Abstract
The negative impact of urbanization on biodiversity can be buffered by blue (e.g., rivers, ponds) and green (e.g., parks, forests) spaces. However, to prevent biodiversity loss and reduce the risk of local extinctions, blue and green spaces need to be connected by corridors, so that organisms may disperse between sites. Landscape connectivity affects local community composition and metacommunity dynamics by facilitating dispersal. The goal of this study was to test the relative roles of pond environmental properties, spatial structure, and functional landscape connectivity on differentiation of invertebrate metacommunities in urban ponds in the city of Stockholm, Sweden. We characterized functional connectivity as blue connectivity (distance to water bodies), green connectivity (land use), and combined blue-green connectivity. We estimated functional connectivity by using electrical circuit theory to identify dispersal corridors. Interestingly, while circuit theory is often used in single-taxon studies, this method has rarely been applied to multiple taxa forming a metacommunity, as we have done in this study. Indeed, our study contributes toward an increased focus on the role of dispersal at the metacommunity level. We determined that functional connectivity was the most important factor in explaining community differentiation, with the local environment contributing comparatively little, and spatial structure the least. Combined blue-green functional connectivity had a major influence on structuring urban pond communities, explaining 7.8% of the variance in community composition across ponds. Furthermore, we found that increased functional connectivity was associated with an increase in the number of species. In summary, our results suggest that to preserve biodiversity in urban ponds, it is important to enhance functional connectivity, and that open green spaces could augment blue corridors in maintaining functional connectivity in urban pond metacommunities. To generalize these findings, future urban biodiversity studies should compare how functional connectivity affects metacommunities across multiple major cities.
Highlights
Landscape connectivity can be defined as the effect that the landscape has on “movement along resource patches” (Taylor, Fahrig, Henein & Merriam, 1999)
We examined the spatial structure of local communities by applying Principal Coordinates analysis of Neighbor Matrices (PCNM) to Euclidean geographic distances
To understand how biodiversity in urban ponds responds to interactions between functional connectivity and the local environment, we investigated how the relationship between connectivity and species diversity varies by pond environment
Summary
Landscape connectivity can be defined as the effect that the landscape has on “movement along resource patches” (Taylor, Fahrig, Henein & Merriam, 1999). Organisms survive in habitat patches that are linked by dispersal (Leibold et al, 2004). Habitat loss and fragmentation are a major threat to biodiversity (Tilman et al, 2017). Optimizing habitat patch connectivity, or landscape connectivity, is one way to reduce the negative impact of habitat loss and fragmentation. To estimate landscape connectivity, we need to understand how landscape features are configured. This leads to two basic estimates of connectivity: structural and functional. Studies investigating landscape connectivity provide useful information for landscape managers on how to optimize patch connectivity and decrease the negative effects of habitat loss on biodiversity (e.g., Mitchell, Bennett & Gonzalez, 2013)
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