FormalPara Key Concepts and Questions: This Chapter Explains

  • The critical role of an ecological understanding in achieving the sustainable use of the biosphere.

  • What we understand by the term ecology, its interdisciplinary scope and the need for an African perspective.

  • Why spatial and temporal scales and the integration of successive levels of biological organisation need to be studied.

  • The importance of understanding the processes of evolution and adaptation in shaping the composition of communities.

  • Why the ecological whole is greater than the sum of its parts.

  • The basis of research—the scientific method—and its application in ecological studies.

  • The structure of this book in phased steps of a learning process.

  • How to use this book in developing knowledge, understanding and a career in ecology.

Context: Why Ecology? Human–Environment Interactions

This book has a pragmatic purpose. It has been written for Angolan students, young and old, to help them to get to know, understand and value the amazing natural life and landscapes of the country. This book aims to introduce the student to the science and practice of ecology by describing examples of key features and concepts which relate to Angola’s terrestrial ecosystems, their structure and functioning. The focus is on providing an enduring understanding of what is special about Angolan ecosystems, in succinct chapters illustrated with easily accessible examples.

Why is an understanding of ecology critical to Angola’s sustainable development? The answer is easy to predict if one recognises that Angola’s human population has increased from 6.5 million at independence in 1975, to 32.8 million in 2022. At its current rate of growth, the population will surpass 50 million by 2035. At Independence, over 80% of the human population comprised rural communities of subsistence farmers, but today 67% of the population lives in cities and towns and only 33% in rural areas. These dramatic demographic changes have had significant and often negative impacts on the natural environment. In urban situations, pollution through injudicious solid waste disposal and erosion through poor storm-water management, are serious problems. In rural areas, the loss of forest and woodland cover (to provide charcoal as the primary domestic energy resource for urban families), extinction of mammal populations (through the bushmeat trade), accelerating soil erosion (through mining operations and unsustainable farming practices) and the transformation of plant communities due to clearance for agriculture or repeated, extensive and uncontrolled bush fires, plus the impacts of invasive plants, accounts for severe loss of the productive potential of landscapes. To these impacts must be added that of global dynamics, most especially the impacts of climate changes. These human–environment interactions are described in a series of Boxes at the end of chapters, demonstrating why an ecological understanding of the structure, functioning and vulnerabilities of the country’s ecosystems is so critical to achieving the sustained wellbeing of Angola’s people.

1 The Science and Practice of Ecology

An ecologist is a person imbued with an insatiable curiosity about the workings of all living things. The great nineteenth-century European explorer-naturalists—Alexander von Humboldt (1769–1859), Charles Darwin (1809–1882) and Alfred Russel Wallace (1823–1913)—were passionate seekers of knowledge, but specifically of explanations as to why certain species were found only in specific regions of the globe and not in others. They were the pioneers of ecology. The term ‘ecology’ was first described as the study of ‘the economy of nature’ (Haeckel, 1866) and ecology is today defined as ‘the scientific study of the distribution and abundance of organisms and the interactions that determine their distribution and abundance’.

An Interdisciplinary Science

In the two centuries of its gestation and development, ecology has become a multi- and interdisciplinary science, being undertaken by researchers in fields as diverse as the biochemical reactions within nitrogen-fixing bacteria—to the feeding habits of elephant—to the influence of the Earth’s tilted axis on the passage of seasons. Both curiosity-driven and applied interests stimulate ecological studies. The workings of insect pollinators in the fertilization of tropical orchids are as fascinating to one ecologist as the resilience of socio-economic systems to the impacts of global climate change is to another.

Ecology has its early nineteenth century roots in the tropics—through the revolutionary thinking of Humboldt, Darwin and Wallace. The theory of evolution through natural selection is a cornerstone of ecology. Humboldt sought explanations for the distribution of vegetation formations across altitude and climate. Darwin sought understanding by studying smaller and smaller pieces of life’s puzzle in a world driven by competition and selection at the species level. Wallace explored life at a planetary scale, in which the world is a web of interdependencies (Flannery, 2010).

Presenting an African Perspective

These broad perspectives were evolved further into specific ecological concepts in the northern temperate latitudes by Andreas Schimper (1856–1901), Arthur Tansley (1871–1955) and Frederick Clements (1874–1945) and others in the early twentieth century. From the 1950s, the science accelerated rapidly in North America and Europe, from where the great majority of concepts and examples quoted in standard textbooks on ecology are drawn. Some concepts developed in temperate latitudes are of limited relevance to tropical African ecosystems, so this volume presents a deliberately African perspective. In recent decades there has been a blossoming of ecological research in South and Central America, Australasia and southern Africa. In Angola, important contributions were made by the pioneers of Angolan biodiversity research—Welwitsch (Swinscow, 1972), Anchieta (Andrade, 1985), Gossweiler (Gossweiler & Mendonça, 1939), Jessen (1936), Barbosa (1970), Monteiro (1970) and Machado (1995). Today there is increasing investment in ecological research across Africa, as scientists and governments recognise the important relationship between biodiversity, environmental health and socio-economic development and sustainability.

Scales in Space and Times

Ecology is an integrative science, working at multiple spatial and temporal scales, from the individual organism to the biosphere. At the level of the individual plant or animal, ecologists examine how features of morphology, physiology and behaviour determine an individual’s ability to survive, grow and reproduce. Successive levels of organization—individual, population, community, ecosystem, landscape, ecoregion, biome, biosphere—all work at different spatial and temporal scales, but are closely linked through positive and negative interactions that determine their dynamics.

An Evolutionary Base

Because ecology is fundamentally about the consequences of natural selection in the evolution of adaptations to the environment, which are based on the differential transfer of genetic material from one generation to the next, the basic unit of ecology is often regarded as the individual. This follows the thinking of Russian/American geneticist Theodosius Dobzhansky (1900–1975) who stated: “Nothing in biology makes sense, except in the light of evolution.” (Dobzhansky, 1973). Townsend et al. (2008), in their comprehensive textbook on ecology, added the cautionary note: “But equally, very little in evolution makes sense except in the light of ecology: ecology provides the stage direction through which the ‘evolutionary play’ is performed. Ecologists and evolutionary biologists need a thorough understanding of each other’s disciplines to make sense of key patterns and processes.” A further interesting perspective on ecology is that of tropical forest ecologist Whitmore (1998): “Ecology as a science is always seeking for generalizations to make sense of the bewildering diversity of Nature.”

Individual and Emergent Properties

Many field and laboratory studies focus at the species level—how a single species interacts with the environment, known as autecology. The study of how species interact with each other at the ecosystem level and higher levels of integration—populations or communities—is referred to as synecology—which will be the focus of attention in this book. Each successive level of the hierarchy places different demands on the research approach—scales of both time and space are fundamental considerations when planning ecological research. An important concept in ecology is that of the emergent properties that can be observed, measured and predicted, operating at different spatial and temporal scales. Emergent properties are usually defined as an output, resulting from an interacting set of variables that have a property, not of the individual, but that emerges from the collective interactions of many different individuals within the system. The concept of the whole being greater than the sum of the parts is at play. Examples include the microclimate created by a community of shady forest trees, the development of fuel loads of combustible material by grasses in savanna ecosystems, or the influence on soil physics and chemistry and plant and animal communities by the activities of termite colonies. In short, an emergent property is a property which a complex system has as the outcome of multiple interactions, but a property which the individual members do not have.

Functional Processes

Recognising the importance of scale is a fundamental requirement in developing an ecological understanding. Within an ecosystem (the living and non-living components of a functioning ecological system) specific ecosystem processes such as photosynthesis, energy flows, water and nutrient cycling, growth, reproduction, survival, adaptation and evolution—are operating at timescales from seconds to millions of years. All ecosystems are ultimately interlinked through their interactions—such as the exchange of materials and energy—across the scales of biosphere, atmosphere, hydrosphere and geosphere. To understand these multiple scales and intimate linkages, terrestrial ecologists have to collaborate with specialists in the earth, ocean and atmospheric sciences, and from the social sciences and economics.

Earth and Biodiversity Sciences

The world of ecological research thus ranges from ‘biodiversity science’, at the level of individuals and populations where competition is emphasised, to the scale of the whole planet, ‘earth system science’, where the web of interdependencies is the focus. While many studies relate to reasonably static features—such as the patterns and composition of soils and vegetation—other factors are constantly changing, such as photosynthetic rates, patterns of grazing and browsing, fire frequency and intensity, and predator–prey relationships. Eco-physiological studies might be conducted in laboratories with hourly or daily iterations and timeframes, while ecosystem-level phenomena such as the impacts of fire regimes on ecosystem structure need long-term field studies running for many decades. Both laboratory and field experiments are needed in the search for the mechanisms—the causation—of observed patterns.

Stability and Heterogeneity

The importance of scale is also linked to pattern and patchiness in communities and ecosystems, and to the role of heterogeneity, the ultimate source of biodiversity richness and of ecosystem resilience. Spatial patchiness (heterogeneity) at different scales enables a system to absorb sudden disturbances. Concepts of scale, patchiness, heterogeneity, redundancy and resilence are fundamental to understanding and effectively managing ecosystems, as demonstrated in the century of research on complex systems such as the Kruger National Park, South Africa, the long-term studies of Serengeti, Tanzania and the 40-year savanna research programme at Lamto, Ivory Coast.

The Scientific Method

Underpinning ecological research is the scientific method. From Humboldt’s time, this has meant careful and repeated observation and measurement, the definition of questions, the gathering of evidence, the formulation of hypotheses that seek to provide answers to questions and predict the outcomes of phenomena, and thereafter the repeated testing of such hypotheses. When successive attempts to disprove a hypothesis fail, it might become a principle. Once accepted by the scientific community, it might be adopted as a theory or ultimately, a law. A theory is an integrated set of hypotheses that together explain a broader set of observations rather than any single hypothesis. However, a word of caution is needed. In ecology, most hypotheses are best regarded as challenges to tease the mind, to give structure to discussions, to serve as challenges for new research. They should not become ends in themselves. Figure 1.1 presents a simple representation of the scientific method.

Fig. 1.1
A model involves 5 steps of scientific studies, observations, question, hypothesis, predictions, and hypothesis testing.

A model of the scientific method. From Smith and Smith (2015) Elements of Ecology. (9th Edition). Pearson, Boston

Full size image

Models and Simulations

Because of the complexity of scales and processes, ecologists use models—simplified representations of real systems. A model begins with a descriptive statement backed by multiple observations, such as Darwin’s theory of evolution. It can be an intuitive and conceptual ‘box and arrow’ chart, providing a plausible set of linkages between components of an ecosystem, such as simple food webs. More sophisticated models incorporate quantitative data and produce predictive mathematical simulations. Models are most effective when the objective of the model is explicit. They should not be expected to replace focused thinking. All models should help to structure thinking and explanation. As examples cited in many chapters of this book demonstrate, ecology is still a work in progress. In essence, ecology is an iterative process of successive approximation to the truth, constantly and rigorously seeking to eliminate incorrect interpretations of natural patterns and phenomena and to find conclusions in which we can be confident.

The practice of ecology has advanced from its foundations in natural history curiosity to many disciplines of direct importance to socio-economic development. Across the broad fields of the environmental sciences—from impact analysis, land use planning and the management of conservation areas—ecological theory helps identify answers to complex questions. The development of resilient socio-ecological systems, of quantifying the economic value of ecosystem services and improving sustainable resource use and governance rests on sound ecological understanding. Ecology is a field employing thousands of professionals in southern Africa—in conservation area management, agriculture, forestry, marine resource management and environmental policy.

Ecology as a Career

Ecology is a career opportunity that requires commitment, passion and an understanding of the essential features, facts and concepts presented in this book. Angola is alive with opportunities for the young ecologist: it is a country with limitless horizons for the enquiring mind.

2 The Structure of This Introduction to Terrestrial Ecology

In this book, several interrelated topics and questions are addressed:

  • What are the main characteristics of Angola’s biomes and ecoregions?

  • What physical and biological forces determine the distribution and abundance of species?

  • Why do the ecosystems and their constituent species occur where they are found?

  • How have plants and animals adapted to specific environmental conditions?

  • How do Angolan ecosystems function as integrated and dynamic systems?

  • Why is an understanding of ecology critical to Angola’s sustainable development?

In addressing these questions, the structure of this book does not follow that of traditional ecology textbooks, which provide stepwise coverage of system organization, from individuals to populations to communities and ecosystems, and interactions from birth, death, competition and predation, and processes such as fluxes of energy and matter through ecosystems. Here the emphasis is on the living environment of Angola, which the student can encounter in the field, ideally in the country’s national parks, where examples of the structure and dynamics of ecosystems can be experienced in situ.

Each chapter is headed by a series of statements that focus on the lessons to be learned in the chapter. An introduction to each chapter provides context to the theme, and in some cases, reference is made to the founders of ecological concepts, to provide a historic background to the development of the science of ecology. Complex concepts or unique phenomena are presented in highlights (Boxes). The purpose of the Boxes is to provide depth on topics that are essential learning, without interrupting the flow of chapter structure.

More generally, this book follows a series of key questions, as addressed below, ultimately brought together within the biomes and ecoregions of the country. The coverage of topics does not specifically embrace the important discipline of conservation biology, for which an excellent reference is available in Wilson and Primack (2019).

What and Where?

Knowing ‘what’ and ‘where’ is the first step. The introduction to the biomes, ecoregions and the biodiversity of Angola in Part l serves to demonstrate their richness and the exciting opportunities for further study. A framework of African biomes provides an entry point for the reader to develop a continental perspective. Understanding the structure, composition and distribution of ecosystems requires knowledge of many ecological terms and concepts, a step that at first might seem challenging. Part I therefore introduces basic terms that will be used repeatedly through the book. Ecological terms are merely the tools for communicating consistent messages. Throughout the text, key terms are highlighted in bold, linked to a succinct definition of the term provided in the Glossary of Ecological Terms.

Why?

Following an outline of Angola’s biomes and ecoregions, the next step is to build an understanding of the factors and processes that determine the structure and distribution of these complex systems. This is provided in Part II by a review of the driving forces—climate, geology, hydrology, soils, fire and herbivory—that determine why species live where they do, and why their distributions are limited to specific conditions for survival, growth and reproduction. These elements are the fundamental tools that an ecologist needs to understand before approaching the living landscape—the ultimate workplace of an ecologist.

How?

With a basic knowledge of the ‘what’, the ‘where’ and the ‘why’ of species and ecosystem distributions and abundance, we can look at questions of ‘how’. Part III explores how plants and animals interact within species, between species, and with their environments to form the patterns we see in nature. In short, what morphological, physiological and behavioural adaptations have evolved to survive and prosper in the diverse landscapes of Angola? General concepts in ecosystem structure, function and dynamics are discussed based on ecological principles and illustrated with examples from Angola and other African countries. Building on this knowledge, one can move to the mechanisms operating at the ecosystem level. Here we will, for example, look at the processes of energy, water and nutrient pathways though savanna ecosystems, adaptation to aridity within the desert biome, and speciation questions within the forest biome. All processes are determined by basic principles of physics and chemistry, and molded by biological interactions.

Ecological Features of Angolan Biomes and Ecoregions

Part IV provides a more detailed examination of the biomes and ecoregions of Angola, looking more closely not only at their defining features, distribution and structure, but also at the evolution of patterns and processes. Unusual features, unique to Angolan or regional landscapes are used to demonstrate the importance of both applied and curiosity-driven research. These include the pattern of soil-vegetation catenas, of termitaria as nutrient hotspots, the possible explanations for ‘fairy circles’ in the Namib and of ‘underground forests’ in miombo.

Synopsis: Key Elements of Angolan Terrestrial Ecology

Part V presents a brief synthesis of the main messages that the student should understand and embrace as she or he explores and studies Angola’s diverse landscapes. These elements of ecology are the building blocks of the learning process. The evolution of Angola’s landscapes, the contemporary drivers of ecosystem structure, function and patterns, and the general theories relevant to conserving Angola’s fauna, flora, ecosystems and human life-support systems are outlined.

3 How to Use This Book: Interconnections and Recurrent Messages

It is not intended that the full breadth of the science of ecology be covered in this brief synthesis of Angola’s biomes and ecoregions and of selected ecological concepts. For a more comprehensive study of ecology, many excellent textbooks are readily available and should be consulted for greater depth (Du Toit et al., 2003; Levin et al., 2012; Owen-Smith, 2021; Shorrocks & Bates, 2015; Smith & Smith, 2015; Townsend et al., 2008; Whitmore, 1998; Wilson & Primack, 2019). For inspiration, young students are encouraged to read biographies of the great pioneers of ecology: Humboldt, Darwin and Wallace (Selsam, 1959; Wallace, 1881; Wulf, 2015). These and many other resources are referenced at the end of each chapter, providing a shortlist of selected textbooks and research papers. Because of the interconnectedness of ecological concepts and processes, cross-referencing will be indicated throughout the book. A major challenge to students is the multitude of terms that need to be understood, and for this reason terms indicated in bold are defined succinctly at first mention and collectively in the Appendix.

Finally, four themes or ‘leitmotifs’ will become evident in this book and underpin its learning objectives:

  • Ecology is about recognizing patterns and processes that operate at widely differing scales of time and space.

  • Nothing in biology makes sense except in the light of evolution. But equally, very little in evolution makes sense except in the light of ecology.

  • Ecological research explores the mechanisms of survival, growth and reproductive output of organisms in relation to their environment.

  • The whole is greater than the sum of the parts. Interactions and webs of interdependencies between individuals, species and populations and their environments create emergent properties that define ecosystem structure and function.