Energy in ecosystems: how our food choices shape the planet’s energy flows
When you were aged 12–14, you learnt that energy flows from producers (plants and algae) to consumers, and that food webs depend on sunlight. Now, let’s take a closer look: how the way we produce and consume food alters terrestrial and marine ecosystems, affecting biodiversity, climate stability and global sustainability. Energy is the invisible thread that connects everything: soils, plants, animals, water, oceans and, of course, our food. Understanding these flows helps you make food choices that reduce pressure on nature.
The foundation of it all: producers and trophic efficiency
All the energy that sustains life comes from the Sun. But only a fraction reaches plants, and an even smaller fraction moves up the food chain. This is due to trophic efficiency: on average, only around 10 per cent of the energy passes from one trophic level to the next.
What does this mean?
- Producing food at the base of the food chain (vegetables, cereals, pulses) is far more efficient than producing food at higher levels (meat, predatory fish).
- The further up the food chain we go, the greater the amount of energy, water and soil required.
This has a direct impact on our diet and the choices we make.
How food production utilises the planet’s energy flows
In terrestrial systems, growing plants allows us to harness solar energy directly, making plant production highly efficient. By contrast, producing animal feed and then producing meat involves two successive energy losses, which means that these foods require more land, water and energy. For this reason, plant-based foods tend to have a significantly smaller ecological footprint.
In aquatic systems, the dynamics are different, but the principles remain the same: predatory fish, such as tuna or swordfish, are at the top of the food chain and exert greater ecological pressure, whilst species at lower trophic levels, such as sardines, mackerel or bivalves, are generally more abundant and sustainable. When fishing removes too much from a particular level of the food chain, overfishing disrupts entire energy flows and undermines the balance of marine ecosystems.
Aquaculture also has different impacts depending on the species being farmed. Herbivorous species, such as tilapia, are more energy-efficient, whilst carnivorous species, such as salmon, require animal feed and therefore have higher energy consumption and a greater environmental impact.
Energy efficiency of animal-based versus plant-based foods
| Type of food | Trophic level | Energy efficiency | Typical environmental impact |
|---|---|---|---|
|
Leguminosas, cereais, hortícolas |
Produtores |
Muito alta |
Bass |
|
Small fish (sardines, mackerel) |
Primary/secondary consumers |
High |
Low/medium |
|
Poultry and pigs |
Secondary/omnivorous consumers |
Media |
Medium |
|
Ruminants (cows, sheep) |
Secondary consumers |
Low |
High |
|
Large predators (tuna, swordfish) |
Tertiary consumers |
Very low |
Very high |
Ecosystems are complex networks. When we take too much from one point in the chain, the impact spreads.
Examples:
- Overfishing of sardines reduces the food supply for predators and disrupts the balance of marine ecosystems.
- The destruction of habitats to make way for monocultures leads to the loss of pollinator species and reduces agricultural productivity.
- Diets that rely heavily on just a few crops, such as wheat, maize or soya, reduce agricultural diversity and increase vulnerability to pests and diseases.