Vegetation
The lack of significant differences in the abundance, richness, and
diversity of plants between urban and rural sites (Figure 6D-F) could be
due to incomplete sampling, with just 76% of potential plant species
identified. Nevertheless, our species accumulation curves exhibited long
tails of rare plants, suggesting that any missed species would have
contributed very little to the overall percentage cover of the plant
communities. Indeed, two of the top three plants by percentage cover in
both rural and urban environments were mastic shrub (P.
lentiscus ) and slender wild oat (A. barbata ), highlighting the
prevalence of native, unmanaged vegetation within urban green spaces on
Lipsi. Whilst rural areas had significantly more shrubs and less bare
ground than urban sites, there was no difference in the cover of trees,
which are scarce on Lipsi, negating the possibility for greater tree
cover to promote butterfly species richness (Kurylo et al. 2020). The
lack of a marked difference in vegetation structure between urban and
rural areas could thus be a key factor in explaining the similarity in
butterfly abundance and diversity across habitats. A prevalence of
non-native plant species in urban areas may prevent larval development
of butterflies (Dylewski et al., 2019), but exotic species were only
present at three urban sites and in low abundance, limiting their
potentially negative effects on butterflies. Furthermore, butterfly
abundance responds negatively to non-native plants in late spring and
positively by mid-summer (Kurylo et al., 2020), highlighting the
importance of greater temporal resolution of sampling to characterise
vegetation effects on butterflies.
Urbanisation altered vegetation community composition (Figure 7C), with
cultivated species such as barley (H. vulgare ), castor bean
(Ricinus communis L., 1753), and scutch grass (Cynodon
dactylon Persoon, 1805) prevalent in urban environments, while natural
desert saltgrass (D. spicata ) dominated in rural environments.
This may have contributed to the observed differences in butterfly
community composition, with cultivated patches hosting different
butterfly assemblages than natural forests and scrub (Chong et al.,
2014). As noted above, the dominant butterflies in urban environments
(geranium bronze, scarce swallowtail, and mallow skipper) are highly
associated with cultivated plants, which were prevalent in urban areas
(Stefanescu et al., 2006; Tzortzakaki et al., 2019). In contrast, the
dominant butterflies in rural environments (Freyer’s grayling and meadow
brown) depend on meadows and grasslands, which were largely absent from
urban areas (Merckx and Van Dyck, 2002; Grill and Cleary, 2003). Thus,
whilst we did not detect any effect of urbanisation on the abundance or
diversity of the vegetation and butterfly assemblages, the observed
changes in dominance patterns and species composition between rural and
urban environments could have major implications for ecosystem
functioning, which should be quantified in future studies.