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Aim: Intraspecific variation in species relative abundance is shaped by a complex interplay of abiotic and biotic factors, making it both necessary and challenging to assess their combined relative importance in explaining variations across space and time. We used two congeneric butterfly species for which extensive count data and a deep understanding of their natural history is available to test three hypotheses explaining intraspecific variation in their abundance: (H1) seasonal dispersal behaviour driven by climate, (H2) resource availability and (H3) apparent competition mediated via shared parasitoids. Taxon: Gonepteryx rhamni (Brimstone) and G. cleopatra (Cleopatra). Location: NE Iberian Peninsula, where both species coexist, and a nearby archipelago (Balearic Islands), where only Cleopatra occurs. Methods: We analysed spatial abundance variations for both species in the mainland and island–mainland differences in the abundance of Cleopatra. Abiotic and biotic factors, including temperature, host plant and overwintering habitat availability, larval parasitism and density dependence, were tested to explain the observed variations. Results: H1 can explain variation in butterfly abundance between mainland regions since in warmer summers populations increased in cooler areas but decreased in warmer areas. H2 explains the variation within mainland climate regions with a strong positive relationship between resource availability and abundance but is unlikely to explain the island–mainland variation in the abundance of Cleopatra. H3 could neither explain biogeographical variation in abundance because although richer parasitoid communities were found on the mainland, larval mortality rates were similar or lower on the mainland than in the islands. Main Conclusions: Climate and resource availability jointly account for variation in butterfly abundance across the mainland, but neither these factors nor parasitism can explain island–mainland differences. Both coexisting butterfly species and their larval parasitoids may have undergone evolutionary processes, resulting in spatial segregation that promotes the coexistence of the two butterfly species on the mainland. [ABSTRACT FROM AUTHOR]

Aim: As parapatric distributions are traditionally studied by pairs of species, this study aims to evaluate the causes of the maintenance of parapatry, specifically to assess whether the case of the three viper species present in the Iberian Peninsula is mainly caused by environmental conditions, historical events, interspecific competition among them, or a combination of these factors. Location: The Iberian Peninsula. Taxon: Vipera aspis, V. latastei and V. seoanei.. Methods: We applied the concept of favourability of occurrence to produce commensurate distribution units unaffected by the prevalence of different species in the Iberian Peninsula. We compared the favourability of each species individually with the favourability of occurrence of more than one species co‐occurring in their overlapping ranges, and identified the areas in which sympatric coexistence, environmental segregation and competitive exclusion are predicted to occur. Results: The main driver of the parapatric pattern was competitive exclusion, which was mediated by gradual changes in the environmental conditions favouring each species. The para‐Mediterranean V. aspis presented fragmented favourable areas outside its range that seemed to be unoccupied due to competitive exclusion by the other vipers. The Mediterranean V. latastei appeared to be limited by competition with the other viper species and by the environment in north‐western Iberia. V. seoanei prevented the other two species becoming established in the north‐western quarter of the Iberian Peninsula due to its better adaption to the humid conditions in this region. Some areas of sustainable coexistence were detected, mainly in the upper reaches of the River Ebro. Main conclusions: Each species is better adapted to particular conditions. However, the existence of ecotones forces them to occur sympatrically and compete for resources. The parapatric pattern is a result of the evolutionary history of the species and of strong competitive interactions between them, which form 'competitive‐exclusion barriers'. However, these barriers are environmentally dependent, so changes in the environment could rapidly affect the limits of the species distribution. [ABSTRACT FROM AUTHOR]