Invertebrate communities across wader habitats in Europe

Grassland breeding waders have been steadily declining across Europe.
Recent studies indicating a dramatic decline in grassland
invertebrates' abundance and biomass, the key food of most grassland
wader chicks, suggest a likely driver of the demise of waders. While
agricultural intensification is generally inferred as the main cause for
arthropod decline, there is surprisingly little information on the
relationship between land use intensity and total arthropod abundance in
grasslands. Here, we explored those relationships across several key wader
breeding habitats by surveying ground-active, aerial and soil-dwelling
invertebrate communities in five European countries that range from
natural undisturbed bogs to intensively managed grasslands. Using maximum
vegetation growth and soil moisture content, we investigated how they
shape the size of the invertebrate community within and across different
countries. We found predominantly positive relationships between grassland
invertebrate abundance, biomass and body weight with increasing vegetation
growth and soil moisture. Maximum vegetation growth was strongly
positively related to ground-active invertebrate abundance and biomass and
abundance of soil-dwelling invertebrates (mainly earthworms). Body weight
of aerial invertebrates furthermore increased with increasing maximum
vegetation growth. Our results provide little support for the hypothesis
that agricultural practices associated with intensification of grassland
management result in an abundance decline of invertebrate prey for wader
chicks. Conservation practices aiming to enhance wader chick survival
require a careful balancing act between maintaining habitat productivity
to secure high prey abundance and keeping productivity low enough to
maintain open swards that do not need to be cut before chicks have
fledged.