AUTHORS: Jessica S. Kurylo*, Caragh G. Threlfall – School of Ecosystem of Forest Sciences, University of Melbourne; Karl L. Evans, Department of Animal and Plant Sciences, University of Sheffield; Nicholas S.G. Williams, Kirsten M. Parris – School of Ecosystem of Forest Sciences, University of Melbourne
ABSTRACT: Variability in urbanization intensity across the landscape generates spatial heterogeneity in urban plant communities. This may influence the fauna dependant on specific plant resources, but outcomes are understudied. We evaluate i) how larval host plant (LHP) richness and cover vary with urbanization, and ii) how these factors influence urban butterfly communities. We use Australia’s 2nd largest city, Melbourne, as a case study. Sixty 1-km transects selected using random stratification across the urbanization gradient were sampled for LHPs and butterflies. Generalized linear models were used to evaluate LHP response along an impervious gradient, the butterfly community response to LHP richness and cover, and to assess the relationship between individual butterfly species and their LHP abundance. Redundancy analysis was also used to understand how much of the variation within the butterfly community was explained by variation in LHP distribution.LHP richness and cover declined with increasing impervious surface cover. Butterfly richness and abundance had a stronger relationship with LHP richness than cover. Impervious surface cover had a negative effect on butterfly richness and abundance, but this effect was than that of LHP richness or cover. Variation in LHP cover explained 57% of the variation in the abundance of the four most common butterflies. Among these, three butterflies had a positive, significant relationship with the cover of one or two of their LHPs. Our study shows the local butterfly community was positively impacted by available LHPs, with LHP richness having more of an effect than either cover or impervious surface cover. The community’s structure was partly influenced by certain exotic LHPs more than natives. Thus, LHPs are providing an important resource for butterflies to complete their life cycle and maintain populations in an altered city landscape. This suggests that increases in certain LHPs may mitigate the negative impacts of urbanization on urban butterflies.
