Introduction:
In the debate regarding global biodiversity decline, urban areas have
sometimes been suggested to promote diversity (Cardinale et al., 2018).
Urbanisation involves changes in the landscape, soil modifications,
climates changes, and biodiversity loss, resulting in a distinct
ecosystem (Rodrigues et al., 2018). Fragments of semi-natural spaces
such as parks, gardens, and other green areas may provide a diverse
plant composition and fulfil ecosystem functions needed to maintain
urban wildlife (Townsend, 2008). But they also host ornamental or
non-native plants which fail to support native wildlife. Urban habitats
place stronger environmental constraints on plant and animal communities
than rural ecosystems and may disrupt ecological interactions between
plants and pollinators via habitat fragmentation (Hennig and Ghazoul,
2011). Impacts on species richness in urban areas are dependent on the
specific taxonomic group, the spatial scale of analysis, and the
intensity of urbanisation (McKinney, 2008). A greater species richness
in urban areas may be due to the increased number of both native and
non-native species, due to the larger species pools that urban areas
maintain (Dolan et al., 2011). Moderate levels of urbanisation lead to
varying patterns of species diversity across taxonomic groups,
particularly when there are sufficient corridors of green space to allow
colonisation from the regional species pool (Rega-Brodsky, et al.,
2022). Effects of urbanisation on top-down control (e.g., altering
predation by birds) or bottom-up control (e.g., altering vegetation
structure) could also lead to indirect effects on abundance, species
diversity, or community composition throughout the food web (Theodorou,
2022).
Urban areas can be characterised as a spatial assemblage of people whose
lives are structured around non-agricultural activities, with rural
areas defined as any place that is not classified as urban (Weeks,
2010). Urban areas can also be classified as land that is built over,
while rural areas consist of land that is not built over and with a much
smaller population size (Bibby and Shepherd, 2004). Rapid urban
development and expansion in recent years have altered many wildlife
assemblages, especially invertebrates (Van Swaay and Warren., 1999).
Perhaps the most well studied group is butterflies, as they are popular,
easy to identify, and have been used as model insects for many years
(Warren et al., 2021). But butterflies are also in decline due to severe
habitat loss and climate change (Zografou et al., 2009). More generally,
butterflies are important indicators of ecosystem health due to their
susceptibility and sensitivity to changes in the environment (Ghazanfar
et al., 2016). Butterflies have a high reproductive rate and occupy low
trophic levels; thus, they respond quickly to environmental stressors
and could be utilised as a proxy for general reductions in wildlife
(Ghazanfar et al., 2016). Here, we focus on butterflies as indicator
taxa, whilst considering the impact of urbanisation on their predators
and resources.
Urbanisation has been shown to degrade bird communities through species
decline and functional homogenisation (Tzortzakaki et al., 2018). The
main factors affecting bird species assemblages are green space
availability and noise pollution (Rodrigues., 2018). Collisions with
buildings in urban areas also heavily affects bird populations,
including species of conservation concern (Hager et al., 2017). Vincze
et al. (2017) found that in urbanised areas there was an increase in
predation of bird nests by urban exploiters such as crows (Corvus spp),
magpies (Pica pica ), and cats (Felis silvestris catus ).
However, it is also suggested that prey populations of birds thrive in
urban areas as these habitats are low in abundance of larger predators
(Vincze et al., 2017). Cities and towns have variability in terms of the
activity or usage of areas, thus bird species distribution in urban
areas is related to the degree of urbanisation and habitat features such
as tree and shrub cover and the density of buildings (Rodrigues et al.,
2018). Moreover, human landscape characteristics favour species that can
exploit novel resources and adapt to new habitats, such as hooded crows
(Corvus cornix ), house sparrows (Passer domesticus ), and
pigeons (Columbidae spp ) (Kark et al., 2007).
The high abundance of adaptive birds in urban environments could thus
have negative impacts on invertebrates, specifically butterfly
populations compared to rural habitats. However, butterflies have
developed various defensive traits against birds, such as chemical cues
and aposematic or cryptic colouration, i.e., bright colours in
conspicuous patterns on the wings (Paladini et al., 2018). Additionally,
many butterflies have adopted fast, unpredictable flight and weak,
fragile wings that allow escape by tearing when pecked by birds
(Pinheiro and Cintra, 2017). Brighter colouration signals are commonly
associated with potent defence and greater reproductive success, as
predators are naturally deterred, within-species rivals are more
cautious, and potential mates are more interested (Yeager and Barnett,
2021). Due to the high frequency of beak marks on the wings of
butterflies, birds are likely their most significant predator (Pinheiro
and Cintra, 2017). Nonetheless, small mammals, toads, and lizards also
feed on adult butterflies, and there may be significant predation by a
variety of invertebrates (Londt, 1999).
Changes in the patterns of vegetation composition and structure in urban
areas, can lead to a reduction of bird species richness and selection
for omnivores, carnivores, and species which nest in cavities (de Toledo
et al., 2012). But native vegetation diversity within green spaces can
strengthen the abundance and richness of specialist and insectivorous
bird species (Silva et al., 2021). Furthermore, urban vegetation is
necessary for mitigating urban heat islands, floods, increasing carbon
storage, improving biodiversity, and benefitting human health (Chen et
al., 2022). Plant biodiversity is greatly affected in urban areas by the
introduction of exotic, non-native species, changes in microhabitat
availability, and altered landscape patterns (Peng and Liu, 2007). The
introduction of non-native plant species in urban areas degrades
habitats and shifts community composition, which can influence ecosystem
services and habitat resilience (Dolen et al., 2011). Urbanisation also
alters the timing of important reoccurring plant phenology events, such
as flowering and leaf-out, leading to cascading consequences on the
species within a community and disturbing important interactions such as
pollination and herbivory (Li et al., 2019). The gross primary
productivity of vegetation also decreases with increasing levels of
urbanisation from loss of green land and changing macro-environment
(Chen et al., 2022). While habitat enhancements of exotic species may
increase ecosystem resilience and integrity, restoration of native
communities in urban areas may increase connectivity to surrounding
rural landscapes and support native ecosystems (de Carvalho et al.,
2022).
There is a mutual and historical co-evolution in operation between
plants and invertebrates (Ghazanfar et al., 2016). Co-evolutionary
traits include adaptive radiation of plants that evolved to have
chemical protection from herbivores, followed by adaptive radiation in
herbivores who developed characteristics to counter this defence (Feeny,
1975). For example, the butterfly proboscis attachment has adapted to
reach the nectar at the base of long-tubed flowers (Ghazanfar et al.,
2016). Alternatively, some skippers (Hesperiidae) are only capable of
utilising shallow blossoms, such as flowers in the myrtle family
(Myrtaceae) (Ghazanfar et al., 2016). Smaller plant patches found in
urban environments tend to receive fewer pollinator visits and suffer
pollen limitation (Barker, 2018). This reduces genetic exchange and
flowering plant diversity, and consequently, supports fewer pollinator
species. Yet, low building density and the presence of green space
within urban areas, may drive pollinator movement and thus gene flow
between patches (Hennig and Ghazoul, 2011).
Whilst anthropogenic disturbances are fostering negative impacts on
butterfly species, human practices have created agricultural and
woodland management systems such as hay meadows and coppicing that
assist the growth of butterfly populations (Dover and Settele, 2009).
The Mediterranean is one of the world’s 25 biodiversity hotspots, mainly
due to the abundance of endemic species within this area (Lopez-Villalta
et al., 2010). The Aegean Sea is located within the Mediterranean where
butterfly species vary between the islands. In this area, Haahtela et
al. (2019) recorded the highest levels of diversity on Samos Island (64
species) and Lesbos Island (63 species) (Haahtela et al., 2019). The
evolution, extinction, and species migration of animals and plant
species over archipelago islands are reflected in the pattern of species
diversity (Dennis et al., 2000). Therefore, a distinct and endemic
species assemblage of butterflies may be present across the Aegean
islands. This highlights the importance of green space within
Mediterranean urban areas and a demand to assess the butterfly species
within this environment. The study of butterflies within the Aegean
region is severely lacking and mainly focuses on biogeographical studies
(e.g., Dennis et al., 2000; Hammoud et al., 2021; Hausdorf and Hennig,
2005), thus, the specific habitat types that butterflies utilise is not
known. When studying Tuz Lake in Turkey, Seven (2017) compared habitat
preferences of butterflies and observed the highest species diversity
within the steppe habitat (defined as semi-arid grassland) and the
lowest diversity in the stony and rocky area (poorly vegetated areas
dominated by rocks), indicating that species may prefer vegetated and
shaded areas. Due to the global decline of butterflies, the exploration
of urban green space as a possible diversity hotspot is crucial and
contributes to current research. As butterfly ecology has been seldom
studied within the Aegean, an investigation of the urban and rural
habitats adopted by butterflies in island ecosystems is of high
ecological importance.
This study aims to compare the ecological communities found in rural
areas and urban green spaces on Lipsi Island, Greece. It is hypothesised
that total abundance, species richness, and Shannon diversity of (1)
butterflies, (2) birds, and (3) vegetation will be higher in rural
compared to urban sites and that (4) urbanisation will have an impact on
community composition of each trophic group.