Which habitats favor evolution of carnivory in plants?

Carnivorous plants grow best in places that are wet, sunny, and low in nutrients, where they don’t face much competition from other plants. Since the soil in these areas can’t provide enough key nutrients like nitrogen and phosphorus, they get them by digesting insects and small animals.

Common Habitats

• Bogs and fens: Wet, marshy areas with nutrient-poor soil. Bogs are especially acidic and low in minerals because moss (Sphagnum) pulls nutrients out of the soil.
• Wet, sandy savannas: Nutrient-poor soils that experience frequent fires. The fires clear away other plants, giving carnivorous plants space and sunlight.
• Mountain tops: Plants like sun pitchers (Heliamphora) grow in isolated, nutrient-poor mountain habitats in South America.
• Tropical rainforests: Pitcher plants (Nepenthes) often grow as epiphytes on other plants or in poor rainforest soils with little available nutrition.
• Wetland edges: Species like the Venus flytrap thrive at the borders of wetlands where the soil is damp but not underwater.
• Freshwater bodies: Aquatic plants like bladderworts (Utricularia) live in lakes, ponds, and swamps with low nutrients.

The Cost-Benefit Model

Carnivory works only in certain conditions, where the benefits of catching prey outweigh the energy costs of making traps.

• High costs: Producing traps, lures, and digestive enzymes uses a lot of energy. Many carnivorous plants also have less efficient leaves for photosynthesis.
• Nutrient stress: Carnivory is helpful when soil nutrients are very limited, making insects a valuable supplement.
• Light and water availability: With enough sun and water, plants can afford to invest energy in traps, balancing out their less efficient leaves.
• Low competition: In rich soils, faster-growing plants dominate. Carnivorous plants do better in poor soils where competition is minimal.

Trade-offs and Adaptations

Carnivorous plants adapt to their special habitats, but this often comes with sacrifices.

• Small root systems: Most have shallow roots that don’t absorb many nutrients, so they rely on capturing prey instead.
• No fungal partnerships: Unlike most plants, many carnivorous species don’t depend on fungi (mycorrhizae) to get nutrients.
• Tolerance to waterlogging: Their shallow roots don’t handle soggy soil well, but carnivory helps them survive in oxygen-poor, waterlogged conditions by giving them another way to get nutrients.