Biodiversity is more than just a list of plants and animals, but a series of critical, life-supporting relationships in a complex web. When one part weakens or disappears, every other part of this complex web is affected, and diminishes in some way. This is particularly impacted when apex predators – animals with few or no predators of their own and which reside at the top of their food chain – are
threatened in number, for a variety of reasons (including loss of habitat due to increased human activity). Such apex predators have a crucial role in maintaining the health of their entire ecosystem. This is true in all different ecosystem types – land, desert, riverine, marine, fresh water, salt marshes and so on.
These trophic cascades, or “cascades of life” demonstrate how the presence of just one species can influence the dynamics of a whole ecosystem. The word “trophic” derives from the Greek “troph” referring to food or nourishment. We now know that biodiverse living systems which retain their large carnivores and large herbivores often behave in radically different ways from those which have lost them.
In the example shown, too much algae has reduced the level of dissolved oxygen in water systems, killing fish and other organisms relying on the aquatic ecosystem. The presence of harmful phytoplankton such as blue-green algae is most commonly caused by the build-up of excess nutrients (eutrophication), which disturbs the ecosystem dynamics. Excess nutrients decrease the population of large fish, causing a cascade that finally results in an abundance of algae. By introducing more fish to the ecosystem, or protecting the current fish populations, the balance between trophic levels can be restored. Such interventions, known as biomanipulation, can also effect the abundance of aquatic vegetation, which effects sediment stability and indeed nutrient cycling.
Another example, closer to home, is the pangolin. Aside from being a very unique, insectivorous creature and the most trafficked mammal in the international illegal wildlife trade, these scaly anteaters also have a job – a very important one. Pangolins provide the earth with all-natural pest control and are fantastic soil caretakers, and they do these things simply through their everyday behaviours of excavating ant and termite nests for food. In doing so, the soil is mixed and aerated, improving the nutrient quality of the soils and aiding the decomposition cycle, providing a healthy soil base for lush vegetation to grow from. The mere presence of pangolins, in conjunction with that of the other organisms and processes within their habitat, is absolutely imperative to continued healthy ecosystem functioning. What’s more, it’s estimated that a pangolin eats some 70 million insects a year (mainly ants and termites), that’s almost 200 000 insects every day, and about 70 times more insects than bats eat.
In the newly released film Eye of the Pangolin, Dr Cleo Graf says pangolins are “in ecological terms, a keystone species, something that has a greater impact than you’d expect for its biomass, in the ecosystem,” and yet they are being illegally traded to China and Vietnam and are threatened with extinction. An estimated 1 900 pangolins are killed for every tonne of scales seized, and at this rate, the threat to ecosystems is very real as the numbers of (uneaten) insects can become super-abundant, and out of balance, increasing the ant and termite threat to plants and vegetation. The Eye of the Pangolin can be watched on YouTube.
The final examples of a trophic cascade are those presented by George Monbiot, about whale poo and marine faecal plumes. In the 1970s it was argued that reduced numbers of large whales in the southern seas would lead to an increase in the krill population, their prey – but this never happened. Instead there has been a long-term decline in krill, and it turns out that whales not only kill their prey but they also maintain prey populations – but how? Whales help sustain the entire living system of the oceans, by returning to the surface to breathe and defecate, transporting nutrients from the depths (where waters are too dark for photosynthesis to occur) into the photic zone, where plants can live. In the southern oceans, iron is a limited nutrient, without which the plant plankton at the bottom of the food chain cannot reproduce and grow. By producing their “poonamis” – faecal plumes – in the surface waters, the whales fertilise the plant plankton on which the krill and fish depend. And it doesn’t end there. Plant plankton, when they die, slowly descend into the dark abyss, taking with them the carbon they have absorbed from the atmosphere, to be stored out of our earth’s atmosphere. You can watch more on How whales change climate on here.
The reintroduction of wolves into Yellowstone National Park, in the United States, in 1975 has impacted ecosystems there by reducing deer numbers and changing deer behaviour. See How wolves change rivers here.
Rewilding is simply the “mass restoration of nature’s ecosystems”. By working with the natural forces of these trophic cascades, there is hope that if adopted quickly, that these natural climate solutions, by restoring living systems, can help avert climate chaos while defending the living world: by drawing carbon dioxide out of the air, by protecting and restoring biodiverse ecosystems. Defending the living world and defending the climate are, in many cases, one and the same. Biodiversity is at the heart of the solution. For more information visit
1. What is an apex predator?
2. What is a trophic cascade?
3. What do we mean by “rewilding”?
4. How many insects does a pangolin eat every day?
5. Name three beneficial actions whales perform in the oceans to support the entire life system?
6. Name three examples of apex predators in Africa?
7. What is a keystone species?
8. Name three services that pangolins offer to their environment?
9. Trophic cascades exist in every type of environment, true or false?
10. What is the world’s most illegally trafficked animal on the verge of extinction?
See answers on page 6
1. An animal with few or no predators of their own and which resides at the top of their food chain given their trophic level.
2. A living system impacted by the presence or absence of an apex predator, influencing the dynamics of the whole ecosystem.
3. The mass restoration of nature’s ecosystems.
4. Almost 200 000 (ants or termites) a day.
5. They defecate near the surface thus fertilising plant plankton in the photic zone; increase nutrients for plant plankton fertilisation (iron and nitrogen); increase amount of plant plankton; support increases in krill and fish populations; increase amount of dead plant plankton that can absorb carbon dioxide at ocean’s floor; assist in composition process of plant plankton; create water columns moving water from depths to shallows giving plant plankton longer time to be fertilised.
6. Elephant, lion, rhino, pangolin, African wild dog (hunting dog), leopard, cheetah, hyena, owls, eagles, birds of prey, gorilla, crocodiles, killer whales
7. A species that has a greater impact than you’d expect for its biomass, in the ecosystem.
8. Dig up the soil, mix the soil, aerate soil, improve nutrient quality of the soils, aid the decomposition cycle, provide a healthy soil base for lush vegetation to grow from, eat insects (ants and termites).
9. True (examples given land – pangolin and insects; riverine – algae and fish; marine – whales and krill)