Persistence of butterfly populations in fragmented habitats along urban density gradients: motility helps

Abstract

In a simulation study of genotypes conducted over 100 generations for more than 1600 butterfly’s individuals, we evaluate how the increase of anthropogenic fragmentation and reduction of habitat size along urbanisation gradients (from 7 to 59% of impervious land cover) influences genetic diversity and population persistence in butterfly species. We show that in areas characterised by a high urbanisation rate (>56% impervious land cover), a large decrease of both genetic diversity (loss of 60–80% of initial observed heterozygosity) and population size (loss of 70–90% of individuals) is observed over time. This is confirmed by empirical data available for the mobile butterfly species Pieris rapae in a subpart of the study area. Comparing simulated data for P. rapae with its normal dispersal ability and with a reduced dispersal ability, we also show that a higher dispersal ability can be an advantage to survive in an urban or highly fragmented environment. The results obtained here suggest that it is of high importance to account for population persistence, and confirm that it is crucial to maintain habitat size and connectivity in the context of land-use planning.

Gene flow and genetic drift in urban environments

“…For organisms that are highly mobile or those that thrive in urban habitats, urbanization may facilitate gene flow among populations directly via humanmediated transport, where humans voluntarily or accidentally move organisms to new habitats (Crispo et al, 2011). For example, highly mobile organisms are expected to be less impacted by habitat fragmentation than less-mobile species (Medina, Cooke, & Ord, 2018;Rochat, Manel, Deschamps-Cottin, Widmer, & Joost, 2017). Human modification to the landscape can also indirectly increase dispersal rates between populations by creating corridors (e.g., linear parks) or removing barriers (e.g., high-traffic roads or stream impoundments) to gene flow (Blair, 1996;Crispo et al, 2011;Holderegger & Di Giulio, 2010).…”

Urbanization‐driven homogenization is more pronounced and happens at wider spatial scales in nocturnal and mobile flying insects

“…For instance, butterfly sampling in and around Boston, Massachusetts, USA, showed that while increased urbanization is associated with decreased butterfly species richness, regionally rare and specialized butterflies are most affected, disappearing 2.9-4.5 times faster than ubiquitous and generalist species (Clark, Reed, & Chew, 2007). Simultaneously, the fragmentation of the remaining habitat types is expected to filter for mobile species (Piano et al, 2017;Rochat et al, 2017;Sattler et al, 2010). For instance, it has been shown for butterflies that the increased costs associated with investment in higher dispersal ability eventually result in enhanced chances of survival in urban environments (Olivier, Schmucki, Fontaine, Villemey, & Archaux, 2016;Rochat et al, 2017;Wood & Pullin, 2002).…”

“…Simultaneously, the fragmentation of the remaining habitat types is expected to filter for mobile species (Piano et al, 2017;Rochat et al, 2017;Sattler et al, 2010). For instance, it has been shown for butterflies that the increased costs associated with investment in higher dispersal ability eventually result in enhanced chances of survival in urban environments (Olivier, Schmucki, Fontaine, Villemey, & Archaux, 2016;Rochat et al, 2017;Wood & Pullin, 2002). Moreover, the UHI-effect is expected to favour thermophilic, warm-adapted species (Brans, Govaert, et al, 2017;Piano et al, 2017), although adaptive thermal evolution to urbanization happens intraspecifically too (Brans, Jansen, et al, 2017).…”

“…Within the context of urbanization, functional homogenization is set to favour generalist species due to a severe reduction in the types of habitat resources on offer within urbanized settings (Deguines, Julliard, Flores, & Fontaine, ; Devictor, Julliard, Couvet, Lee, & Jiguet, ; Knop, ; Lizée, Mauffrey, Tatoni, & Deschamps‐Cottin, ). Moreover, the fragmentation sensu stricto of the remaining habitat types is expected to filter against low‐mobility species (Rochat, Manel, Deschamps‐Cottin, Widmer, & Joost, ; Sattler, Duelli, Obrist, Arlettaz, & Moretti, ), since mobility mitigates reduced resource connectivity (Cote et al, ; Parris, ). For instance, local filtering on traits known to covary with increased dispersal has been demonstrated for urban communities of vascular plants, carabid beetles and macro‐moths (Concepción, Moretti, Altermatt, Nobis, & Obrist, ; Merckx, Kaiser, & Van Dyck, ; Piano et al, ).…”

Increased body size along urbanization gradients at both community and intraspecific level in macro‐moths

“…However, because smaller size is linked to reduced dispersal capacities in macro‐moths (Nieminen, Rita, & Uuvana, ; Slade et al., ), we predict local filtering for larger moths with increasing urbanization, so as to effectively mitigate the increased fragmentation (i.e., reduced functional connectivity among habitat resources) in urban settings (Parris, ; Bonte & Dahirel, ; Cheptou, Hargreaves, Bonte, & Jacquemyn, ; Cote et al., ). For instance, for butterflies it has been shown that the increased costs associated with investment in higher dispersal ability eventually result in enhanced chances of survival in urban environments (Wood & Pullin, ; Rochat, Manel, Deschamps‐Cottin, Widmer, & Joost, ). Similarly, local filtering on traits known to covary with increased dispersal behaviour has been demonstrated for urban communities of vascular plants and carabid beetles (Concepción, Moretti, Altermatt, Nobis, & Obrist, ; Piano et al., ).…”