The urbanization process systematically leads to the loss of biodiversity. Only certain arthropods are resilient to the urbanization process and can thrive in the novel conditions of urbanized landscapes. However, the degree to which arthropod communities survive in urban habitats depends on landscape and local effects and biological interactions (e.g., trophic interactions). In the present study, we examined the relative importance of various factors at landscape (isolation, edge density and area of surrounding greenery) and local (size of park, canopy cover, understory vegetation cover, defoliation depth, weight of dried leaves, soil temperature, soil moisture, and soil pH) spatial scales on the diversity of ants, beetles and spiders in urban parks. Our results indicated that park edge density was negatively correlated with diversity metrics in ants, beetles, and spiders in urban parks relative to the degree of proximity with the peri-urban forest. In other words, parks that located adjacent to the peri-urban forest may not necessarily have high biodiversity. The results suggested that man-made structures have been effective dispersal barriers that limit the spillover effects of ants and spiders but not the spillover of comparatively strong fliers, such as beetles. However, the area of surrounding greenery may have facilitated the colonization of forest-dependent taxa in distant parks. Large parks with reduced edge density supported a higher arthropod diversity because of the minimal edge effect and increased habitat heterogeneity. Vegetation structure consistently explained the variability of ants, beetles, and spiders, indicating that understory plant litter is crucial for providing shelters and hibernation, oviposition, and foraging sites for the major taxa in urban parks. Therefore, efforts should focus on the local management of ground features to maximize the conservation of biological control in urban landscapes.

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Living in aggregations likely gives fitness benefits to resistant German cockroaches. We first investigated the trade‐offs in life‐history traits between six field pyrethroid‐resistant German cockroach strains and a laboratory susceptible strain (SUS‐1). Second, each strain was placed in groups of 2, 10, 20, 30 and 40 individuals with an equal sex ratio in each group to investigate the effect of social aggregation on fitness and overall population parameters. All resistant strains exhibited reduced nymphal survival (50%–83%) and a prolonged development period in both male (49–63 days) and female (47–62 days) nymphs when compared to SUS‐1 individuals (nymphal development period: 39 ± 2 days for male and 40 ± 3 days for female). Such fitness costs were minimized when the resistant cockroaches were in aggregations. Specifically, male (54 ± 3 days) and female nymphal development periods (52 ± 3 days) of German cockroach significantly decreased to 44 ± 1 days in the largest group. The nymphal survival was substantially enhanced (more than 80% survival) in German cockroaches with elevated cytochrome P450 monooxygenases, or both cytochrome P450 monooxygenases and esterases activities in the largest group. The effect of pyrethroid resistance on the life‐history traits of adult German cockroaches was limited; only adult male longevity was significantly prolonged. Group living did not significantly extend adult longevity and increase the number of offspring per ootheca. Contrary to expectations, the number of nymphs produced by a female and the oothecal hatchability were inversely proportional to the number of individuals in aggregations. Moreover, a lower proportion of viable oothecae were produced in German cockroaches when living in aggregations. Because of low fecundity, population parameters of German cockroaches living in aggregations (net reproductive rate and intrinsic rate of increase) were significantly lower than the parameters of those living in pairs.

Numerous case studies have reported that newly introduced ant species become established invaders outside their native ranges, even if they experience a substantial genetic bottleneck during colonization, which may hinder their fitness (Suarez & Tsutsui, 2008;Tsutsui et al., 2000). This characteristic suggests that the consequences of reduced genetic diversity are not always negative. The apparent