A new measure of longitudinal connectivity for stream networks

Abstract

Habitat connectivity is a central factor in shaping aquatic biological communities, but few tools exist to describe and quantify this attribute at a network scale in riverine systems. Here, we develop a new index to quantify longitudinal connectivity of river networks based on the expected probability of an organism being able to move freely between two random points of the network.We apply this index to two fish life histories and evaluate the effects of the number, passability, and placement of barriers on river network connectivity through the use of simulated dendritic ecological networks. We then extend the index to a real world dendritic river system in Newfoundland, Canada.Our results indicate that connectivity in river systems, as represented by our index, is most impacted by the first few barriers added to the system. This is in contrast to terrestrial systems, which are more resilient to low levels of connectivity. The results show a curvilinear relationship between barrier passability and structural connectivity. This suggests that an incremental improvement in passability would result in a greater improvement to river network connectivity for more permeable barriers than for less permeable barriers. Our analysis of the index in simulated and real river networks also showed that barrier placement played an important role in connectivity.Not surprisingly, barriers located near the river mouth have the greatest impact on fish with diadromous life histories while those located near the center of the river network have the most impact on fish with potadromous life histories. The proposed index is conceptually simple and sufficiently flexible to deal with variations in river structure and biological communities. The index will enable researchers to account for connectivity in habitat studies and will also allow resource managers to characterize watersheds, assess cumulative impacts of multiple barriers and determine priorities for restoration.Response to Reviewers: July 21, 2008 To the Editor of Landscape Ecology, Thank you for your thorough review of our manuscript "A riverscape connectivity index" (LAND-08-1528R1). We have addressed each criticism and comment (see indented comments added to the LE decision letter below). In particular we have significantly shortened the introduction, replaced the simulated single channel system with that of a dendritic, added a conceptual cartoon and have Thank you for your submission to Landscape Ecology. Your paper has been recommended for publication with revisions. The reviews were all positive-each indicating that the connnectivity index is a valuable contribution to the aquatic landscape ecology literature. All of the reviewers suggest, and I concur that the manuscript is far too long, and thus, your major task in the revision will be to reduce the length substantially. The second issue, again raised by Reviewer # 1 is to address the issue of travel distance versus stream length. That reviewer presents a logical arguement that these two measures are no...

The impact of a small-scale riverine obstacle on the upstream migration of Atlantic Salmon

“…In rivers, habitat connectivity is primarily longitudinal and in general confined to the river corridor. A single impoundment thus has the potential to isolate adjacent habitats completely for many species (Jager et al, 2001;Cote et al, 2009;Branco et al, 2012). In-river structures, both natural and artificial such as waterfalls and weirs can have major impacts on species that have multiple, life stage dependent, aquatic habitat requirements.…”

Eco-friendly location of small hydropower

“…Our modeling framework could be easily adapted to handle potadromous dispersal patterns (Cote et al, 2009;O'Hanley et al, 2013b), where sh regularly move between di erent sections within a river network over the course of a year. One could also take a more in-depth approach by incorporating spatially explicit sh population dynamics (Ziv et al, 2012).…”

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“…Many barriers, however, are somewhat passable [19]. A relatively recent path-counting metric that allows for partial passability is the dentritic connectivity index (DCI) [4]. Clearly, passability is species specific, and so the definition of this index was specialized [4] depending on the life history of the fish species under consideration: DCI P for potadromous (migrating within freshwater) and DCI D diadromous (migrating between freshwater and sea) species.…”

“…A relatively recent path-counting metric that allows for partial passability is the dentritic connectivity index (DCI) [4]. Clearly, passability is species specific, and so the definition of this index was specialized [4] depending on the life history of the fish species under consideration: DCI P for potadromous (migrating within freshwater) and DCI D diadromous (migrating between freshwater and sea) species. In either case, DCI is a network-scale measure of connectivity, specific to freshwater systems, simple enough to examine the effects and interactions of multiple barriers and their permeability, i.e.…”

“…In either case, DCI is a network-scale measure of connectivity, specific to freshwater systems, simple enough to examine the effects and interactions of multiple barriers and their permeability, i.e. the movement probability of individuals between sections connected by the obstacles [4,16,20].…”