The issue of species persistence may be a central theme in population ecology, but it is also crucial to infectious disease control. While ecologists aim at preserving biodiversity, disease eradication seeks to drive selected pathogens to global extinction; understanding the mechanisms explaining species persistence at local and regional levels underpins both goals.
In Consumer-Resource Dynamics, Murdoch, Briggs & Nisbet attempt to provide a unifying theory of population dynamics which, starting from the most fundamental of interactions, the consumer-resource duo in a homogeneous environment, expands into multispecies interactions, collapses into single population dynamics, or ventures into unpredictability and spatial heterogeneity. The fact that disease-host systems are hardly mentioned does not detract from the relevance this book can have to parasite population biologists, field parasitologists, and those interested in pathogen and pest control. The following synopsis highlights some salient points.
Chapters 1 and 2 provide conceptual and empirical contexts for the notion of population dynamics, focusing on population regulation and persistence, and discussing the concepts of deterministic and stochastic persistence and the importance of scale. Chapters 3 and 4, on simple predator-prey models, explore the reasons behind these being inherently unstable interactions, which nonetheless embody the various manifestations of population regulation. In particular, Chapter 3 discusses Lotka-Volterra (continuous time) models, whilst Chapter 4 deals with Nicholson-Bailey (discrete time) models, and introduces discrete generation parasitoid-host systems. Chapters 5 to 7 incorporate successive layers of biological realism into the latter, with Chapter 5 introducing stage-structure, Chapter 6 exploring the dynamical effects of various parasitoid life-history strategies, and Chapter 7 bringing aspects of behavioural and evolutionary ecology in focus with population dynamics theory. Chapter 8 is dedicated to competition and multispecies interactions, leading to Chapter 9 on biological control, which ends with a discussion on the need for a resurgence of past interest in placing such control in an appropriate and rigorous ecological framework (the same can be said about disease control programmes). Chapter 10 concentrates on the dynamical consequences of making space explicit, with an insightful discussion on the origins of instability and persistence in single-species vs consumer-resource metapopulations. Chapter 11 develops a ‘phylogeny’ of models by presenting the common origin of frameworks for the description and analysis of predator-prey, parasitoid-host, pathogen-host, and herbivore-plant interactions. It is also argued that few-species models may be appropriate to describe the dynamics of populations living in many-species food-webs (by virtue of decoupling the consumer-resource interaction). The striving for a unifying and coherent population dynamics theory, present throughout the book, culminates in Chapter 12's hierarchy of models, which draws together preceding insights and points towards future theoretical and empirical research directions.
Although not presupposing a mathematical biology background, some familiarity on the part of the reader with simple population ecology models may provide a useful backdrop. The uninitiated will find the various appendices on stability analyses most helpful. The book is very well written, with interspersed tables and boxes that list the various models and their stability properties, and concluding remarks at the end of each chapter that summarize main messages and lead naturally into following chapters. On a more personal note, I found this book profoundly stimulating and found myself often discussing the various insights gained through its reading with my students and colleagues. I particularly enjoyed the sections about age- and/or stage-structured models and the advantages and pitfalls of the (often implicit) assumption of exponentially distributed waiting times. The dynamical differences between constant maturation rates and fixed maturation times are relevant to the problem of incorporating latency in parasite-host models. Ratio-dependency in models, where consumer attack rate depends on the ratio of consumers to prey, is akin to the formulation of the vector to host ratio times the biting rate in (dipteran) vector-borne disease models, most of which do not link vector abundance and biting rates to host abundance. Incorporation of overdispersion in parasitoid-host systems is effected through the widely used negative binomial distribution (May-Hassell models), with the degree of overdispersion mainly independent of host or parasitoid density. The development of stochastic models in which the distributional properties of parasitoid or parasite populations emerge from model results clearly remains a research priority. The question as to whether few-species models can appropriately describe the dynamics of many-species systems is also relevant to the topical theme of multiparasitism and the detection and importance of interspecific interactions in shaping parasite communities. If these interactions were less important than intraspecific effects in determining transmission dynamics, the traditional approach to single-species parasite-host models would be adequate. Finally, the results of the Jansen-de Roos spatial versions of the Rosenzweig-MacArthur model (with logistic growth prey and saturating predator attack rate), in which restricted movement leads to substantial decreases in local and global fluctuations, may have important implications for understanding arthropod-borne disease dynamics, as some vectors have limited mobility (ticks, mites), whilst others may connect to a greater extent pathogen-host subpopulations.