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Quantifying the complexity of life

Posted 25th September 2025

Biological diversity in ecosystems and how we measure it

Biodiversity is a simple term often used to describe the variety of life on Earth, or within a specific ecosystem. A high level of biological diversity – from soil microbes to plants and animals – facilitates intricate connections between species that form complex webs of interdependence, resulting in healthy, resilient ecosystems (1).

These ecosystems, in turn, provide critical services that humans depend on like air purification, water filtration, pollination, climate regulation, medicines, and many more (2). But as ecosystems face increasing pressure, key elements of biodiversity are lost. With each missing piece, the system grows less resilient (3). At some stage, these complex webs may unravel to the point of collapse.

When an entire ecosystem disappears, the biodiversity it contains vanishes with it. This loss impacts regional and global natural processes (4), leading to cascading effects that are often far more costly down the line (5). It has become overwhelmingly clear that biodiversity underpins both ecological balance and human well-being (6). That’s why it is critical for scientists and conservationists to measure it. Measuring biodiversity can act as an early warning system, it can assist the sustainable management of a system and can inform regulations and policies (7).

Yet measuring biodiversity is no easy feat. Ecosystems contain immense numbers of interconnected species, many of which are microscopic or hidden. We cannot simply observe them all. Luckily, scientists have developed effective and innovative ways to estimate diversity (8), giving us insight not only into what species are present and how rare they are, but also into how healthy an ecosystem is, and which processes sustain its function (9). By understanding the parts we can see, we gain clues about the parts we cannot.

Measuring Biodiversity in Practice

Species Richness and Abundance

Scientists and field ecologists have developed many interesting and effective ways to assess biodiversity. These methods try to capture three main dimensions: what’s there, how much of it is there, and how it interacts.

The simplest way to measure biodiversity is to count how many species are present (Species Richness) and how many individuals of each species occur (Species Abundance). This gives us insight into which species are more prevalent, or which are rare (10).

Various methods are used to measure species richness and abundance.

  • Quadrat sampling assesses a small sample area and records species richness and abundance. This is effective for plants and slow-moving animals (11).
  • Transect surveys sample a larger area as ecologists record species walking along a line (12).
  • Sweep nets, pitfall traps, and light traps are often used for insects and other invertebrates (13).
  • Point counts or camera traps are very effective at monitoring more elusive mammals or for birds. These camera traps often remain in the field for weeks recording large amounts of data without causing any disturbance to the animals (14).

Sometimes, we cannot find every species of interest. In such cases, we rely on indicator species or bioindicators that represent the health of a broader community (15). Indicator species allow ecologists to efficiently monitor ecosystem health, often providing early-warning signals of environmental change before broader biodiversity declines are apparent (16). Dragonflies and mayflies in rivers and wetlands are sensitive to pollution, making them excellent indicators of freshwater quality (17). Invertebrates in particular respond quickly to environmental change (18), making them especially valuable for monitoring, not only as a tool of assessing health, but also as a proactive management strategy.

Diversity indices

While counting species gives us important information, it doesn’t capture the full picture of biodiversity. Ecologists often use statistical indices like Shannon or Simpson’s Diversity Index to capture both richness and evenness (how well each species is represented within the larger community) (19). These indices help compare communities or ecosystems and track their changes over time. Using the diversity indices, one can gain important insight into how the ecosystem may react to changes and how biodiversity is organised within an ecosystem (20).

Functional and Structural Diversity

To truly understand ecosystem health and further explore biodiversity at different scales, ecologists also study functional (what species do) and structural (how ecosystems are physically organized) aspects. In a forest, ecologists may measure vegetation structure by looking at tree height, canopy cover, and understory density as a multilayered forest canopy supports more birds, insects, and mammals than a uniform plantation (21). Structural complexity often translates to higher habitat diversity and more niches for species to occupy (22).

Biodiversity also depends on how habitats are arranged across the landscape. Connected habitat patches allow species to move, disperse, and maintain genetic diversity (23). Large, continuous areas tend to support more species than small, fragmented patches (24), while a mosaic of habitat types (forests, wetlands, grasslands) provides more niches and ecological interactions (25). Even edges between habitats influence which species thrive, and which avoid the area (26). Remote sensing and satellite imagery now allow ecologists to map patch size, connectivity, and habitat heterogeneity, helping guide conservation and restoration efforts at a regional scale (27).

Table Mountain Ecosystems and Habitats

Figure 1. Example of rich and diverse habitat types at Table Mountain, Cape Town, South Africa.

When measuring Ecosystem Functions, high decomposition rates can suggest a more active and diverse decomposer community (fungi, bacteria, invertebrates) (28), measured by placing mesh litterbags filled with leaves in the field, then observing how fast they break down. Pollination activity can be tracked by observing flower visitation rates as the diversity of pollinators directly affects fruit and seed set in many ecosystems (29). Soil cores can reveal microbial diversity through DNA sequencing, assessing the functional role of these organisms as healthy soils often contain thousands of microbial species that cycle nutrients and support plant growth (30). Soils with higher microbial diversity tend to resist disease outbreaks and recover more quickly after disturbance (31). These processes maintain soil fertility, productivity, and regeneration – the backbone of long-term ecosystem health (32).

Microbial diversity

Figure 2. Microbial diversity refers to the variety and variability of microorganisms, including bacteria, archaea, eukaryotes, and viruses, found in various environments on Earth.

The future of Biodiversity Monitoring

Scientists have relied on most of these methods of measuring and estimating biodiversity for many years. Although well-used and supported, novel technologies are allowing more effective, large-scale assessments that are becoming more practical and accurate, and reducing the costs and challenges of field measurements (33). Advances in eDNA (Environmental DNA) detects genetic material from various species from water or soil samples (34). Remote sensing and drone imagery are giving researchers unprecedented access to difficult-to-reach ecosystems, enabling global mapping of diversity at various scales (35). The field of Bioacoustics analyses sound recordings taken in nature to detect how many species of frog, bat or bird were found at a certain location (36). This has allowed us to study species that are normally very elusive (micro-frogs and bats) and confirm their presence and population dynamics without ever seeing an individual (37). The technologies of biodiversity measurement is an exciting and constantly developing field.

With so many methods – some well-tested, others cutting-edge – scientists can piece together remarkably accurate estimates of biodiversity. This information is vital for protecting ecosystems, conserving species, and sustaining the processes that support all life, including our own.

Biodiversity may seem infinite and impossible to fully measure, but every method brings us closer to understanding the complex systems that sustain us. By learning to quantify life’s diversity, we don’t just collect data — we learn how to better protect the fragile balance of ecosystems, and in turn, secure our own future.

About the Author

MICHIEL GROBLER BSC (HONS) CONSENT MSC (BIOSCI)
ASSOCIATE CONSULTANT

Michiel is an Ecological Entomologist and Restoration Ecologist with nearly a decade of experience in ecological conservation and restoration across southern Africa. His work spans diverse ecosystems — from the wetlands of Botswana to the Afro-montane forests of South Africa and the mountains of Saudi Arabia — where he has contributed to projects on biodiversity monitoring, long-term ecological restoration, and provincial conservation initiatives.

His research, including pioneering species inventories of invertebrates in the Okavango Delta, has informed biodiversity assessments, while his role in managing the monitoring and evaluation of over 20 forest restoration sites across two countries has advanced best practices for ecosystem restoration. Michiel’s expertise assists him to develop management protocols in collaboration with international EIA companies to refine and standardise global invertebrate sampling protocols, develop novel mitigation strategies for renewable energy developments and advocate the large-scale use of invertebrates as bio-indicators.

Committed to knowledge sharing, Michiel has trained conservation rangers, facilitated large-scale citizen restoration events, and engaged in community-focused social impact projects. By integrating science with community involvement, he strives to develop holistic, sustainable solutions to complex environmental challenges.

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