Can you tell the health of an ecosystem by looking inside its flowers?
A tiny detail inside cowslips may enable the diagnosis of overall grassland health
Ecosystems, just like people, can vary in their health status. A healthy ecosystem hums with activity, the physical and biological components work together as a connected whole and it supports a vast diversity of life. An unhealthy ecosystem does not function well, it can be ravaged with outbreaks of species that cause problems – such as algal blooms – or it can have low productivity and be unable to support its normal complement of species.
Prevention is certainly better than cure for ecosystem health. By keeping it in good shape you retain critical ecosystem functions such as water quality provision, prevention of erosion, and pollination. But how do you know whether an ecosystem is healthy or is slipping into decline? Are there indicators, like the pulse and blood pressure of a human, that can act as early warning signals for ecosystem health?
Take a grassland, for example. The size, location and quality of a grassland all have roles to play in enabling it to support a diverse range of different plant, animal and microbe species. Bigger patches of grassland can support more individuals and species, and larger populations provide more potential mates and prevent damaging inbreeding.
The proximity of a patch of grassland to similar patches can enable individuals to disperse across the landscape to take advantage of changes in resources from year to year. In contrast, being close to dense human populations can increase trampling and disturbance, change the hydrology of an area and increase the introduction of non-native species.
In addition to looking at the “big picture” of ecosystem health, you can examine the details. Just as a doctor might look at the concentration of biomarkers to diagnose disease or build up a picture of overall health, an ecologist can use tiny indicators to detect bigger problems.
The delicate pale yellow cowslip (Primula veris) is a spring flower that thrives in natural and semi-natural grassland and declines if grassland is abandoned or intensified, or if it is picked to extinction by people. While it seems to be doing reasonably well in the Republic of Ireland, it is a protected species in Northern Ireland, where natural populations are rare. A Europe-wide citizen science project on a tiny detail of the mating system of this plant is being undertaken to see if it can be used as an indicator of ecosystem health.
The project Looking for Cowslips is recruiting volunteers to notice something unusual about cowslip flowers. If you look inside a cowslip flower, you see either a “pin” flower with a tall, pin-shaped stigma or a “thrum” flower, where the pollen-holding anthers are taller than the stigma.
All cowslip flowers have a stigma and anthers, but in about half of the population the stigma is longer than the anthers. Charles Darwin was the first to solve the riddle of why this occurs. It is to prevent inbreeding: a “pin” flower cannot mate with another “pin” because of the way pollinators access the flowers and where the pollen lands on their bodies.
Half and half
A healthy population of cowslips has a 50:50 ratio of “pin” to “thrum” flowers. Finding this even ratio of flower types indicates that the grassland ecosystem is big enough to hold enough cowslips to maintain the population. If the ratio starts to get unbalanced, there is a risk that cowslip plants will fail to be pollinated, or inbreeding may affect their genetic health. With only a few plants in a population, there is a higher probability that the ratio will become unbalanced.
Looking for Cowslips researchers have already found populations with skewed ratios of pin and thrum flowers are more likely to occur in small grassland patches and in grasslands close to high human population densities. With more data from grasslands all over Europe, they are hoping to better understand whether this tiny detail can be used to diagnose grassland health more generally.