The concept of a 'food chain' is well understood by most people, as is the idea of 'food webs'. The full implications of these relationships between animals (and plants) are a little more complicated to get to grips with, and the recent term – 'interaction webs' needs a bit of explaining.
Food Chains and Webs
- Lettuce is eaten by rabbits, and rabbits are eaten by foxes – that's a simple 'food chain'.
- Lettuce is eaten by rabbits, and snails, and humans. Lettuce and rabbits (and in some places snails) are all eaten by humans, but snails are also eaten by thrushes and hedgehogs, and thrushes are eaten by predatory birds – and so on into a very complicated 'food web'.
The concept of 'interaction webs' goes further than this – it considers the way one animal species can affect the well-being of others without actually eating them.
Interaction Webs
Earthworms burrow through the soil and aerate it, and moles do the same sort of thing. Both have a direct effect on soil structure and fertility, influencing thousands of plants and animals that require specific soil conditions. Moles eat earthworms, so the balance between these two species will also be important.
Many other animals will also eat earthworms (food webs), and although these animals may not eat the small soil-dwelling creatures or plants, they will affect them – they will interact in a web-like way.
So – much more needs to be considered than just what eats what. How different animals (and plants) interact with their whole ecosystem and environment needs to be taken into account if we are to understand the ways in which any animal affects its environment.
Top Predators
Jenny Marder (Scientific American, 2011) quotes from a recent paper which is a synthesis of the work of more than 20 scientists ... to study the impacts of large predators across global systems (Science, 2011): '... ecosystems are built around "interaction webs" within which every species can influence many other species'.
Top predators play a very important role, and while many examples of the ways in which they influence their ecosystems could be quoted, two suffice:
- 'Sea Urchins are capable of rapidly destroying kelp by nibbling away at the holdfasts (which anchor the kelp to the sea-bed), and the urchins are only kept under control by Sea Otters who like to eat them. Remove the Otters and the urchins have a field-day, rapidly destroying the kelp.' From Sea Otters – Kelp Management Specialists Hunted to the Edge of Extinction.
- 'The removal of top predators causes lasting damage to coral reefs and is even more serious a threat than overfishing.' From Spearguns and Powerboats Harm Reef Biodiversity – Trophy Hunting for Specimen Fish Alters Ecosystems.
Implications for Resource Managers
Marder quotes Paul Dayton, of the Scripps Institution of Oceanography, as saying: '... we manage through the Endangered Species Act ... it's a horrible way to manage ecosystems ... we're trying to save little fragments ...' , and Estes (Science 2011) makes the point that by looking at ecosystems primarily from the bottom up, resource managers have been focusing on only half of a very complex equation.
This means that managing ecosystems needs to take into account a vast number of animal-animal, animal-plant, plant-plant (and fungi, algae, micro-organism, ...) interactions if they are to be effective. The real problem is that most of what is needed has never been researched.
And – it is worth remembering that the top predator of all is, of course, us!
Sources:
- 'Trophic Downgrading of Planet Earth', Estes and Pikitch - Science, July 15 2011.
- 'Loss of top animal predators has massive ecological effects' - Science News, 2011.
- 'Loss of Top Predators Has More Far-Reaching Effects than Thought', Jenny Marder - Scientific American, 2011.
