Quantitative Viral Ecology: Dynamics of Viruses and Their Microbial Hosts

Quantitative Viral Ecology: Dynamics of Viruses and Their Microbial Hosts takes on a topic of vast scientific and societal importance. Consider, for example, the ocean’s surface, where microbes constitute most of the biomass. Viruses control the microbe population through infection and release organic carbon and other nutrients back into the environment. That has big effects on ecosystem function, since without the turnover of biomass, many sources of food would not be available to other organisms.

The same scenario plays out in many locations. Indeed, microbes, and consequently microbial viruses, inhabit essentially every natural niche on Earth, including waters, soils, sediments, higher organisms, and air. They also live in artificial environments such as homes, waste reactors, and city streets.

The book’s topic is not something a traditional physicist would study. However, physical ways of thinking permeate every chapter. Author Joshua Weitz, whose research is in ecology but who holds a PhD in physics, takes a theoretical, model-building viewpoint as the key to interpreting classic and state-of-the art experiments. Modeling is a central and defining feature of physics, and oftentimes simple models—of springs, beads, liquid droplets, and so forth—are immensely useful for conceptualizing problems and identifying main drivers of observed behavior.

The book is aimed at a scientifically educated audience ranging from students to researchers. Each chapter ends with a concise, point-by-point summary that I found useful for quick reference. The chapters contain tutorials on important modeling tools such as mean-field theories, dimensional analysis, and qualitative analysis of dynamical systems. There are also simple explanations of sophisticated tools, including agent-based models and complex networks. I personally loved the book’s spherical-cow attitude—though I should talk about “spherical viruses” in this case—and I use this approach in my daily working routine.

The tone is relaxed and matter-of-fact, and Weitz avoids promoting specific visions, paradigms, or interpretations. Rather, he gives a precise account of the state of debates in the literature and explicitly addresses both the limitations and the potential of current approaches. Chapter 2, one of my favorites, contains dimensional analysis of the key parameters—“life history traits” in ecological terms—that affect viral dynamics. It contains some extraordinarily clear demonstrations of the powerful insight dimensional reasoning can provide. Chapter 6 is also intriguing; it gives a global perspective on ocean viruses’ abundance and diversity and discusses virus– microbe infection networks. Viral diversity and sheer number are incredible and probably still incompletely understood.

Chapters 3–5 use ordinary differential equation models to describe population dynamics and the evolution of viruses and their microbial hosts. Chapter 7 addresses the wide-open and complex problem of the coexistence of many viral and microbial species in the ocean, where predators such as zooplankton are also present. The last chapter offers a more speculative overview of open problems and should be valuable for any reader.

My favorite quote from the book is, “A healthy scientific field requires a balance of theory and empiricism,” and I can definitively say that the text practices what its author preaches. Although the emphasis is on theory, both classic and state-of-the-art experiments are discussed and compared with predictions—and at times theory and experiment obviously disagree. Readers with an experimental background can obtain ideas for new experiments and specific questions to test.

The book will be especially exciting for theorists with an applied math, engineering, or physics background. According to Weitz, quantitative viral ecology is an area in which new, “big” data are becoming available. But, as many probably know, a big pile of messy data does not necessarily mean more knowledge. New theoretical tools will be needed, together with new theoreticians to design them. Quantitative Viral Ecology offered me a great opportunity to discover a new area, and I cannot exclude the possibility that I will be among those exploring it.