This diagram shows the drop in biomass (or energy) between trophic levels in what is often called a trophic pyramid. It also brings in the links that complete the chain. All creatures die, and all animals produce waste products, and this now non-living material is consumed and broken-up by detritus eaters like woodlice, millipedes and many insects.
Decomposers such as bacteria and fungi complete the process of breakdown, turning waste matter back into the nutrients that plants turn into biomass.
Primary producers - the plants
Plants are the powerhouse of your garden, and generally you can choose the species that grow in your garden. All plants need light, air, water and nutrients but they come in a huge variety. As well as trees, shrubs, perennials and annuals, there are algae growing in your pond and on shaded tree trunks, and lichens on walls and trees.
Some plants, such as legumes, have symbiotic nitrogen-fixing bacteria in their root nodules, and so can fix atmospheric nitrogen and increase their nutrient supply. Many plants - in fact the majority - have a relationship with mycorrhizal soil fungi in their roots, which make them much more efficient at extracting water and nutrients.
Find out more about garden plant ecology in our leaflet Garden Plant Ecology
and find lots of advice about using plants in the garden in our Plants and Planting section. Gardens contain wild plants too, and you can find more about them in the Plants section of Garden Wildlife
It’s clear that herbivores don’t destroy all plant material in gardens (with my cabbages a possible exception). Most plant primary production is recycled as dead material, such as fallen leaves, in the soil and in the compost heap. Nevertheless, there is a great diversity of garden herbivores, many of which are definitely not a problem, and even beneficial. The principal groups of herbivores are:
- Slugs and snails
- Sucking insects: True bugs, including aphids, spittle-bugs and shield bugs
- Chewing insects: Beetles, sawflies and caterpillars of butterflies and moths.
- Leaf miners and galls: insects living inside leaves or within plant overgrowths.
- Pollinators: Bees, hoverflies and other insects that take nectar (and pollen) are beneficial herbivores, although some (like aphid-eating hoverfly larvae) may have a different way of feeding as larvae.
Read more about the range of herbivores in our leaflet Garden Herbivores
and find out about individual groups of herbivores in the Garden Wildlife section of this website.
Predators and parasites
Garden predators are high up the trophic pyramid, so that they are less numerous and add up to less biomass than herbivores or detritus eaters, but they are by far the most diverse group of animals in the garden. By eating other animals, predators get very concentrated high quality food, and can afford to put a lot of energy into getting it, or surviving without feeding frequently. Many predators have evolved very specialist and cunning techniques to catch food. This perhaps explains the diversity of predators, compared with herbivores that have to spend most of their time eating, because plant leaves are not very nutritious. The main groups of garden predators are:
- Vertebrates:Many garden vertebrates are predators or take at least some animal food.
- Predatory true bugs: Not all bugs suck plant juices, many do the same to herbivores and can be useful pest controls.
- Parasitoids: Crucially important and diverse insects that lay their eggs in other insects, and provide natural (and commercially available) pest control.
See Garden Predators
for an introduction to these animals, and look in Garden Wildlife for more about individual groups.
Detritivores and decomposers
Plants may be the primary producers, but gardens and the whole world would be knee-deep in dead matter without the countless usually tiny organisms that break down dead material and waste. As ever, the boundaries between trophic levels can be blurred, and some herbivores, such as snails and slugs, eat dead or dying plant material as well as living. The main groups of detritivores and decomposers are:
- Bacteria, fungi and actinomycetes - which do the bulk of decomposing
- Nematodes and springtails
- Woodlice - not insects but terrestrial crustaceans
- Beetles and flies
Find out more about these important creatures in Detritivores and Decomposers
, and in the Garden Wildlife section. Look at the Compost and Fertility page to see how gardeners can make good use of their garden decomposers.
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