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Abstract Cultivated exotic plants are often introduced for their aesthetic value and today comprise a substantial fraction of the flora of urban domestic gardens. Yet, their relative contribution to the functional diversity of domestic gardens and how it changes across different climate zones is insufficiently understood. Here, we investigated whether the effects of cultivated exotics on functional diversity of three plant traits related to plant aesthetics (that is, plant showiness, plant height, and leaf area) varied in suburban domestic gardens in three regions (Minnesota, USA; Alt Empordà, Spain; and central South Africa) that differ in aridity. For each garden, we calculated the mean and variance of each plant trait considering all co-occurring species and also splitting them into co-occurring cultivated exotics and natives. Our results revealed that mean plant showiness increased linearly with the proportion of cultivated exotics both across and within studied regions. Moreover, co-occurring cultivated exotics were, on average, showier than natives in all regions, but differences in their trait variances were context-dependent. The interaction between cultivated exotics and aridity explained variation in mean plant height and leaf area better than either predictor alone, with the effect of cultivated exotics being stronger in more arid regions. Accordingly, co-occurring cultivated exotics were taller and had larger leaves than natives in warmer and drier regions, while the opposite was true in cooler and wetter regions. Our study highlights the need to consider the combined effects of exotic species and climate in future studies of urban ecology. 

Urbanization has a homogenizing effect on biodiversity and leads to communities with fewer native species and lower conservation value. However, few studies have explored whether or how land management by urban residents can ameliorate the deleterious effects of this homogenization on species composition. We tested the effects of local (land management) and neighborhood-scale (impervious surface and tree canopy cover) features on breeding bird diversity in six US metropolitan areas that differ in regional species pools and climate. We used a Bayesian multiregion community model to assess differences in species richness, functional guild richness, community turnover, population vulnerability, and public interest in each bird community in six land management types: two natural area park types (separate and adjacent to residential areas), two yard types with conservation features (wildlife-certified and water conservation) and two lawn-dominated yard types (high- and low-fertilizer application), and surrounding neighborhood-scale features. Species richness was higher in yards compared with parks; however, parks supported communities with high conservation scores while yards supported species of high public interest. Bird communities in all land management types were composed of primarily native species. Within yard types, species richness was strongly and positively associated with neighborhood-scale tree canopy cover and negatively associated with impervious surface. At a continental scale, community turnover between cities was lowest in yards and highest in parks. Within cities, however, turnover was lowest in high-fertilizer yards and highest in wildlife-certified yards and parks. Our results demonstrate that, across regions, preserving natural areas, minimizing impervious surfaces and increasing tree canopy are essential strategies to conserve regionally important species. However, yards, especially those managed for wildlife support diverse, heterogeneous bird communities with high public interest and potential to support species of conservation concern. Management approaches that include the preservation of protected parks, encourage wildlife-friendly yards and acknowledge how public interest in local birds can advance successful conservation in American residential landscapes. 

Despite interest in the contribution of evapotranspiration (ET) of residential turfgrass lawns to household and municipal water budgets across the United States, the spatial and temporal variability of residential lawn ET across large scales is highly uncertain. We measured instantaneous ET (ET_inst) of lawns in 79 residential yards in six metropolitan areas: Baltimore, Boston, Miami, Minneapolis‐St. Paul (mesic climates), Los Angeles and Phoenix (arid climates). Each yard had one of four landscape types and management practices: traditional lawn‐dominated yards with high or low fertilizer input, yards with water‐conserving features, and yards with wildlife‐friendly features. We measured ET_instin situ during the growing season using portable chambers and identified environmental and anthropogenic factors controlling ET in residential lawns. For each household, we used ET_instto estimate daily ET of the lawn (ET_daily) and multiplied ET_dailyby the lawn area to estimate the total volume of water lost through ET of the lawn (ET_vol). ET_dailyvaried from 0.9 ± 0.4 mm d¹in mesic cities to 2.9 ± 0.7 mm d⁻¹in arid cities. Neither ET_instnor ET_dailywas significantly influenced by yard landscape types and ET_instpatterns indicated that lawns may be largely decoupled from regional rain‐driven climate patterns. ET_volranged from ∼0 L d⁻¹to over 2,000 L d⁻¹, proportionally increasing with lawn area. Current irrigation and lawn management practices did not necessarily result in different ET_instor ET_dailyamong traditional, water‐conserving, or wildlife‐friendly yards, but smaller lawn areas in water‐conserving and wildlife‐friendly yards resulted in lower ET_vol.

 

Global change has accelerated local species extinctions and colonizations, often resulting in losses and gains of evolutionary lineages with unique features. Do these losses and gains occur randomly across the phylogeny?

We quantified: temporal changes in plant phylogenetic diversity (PD); and the phylogenetic relatedness (PR) of lost and gained species in 2672 semi‐permanent vegetation plots in European temperate forest understories resurveyed over an average period of 40 yr.

Controlling for differences in species richness, PD increased slightly over time and across plots. Moreover, lost species within plots exhibited a higher degree of PR than gained species. This implies that gained species originated from a more diverse set of evolutionary lineages than lost species. Certain lineages also lost and gained more species than expected by chance, with Ericaceae, Fabaceae, and Orchidaceae experiencing losses and Amaranthaceae, Cyperaceae, and Rosaceae showing gains. Species losses and gains displayed no significant phylogenetic signal in response to changes in macroclimatic conditions and nitrogen deposition.

As anthropogenic global change intensifies, temperate forest understories experience losses and gains in specific phylogenetic branches and ecological strategies, while the overall mean PD remains relatively stable.

 

Whether cities are more or less diverse than surrounding environments, and the extent to which non‐native species in cities impact regional species pools, remain two fundamental yet unanswered questions in urban ecology. Here we offer a unifying framework for understanding the mechanisms that generate biodiversity patterns across taxonomic groups and spatial scales in urban systems. One commonality between existing frameworks is the collective recognition that species co‐occurrence locally is not simply a function of natural colonization and extinction processes. Instead, it is largely a consequence of human actions that are governed by a myriad of social processes occurring across groups, institutions, and stakeholders. Rather than challenging these frameworks, we expand upon them to explicitly consider how human and non‐human mechanisms interact to control urban biodiversity and influence species composition over space and time. We present a comprehensive theory of the processes that drive biodiversity within cities, between cities and surrounding non‐urbanized areas and across cities, using the general perspective of metacommunity ecology. Armed with this approach, we embrace the fact that humans substantially influence β‐diversity by creating a variety of different habitats in urban areas, and by influencing dispersal processes and rates, and suggest ways how these influences can be accommodated to existing metacommunity paradigms. Since patterns in urban biodiversity have been extensively described at the local or regional scale, we argue that the basic premises of the theory can be validated by studying the β‐diversity across spatial scales within and across urban areas. By explicitly integrating the myriad of processes that drive native and non‐native urban species co‐occurrence, the proposed theory not only helps reconcile contrasting views on whether urban ecosystems are biodiversity hotspots or biodiversity sinks, but also provides a mechanistic understanding to better predict when and why alternative biodiversity patterns might emerge.