William Murdoch

William Murdoch
University of California, Santa Barbara | UCSB · Department of Ecology, Evolution, and Marine Biology

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88
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Publications

Publications (88)
Article
Despite often violent fluctuations in nature, species extinction is rare. California red scale, a potentially devastating pest of citrus, has been suppressed for fifty years in California to extremely low yet stable densities by its controlling parasitoid. Some larch budmoth populations undergo extreme cycles; others never cycle. In Consumer-Resour...
Article
The rapid global loss of natural habitats and biodiversity, and limited resources, place a premium on maximizing the expected benefits of conservation actions. The scarcity of information on the fine-grained distribution of species of conservation concern, on risks of loss, and on costs of conservation actions, especially in developing countries, m...
Chapter
IntroductionBackground to global conservation priority schemesMethods in relation to goalsThresholds for identifying priority regionsScoring systems for identifying priority regionsGeneral issues relating to existing approachesReturn on investmentConclusions AcknowledgmentsReferences
Article
It is well known that the model equilibrium in the Nicholson-Bailey framework for parasitoid-host interactions can be stabilized if there is variation in the risk of parasitism among individual hosts. We show that the shape of the distribution of risk among hosts is crucial in determining stability. Stability for all values of the reproduction rate...
Article
We address the problem of relating information on the effects of a particular stress on individuals to possible effects at the population level. Structured population models aim to predict population dynamics from a careful specification of the dynamics of individuals; however, in spite of major mathematical advances, there are only a few cases whe...
Article
Full-text available
Guilhaumon et al. (1) use an extensive dataset to determine the most appropriate functional form for species–area relationships (SARs) among terrestrial plants and vertebrates. Their discovery that the traditional power-law relationship is not the most appropriate model in the majority of ecoregions raises compelling macroecological questions. Howe...
Article
1. Laboratory experiments and field studies were conducted to explain the coexistence of an endoparasitoid, Encarsia perniciosi Tower, and an ectoparasitoid, Aphytis melinus DeBach, both of which were introduced into California to control the California red scale, Aonidiella aurantii (Mask.). 2. Encarsia parasitized all scale stages but it preferre...
Article
In many consumer-resource systems the consumer population has synchronized reproduction at regular intervals (e.g., years) but consumes the resource and dies continuously, while the resource population grows continuously or has overlapping generations that are short relative to the time between consumer reproductive events. Such systems require "se...
Article
This paper explores the effect of spatial processes in a heterogeneous environment on the dynamics of a host-parasitoid interaction. The environment consists of a lattice of favourable (habitat) and hostile (matrix) hexagonal cells, whose spatial distribution is measured by habitat proportion and spatial autocorrelation (inverse of fragmentation)....
Article
Global conservation needs far exceed the available resources, so scarce resources must be used cost-effectively. Although many conservation priory-setting frameworks used by NGO’s or public agencies explicitly claim to emphasize efficiency or wise investment, none actually incorporates costs in a formal return-on-investment (ROI) framework. We illu...
Article
Full-text available
Conservation priority-setting schemes have not yet combined geographic priorities with a framework that can guide the allocation of funds among alternate conservation actions that address specific threats. We develop such a framework, and apply it to 17 of the world's 39 Mediterranean ecoregions. This framework offers an improvement over approaches...
Data
Characteristics of the 39 mediterranean ecoregions: total ecoregion area, projected habitat loss (%yr-1), area of natural and semi-natural habitat, area converted and area protected, cost (US$) per km-2, and information on plant species richness (6), vertebrate (‘Vert’) species richness and endemic richness (9). The number of threatened vertebrate...
Data
Derivation of the Parameter α (25 KB DOC)
Data
Data Obtained for Each Ecoregion to Apply Our Ecoaction-Specific Framework (234 KB DOC)
Chapter
Successful classical biological control in long-lived ecosystems occurs when an imported natural enemy keeps the density of the alien pest insect below the density at which it causes economic damage. It has been generally accepted for some 75 years that such enemies establish a low stable equilibrium pest density and maintain it by imposing density...
Article
A 20-year study of suppression of California red scale, a world-wide pest of citrus, by the parasitoid Aphytis melinus has established that the interaction is dynamically stable and that the mechanisms leading to control and stability operate at a local scale: spatial processes are not important. Key features appear to be an invulnerable class in t...
Article
Full-text available
We elucidate the mechanisms causing stability and severe resource suppression in a consumer-resource system. The consumer, the parasitoid Aphytis, rapidly controlled an experimentally induced outbreak of the resource, California red scale, an agricultural pest, and imposed a low, stable pest equilibrium. The results are well predicted by a mechanis...
Article
The forest insect pest Bupalus piniarius (pine looper moth) is a classic example of a natural population cycle. As is typical for populations that exhibit regular oscillations in density, there are several biological mechanisms that are hypothesized to be responsible for the cycles; but despite several decades of detailed study there has been no de...
Article
Full-text available
1. Most of what is known about parasitoid behaviour comes from laboratory observations: field quantitative observations on searching parasitoids are extremely difficult to do and are rare. The basic components of Aphytis melinus's response to California red scale (Aonidiella aurantii) were studied in the laboratory: encounter, rejection, drumming,...
Article
Dynamic energy budget models relate phenomena at many levels of eco- logical organization and can provide quantitative links from individual physiology to pop- ulation, community, and ecosystem dynamics. A prerequisite for making these links is an empirically tested model of growth and reproduction for individual organisms in a tem- porally variabl...
Article
Full-text available
Conservation hatcheries are unproven in restoring threatened and endangered populations of salmon to sustainable levels, and may cause more harm than good. Nonetheless, a recent court decision found that the National Marine Fisheries Service (NMFS) must include hatchery salmon in Endangered Species Act listings, where NMFS has included those fish a...
Article
Coexistence of resource specialists can be maintained through various spatial mechanisms, each potentially inducing different resource dynamics. We used observational data to suggest plausible spatial coexistence mechanisms for Aphytis melinus and Encarsia perniciosi, two parasitoids of California red scale. Aphytis consistently produced more proge...
Article
Although ecological theory exists to predict dynamics in communities with intraguild predation (IGP), few empirical tests have examined this theory. IGP theory, in particular, predicts that when two competitors interact via IGP, with increasing resource productivity: (1) the IG predator will increase in abundance as the IG prey declines, and (2) in...
Article
1. Visual surveys for small organisms on complex substrates often yield serious underestimates of true counts. When both visual counts (relative estimates of abundance) and absolute counts can be obtained from the same sample, however, the visual counts can be calibrated such that absolute estimates can be obtained in the future from visual surveys...
Article
The dynamical consequences of multiple-species interactions remain an elusive and fiercely debated topic. Recently, Murdoch and colleagues proposed a general rule for the dynamics of generalist natural enemies: when periodic, they exhibit single generation cycles (SGCs), similar to single species systems. This contrasts markedly with specialists, w...
Article
Population cycles have been remarkably resistant to explanation, in part because crucial experiments are rarely possible on appropriate spatial and temporal scales. Here we show how new approaches to nonlinear time-series analysis can distinguish between competing hypotheses for population cycles of larch budmoth in the Swiss Alps: delayed effects...
Chapter
Full-text available
The population dynamics of the larch budmoth (LBM), Zeiraphera diniana, in the Swiss Alps are perhaps the best example of periodic oscillations in ecology (figure 7.1). These oscillations are characterized by a remarkably regular periodicity, and by an enormous range of densities experienced during a typical cycle (about 100,000-fold difference bet...
Article
In a set of three new papers, Grenfell and collaborators lay bare measles dynamics in England and Wales over 50 years. They use a simple mechanistic model and current statistical techniques to analyse records of measles infections in every town and city, and show that measles dynamics, including the spatial spread of the disease, is astonishingly c...
Article
Full-text available
Most species live in species-rich food webs; yet, for a century, most mathematical models for population dynamics have included only one or two species. We ask whether such models are relevant to the real world. Two-species population models of an interacting consumer and resource collapse to one-species dynamics when recruitment to the resource po...
Article
Full-text available
A major problem in insect pest and weed management is uncertainty. Managers are faced with three main types of uncertainty: uncertainty about biological and environmental processes, and observational uncertainty. Active adaptive management (AAM) is management with a deliberate plan for learning about the managed system, so that management can be im...
Article
1. This paper develops and tests in the field a model that predicts the oviposition rate and the rate of egg maturation of a synovigenic parasitic wasp during a foraging period. The parasitoid is Aphytis melinus, the highly successful biological control agent of California redscale (Aondiniella aurantii), a pest of citrus worldwide. 2. Females were...
Article
Full-text available
Understanding spatial population dynamics is fundamental for many questions in ecology and conservation1-4. Many theoretical mechanisms have been proposed whereby spatial structure can promote population persistence, in particular for exploiter-victim systems (host-parasite/pathogen, predator-prey) whose interactions are inherently oscillatory and...
Article
This paper considers the relationship between the demographic mechanisms of population control and the energetics of the individuals who comprise the population. We examine the equilibrium properties of a class of structured population models in which individuals compete for some environmental resource (such as food) and demonstrate that population...
Article
Full-text available
We examine how spatial subdivision of predator-prey systems affects col- onization processes in metapopulations. Dynamics of the herbivorous spider mite Tetran- ychus urticae (prey) and the predatory mite Phytoseiulus persimilis are highly unstable on isolated bean plants (Phaseolus lunatus) and ultimately result in extinction of prey and predators...
Article
Full-text available
Ecological theory predicts that stable populations should yield to large-amplitude cycles in richer environments. This does not occur in nature. The zooplankton Daphnia and its algal prey in lakes throughout the world illustrate the problem. Experiments show that this system fits the theory's assumptions, yet it is not destabilized by enrichment. W...
Article
FULL TEXT FREELY AVAILABLE AT www.escholarship.org/uc/item/7sr3f7bk . . . Population cycles have long fascinated ecologists. Even in the most-studied populations, however, scientists continue to dispute the relative importance of various potential causes of the cycles. Over the past three decades, theoretical ecologists have cataloged a large numbe...
Article
Full-text available
 Continuous-time, age structured, host–parasitoid models exhibit three types of cyclic dynamics: Lotka–Volterra-like consumer-resource cycles, discrete generation cycles, and “delayed feedback cycles” that occur if the gain to the parasitoid population (defined by the number of new female parasitoid offspring produced per host attacked) increases w...
Article
1. Dynamic energy budget (DEB) models describing the allocation of assimilate to the competing processes of growth, reproduction and maintenance in individual organisms have been applied to a variety of species with some success. There are two contrasting model formulations based on dynamic allocation rules that have been widely used (net productio...
Chapter
For decades, biological control of insect pests has been a rich source of concepts and theory for population ecology. Researchers interested in biological control introduced both the basic idea of density dependence (Howard and Fiske, 1911) and early parasitoid-host models (Nicholson and Bailey, 1935). Even metapopulation theory had its origins as...
Article
Full-text available
We present an overview of a long-term research programme that is aimed at revealing the relations between individual feeding, growth, reproduction and mortality in Daphnia pulex and the state and dynamics of the population. We analyse a physiologically structured population model, in which individual performance is described using an energy budget...
Chapter
This chapter uses simple models to clarify the issues involved in determination of the impacts of human activities on populations of marine fish. It reviews issues, such as, can any of the various compensation mechanisms that may exist in marine fish prevent additional immature losses from causing a reduction in the average abundance of adult fish;...
Article
California red scale, an insect that is a worldwide pest of citrus, is controlled in many areas by parasitoids of the genus Aphytis. In southern California, Aphytis lingnanensis provided inadequate control of red scale in inland valleys. Aphytis melinus was introduced, competitively displaced A. lingnanensis within a few red scare generations, and...
Article
1. We investigate the potential effects of parasitoid egg limitation on host-parasitoid population dynamics. We define a parasitoid as egg-limited if a shortage of eggs means that at some time she cannot utilize an opportunity to oviposit. 2. We develop models which consider the differing physiologies of pro-ovigenic and synovigenic parasitoids to...
Article
Full-text available
In this paper, we investigate whether a stage-structured population model can explain major features of dynamics of the herbivores Daphnia galeata and Bosmina longirostris reared under controlled laboratory conditions. Model parameters are determined from independent individual-based information gleaned from the literature on feeding, growth, repro...
Article
Review recent developments in the theory and argue that they are likely to be of more use in the selection of biocontrol agents then has been the case in the past.
Article
Full-text available
Red scale, an insect pest of citrus, is under control by the parasitoid Aphytis melinus in many areas, and in our study area the interaction appears dynamically stable. The bark on the interior branches and trunk of trees provides a partial refuge for red scale, which are rarely attacked there by the parasitoid. In a grapefruit grove, we carried ou...
Article
Considers the use of unstructured, biomass-based 'box' models. Although models of this type are generally considered unverifiable, the authors discuss the case of a fjordic ecosystem model where the nature of the system, and a large body of data, allowed a rigorous cycle of model falsification and improvement. To assess the information requirements...
Article
Full-text available
A common measure of the temporal variability of a population is the standard deviation of the logarithms of successive estimated population sizes, In(D-t). This measure overestimates true temporal variability (the standard deviation of the logarithms of true population density, In[Delta(t)]) because it is contaminated by spatial variance (variabili...
Article
1. Synovigenic parasitoids emerge as adults with fewer mature eggs than they can ultimately lay. They need to feed on host fluid or tissue to gain protein in order to mature additional eggs. The decision to host-feed or parasitize an encountered host depends in part on the current number of mature eggs that the parasitoid is carrying (its egg load)...
Article
California red scale is suppressed to very low densities by the parasitoid Aphytis melinus. The system also appears stable. We report on an experimental test of the hypothesis that stability is caused by a refuge for scale. In a grapefruit grove in southern California in 1984-1985, the bark in the interior part of the tree provided a partial refuge...
Article
1. We make and test predictions about how the number of eggs a female parasitoid is carrying (her `egg load') influences her propensity for `host-feeding', the consumption of host body fluids. 2. We first develop a simple dynamic state variable model that predicts that parasitoids should host-feed only when completely empty of eggs. This result ref...
Article
Goes through models of hypothetical situations to point out that yu can have a regulated popuylation at an equilibrium and feedback even without having stabilizing regulation a particular feedback dynamic. Can also have locally unstabilized populations that are stilized depending onthe immigration mechanisms. Litle can be inferred from time series;...
Article
Several special cases of a general model in which two parasitoid species attack different developmental stages of a single host species are presented. The inclusion of different mathematical forms of a maturation weighting function allows us to investigate the effect of several aspects of variation in immature stage durations on the outcome of comp...
Chapter
The concept of metapopulation is widely used by modelers exploring the effects of spatial heterogeneity on population dynamics. Yet prima facie, it is a remarkably restrictive idealization implying that a population is distributed over a number of patches, each sufficiently well defined to permit local definition of vital rates, with migration betw...
Article
We analyze a metapopulation model of the interactions between Lotka-Volterra-type prey and predators that occur in two environmentally distinguishable patches and are linked by migration. Environmental differences between the patches tend to stabilize the otherwise neutrally stable model by causing the per capita immigration rate on a patch to be t...
Article
Some previously published single-species models of spatial density dependence are stable because they contain explicit temporal, as well as spatial, density dependence. Because of this, the models are stable even without spatial heterogeneity. To obtain spatial density dependence without temporal density dependence, the authors derive a model diffe...
Article
Proposes and tests a new hypothesis based on the idea that allometric relationships for physiological rates are stage dependent. Ingestion rates increase much faster with juvenile body size than with adult body size for several Daphnia species. Allometric relationships for respiration are not stage dependent. A maintenance function takes into accou...
Article
In the preceding paper (McCauley et al. 1990) we developed a new model for the growth and fecundity of Daphnia based on a quantitative review of short-term physiological rates and energy allocation for D. pulex. In this paper, we formulate a fully dynamic version of this model and test its predictions against experimentally observed growth and fecu...
Article
STABLE predator–prey models with a tension between the stabilizing effect of prey density-dependence and the destabilizing effect of predators generally become unstable when the nutrient environment of the prey is enriched1–3. This 'paradox of enrichment' occurs in a wide range of models incorporating realistic features4–6. Enriched models quickly...
Chapter
Good review of basic models applied to biological control. Suggests that stability may not be a good criterion for successful biolcontrol - suggests host suppression and low variability as better criteria.
Article
Red scale populations in eight grapefruit trees in a grove in southern California were sampled over 18 mo. We established that the interior of the trees was an area of partial refugee from parasitism by the major control agent, the parasitoid Aphytis melinus, and also by Encarsia, which was the second major parasitoid in the system. The refuge (int...
Article
Predators and insect parasites (parasitoids) sometimes aggregate in patches containing high prey (host) densities because they search longer there, causing higher death (parasitism) rates in patches with more prey (hosts). This behavior can stabilize the otherwise unstable, discrete-time, Nicholson-Bailey model, typically at the cost of increasing...
Article
Tested the ability of simple predator-prey models to predict how average densities change along a gradient of nutrient enrichment. Total algal carrying capacity increases from nutrient-poor to nutrient-rich lakes. This is true also for edible algae alone. Realized per capita growth rate of edible algae increases with trophy (trend 1). A synthesis o...
Article
The hypothesis is that the presence or absence of cycles is determined by the relationships between time delays in Daphnia and other rates in the interacting populations. There is, however, no obvious environmental factor affecting these rates and delays, thereby determining which dynamic class a particular system fits at a particular time. It does...
Article
Full-text available
There may be problems concerning the appropriate design of sampling programs to assess the impact upon the abundance of biological populations of, for example, the discharge of effluents into an aquatic ecosystem at a single point. Key to the resolution of these issues is correct identification of the statistical parameter of interest, which is the...
Article
Models in which parasitoid density in a patch is strictly a function of host density in the patch, with no 'error' about this function, are pure-regression models. Those in which there is random variation in the number of parasitoids per patch, with no relationship between local parasitoid density and local host density, are pure-error models. The...
Article
A wide range of dynamic behaviour has been uncovered by studying disparate predator-prey systems1, ranging over population stability, cycles and non-cyclic fluctuations. We know of no instance, however, in which qualitatively different dynamics have been found in the same natural predator-prey populations at different times, or in a given predator-...
Article
Full-text available
A stable pest equilibrium is neither a necessary nor a sufficient condition for control: satisfactory control in model systems is compatible with both local extinction of the pest and polyphagy in the natural enemy. Only one of 9 real examples of successful control is convincingly a stable interaction; the remainder show either strong evidence for...
Article
A general predator is assumed to divide its hunting time between two sub-habitats with different prey species, spending a larger fraction (φ) of search time in an area as the relative prey abundance there increases. This always causes switching in the model, and changes a functional response from one that imposes a risk on the average prey that dec...
Article
We report new analyses to test competing models of the Daphnia/algal interaction. Our model is good at predicting equilibrium algal densities, and if our new insights can account for stability in this system across a wide range of natural environments, this may contribute to understanding predator-prey dynamics in general.
Article
Traducción de: The poverty of nations Incluye bibliografía Se analiza y evalúa las investigaciones modernas en demografía, economía del desarrollo y economía agrícola, con el objeto de identificar los mecanismos de base que fomentan y constriñen la producción agrícola en el Tercer Mundo. A partir de ello, propone una reforma social, económica y pol...

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