Mapping the potential extinction debt of butterflies in a modern city: implications for conservation priorities in urban landscapes

Assessing habitat connectivity of rare species to inform urban conservation planning

Urbanization is commonly associated with biodiversity loss and habitat fragmentation. However, urban environments often have greenspaces that can support wildlife populations, including rare species. The challenge for conservation planners working in these systems is identifying priority habitats and corridors for protection before they are lost. In a rapidly changing urban environment, this requires prompt decisions informed by accurate spatial information. Here, we combine several approaches to map habitat and assess connectivity for a diverse set of rare species in seven urban study areas across southern Michigan, USA. We incorporated multiple connectivity tools for a comprehensive appraisal of species-habitat patterns across these urban landscapes. We observed distinct differences in connectivity by taxonomic group and site. The three turtle species (Blanding's, Eastern Box, and Spotted) consistently had more habitat predicted to be suitable per site than other evaluated species. This is promising for this at-risk taxonomic group and allows conservation efforts to focus on mitigating threats such as road mortality. Grassland and prairie-associated species (American Bumble Bee, Black and Gold Bumble Bee, and Henslow's Sparrow) had the least amount of habitat on a site-by-site basis. Kalamazoo and the northern Detroit sites had the highest levels of multi-species connectivity across the entire study area based on the least cost paths. These connectivity results have direct applications in urban planning. Kalamazoo, one of the focal urban regions, has implemented a Natural Features Protection (NFP) plan to bolster natural area protections within the city. We compared our connectivity results to the NFP area and show where this plan will have an immediate positive impact and additional areas for potential consideration in future expansions of the protection network. Our results show that conservation opportunities exist within each of the assessed urban areas for maintaining rare species, a key benefit of this multi-species and multi-site approach.

Ecological time lags in biodiversity response to habitat changes

The decline of biodiversity can occur with a substantial delay following habitat loss, degradation, and other environmental changes, such as global warming. Considerable time lags may be involved in these responses. However, such time lags typically pose a significant but often unrecognized challenge for biodiversity conservation across a wide range of taxa and ecosystems. Here, we synthesize the current knowledge, categories, manifestations under different scenarios and impacts of ecological time lags. Our work reveals that studies on ecosystem structure lags are far more than ecosystem process and function lags. Due to the presence of these time-lag effects, the 'window phase' typically exists, which is widely recognized as 'relaxation time', providing a particular opportunity for biodiversity conservation. The manifestations of time lags vary under different scenarios. In addition, the different mechanisms that can result in ecological time lags are hierarchically nested, in which mechanisms at the population and metapopulation level have routinely been suggested as explanations for ecological time lags. It generally takes longer time to reach equilibrium at the metapopulation level than it takes for effects to be fully expressed at the level of individuals. Finally, we propose corresponding implications for biodiversity conservation and management. Our research will provide priorities for science and management on how to address the impact of ecological time lags to mitigate future attrition of biodiversity.

Hypotheses in urban ecology: building a common knowledge base

Urban ecology is a rapidly growing research field that has to keep pace with the pressing need to tackle the sustainability crisis. As an inherently multi-disciplinary field with close ties to practitioners and administrators, research synthesis and knowledge transfer between those different stakeholders is crucial. Knowledge maps can enhance knowledge transfer and provide orientation to researchers as well as practitioners. A promising option for developing such knowledge maps is to create hypothesis networks, which structure existing hypotheses and aggregate them according to topics and research aims. Combining expert knowledge with information from the literature, we here identify 62 research hypotheses used in urban ecology and link them in such a network. Our network clusters hypotheses into four distinct themes: (i) Urban species traits & evolution, (ii) Urban biotic communities, (iii) Urban habitats and (iv) Urban ecosystems. We discuss the potentials and limitations of this approach. All information is openly provided as part of an extendable Wikidata project, and we invite researchers, practitioners and others interested in urban ecology to contribute additional hypotheses, as well as comment and add to the existing ones. The hypothesis network and Wikidata project form a first step towards a knowledge base for urban ecology, which can be expanded and curated to benefit both practitioners and researchers.

Half-millennium evidence suggests that extinction debts of global vertebrates started in the Second Industrial Revolution

Extinction debt describes the time-lagged process of species extinction, which usually requires dozens to hundreds of years to be paid off. However, due to the lack of long-term habitat data, it is indeterminate how strong the signal of extinction debts is at the global scale and when the debts started. Here, by compiling the geographical distributions of 6120 reptiles, 6047 amphibians, and 4278 mammals and correlating them with annual forest cover data from 1500 to 1992, we show that the beginning of the Second Industrial Revolution (the mid-19^th century) was the earliest signal of cumulative extinction debts for global forest-dwelling vertebrate groups. More importantly, the impact of global protected areas on mitigating accumulated vertebrate extinction debt is not as immediate as that of mitigating reduced forest cover but rather suffers from pronounced time-lag effects. As the disequilibrium of vertebrate richness and forested habitat is currently taking place, preventive actions should be taken to promote a well-balanced status among forest restoration, protected areas, and biodiversity conservation to slow the accumulating debts for global forest-dwelling vertebrates.

The role of invasion and urbanization gradients in shaping avian community composition

The extent to which native species utilize urban environments depends on species responses to multiple threatening processes. Here, we aimed to quantify changes in bird communities in response to changing habitat structure, invasive species and aggressive native species. We conducted surveys in two independently invaded regions with similar patterns of urban development. The study regions were New South Wales (NSW) and Queensland (QLD), Australia. We observed 127 species in NSW and 144 species in QLD. Most species (NSW 83 and QLD 84) are urban adapters making use of some or all urban sub-environments. Urban avoiders, species only found in remnant vegetation, were the second largest group (urban avoiders: NSW 23 and QLD 31). We found the lowest richness in the most urban sites (urban exploiters: NSW 10 and QLD 15). Using generalized linear mixed models, we found a non-significant relationship between species richness and the abundance of aggressive species like the common myna and noisy miners, Manorina melanocephala, but a significant positive correlation with the percentage of shrub cover at a site. As there is a gradual loss of species with increasing urbanization, retaining higher complexity in vegetation structure in urban areas will support large numbers of species and could help mitigate the potential impacts of aggressive urban-adapted species and habitat loss.

Composition and diversity of butterflies (Lepidoptera, Papilionoidea) along an atmospheric pollution gradient in the Monterrey Metropolitan Area, Mexico

This study compares the variation of richness, abundance and diversity of butterfly species along an atmospheric pollution gradient and during different seasons in the Monterrey Metropolitan Area, Mexico. Likewise, we analyse the influence of environmental variables on the abundance and richness of butterfly species and quantify the indicator species for each atmospheric pollution category. Based on spatial analysis of the main atmospheric pollutants and the vegetation cover conditions, four permanent sampling sites were delimited. The sampling was carried out monthly in each of the sites using aerial entomological nets and ten Van Someren-Rydon traps during May 2018 to April 2019. A total of 8,570 specimens belonging to six families and 209 species were collected. Both species richness and abundance were significantly different between all sites, except for the comparison between the moderate contamination site and the high contamination site; diversity decreased significantly with increasing levels of contamination. The seasonality effect was absent on species richness; however, for species abundance the differences between dry season and rainy season were significant in each site excepting the moderate contamination site. Regarding diversity, the seasonal effect showed different distribution patterns according to each order. Relative humidity, vegetation cover and three pollution variables were highly correlated with both abundance and species richness. From the total number of species found, only 47 had a significant indicator value. This study constitutes the first faunistic contribution of butterflies as indicators of the environmental quality of urban areas in Mexico, which will help in the development of strategies for the management, planning and conservation of urban biodiversity.

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

Urbanization involves a cocktail of human-induced rapid environmental changes and is forecasted to gain further importance. Urban-heat-island effects result in increased metabolic costs expected to drive shifts towards smaller body sizes. However, urban environments are also characterized by strong habitat fragmentation, often selecting for dispersal phenotypes. Here, we investigate to what extent, and at which spatial scale(s), urbanization drives body size shifts in macro-moths-an insect group characterized by positive size-dispersal links-at both the community and intraspecific level. Using light and bait trapping as part of a replicated, spatially nested sampling design, we show that despite the observed urban warming of their woodland habitat, macro-moth communities display considerable increases in community-weighted mean body size because of stronger filtering against small species along urbanization gradients. Urbanization drives intraspecific shifts towards increased body size too, at least for a third of species analysed. These results indicate that urbanization drives shifts towards larger, and hence, more mobile species and individuals in order to mitigate low connectivity of ecological resources in urban settings. Macro-moths are a key group within terrestrial ecosystems, and since body size is central to species interactions, such urbanization-driven phenotypic change may impact urban ecosystem functioning, especially in terms of nocturnal pollination and food web dynamics. Although we show that urbanization's size-biased filtering happens simultaneously and coherently at both the inter- and intraspecific level, we demonstrate that the impact at the community level is most pronounced at the 800 m radius scale, whereas species-specific size increases happen at local and landscape scales (50-3,200 m radius), depending on the species. Hence, measures-such as creating and improving urban green infrastructure-to mitigate the effects of urbanization on body size will have to be implemented at multiple spatial scales in order to be most effective.

Evidence and mapping of extinction debts for global forest-dwelling reptiles, amphibians and mammals

Evidence of extinction debts for the global distributions of forest-dwelling reptiles, mammals and amphibians was tested and the debt magnitude was estimated and mapped. By using different correlation tests and variable importance analysis, the results showed that spatial richness patterns for the three forest-dwelling terrestrial vertebrate groups had significant and stronger correlations with past forest cover area and other variables in the 1500 s, implying the evidence for extinction debts. Moreover, it was likely that the extinction debts have been partially paid, given that their global richness patterns were also significantly correlated with contemporary forest variables in the 2000 s (but the absolute magnitudes of the correlation coefficients were usually smaller than those calculated for historical forest variables). By utilizing species-area relationships, spatial extinction-debt magnitudes for the three vertebrate groups at the global scale were estimated and the hotspots of extinction debts were identified. These high-debt hotspots were generally situated in areas that did not spatially overlap with hotspots of species richness or high extinction-risk areas based on IUCN threatened status to a large extent. This spatial mismatch pattern suggested that necessary conservation efforts should be directed toward high-debt areas that are still overlooked.

Citizen Science Program Shows Urban Areas Have Lower Occurrence of Frog Species, but Not Accelerated Declines

Understanding the influence of landscape change on animal populations is critical to inform biodiversity conservation efforts. A particularly important goal is to understand how urban density affects the persistence of animal populations through time, and how these impacts can be mediated by habitat provision; but data on this question are limited for some taxa. Here, we use data from a citizen science monitoring program to investigate the effect of urbanization on patterns of frog species richness and occurrence over 13 years. Sites surrounded by a high proportion of bare ground (a proxy for urbanization) had consistently lower frog occurrence, but we found no evidence that declines were restricted to urban areas. Instead, several frog species showed declines in rural wetlands with low-quality habitat. Our analysis shows that urban wetlands had low but stable species richness; but also that population trajectories are strongly influenced by vegetation provision in both the riparian zone and the wider landscape. Future increases in the extent of urban environments in our study area are likely to negatively impact populations of several frog species. However, existing urban areas are unlikely to lose further frog species in the medium term. We recommend that landscape planning and management focus on the conservation and restoration of rural wetlands to arrest current declines, and the revegetation of urban wetlands to facilitate the re-expansion of urban-sensitive species.