Over 8,000 species?
The total only included the invertebrate groups Owen could sample and identify. Adding in the many groups (such as most flies and soil creatures) she couldn’t study, and assuming a similar proportion of the British species of these groups live in gardens, she arrived at a best estimate of 8,450 species of insects in her garden. She also presented evidence that the great majority of the animals she found were feeding in the garden, and that, depending on the group, between 20% to all of them were resident breeders. As Ken Thompson’s account shows, later work in Sheffield and several other cities has broadly confirmed Jennifer Owens findings.
Owen’s remarkable total is primarily a tribute to the intensity of her collecting and observation in one place over a long period. Few nature reserves have remotely such comprehensive lists, and a thirty year study in some could yield comparable diversity. Nevertheless, her work, backed up by later studies, shows a single garden can hold exceptional biodiversity in a tiny area.
The flies of Malham Tarn National Nature Reserve in North Yorkshire have been subject to intensive scrutiny for decades, and the total list is far in excess of the number of species recorded in Owen’s garden. Partly that’s because the garden is much smaller, and partly because only one family of flies (hoverflies) has been studied intensively in the garden.
Remarkably, more species of hoverflies have been recorded in Owen's garden than in the nature reserve. Does that mean Owen’s garden is in any sense ‘better’ than the nature reserve? No, it doesn’t, but it does illustrate just how good gardens can be for groups of animals that find the habitat particularly suitable for them.
How do gardens sustain great biodiversity?
Jennifer Owen considered this question, and came up with some answers that still seem reasonable. In summary, we can suggest the following factors:
Contrived plant diversity - Gardeners putting in lots of different plants
Garden habitats emulate semi-natural habitats in our countryside
Changes in garden biodiversity
Unfortunately, the wildlife of Britain is generally in steep decline, and that of gardens is following the same trend. Read Changing garden biodiversity
for some facts and figures on declining - and a few increasing species. With mounting pressure on the countryside for housing and growing food gardens may become increasingly important for wildlife.
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