Urbanization and wetland communities: applying metacommunity theory to understand the local and landscape effects

Abstract

Summary1. Urbanization is a growing threat to ecological communities and has become a leading cause of population extirpations in a wide range of taxa. Because the effects of urbanization are often multifaceted, identifying the pathways through which changes in communities occur has remained a persistent challenge. 2. We draw upon metacommunity theory to evaluate competing explanations for the effects of urbanization, focusing on the relative importance of processes at local (e.g. abiotic and biotic characteristics) and regional (e.g. habitat connectivity and dispersal) scales. Over 4 years, we sampled 201 wetlands in the Front Range region of Colorado, which is one of the most rapidly developing areas in the USA. 3. Wetlands embedded within urban areas exhibited significantly lower taxonomic richness and diversity compared to those in agricultural or grassland areas. Relative to grassland wetlands, urban wetlands supported a 60% lower richness of amphibians and aquatic reptiles and a 33% lower richness of aquatic insects, molluscs and crayfish. These patterns were associated with changes in biotic factors (introduced fishes and bullfrogs), abiotic factors (nutrients, conductivity and vegetation) and landscape characteristics (road density and surrounding wetland area). 4. The use of an information-theoretic approach and structural equation modelling suggested that the effects of urbanization on richness were mainly driven by changes in road density. Analyses of community composition indicated that discrete communities formed along the urban systems gradient, such that actively dispersing predators associated more negatively with urban system relative to herbivores with passive dispersal. 5. Synthesis and applications. These results highlight the importance of considering both local and regional factors in addressing conservation-related challenges and underscore the benefits of linking conceptual work on metacommunity theory with applied efforts to mitigate the effects of urbanization.

Effects of roads and land use on frog distributions across spatial scales and regions in the Eastern and Central United States

“…Second, our results show that the effects of road density on amphibian richness, well documented in previous studies (Findlay et al, 2001;Pellet et al, 2004;Johnson et al, 2013), are primarily associated with smallscale effects of larger roads, and secondarily associated with larger-scale effects of smaller roads. First, we demonstrate that the effects of localized landscape features such as roads and development are scale dependent.…”

The influence of landscape and environmental factors on ranavirus epidemiology in a California amphibian assemblage

“…We assessed pond permanence, per cent forest or wetland surrounding ponds, pond area and water quality factors at each site. For pond permanence, we classified ponds as “temporary” if they were observed going dry during direct field visits (2011–2013) or using historical images in Google Earth (Johnson, Hoverman, Mckenzie, Blaustein, & Richgels, ); ponds that held water throughout the course of the study were classified as “permanent.” We measured conductivity (S/m), total dissolved solids (mg/L), salinity (mg/L) and pH with a YSI meter (Model 556; Yellow Spring Instrument, Yellow Springs, Ohio, USA). We quantified total nitrogen (mg/L), dissolved organic carbon (mg/L) and total ammonia (mg/L) using standard methods (https://instaar.colorado.edu/research/labs-groups/arikaree-environmental-lab/free-play/; Johnson, Hoverman, et al., ).…”

Investigating Differences across Host Species and Scales to Explain the Distribution of the Amphibian Pathogen Batrachochytrium dendrobatidis

“…The abundance of invasive L. catesbeianus in the Front Range is staggering; a recent study identified populations of L. catesbeianus in nearly 50% of 243 wetlands surveyed in the region [28]. Additional work in this system has identified that the degree of urbanization surrounding wetlands is strongly negatively related to vertebrate richness, though invasive L. catesbeianus are still highly abundant in these urbanized sites [29]. A re-survey of historical native Northern leopard frog ( L. pipiens ) sites found that the Front Range region had only 2% of sites still supporting leopard frogs, compared with 52% of sites in the Western Slope region (west of the Rockies) [30].…”