Ecological spillover dynamics of organisms from urban to natural landscapes

Abstract

Urbanization and anthropogenic development have fundamentally altered ecosystem dynamics on a global scale. Conservation and management of comparatively less modified landscapes adjacent to highly modified landscapes requires careful consideration of interactions between landscape types. Restoration or conservation of habitat within a developed matrix is generally thought to have beneficial effects on landscape-level ecological processes. We propose an ecological spillover framework to critically assess how restoring or conserving species populations within anthropogenically modified landscapes may affect adjacent wildland populations. Within the framework, the spillover process is divided into seven interconnected 'nodes', which identify points at which potential cause-effect relationships may exist between urban and wildland populations. The framework is useful for a wide range of project-specific ecological relationships, and can help scientists and managers identify knowledge gaps and weigh risk in conservation decision-making. We queried the conservation literature to identify research focused on the impacts of urban species populations on regional wildland populations. Our search revealed seven ecological processes that have the potential to be affected by urban to wildland spillover and we found relatively few studies that explicitly analyze spillover effects from urban to wildland areas. Organisms living in urban areas within restored or remnant habitats located in an urban matrix, or within the built environment have largely unknown effects on landscape-level ecological processes. We conclude with a discussion on the critical gaps in research linking these habitats to larger landscape-level ecological understanding, and provide recommendations for research priorities that might illuminate this important aspect of 21st century conservation planning.

Butterfly richness and abundance along a gradient of imperviousness and the importance of matrix quality

“…Further, larval host plants are another key resource that can affect butterfly communities and their responses to environmental change (Curtis et al 2015, Soga et al 2015). Remnant native vegetation patches can support diverse butterfly assemblages through provision of habitat resources, including larval host plants, shade trees (Williams 2011), and native floral resources, the benefits of which could facilitate spillover effects to influence butterfly communities within the urban matrix (Spear et al 2018). Further, most butterflies have known habitat affinities (e.g., grassland or woodland; Dennis 2010) and will use a matrix that is structurally similar (i.e., woodland butterflies may key in on trees in the matrix), particularly if food plants are available (Lütolf et al 2009, Ibbe et al 2011, Öckinger et al 2012, Soga and Koike 2012).…”

The Biological Deserts Fallacy: Cities in Their Landscapes Contribute More than We Think to Regional Biodiversity

“…In these cases, the contribution of urbanization-adapted individuals may increase genetic diversity at the landscape scale. Although it is possible that this could lead urban environment–adapted individuals to be maladapted to their surrounding landscapes (Spear et al 2018 ), greater genetic diversity is also associated with an increased capacity to withstand environmental change, can be related to higher productivity and fitness, and can have cascading community effects that benefit other species (Hughes et al 2008 ).…”

“…Although urbanization poses a substantial threat to biodiversity (McDonald et al 2020 ), cities also support many species, some of which have larger populations, faster growth rates, and higher productivity in cities than elsewhere (Faeth et al 2011 , Bateman and Fleming 2012 ). Despite this fact, discussion of the implications of ecological links between cities and their surrounding landscapes has focused primarily on the negative impacts, including the export of pollution (Grimm et al 2008b , Hien et al 2020 ) and invasive species (Aronson et al 2007 , Von der Lippe and Kowarik 2008 , Bar-Massada et al 2014 , Padayachee et al 2017 ), the impacts of domesticated animals on wildlife in adjacent wildland areas (Lepczyk et al 2004 , Metsers et al 2010 , Hanmer et al 2017 ), and the potential of cities to create ecological traps (Battin 2004 , Sumasgutner et al 2014 , Spear et al 2018 , Tella et al 2020 ). However, the successes of some native, nonpest species in cities suggests that we have an incomplete understanding of the full suite of ecological roles cities play within their landscapes and of how positive roles can be bolstered through intentional design.…”

What’s wrong with the Australian River Assessment System (AUSRIVAS)?

“…Ogden 2000;Maloney et al 2008;Wohl 2019), and transmission of stressors and biota between potential reference sites and other parts of the landscape (e.g. Pringle 1997;Lake et al 2010;Spear et al 2018). Inappropriate model predictors The AUSRIVAS models collectively use a great variety of environmental variables for matching an assessment site to particular groups of reference sites, so as to generate occurrence probabilities of macroinvertebrate taxa at the assessment site (Simpson and Norris 2000).…”