Ground-dwelling invertebrate diversity in domestic gardens along a rural-urban gradient: Landscape characteristics are more important than garden characteristics

Abstract

Urbanisation is increasing worldwide and is regarded a major driver of environmental change altering local species assemblages. Private domestic gardens contribute a significant share of total green area in cities, but their biodiversity has received relatively little attention. Previous studies mainly considered plants, flying invertebrates such as bees and butterflies, and birds. By using a multi-taxa approach focused on less mobile, ground-dwelling invertebrates, we examined the influence of local garden characteristics and landscape characteristics on species richness and abundance of gastropods, spiders, millipedes, woodlice, ants, ground beetles and rove beetles. We assume that most of the species of these groups are able to complete their entire life cycle within a single garden. We conducted field surveys in thirty-five domestic gardens along a rural-urban gradient in Basel, Switzerland. Considered together, the gardens examined harboured an impressive species richness, with a mean share of species of the corresponding groups known for Switzerland of 13.9%, ranging from 4.7% in ground beetles to 23.3% in woodlice. The overall high biodiversity is a result of complementary contributions of gardens harbouring distinct species assemblages. Indeed, at the garden level, species richness of different taxonomical groups were typically not inter-correlated. The exception was ant species richness, which was correlated with those of gastropods and spiders. Generalised linear models revealed that distance to the city centre is an important driver of species richness, abundance and composition of several groups, resulting in an altered species composition in gardens in the centre of the city. Local garden characteristics were important drivers of gastropod and ant species richness, and the abundance of spiders, millipedes and rove beetles. Our study shows that domestic gardens make a valuable contribution to regional biodiversity. Thus, domestic urban gardens constitute an important part of green infrastructure, which should be considered by urban planners.

Owners’ Perceptions Do Not Match Actual Ground-Dwelling Invertebrate Diversity in Their Gardens

“…The number of native plant species was thereby regarded as a surrogate of the naturalness of a garden. We recorded native plant species along transect lines proportional to the relative area of different habitat types (see [20]). We did not assess species richness of horticultural plants, as many of them are characterized by several varieties.…”

“…Additional techniques were employed for snails and slugs (visual search and soil sieving) and millipedes and ants (visual search). Sampling was performed between 31 May and 18 October 2018 (for details see [20]). The collected individuals were determined at the species level by experts during the following months.…”

“…We found 173 native plant species in the 33 gardens examined. Altogether, we obtained 3181 individuals of snails and slugs (39 species), 3014 spider individuals (52 species), 7834 woodlice individuals (10 species), 33 ground beetle individuals (20 species) and 1211 rove beetle individuals (85 species), 6373 millipede individuals (21 species) and ant individuals belonging to 28 species [20].…”

“…For example, in Switzerland, private gardens cover more than 1% of total land area (see [18]). Furthermore, there is increasing evidence that the private gardens of a city taken together harbor significant shares of the countrywide biodiversity [19,20]. This is of particular importance in light of the dramatic biodiversity crisis, including insect decline [21][22][23][24][25].…”

“…An individual's perception of overall biodiversity is frequently based on the abundance of conspicuous taxa such as flowering plants, butterflies, birds and some small vertebrates (e.g., frogs, lizards, hedgehogs, squirrels) [10,34,35]. Similarly, studies of garden biodiversity have often focused on conspicuous groups including flowering plants, pollinators and birds (e.g., [30,[36][37][38]) and did not consider small ground-dwelling invertebrates (see [20,31,39,40]). Numerous studies have shown that these proxies do not necessarily reflect overall biodiversity in open habitats including gardens [20,35,41].…”