Experience has shown that a ‘hope-for-the-best’ general approach to habitat management very often fails - invertebrates have been declining on many nature reserves as well as in the wider countryside. Ideally habitat management would be fine-tuned to suit every single species. This is currently impractical, firstly because knowledge of the ecology of most species is too imprecise, and secondly ecosystems are too complicated.
In recent decades the general pattern is that the commonest and ecologically most generalised species are mostly flourishing. However, those species with specialised habitat, or the least mobile, are declining. The loss of one or ten tiny species a year may not be noticed, but the cumulative loss mounts-up over the years and decades. Without appropriate action, the outlook could be a much impoverished invertebrate fauna in Britain.
The most practical approach has two elements:-
- Following the basic ecological principles tuned to invertebrates (see below).
- Developing a more refined knowledge and approach for species of particular conservation concern, and for species that can act as key indicator species for the well-being of many others.
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| Dolichopus sp© Ben Hamers |
What do invertebrates need?
1. Not all invertebrates have the same needs. This follows from the fact that many hundreds or thousands of species occupy the same site. Simple uniform approach to habitat management may not maintain biodiversity.
2. Invertebrates generally have to successfully breed every year, so it may only take one bad year to cause local extinction. Thus the right conditions have to be available every year and at the right time of year.
3. Continuity of habitat is essential. This may be at a fixed spot, or by rotational management (as in coppice woodland). The timing of habitat management may also have profound effects.
4. Vegetation structure is important. Some species like either short or long vegetation, or indeed bare ground. Isolated bushes may have a different fauna from a hedge or wood; young saplings different species from trees.
5. Shelter and aspect. Some species like to be exposed to wind, or live on cool moist north facing slopes. Most prefer warmth and some shelter so hedges and sunny nooks can be important.
6. Invertebrates need space to live. Although some species may survive within a few square metres, many only occur in very low numbers over a wide area, even if ideal habitat is available. A viable population of bumblebees may need a large area since each nest requires a large territory. There is now growing acceptance that small isolated colonies are doomed unless there is some genetic exchange with other colonies (the metapopulation concept), so acknowledging that many nature reserves are too small and restoring habitat links within the countryside will be crucial. The consequences of climatic change are all the more serious now that many habitats only survive as isolated fragments.
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| Adelphocoris © Ben Hamers |
7. Invertebrates often depend on juxtaposition of habitats, including edges, transitions in vegetation and habitat mosaic. Even something as simple as the presence or absence of certain flowers (perhaps cut for silage) can be crucial within the mosaic, or the location of bare ground (bee nesting places, sun bathing etc). Many invertebrates have different needs in different stages of their life cycle. This means that that sites managed for a single habitat (such as green parks) are unable to support a diverse and interesting fauna.
8. Invertebrate mobility is often limited. Whereas mobility is no real problem for a bird, many invertebrates lack the power of dispersal. This makes them extremely vulnerable to localised extinction, as they struggle to re-colonise from far afield. Species without wings have a particular problem, but even those that can fly may not move far enough. Thus site restoration may only work for part of the fauna. It is essential to act to prevent sites becoming impoverished in the first place.
9. The complexity of the web of life. Ecosystems are like a house of cards - pull out one too many and the whole edifice is vulnerable to collapse. For instance, many plants depend on certain types of pollinators, while insectivorous vertebrates (such as bats, shrews, birds) need their correct diet in plenty. Invertebrates themselves have complex webs of specialists on decaying organic matter, plants, predators and parasites within the balance of nature. Parasites may have their own parasites, which in turn have other parasites. As a particular species declines in numbers its parasites and also decline, so the consequences of losing one species could include the loss of many more dependent species.
10. Invertebrates have special habitats that historically have been poorly appreciated by the conservation movement.
For example:-
- Dead wood and veteran trees are essential to over 1,000 species found nowhere else.
- River banks and exposed river sediments-home to over 3,000 species of invertebrate.
- Stream faunas are also under threat from pollution and invasive alien species.
- Grazing levels ditches have especially good brackish (salty) invertebrate faunas.
- Soft rock cliffs and landslips (contain many rare species).
- Groundwater seepages / water abstraction (immense invertebrate importance).
- Wet woodland (under-rated by other naturalists).
- Brownfield sites (the last refuge for large faunas of pioneer habitats).
- Quarries (inappropriate restoration often results in invertebrate extinctions).
- Dung fauna (modern farm grass and veterinary products a big problem).
- Fungus faunas (about 1,000 species are dependent on fungus; may be severely impacted by the 'food-for-free' philosophy).
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| Garden cross spider (Araneus diadematus)
© Roger Key |
11. Wildlife under constant attack. Many of Britain's historically important invertebrate sites have declined due to a prolonged sequence of inappropriate habitat management decisions. The loss of one species a year in a large species group may not sound much, but over 50 or 100 years it amounts to a major reduction that leaves behind only the commonest species.
How do we conserve them?
Buglife is advocating a holistic (all embracing) approach to wildlife conservation, and that is the ideal that most conservation organisations aspire to. The plants and vertebrates are important, but so too is the largest element of animal life, the insects and other invertebrates. Buglife is promoting better understanding, and the will to ensure that biodiversity is maintained as a whole in order to overcome decline and impoverishment of habitats.
Click here to find out more about habitats and how to manage them for invertebrates.
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