Biodiversity underpins nearly every benefit that ecosystems provide to people, from clean water and fertile soil to protection from storms and diseases. Two decades of experimental and observational research have built a strong empirical case that species-rich communities tend to produce more biomass, cycle nutrients faster, resist disturbances better, and deliver a wider range of services than species-poor ones. But the relationship is not as simple as “more species equals more benefits.” Which species are present, what roles they play, and how they interact with each other and with the physical environment all shape what ecosystems actually deliver, and those details matter enormously for conservation and land management decisions.
Why More Species Usually Means More Function
The core finding from hundreds of biodiversity experiments is that communities with more species generally outperform communities with fewer species when it comes to ecosystem functions like plant productivity, decomposition, or nutrient uptake. One of the main explanations is that different species use resources in different ways. When a community includes species that feed at different depths, bloom at different times, or tolerate different temperatures, the group as a whole captures more of the available energy and nutrients than any single species could alone. Research confirms that when this kind of complementarity increases among plants without intensifying competition within individual species, the positive relationship between diversity and ecosystem function gets steeper.1Functional Ecology. Niche complementarity among plants and animals can alter the biodiversity–ecosystem functioning relationship
This logic extends across space and time. Larger landscapes encompass a wider range of environmental conditions, which means more opportunities for different species to fill distinct roles. Even when species do not coexist at a single small site, variation in which species dominate across different patches can generate complementarity at the landscape level. A meadow that supports one set of grasses on its wet end and another on its dry end may outperform a uniform meadow in total productivity, simply because each patch is better matched to its local conditions.2PubMed Central. Scaling‐up biodiversity‐ecosystem functioning research
It Is Not Just About Counting Species
A persistent misconception is that conserving “the most species” automatically maximizes ecosystem benefits. The evidence increasingly points to functional diversity as a stronger predictor of how well an ecosystem works. Functional diversity refers to the range of ecological roles present in a community. Two forests could have the same number of tree species, but if one contains fast-growing pioneer trees, deep-rooted hardwoods, nitrogen-fixers, and fruit-bearing species while the other has twenty closely related species that all fill similar roles, the first forest will likely store more carbon, support more wildlife, and cycle nutrients more efficiently.
Studies on animal communities reinforce this point. Research comparing trait-based measures against simple species counts found that the combination and distribution of functional traits in a community consistently predicted ecosystem functioning better than species richness or abundance alone.3PubMed Central. Functional identity and diversity of animals predict ecosystem functioning better than species-based indices Functional diversity can even explain variation in ecosystem performance when species richness alone does not, meaning that in some cases, losing a species with a unique ecological role matters far more than losing a species whose function is duplicated by others in the community.4Journal of Applied Ecology. Beyond species: functional diversity and the maintenance of ecological processes and services
Biodiversity as Insurance Against Bad Years
Beyond boosting average performance, biodiversity stabilizes ecosystems over time. The reasoning is intuitive: if a drought kills off one grass species but another drought-tolerant species thrives in its place, total productivity barely dips. Biological insurance theory predicts exactly this pattern, and ecology has now accumulated strong evidence for it. In diverse communities, declines in one species tend to be offset by gains in others, so the aggregate output varies less from year to year.5PubMed Central. Biodiversity as insurance: from concept to measurement and application
A vivid illustration comes from Pacific salmon. Individual local populations of sockeye salmon fluctuate wildly, sometimes even chaotically. But when many genetically distinct populations are aggregated at the regional scale, interannual variability drops substantially. One analysis found that regional variability decreased by about 47% compared to individual populations, because different populations peaked in different years. This is the “portfolio effect,” the same principle behind financial diversification. Lose that diversity, and the whole regional fishery becomes far more boom-and-bust.6PubMed Central. Ecological stability through nonlinear fluctuations and the portfolio effect
Pollination and Crop Yields
Agriculture is where the biodiversity-services link hits people’s wallets most directly. Roughly three-quarters of leading food crops depend to some degree on animal pollination, and wild pollinators do a large share of the work, even on farms that also use managed honeybees. A global analysis found that landscapes with greater crop diversity supported higher pollinator species richness and abundance, and that this translated into higher crop production. Notably, simply expanding the total area devoted to crops had the opposite effect: pollinator abundance and crop production both declined as farm area increased, suggesting that monoculture expansion undermines the very services that farms depend on.7Agriculture, Ecosystems & Environment. Crop diversity in the landscape boosts pollinators and yield of pollinator dependent crops across the world
The benefits show up at different farm scales. A large global study found that on small fields (under two hectares), increasing the density of flower visitors could close yield gaps by a median of 24%. On larger fields, achieving those same benefits required high pollinator species richness, not just more individual bees, because different pollinator species work flowers differently, visit at different times of day, and tolerate different weather conditions.8PubMed. Mutually beneficial pollinator diversity and crop yield outcomes in small and large farms Wild pollinator diversity therefore matters on top of sheer pollinator numbers.9Frontiers in Ecology and the Environment. From research to action: enhancing crop yield through wild pollinators
Natural Pest Control
The same complementarity principle that applies to pollinators also applies to the animals that eat crop pests. Predatory insects, spiders, parasitoid wasps, and insect-eating birds all attack pests in different ways, at different times, and in different microhabitats. When multiple types of natural enemies are present, pest suppression tends to be stronger because the pests face overlapping threats they cannot escape by changing behavior or location.10Biological Control. Give predators a complement: Conserving natural enemy biodiversity to improve biocontrol
There is a complication, though. In simple environments with few prey species, predators in diverse communities sometimes end up eating each other rather than focusing on pests. This intraguild predation can weaken or even erase the benefits of predator diversity. The overall picture from reviews of this literature is that natural enemy diversity generally strengthens biological control, but outcomes range from strongly positive to occasionally negative depending on the specific community and environment. A trait-based approach, one focused on what predators do rather than how many there are, helps predict when adding more predator species will help and when it will not.11PubMed. Relationships between natural enemy diversity and biological control
Carbon Storage in Forests
Forests are the planet’s largest terrestrial carbon sink, and how much carbon a forest stores is partly a function of how many tree species it contains. A detailed study of subtropical forests in southeast China found that for each additional tree species, total carbon stock increased by about 6.4%, with species richness explaining roughly 29% of the variation in total carbon across stands.12PubMed Central. Tree species richness increases ecosystem carbon storage in subtropical forests Broadleaf forests in the same region stored more carbon per hectare than coniferous or mixed forests.13PubMed Central. Effects of Species and Structural Diversity on Carbon Storage in Subtropical Forests
The picture gets more complicated at larger scales. An analysis of forests across the United States using satellite and inventory data found that species diversity did not show strong associations with carbon storage in natural forests, though it did show a positive relationship in mixed planted forests.14Remote Sensing of Environment. Structural and species diversity explain aboveground carbon storage in forests across the United States Structural diversity, meaning variation in tree heights and canopy layers, turned out to be a strong predictor as well. The takeaway is that the diversity-carbon relationship is real but depends on context: it tends to be clearest in species-rich tropical and subtropical forests, and it is mediated by which particular species are present and how they arrange themselves vertically.
Soil Biodiversity and the Underground Economy
Beneath every productive landscape is a soil community of bacteria, fungi, earthworms, mites, and nematodes that drives decomposition and nutrient cycling. Reviews of experiments manipulating soil biodiversity found a positive relationship between species richness and carbon cycling in 77 to 100% of low-diversity experiments. At higher diversity levels, the relationship weakened, and positive effects were observed in only about 35 to 64% of studies.15European Journal of Soil Science. Soil biodiversity and carbon cycling: a review and synthesis of studies examining diversity–function relationships This pattern suggests functional redundancy: once the basic ecological roles are filled, adding more species provides diminishing returns for any single function. The first few species you lose from a soil community may not matter much, but continued losses eventually cross a threshold where key functions start declining sharply.
Coastal Protection From Reefs, Seagrass, and Mangroves
Coastal ecosystems provide a defense against waves and storms that engineered seawalls struggle to match in cost-effectiveness. Coral reefs, seagrass meadows, and mangrove forests each reduce wave energy through different mechanisms. Reefs break incoming waves offshore. Seagrasses slow water flow and trap sediment across shallow bottoms. Mangroves absorb wave energy and reduce flooding at the shoreline. Modeling work has shown that all three habitats together supply more protection than any individual habitat or combination of two.16PubMed Central. The Power of Three: Coral Reefs, Seagrasses and Mangroves Protect Coastal Regions and Increase Their Resilience In barrier reef settings, seagrasses can even partially compensate for the long-term degradation of the reef itself.
Among these habitats, coral reefs have the greatest potential for coastal protection because they face and reduce the highest, most powerful waves. The most effective reefs are at least twice as wide as the wavelength of incoming swells.17PLoS ONE. The Effectiveness, Costs and Coastal Protection Benefits of Natural and Nature-Based Defences Losing biodiversity on a reef, particularly the large reef-building coral species, reduces the structural complexity that dissipates wave energy, leaving coastal communities more exposed to storms and sea-level rise.
Disease Regulation and the Dilution Effect
One of the more counterintuitive services biodiversity provides is disease regulation. The “dilution effect” hypothesis holds that in diverse host communities, disease transmission drops because vectors like ticks or mosquitoes end up biting species that are poor pathogen reservoirs, effectively wasting their blood meals. Modeling work on tick-borne diseases found that more functionally diverse communities resulted in fewer infectious rodents, supporting the dilution hypothesis, though the outcome depended on how specialized the vector was.18PubMed Central. An eco-epidemiological modeling approach to investigate dilution effect in two different tick-borne pathosystems
Dilution is not guaranteed, however. Theoretical models show that adding host species can either dilute or amplify disease risk, depending on which species the vector prefers and how competent each host is at transmitting the pathogen. If the vector strongly prefers the most competent host, adding poor hosts to the community does little to reduce transmission. Dilution works best when the added species are less competent transmitters and are fed upon at rates comparable to the competent host.19PLOS ONE. The Effects of Host Diversity on Vector-Borne Disease: The Conditions under Which Diversity Will Amplify or Dilute the Disease Risk The practical lesson: preserving wildlife community diversity can reduce disease transmission to humans, but the specific composition of that community matters as much as its richness.
When Invasive Species Unravel the Link
Invasive species offer a natural experiment in what happens when biodiversity’s structure is disrupted. A study of the invasive tree Prosopis found that its indirect effects on ecosystem functions, those routed through changes in local biodiversity and plant biomass, were roughly twice as large as its direct effects.20Journal of Ecology. Direct and indirect effects of invasive species: Biodiversity loss is a major mechanism by which an invasive tree affects ecosystem functioning In other words, the damage an invader does by outcompeting native species and reducing diversity is often worse than any direct physical or chemical impact it has on the soil or water. Biodiversity loss was not just a side effect of invasion but a primary pathway through which ecosystem services degraded. This finding reinforces that protecting the diversity of a community is not just about preserving species for their own sake; it is about maintaining the functional architecture that delivers services.
Water Purification and Wetland Plants
Wetland plants are natural water filters. Their roots absorb excess nitrogen and phosphorus, slowing the eutrophication that chokes lakes and rivers with algal blooms. A mesocosm experiment testing endemic wetland plants found that under nutrient-rich conditions, floating wetlands could remove up to 312 grams of nitrogen and 47 grams of phosphorus per square meter per year. Some of the tested species stored most of their absorbed nutrients in shoot tissue rather than roots, meaning nutrients could be permanently removed from the system through periodic harvesting.21Wetlands. How Well Do Endemic Wetland Plant Species Perform in Water Purification? Using locally adapted, diverse plant assemblages rather than a single species increases the odds of capturing nutrients under varying conditions, another expression of the insurance principle.
Biodiversity and Mental Health in Cities
The services biodiversity provides are not only ecological and economic. Growing evidence connects urban biodiversity to psychological well-being. An analysis across 36 Canadian cities found that neighborhoods with higher bird diversity and tree species richness had residents reporting better mental health, even after adjusting for income, education, and other neighborhood characteristics. Living in a postal code with bird diversity one standard deviation above the city mean was associated with a roughly 7% increase in self-reported good mental health, and an equivalent bump in tree species richness added about 5%.22PubMed Central. Mental health is positively associated with biodiversity in Canadian cities
The relationship is not settled everywhere. A study of urban adolescents in London looking at proximity to biodiverse sites did not find a statistically significant link to mental health outcomes, though the researchers cautioned that their measures of both biodiversity exposure and mental health may have been too coarse to detect an effect.23Journal of Environmental Psychology. Urban biodiversity and adolescent mental health and well-being The discrepancy is a useful reminder that how biodiversity is measured and experienced matters. Simply living near a designated nature site is not the same as regularly hearing birdsong or walking through a street lined with diverse tree species.
Trade-offs Between Ecosystem Services
Managing landscapes for one service often comes at the expense of another. Research on China’s Loess Plateau found significant trade-offs between agricultural production and regulating services like water yield, soil conservation, carbon sequestration, and biodiversity. An ecological restoration scenario maximized regulating services but cut agricultural output by about 15%, while a sustainable intensification scenario boosted crop production by 15% at the cost of moderate declines in ecosystem service provision.24Scientific Reports. Trade-offs between agricultural production and ecosystem services under different land management scenarios in the Loess Plateau of China Similarly, evidence from European agricultural grasslands shows that intensive management can improve provisioning services like hay or livestock production but reduce plant and soil biodiversity, which in turn erodes other services that local communities depend on.25Ecological Indicators. An ecosystem service trade-off management framework based on key ecosystem services
These trade-offs are real, but they are not fixed. The whole point of understanding biodiversity’s role is to find management strategies that soften the trade-offs, maintaining productive agriculture while preserving enough biological diversity to keep pollination, pest control, soil health, and water quality services functioning.
Putting a Price on the Link
Economists and policymakers have pushed hard to quantify the monetary value of biodiversity’s contribution to ecosystem services, partly to make the case for conservation in cost-benefit terms. The dominant assumption in policy circles has been that the relationship between biodiversity and economic value follows a positive but diminishing-returns curve: more biodiversity always adds value, but each additional species adds less than the last. A review of the underlying economic literature found that reality is more complicated. Depending on which ecosystem services are being valued, how many are considered simultaneously, and how human preferences are modeled, the biodiversity-value relationship can also be convex, meaning each additional species adds more value than the last, or even negative over certain ranges.26PubMed Central. On the functional relationship between biodiversity and economic value This variability means that blanket economic arguments like “biodiversity is always worth more if you just measure it right” are oversimplified. The economic case depends on which services matter locally and whether they trade off against each other.
Nature-Based Solutions and Traditional Knowledge
The concept of nature-based solutions has become a central framework in environmental policy, spanning everything from urban green infrastructure to coastal habitat restoration. These approaches explicitly aim to generate human benefits while also supporting biodiversity.27Ecosystem Services. Aligning nature-based solutions with ecosystem services in the urban century Case studies of organic farming, rewilding, land restoration, and constructed wetlands across multiple countries have shown nature-based approaches to be cost-effective long-term solutions for problems like soil degradation and flooding, particularly when they work at the landscape scale rather than treating individual plots in isolation.28PubMed. The superior effect of nature based solutions in land management for enhancing ecosystem services In marine and coastal contexts, these strategies can rebuild resilience while contributing to local economies, though their success depends on a much better understanding of which interventions work where.29Nature-Based Solutions. Embracing Nature-based Solutions to promote resilient marine and coastal ecosystems
One dimension often undervalued in formal policy is traditional ecological knowledge held by Indigenous and local communities. A study modeling the drivers of ecosystem services found that traditional ecological knowledge was the most significant component influencing cultural and provisioning services, while habitat quality was the strongest factor for supporting and regulating services.30Scientific Reports. The role of traditional ecological knowledge and ecosystem quality in managing ecosystem services Communities that have managed landscapes for generations often possess detailed, place-specific knowledge of how species interactions sustain the services they depend on, knowledge that formal biodiversity assessments can miss entirely.
Global Trade and Displaced Impacts
A final layer of complexity is that the places where ecosystem services are consumed and the places where biodiversity is lost to produce those services are often thousands of miles apart. International food trade links consumers in wealthy countries to agricultural expansion in biodiversity hotspots. An analysis of global trade flows found that non-hotspot countries share responsibility for biodiversity loss and greenhouse gas emissions from agriculture in biodiversity hotspot countries, because demand for exported food drives habitat conversion in those regions.31Global Trade Analysis Project. Global impacts of international food trade on biodiversity: Application of the telecoupling framework A European consumer buying soy-fed chicken is, in a meaningful sense, drawing on ecosystem services generated in South American landscapes while exporting the biodiversity costs. This spatial decoupling makes the biodiversity-services link harder to see, but no less real. It also means that local conservation efforts, no matter how well designed, cannot fully protect ecosystem services if the economic pressures driving biodiversity loss originate on the other side of the planet.