Depending on the scholarly texts consulted, there are slight variations in the emphasis placed on the precise definition of ecology. For example, ecologists Robert Ricklefs and Rick Relyea (2014) define ecology as “the scientific study of the abundance and distribution of organisms in relation to other organisms and environmental conditions.”

In simpler, layperson terms, ecology is the study of the complex interactions and relationships between living (and once-living) organisms and their non-living physical environment. In other words, it examines the interactions between the biotic (living) and abiotic (non-living) components of nature.

At its most fundamental level, ecology includes the atoms that form molecules, which in turn give rise to all micro- and macro-organisms. It also includes the non-living physical elements that make up the environment: land, sea, air, water, and climate.

Ecology is interwoven with, and inseparable from, many other specialist disciplines, including entomology, zoology, geology, biology, chemistry, horticulture, agriculture, and numerous other scientific fields.

In a garden setting, the physical environment includes soil structure and composition—such as mineral content, organic matter, moisture levels, and drainage—alongside the macro- and microclimate. This encompasses seasonal temperatures, air and light quality, rainfall, wind exposure, frost, snow, and drought.

The living organisms within the soil, on the soil surface, on plants, and within other organisms represent the diversity of life interacting within this environment. These organisms are commonly grouped into seven kingdoms, as recognised and proposed by Thomas Cavalier-Smith (1942–2021), Professor of Evolutionary Biology at the University of Oxford. These kingdoms are: plants, animals, fungi, bacteria, archaea, protozoa, and Chromista. Together, they form the biodiversity that underpins all natural ecosystems.

 
Darwinism and Neo-Darwinism

The immense number of species and subspecies that exist today—having evolved over vast geological timescales—and the even greater number that have gone extinct are central to the Darwinian concept of evolution through natural selection. This process is often summarised as “survival of the fittest,” meaning survival of those organisms best adapted to their environment.

Although Charles Darwin (1809–1882) is credited with developing the theory of evolution by natural selection, historical records show that several other scientists were working on similar ideas at the same time. One notable example is the British naturalist Alfred Russel Wallace (1823–1913). Darwin, however, had the resources, time, and social connections necessary to publish and promote his work widely.

While Darwin’s theory was eventually accepted by much of the scientific community, it faced strong opposition when first proposed. Resistance came largely from religious institutions and belief systems, which at the time held far greater influence over public thought than they do today.

Interestingly, many scientists of the era favoured an alternative theory known as orthogenesis, or directed progressive evolution. This theory—now largely rejected—suggested that evolution followed a predetermined direction towards increasing complexity, rather than being shaped by environmental pressures and chance variation.

In contrast, later theories introduced the idea of punctuated equilibrium, which proposes that evolution is characterised by long periods of relative stability (stasis), interrupted by relatively brief periods of rapid evolutionary change. These bursts are often associated with environmental upheaval or population isolation. Today, most evolutionary biologists recognise that both gradual (incremental) and punctuated processes play roles in evolution.

Darwin himself did not fully understand the mechanisms by which variation and inheritance occur. At the time, genetics was poorly understood and heavily debated. It was the work of the Austrian monk Gregor Mendel (1822–1884), often called the father of genetics, that laid the foundations for our modern understanding of inheritance.

However, Mendel’s work was largely overlooked until the early 20th century. In the 1930s, scientists such as Ronald Fisher (1890–1962), J. B. S. Haldane (1892–1964), and Sewell Wright (1889–1988) applied mathematical principles to genetics. Their work demonstrated how Mendelian inheritance could explain variation within populations and provided strong support for natural selection.

Species survive and evolve because individuals with advantageous traits—arising from genetic and chromosomal mutations—are better able to exploit changing environmental conditions. Both the abiotic environment (such as climate and habitat) and the biotic environment (including competitors, predators, prey, parasites, and symbiotic partners) influence whether an organism can survive and reproduce.

This integrated understanding of genetics and natural selection is known as neo-Darwinism, or the modern evolutionary synthesis, a term popularised by the British evolutionary biologist Sir Julian Huxley (1887–1975) in his 1942 book Evolution: The Modern Synthesis.

Darwin also believed that sudden gaps in the fossil record were due largely to its incompleteness, rather than catastrophic events. Modern science, however, has shown that mass extinction events—caused by meteorite impacts, volcanic activity, and rapid climate change—have repeatedly reshaped life on Earth.

Mass extinctions do not favour the “fittest” organisms. Catastrophic events indiscriminately destroy ecosystems, wiping out both well-adapted and poorly adapted species alike. Survival during such events is often a matter of chance. A previously weaker competitor may survive simply because it was in a protected location, later becoming dominant in the newly altered environment.

Although scientific debate continues, it is now widely accepted that both gradual evolutionary change and sudden, dramatic shifts contribute to the history of life on Earth.

 
Biodiversity and the Ecological Perspective
Life on Earth is still constantly evolving. In evolutionary ecology, biodiversity describes the abundance and complexity of life that has developed over millions of years, resulting in the extraordinary variety of organisms we see today.

Present-day biodiversity is studied at three main levels:

Ecosystem diversity
Species diversity
Genetic diversity within species
As eco-conscious gardeners, our primary concern is ecosystem diversity. By appreciating and maintaining balanced ecosystems, we support the natural interactions between organisms and their physical environment. This means encouraging biodiversity, enhancing habitat complexity, and keeping human interference to a minimum wherever possible.

When current extinction rates are compared with those inferred from the fossil record, the evidence strongly suggests that extinctions are now occurring at an unprecedented pace. Many studies estimate that modern extinction rates are between 10 and 100 times higher than pre-human background levels.

The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) estimates that around one million plant and animal species are currently threatened with extinction, largely as a result of habitat loss, climate change, pollution, and unsustainable land use.

For gardeners, this highlights the vital role even small, wildlife-friendly spaces can play in supporting biodiversity and helping to slow this accelerating loss of life on Earth.