12. Historical Origin of Population Ecology

Abstract

This chapter traces the historical development of population ecology from its conceptual foundations in the mid-19th century through the emergence of quantitative modeling approaches in the early 20th century that established it as the discipline of population ecology. It examines the influential ideas of early thinkers like Darwin, Spencer and Forbes and how the works of Clements, Adams, Lotka, and Volterra formalized theoretical understandings into foundational mathematical expressions of population growth, competition, and predator-prey relations. By outlining the progression and integration of ideas between these pioneering scientists across disciplines, the chapter delineates how population ecology emerged as a rigorous field centered on predictive modeling of demographic processes and the biotic and abiotic factors that influence population change over successive generations.

Introduction¶

The discipline known today as mathematical biology is the confluence on many traditions and research fields. One of them is population ecology, which aims to understand the dynamics of biological populations and the factors that cause fluctuations in population size over time. This includes seeking to explain how intrinsic growth rates interact with environmental constraints like resource availability, competition, and predation. While these questions have intrigued biologists and natural philosophers for centuries, it was not until the late 19th century that population ecology truly emerged as a distinct discipline within ecology.

This chapter traces the historical origin and development of population ecology as a quantitative, mathematical field of study. It explores the influential early thinkers who established the conceptual foundations, from Darwin and Spencer’s formative works on competition and population regulation, to Forbes pioneering quantitative field studies. The chapter then focuses on the key figures around the early 20th century who significantly advanced population ecology through new theoretical and modeling approaches---Clements, Adams, Lotka, and Volterra. Their innovative works helped define population ecology not just as a field of qualitative explanations, but as a discipline incorporating quantitative modeling of factors driving demographic change in populations.

By examining these pioneering scientists and how their ideas intertwined and built upon one another, this chapter aims to outline the lineage of thought that ultimately established population ecology as a the investigative framework still used today. The objective is to recognize population ecology’s intellectual roots and appreciate how incremental progress occurs in science through the efforts of diverse thinkers synthesizing different perspectives over generations. In crafting this overview of key topics and milestones, the chapter drew upon insights from the publication by Mira (1997). For readers seeking deeper exploration of population conceptual underpinnings and progressive development, the referenced work offers more encompassing examination of these subjects.

Early Foundations of Population Ecology¶

The foundations of population ecology emerged in the mid-19th century, paralleling the rise of ecology more broadly. Charles Darwin and Alfred Russel Wallace made enormous contributions through their formulation of the theory of evolution by natural selection. In On the Origin of Species (1859), Darwin established competition between individuals for limited resources as a key mechanism driving evolutionary change. He recognized populations as growing exponentially until constrained by environmental carrying capacities.

Herbert Spencer built on these ideas in Principles of Biology (1864) with one of the first conceptual frameworks of population regulation. He theorized that populations achieve stable size through a balance of “nurturent” forces like reproduction and “accidental” forces like mortality. This introduced the principles of opposing demographic factors achieving dynamic equilibrium. Spencer envisioned ecology as encompassing networks of interdependencies rather than just adaptation.

Around the same time, the German biologist Ernst Haeckel coined the term “ecology” and defined it as the study of organism-environment interactions. He highlighted interdependence between organisms and their environments, foreshadowing systems-thinking in ecology. Haeckel developed one of the first energy flow frameworks, seeing communities as integrated systems maintained through negative feedback loops.

Stephen Alfred Forbes conducted extensive field work on Illinois lakes in the late 1800s. His meticulous surveys provided empirical evidence supporting early theories, demonstrating density fluctuations between predator and prey populations over time. Forbes was also the first to propose that populations self-regulate through birth and death responses to environmental variables like resource availability. His work helped establish population ecology as an empirical, quantitative science.

Formative Years of the Discipline¶

Frederic Clements, a botanist, studied plant succession and published an influential book called Plant Succession in 1916. He developed the analogy that plant communities mature through predictable stages of development akin to an organism. Clements stressed the community as a holistic superorganism shaped over time by interspecific cooperation as well as competition for resources.

While criticized for underestimating stochastic events, Clements’ organismic perspective shaped early theoretical ecology. He recognized that populations do not fluctuate independently but are interconnected, with species influencing community trajectories through direct and indirect effects on one another. Clements also highlighted the importance of long-term ecological processes like facilitation and inhibition in driving dynamic changes to communities.

Joseph Adams’ background in physical chemistry strongly influenced his development of quantitative population models. Concepts from statistical mechanics and chemical kinetics inspired Adams to mathematically relate observed macro-level population patterns to underlying micro-level reproductive and mortality processes.

Models from physical chemistry describing how reaction rates change over time also motivated Adams to capture variation in demographic rates based on density dependence and environmental conditions. Additionally, viewing chemical systems as dynamic and open, rather than closed and static, aligned with Adams’ thinking of populations as regulated through inputs and outputs over generations.

Adams was also influenced by emerging ideas in the field of geology during his career. Geologists were developing theories of dynamic equilibrium in integrated Earth systems achieved through compensatory positive and negative feedbacks acting over long timescales. These likely informed Adams’ consideration of population regulation around equilibrium levels.

Through such interdisciplinary lenses, Adams published highly influential works in the 1920s and 30s that established conceptual and methodological foundations for modern demographic analyses. His formulation of exponential and logistic population growth models represented pioneering efforts to quantitatively model intra-specific regulating factors theoretically posited by past scholars.

Adams’ approach helped shift population ecology towards a more predictive science based on mathematical descriptions of population behavior over time. His integration of both empirical field data and theoretical modeling lenses established population ecology as a distinct quantitative discipline within ecology.

Lotka’s Interdisciplinary Approach and Influence from Adams¶

Like Adams, Alfred Lotka’s diverse educational and professional background proved formative for his groundbreaking theoretical population ecology work. Lotka studied chemistry and worked as both a chemist and actuary, applying mathematical techniques to insurance calculations.

This quantitative training was evident in Lotka’s 1925 paper, where he published differential equations modeling predator-prey populations over time. Lotka was directly influenced by Adams’ prior logistic modeling concept, which he built upon by including additional interspecific interactions such as predation. Lotka’s 1925 work demonstrated how physical chemistry principles could be applied to biological systems. Inspired by concepts of energy flows and dissipation from his chemistry background, Lotka framed evolution as optimizing energy pathways through ecological networks.

This interdisciplinary energy perspective proved highly influential and represents an early application of systems thinking to theoretical ecology. By synthesizing demographic and interspecific modelling approaches, Lotka established theoretical population ecology’s focus on quantifying factors driving changes in population size and composition over generations.

Lotka-Volterra Equations¶

Lotka’s 1925 differential equation model of predator-prey population change became highly influential and established the foundation for modern population ecology. However, Lotka was not the only pioneering thinker formulating such models at this time.

The Italian mathematician Vito Volterra independently developed near-identical nonlinear equations describing oscillating predator and prey densities in 1926. Published in Italian, Volterra’s work went initially unnoticed by the international science community.

However, subsequent discussions between Lotka and Volterra revealed their remarkable convergence in conceiving mathematical population models. Their collaborative connection helped define what are now universally known as the Lotka-Volterra equations.

Volterra brought his advanced mathematical expertise, allowing for the first rigorous analysis of conditions defining stable limit cycles predicted by the prey-predator framework. His contributions helped establish theoretical population ecology on a firm theoretical footing through analytical validation of early modeling approaches.

Their seminal collaboration highlights how great scientific progress emerges through the intersecting ideas of diverse thinkers globally exploring challenges through their own insightful lenses.

Discussion¶

This chapter has outlined the major developments that established population ecology as a theoretical, quantitative field of study. It traced ideas from early conceptual works of Darwin, Spencer and Forbes through to modelers like Adams, Lotka and Volterra who incorporated mathematics.

Their contributions defined population ecology not just as natural history observation, but as a predictive discipline seeking to understand population behaviors and interdependencies through quantitative models of birth, death and interaction over successive generations.

While individual pioneers built upon each other, their synergistic efforts collectively transformed population ecology into a rigorous mathematical science. Concepts like intra-specific constraints, inter-trophic level connections, and achieving dynamic equilibrium through opposing factors endure as foundational principles.

Later 20th century population modelers drew upon this lineage, extending formulations to incorporate more complex influences like age structure, nonlinear feedbacks and stochasticity. Their works have found diverse interdisciplinary applications from economics to epidemiology.

The intellectual lineage outlined highlights both incremental progress through extended works, as well as how convergence of independent yet complementary views can drive paradigm shifts. It recognizes population ecology’s multifaceted roots and distributed nature of scientific thinking that together establish robust new fields.