Hugh Harris: MBAN Abroad - Wicken Fen, part 1


Food Web in Wicken Fen

The century old habitat is made up of many different species. The Saw sedge Cladium mariscus predominates but other plants also thrive. These include Marsh bedstraw Galium palustre and Bindweed Convolvulus arvensis. Invertebrate species found here include snails and beetles. 

This can be clearly seen by comparing the species of two neighbouring fen habitats-- a fen meadow and woodland. The meadow is filled with grass and wildflower species. There's the Marsh pea Lathyrus palustris, for instance and Thistles Asteraceae. These plants are home to a wide variety of invertebrate species.

The woodland habitat beside the meadow includes tree and shrub species like Hawthorn Crataegus monogyna. This habitat is suitable for a different group of invertebrates.

Biodiversity doesn't simply depend on the range of habitats. It's also influenced by the way species interact with one another. This is the Lode, the main water channel running through Wicken Fen. One way its plants and animals interact is through the food web. Each species is food for other species. The more species there are to eat, the more there will be eating them. The food web underpins biodiversity because it means many different organisms can coexist.  At the base of a food web are plants. The slow-flowing clear waters of the Lode offer the perfect growing conditions for submerged aquatic plants. Plants use energy from the sun to create new tissue through photosynthesis. 

In the Lode waters, herbivores like Water snails Gastropoda nibble the aquatic vegetation. Small carnivorous fish, including Roach Rutilus rutilus and Minnow, Phoxinus phoxinus are prey for larger, freshwater carnivores like Pike Esox lucius. While some of these species spend their entire lives under water, others may move between habitats at different stages of their development and so become part of different food webs. 

Dragonflies and damselflies Ordonata, for instance, spend much of their life under water as larvae and emerge from the water when they mature. In the process, they're part of two food webs-- the aquatic and the terrestrial.

Underwater the larvae are carnivorous even pursuing a water snail. But at the same time they are food for other carnivores. A carnivorous insect, the Water boatman, feeds on damselfly larva. Within the aquatic food web, the larvae are both predator and prey. 

Now part of the terrestrial food web, adult damselflies and dragonflies are also prey for a diversity of carnivores including Spiders Araneae, Wasps Vespidae, Frogs Anura, and small mammals. This example demonstrates how complex food webs support many species within the habitat. So the range of habitats, the diversity of species, and the complicated way in which parts of the food web interact, are all factors in determining biodiversity.