Invertebrate biodiversity in the UK
Invertebrate biodiversity in the UK is huge – there are more than 24,000 species of insect alone. We know that many butterflies, moths and bees have declined in abundance over recent decades, but there are thousands of species that we know almost nothing about – not many people can (or want!) to identify flies, for example. That said, the UK probably has the greatest wealth of amateur naturalists and species experts anywhere in the world, and their species records and expert knowledge are invaluable in our effort to understand how invertebrates are being affected by climate change. In addition, more and more members of the public are recording the plants and animals they see in their gardens and when out and about, and through schemes such as iSpot and National Moth Night. These combined mean that we have a huge database of over 100 million records of species in the UK, which we can use to investigate if species are being affected by changing climate.
As temperatures in the UK have increased over the past decades, many invertebrates have moved towards the cooler north, including those that we might not expect to be very mobile like woodlice. Other insects have recently arrived in the UK from continental Europe, such as the small red-eyed damselfly and tree bumblebee, and are now spreading through the country.
As species move northwards, they replace similar but more northern species. This ‘simple’ switching of species can have unexpected consequences. For example, invertebrate grazers of seaweed on rocky shores are more diverse in the warmer southern waters of the UK. As these southern grazers move north with rising temperatures, they can reduce the abundance and diversity of seaweed, reducing the shelter and protection available to other species.
With the warmer springs of recent years, life-cycle events of many species now occur about two weeks earlier. But not all species have shifted their timing at the same rate and there is now mis-match between plants, herbivores and predators, and between plants and their pollinators. Blue tit chicks are no longer hatching at the same time as when their caterpillar food is most abundant, resulting in fewer and smaller chicks surviving. The only pollinator of the Early-Spider Orchid, the solitary bee Andrena nigroaenea, now emerges earlier than the orchid flowers, leading to poorer pollination.
Some animals will be able to adapt to changing climate by altering their behaviour. For example, butterflies like the silver-spotted skipper could switch to use taller, shadier vegetation where the microclimate is cooler. So we might be able to manage habitats to make them more suitable in the face of changing climate – e.g. leaving areas of taller grass or shading streams with trees.
Some species can also move northwards with increasing temperatures. However, habitats in the UK are highly fragmented and without management to connect these patches, species will be less able to keep pace with climate change.
Also, some habitats and their specialist invertebrates, are particularly vulnerable to climate change. Montane and snow bed habitats in the Scottish Highlands are already being lost as temperatures increase, threatening the already rare Arctic whorl snail and Scottish mountain spider. Salt marshes are threatened by rising sea levels but, unlike snow beds, we are able to create new habitat to replace the losses. Managed Coastal Realignment, where sea walls are moved inland and the sea is allowed to flood former agricultural land, creates new salt marsh habitat for specialist plants and animals, and has the additional benefit of providing being a sea defence in its own right. These sites, such as Steart Marshes (http://steart.wwt.org.uk/), are quickly colonised by salt marsh plants (centre image), which in turn support invertebrates. Schemes such as these are essential to help mitigate the impacts of climate change.