant as density declined and the density dependence became less intense.

N. D. Barlow

Papers

How should pathogen transmission be modelled

The population consequences of natural enemy enhancement, and implications for conservation biological control

A simulation model for the spread of bovine tuberculosis within New Zealand cattle herds

Modelling the relative efficacy of culling and sterilisation for controlling populations

A model for the effect of Sphecophaga vesparum vesparum as a biological control agent of the common wasp in New Zealand