Ecological Networks Research Papers - Academia.edu (original) (raw)

The use of hedgerows as corridors for forest vascular species has been widely studied, but only in humid oceanic and continental climates; no replicated trials have ever been performed on corridor function. Given these premises, a study... more

The use of hedgerows as corridors for forest vascular species has been widely studied, but only in humid oceanic and continental climates; no replicated trials have ever been performed on corridor function. Given these premises, a study was done on the eastern Po Plain, in a transition area between the Temperate (Eurosiberian) and Mediterranean climatic zones, adopting the same sample shape and dimensions as a North-American study [Corbit et al. (1999) J Ecol 87:220–232]. The following research questions were posed: (1) how common are forest species in hedgerows? (2) do origin, isolation, distance from source, width and adjacent land-use factors correlate with the frequency of forest species? (3) are hedgerows corridors for forest species? To address these, three functional types of hedgerows, identified by comparing old aerial-photos, were sampled: remnant attached (n = 12) and remnant isolated (n = 6) with respect to the nearest woodland and regenerated attached (n = 4). If wooded patches were a source for hedgerows, then regenerated hedgerows should be more similar to an adjacent woodland than an isolated remnant. A 900 m2 circular plot in woodlands and an adjacent 90-m transect along hedgerows were sampled for the presence and cover of all plant species, then 39 woodland taxa were selected. Significant differences between the three hedgerow types emerged in forest species richness, but not in cover. The forest species composition in both remnant and regenerated attached hedgerows showed a strong affinity with the adjacent stand, implying a dispersal process from woodland (source) to regenerated hedgerows (sink). A distance effect on forest species distribution clearly linked to a corridor function was found only in regenerated hedgerows, while in the remnant attached ones, even with a composition similar to that of the nearest woodland source, other additional factors cannot be ignored to explain the fine scale distribution of forest species. The cover of the most common ant-dispersed species showed a similar distance effect while vertebrate-dispersed ones did not show any significant trend with distance from woodlands. Habitat suitability for forest species was affected by width, especially in hedges wider than 12 m, but not by adjacent land use.

The objective of this study was to test a method for analysing long-term structural changes in non-forest wood elements, using a newly developed classification system and relevant landscape characteristics. Although these non-forest wood... more

The objective of this study was to test a method for analysing long-term structural changes in non-forest wood elements, using a newly developed classification system and relevant landscape characteristics. Although these non-forest wood elements are biotopes that have positive effects for the ecological stability of the landscape little is known about their long-term dynamics. The newly developed knowledge of the historical impact of various landscape management practices on non-forest wood elements can be applied in landscape planning procedures (e.g. planning ecological networks) in order to ensure relevant landscape management in the future. The method was applied in two contrasting study sites, Honbice (244 ha) and Krida (268 ha), located in east Bohemia and north Bohemia, in the Czech Republic. The study was based on old cadastral maps (from 1839 to 1843), black and white aerial photographs (from 1938, 1950, 1966, 1975 to 2006) and field control data from 2006. At the Honbice study site, the proportion of non-forest wood elements increased from 2.0 to 2.9% of the study site, due to large plantations of scattered vegetation in the open landscape. On the other hand, more than half of the wood vegetation in the village was cut down between 1966 and 2006. In addition, the relative length of the tree alleys decreased from 0.021 km ha(-1) to 0.018 km ha(-1) between 1950 and 1966. At the Krida study site, there was a significant increase in non-forest vegetation (from 2.4 to 8.2%), due to abandonment of the landscape (former military area). As the village disappeared, the total amount of scattered vegetation grew, due to the natural succession process. The relative length of the tree alleys decreased from 0.009 km ha(-1) to 0.005 km ha(-1). The method that was applied and based on the analysis of long-term structural changes in non-forest wood elements, using a (newly developed) classification system and relevant landscape characteristics has proved to be a suitable procedure for making a detailed description of long-term structural changes in non-forest wood elements in the landscape. The detailed classification system can be used most efficiently when it is applied to rather small territories. Some characteristics display a similar ability to describe changes in non-forest wood structures (e.g. relative length, proportion of the category).

Best practices for green infrastructures. A path. In nine points (ecosystems, landscapes, networks, reconstruction, principles and policies, administration, compensation management, participation) a path through twelve years of... more

A discussion of ecological networks in cities.

Find open access link to the article in the 'Publications' section of www.melissasterry.com

Top-down trophic cascades are well known in many autotrophic systems, yet their role in heterotrophic food webs is less clear. We collated data from 78 investigations and applied meta-analysis to evaluate the strength of detrital trophic... more

Top-down trophic cascades are well known in many autotrophic systems, yet their role in heterotrophic food webs is less clear. We collated data from 78 investigations and applied meta-analysis to evaluate the strength of detrital trophic cascades in freshwater and terrestrial food webs. Predators exerted significant, indirect controls on detrital
resources, in line with theoretical predictions, whereas this was not the case for omnivores, suggesting that detritivory prevailed over predation and disrupted trophic cascades.
Significant relationships were observed for both types of consumer in terms of their responses to detrital quality: specifically, unimodal curves across C:N and N:P gradients were the best fits for predators, whilst cascade strength responses to detrital quality were saddle shaped. These insights suggest that while predatory strategy is determining cascades within detrital-based systems, resource quality has bottom-up role effects on predators and on preferential consumption by omnivores. As such, these environmental responses seem to mirror some provisioning and supporting services; our findings are discussed within conceptual frameworks related to ecological stoichiometry and ecosystem services.

This thesis regards the planning and design of a new continental-scale green infrastructure for Australia, the National Green Network. This research project aims to spatially illustrate key international and national environmental policy... more

This thesis regards the planning and design of a new continental-scale green infrastructure for Australia, the National Green Network. This research project aims to spatially illustrate key international and national environmental policy targets and to augment Australia's currently limited protected area network through a design that addresses multiple contemporary and future environmental challenges. Theoretically, such an infrastructure could help to sustain the Australian continent, its landscapes, biota and peoples through a robust and interconnected network of vegetated corridors spanning across the Australian continent. These are illustrated through a substantial creative component involving mapping and design work at multiple scales.

The pan European biological and landscape diversity strategy (PEBDLS) was developed under the auspices of the Council of Europe in order to achieve the effective implementation of the convention of biological diversity (CBD) at the... more

The pan European biological and landscape diversity strategy (PEBDLS) was developed under the auspices of the Council of Europe in order to achieve the effective implementation of the convention of biological diversity (CBD) at the European level. A key element of PEBLDS has been the development of the Pan European Ecological Network (PEEN) as a guiding vision for coherence in biodiversity conservation. PEEN has been developed in three subprojects: Central and Eastern Europe, completed in 2002; South-eastern Europe, completed in 2006; and Western Europe, also completed in 2006. The methodology of the development of the three maps has been broadly comparable but data availability, differences in national databases, technical developments and geographical differences caused variations in the detailed approach. One of the challenges was to find common denominators for the habitat data in Europe; this was solved differently for the subprojects. The project has resulted in three maps that together constitute the PEEN. They differ in terms of ecological coherence and the need for ecological corridors; for example, in Central and Western Europe corridors are essential to provide connectivity, while in Northern, Eastern and South-eastern Europe larger, coherent natural areas still exist. The future steps in developing PEEN should include the implementation of national ecological networks and, in particular, the pursuit of international coherence through the development of trans-European ecological corridors. The big challenge is to develop a common approach among the over 100 European-wide agencies that are responsible for biodiversity conservation.

Книга посвящена характеристике экологического каркаса Республики Башкортостан и предложениям по его сохранению. Экологический каркас понимается как совокупность малонарушенных природных экосистем и местообитаний ключевых видов животных.... more

Книга посвящена характеристике экологического каркаса Республики Башкортостан и предложениям по его
сохранению. Экологический каркас понимается как совокупность малонарушенных природных экосистем
и местообитаний ключевых видов животных.
Разработаны принципы и критерии выявления регионального экологического каркаса; ранжированы по
значению и выполняемым функциям основные элементы экологического каркаса, разработаны принципы
оптимизации территориальной охраны природы. Представлены конкретные предложения по обоснованию
и созданию региональной системы охраняемых природных территорий Башкортостана, оценена степень
защищенности естественных экосистем существующими резерватами.
Книга рассчитана на специалистов в области охраны природы, экологов, студентов и преподавателей биоло-
гических и экологических факультетов.

Il documento, realizzato in collaborazione tra ISPRA e Dipartimento Città e Territorio dell’Università di Palermo, contiene i risultati del primo censimento a scala nazionale sul grado di traduzione del concetto di rete ecologica nelle... more

Il documento, realizzato in collaborazione tra ISPRA e Dipartimento Città e Territorio dell’Università di Palermo, contiene i risultati del primo censimento a scala nazionale sul grado di traduzione del concetto di rete ecologica nelle prassi pianificatorie, con particolare attenzione ai Piani Territoriali di Coordinamento Provinciale. Parallelamente è stata condotta un’analisi sulla realtà normativa regionale, perché a quest’ultima è affidato sia il compito operativo della perimetrazione dei SIC e ZPS e della predisposizione dei piani di gestione delle aree Rete Natura 2000, sia perché costituisce l’unità territoriale minima in grado di legiferare in tale materia.
Il lavoro si articola partendo dal livello provinciale di analisi, da sempre immaginato come ottimale per interpretare correttamente un percorso pragmatico di rete ecologica. Tale scelta ha consentito di allestire un primo monitoraggio sullo stato di avanzamento del recepimento del concetto di rete ecologica negli strumenti di pianificazione ordinaria (preordinato come permanente) e sulle eventuali criticità che il sistema di governo del territorio evidenzia per tale tematica, restituendo un’immagine appropriata circa l’evoluzione dello specifico fenomeno tecnico-culturale nei diversi contesti del nostro Paese.
Con l’obiettivo, dunque, di realizzare un primo bilancio della situazione italiana, l’attività della ricerca si è sviluppata attraverso la verifica del livello e delle forme di declinazione concettuale e normativa delle reti ecologiche; l’analisi del livello di strutturazione di tale tematica all’interno degli strumenti di pianificazione urbanistica e territoriale e l’approfondimento delle modalità con cui avviene tale processo di strutturazione. I risultati di questa fase di studio sono stati organizzati in un database aperto e aggiornabile, progettato per rendere le informazioni facilmente fruibili e gestibili. Il lavoro è corredato, inoltre, da un’adeguata bibliografia di base indicizzata che, oltre ad essere un utile riferimento per eventuali approfondimenti sull’argomento, rappresenta uno strumento per possibili evoluzioni del presente studio.

The ecological status of the retting ponds in the province of Ferrara (Italy), the distribution of their fauna in dependence of the environmental variables and some suggestions for the management. The ponds for retting the hemp (Cannabis... more

The ecological status of the retting ponds in the province of Ferrara (Italy), the distribution of their fauna in dependence of the environmental variables and some suggestions for the management.
The ponds for retting the hemp (Cannabis sativa) are typical artificial ecosystems of the Eastern part of the Po River plain. They were built in the past centuries and abandoned after World War Two. Now in the province of Ferrara (Italy) there are about 1420 ponds still remaining. They are used as water storage for irrigation, for the drainage of excessive water from the cultivated fields or they are completely abandoned. They have great importance as cultural heritage and as “stepping stones” for the water fauna and flora inside the ecological networks.
In 2009, the Ecological Station of the Natural History Museum of Ferrara started a sampling program of the invertebrate fauna, which was collected with a 1 mm mesh net in 63 ponds. The presence of aquatic Vertebrate species and 17 environmental variables were also recorded. The environmental data of 47 ponds were analyzed by a cluster analysis. A Canonical Correspondence Analysis (CCA) was performed on the presence/absence data of thefauna, together with the environmental variables characterizing each pond. The most influent parameter resulted to be the presence or the absence of a connection to the network of the surface channels, made of about 4200 km of canals used for both the water drainage and the agricultural watering.
The ponds connected to the freshwater network, that receives water from the Po River, are invaded by alien species, whilst the most precious species (autochthonous gastropods, water beetles, amphibians and reptiles) prefer the ponds not connected to the channel network.
However it resulted that, when a pond is surrounded by a large, not exploited strip, with a well developed terrestrial vegetation with a relatively high number of species, some important native species can coexist with alien species even in ponds that communicate with the channel network.
Some interesting species were recorded, such as Gyraulus laevis and G. acronicus, two gastropods that are vulnerable to extinction in some European countries. Two species of water beetles, Hygrotus decoratus and Copelatus haemorroidalis, new to the province of Ferrara, were collected. It was
possible to list both the native species which can cope high trophic levels and the coexistence with invasive alien species and, on the other side, the native species with higher ecological requirements. The ponds have proved to be highly sensitive to global climate change effects.

The concept and establishment of Ecological Networks (EN) have been seen as a solution towards nature conservation strategies targeting biodiversity and ecological connectivity. Within this, the EN assumed a holistic view of land-use... more

The concept and establishment of Ecological Networks (EN) have been seen as a solution towards nature conservation strategies targeting biodiversity and ecological connectivity. Within this, the EN assumed a holistic view of land-use planning and biodiversity conservation as the core of the wider Green Infrastructure (GI) framework. The EN is considered a spatial concept recognized as a system of landscape structures or ecosystems, and a strategically connected fundamental infrastructure of abiotic and biotic systems, underlying the provision of multiple functions valuable to society. This concept moves beyond traditional approaches of "nature protection and preservation", (re)focusing on the ecosystemic approach and the "continuum naturale", emphasising the quality or potentiality of physical components, allowing the articulation with the nature conservation and at-risk areas. Portugal has long had legislation in place meant to protect the natural resources. Although the environmental policies are sectoral and unarticulated, and the environmental data is dispersed and absent. In addition, this study shows that the existing protected areas in Portugal, namely Natura 2000 and classified protected areas, are insufficient to ensure landscape ecological balance and avoid fragmentation. The main goal is to develop a methodology to map a National Ecological Network (NEN) for mainland Portugal, establish the theoretical framework of the EN/GI, by identifying and mapping the most valuable and sensitive areas that guarantee the ecosystem functioning through a multi-level ecological evaluation criteria that integrate the physical and biological systems. The Portuguese NEN map, with a 25 m spatial resolution, integrates in a single tool the Portuguese environmental policies more effectively, in order to facilitate its understanding and application into planning. Regarding the EN mapping method, it was used a GIS-based model made up of a sequence of analyses and evaluations that are driven by a GIS supported assessment of several indices/models used for each EN component. These NEN components were studied individually and collectively and the results, hierarchized in two levels, show that most of the ecological components do not overlap. The NEN1 has high biodiversity and ecological value, which means they are more vulnerable to anthropogenic activity. NEN1 covers a total of 67 % of the mainland, yet as of 2018, only 25 % is protected in nature conservation areas. Priority of action must be given to NEN1 in order to avoid/decrease landscape fragmentation, environmental risks, and natural disaster prevention. This paper contributes to the understanding of the NEN importance as an ecologically based tool towards a more sustainable landscape planning, and the basis of the development plans at national, regional and local levels in an integrated manner, instead of a compilation of disassociated often-contradictory planning tools. The benefits of a Portuguese NEN into a GI development and part of a (broader) nature base solutions by increasing the ecosystems quality and become less dependent on economic and social activities, helping in the restoration of degraded ecosystems and environmental risk prevention. Moreover, it represents the first attempt to map Portuguese EN, and addresses the lack of mapping and the inconsistent EN criteria. It is available online at http://epic-webgis-portugal.isa.ulisboa.pt.

The International Journal of Computer Networks & Communications (IJCNC) is a bi monthly open access peer-reviewed journal that publishes articles which contribute new results in all areas of Computer Networks & Communications. The journal... more

The International Journal of Computer Networks & Communications (IJCNC) is a bi monthly open access peer-reviewed journal that publishes articles which contribute new results in all areas of Computer Networks & Communications. The journal focuses on all technical and practical aspects of Computer Networks & data Communications. The goal of this journal is to bring together researchers and practitioners from academia and industry to focus on advanced networking concepts and establishing new collaborations in these areas.

Marine reserves are widely used to protect species important for conservation and fisheries and to help maintain ecological processes that sustain their populations, including recruitment and dispersal. Achieving these goals requires... more

Marine reserves are widely used to protect species important for conservation and fisheries and to help maintain ecological processes that sustain their populations, including recruitment and dispersal. Achieving these goals requires well-connected networks of marine reserves that maximize larval connectivity, thus allowing exchanges between populations and recolonization after local disturbances. However, global warming can disrupt connectivity by shortening potential dispersal pathways through changes in larval physiology. These changes can compromise the performance of marine reserve networks, thus requiring adjusting their design to account for ocean warming. To date, empirical approaches to marine prioritization have not considered larval connectivity as affected by global warming. Here, we develop a framework for designing marine reserve networks that integrates graph theory and changes in larval connectivity due to potential reductions in planktonic larval duration (PLD) associated with ocean warming, given current socioeconomic constraints. Using the Gulf of California as case study, we assess the benefits and costs of adjusting networks to account for connectivity, with and without ocean warming. We compare reserve networks designed to achieve representation of species and ecosystems with networks designed to also maximize connectivity under current and future ocean-warming scenarios. Our results indicate that current larval connectivity could be reduced significantly under ocean warming because of shortened PLDs. Given the potential changes in connectivity, we show that our graph-theoretical approach based on centrality (eigenvector and distance-weighted fragmentation) of habitat patches can help design better-connected marine reserve networks for the future with equivalent costs. We found that maintaining dispersal connectivity incidentally through representation-only reserve design is unlikely, particularly in regions with strong asymmetric patterns of dispersal connectivity. Our results support previous studies suggesting that, given potential reductions in PLD due to ocean warming, future marine reserve networks would require more and/or larger reserves in closer proximity to maintain larval connectivity.

Cities are defined as heterotrophic systems (Odum, 1983) as they depend mainly on external resources and cause habitat loss and fragmentation. Green roofs represents a fundamental means of ecological compensation within the built... more

Cities are defined as heterotrophic systems (Odum, 1983) as they depend mainly on external resources and cause habitat loss and fragmentation. Green roofs represents a fundamental means of ecological compensation within the built environment, i.e. in highly altered and disturbed places by humans. In particular, green roofs for biodiversity (or biodiversity green roofs), being characterised by different but contiguous microhabitat (habitat mosaics or patches), can host several species with different mor- phological and functional traits (Brenneisen, 2003). The method known as the habitat template consists of choosing suitable plant species for green roofs from among the one that live in nature under similar conditions e.g. shallow and nutrient poor substrate, drought resistant (Lundholm, 2006). The phytosociological approach applied to green roofs considers the habitat analogue not only as a species pool, but also as a model to group plants in specific associations.

Analysis of habitat conservation in the SIC Nature 2000 "ITA040005 - Monte Cammarata, Contrada Salaci", Monti Sicani (Sicily, Italy). The European ecological NATURA 2000 network is constituted by "Special Conservation... more

Analysis of habitat conservation in the SIC Nature 2000 "ITA040005 - Monte Cammarata, Contrada Salaci", Monti Sicani (Sicily, Italy). The European ecological NATURA 2000 network is constituted by "Special Conservation Zones" (SCZ) and "Community Importance Sites" (CIS). The main objective of this European initiative is to limit the erosion of natural habitats and species through the identification of appropriate areas

Understanding species’ interactions and the robustness of interaction networks to species loss is essential to understand the effects of species’ declines and extinctions. In most studies, different types of networks (such as food webs,... more

Understanding species’ interactions and the robustness of interaction networks to species loss is essential to understand the effects of species’ declines and extinctions. In most studies, different types of networks (such as food webs, parasitoid webs, seed dispersal networks, and pollination networks) have been studied separately. We sampled such multiple networks simultaneously in an agroecosystem. We show that the networks varied in their robustness; networks including pollinators appeared to be particularly fragile. We show that, overall, networks did not strongly covary in their robustness, which suggests that ecological restoration (for example, through agri-environment schemes) benefitting one functional group will not inevitably benefit others. Some individual plant species were disproportionately well linked to many other species. This type of information can be used in restoration management, because it identifies the plant taxa that can potentially lead to disproportionate gains in biodiversity.

Conservation of species is often focused either only on those that are endangered, or on maximising the number recorded on species lists. However, species share space and time with others, thus interacting and building frameworks of... more

Conservation of species is often focused either only on those that are endangered, or on maximising the number recorded on species lists. However, species share space and time with others, thus interacting and building frameworks of relationships that can be unravelled by community-level network analysis. It is these relationships that ultimately drive ecosystem function via the transfer of energy and nutrients. However interactions are rarely considered in conservation planning. Network analysis can be used to detect key species (“hubs”) that play an important role in cohesiveness of networks. We applied this approach to plant-pollinator communities on two montane Northern Apennine grasslands, paying special attention to the modules and the identity of hubs. We performed season-wide sampling and then focused the network analyses on time units consistent with plant phenology. After testing for significance of modules, only some modules were found to be significantly segregated from others. Thus, networks were organized around a structured core of modules with a set of companion species that were not organized into compartments. Using a network approach we obtained a list of important plant and pollinator species, including three Network Hubs of utmost importance, and other hubs of particular biogeographical interest. By having a lot of links and high partner diversity, hubs should convey stability to networks. Due to their role in the networks, taking into account such key species when considering the management of sites could help to preserve the greatest number of interactions and thus support many other species.

Species assemblages often have a non-random nested organization, which in vertebrate scavenger (carrion-consuming) assemblages is thought to be driven by facilitation in competitive environments. However, not all scavenger species play... more

Species assemblages often have a non-random nested organization, which in vertebrate scavenger (carrion-consuming) assemblages is thought to be driven by facilitation in competitive environments. However, not all scavenger species play the same role in maintaining assemblage structure, as some species are obligate scavengers (i.e., vultures) and others are facultative, scavenging opportunistically. We used a database with 177 vertebrate scavenger species from 53 assemblages in 22 countries across five continents to identify which functional traits of scavenger species are key to maintaining the scavenging network structure. We used network analyses to relate ten traits hypothesized to affect assemblage structure with the "role" of each species in the scavenging assemblage in which it appeared. We characterized the role of a species in terms of both the proportion of monitored carcasses on which that species scavenged, or scavenging breadth (i.e., the species "normalized degree"), and the role of that species in the nested structure of the assemblage (i.e., the species "paired nested degree"), therefore identifying possible facilitative interactions among species. We found that species with high olfactory acuity, social foragers, and obligate scavengers had the widest scavenging breadth. We also found that social foragers had a large paired nested degree in scavenger assemblages, probably because their presence is easier to detect by other species to signal carcass occurrence. Our study highlights differences in the functional roles of scavenger species and can be used to identify key species for targeted conservation to maintain the ecological function of scavenger assemblages.

The aim of this paper is to present the relationship between natural and technical sciences in the context of spatial planning, which should follow the strategy of sustainable development. Today the main task of conservation is to... more

The aim of this paper is to present the relationship between natural and technical sciences in the context of spatial planning, which should follow the strategy of sustainable development. Today the main task of conservation is to preserve biodiversity. This is only possible by maintaining ecological connectivity, i.e. the protection of ecological corridors linking natural areas. Spatial planning constitutes one of the basic tools of nature conservation. Today, both naturalists and planners face the challenge concerning the creation of ecological network of the country, which should be confirmed in law. The idea of sustainable development will only be possible through close cooperation between specialists in spatial planning and natural sciences.

Ecological analysis of ground beetles communities (Coleoptera Carabidae) in retting ponds from Ferrara countryside (Italy). The Coleoptera Carabidae were sampled with pitfall traps in 8 ancient artificial ponds, used in the past for the... more

Ecological analysis of ground beetles communities (Coleoptera Carabidae) in retting ponds from Ferrara countryside (Italy).
The Coleoptera Carabidae were sampled with pitfall traps in 8 ancient artificial ponds, used in the past for the treatment of hemp (Cannabis sativa).
The traps were put among trees and shrubs and reeds around the ponds. 10 environmental parameters were measured. Statistical analyses have
denied possible effects of the vegetation on Carabid beetles communities. The most influent parameters were: connectivity, fragmentation, surface
area, the presence of other ponds in a radius of 500 m, average width of the surrounding strip not used by man and the type of management in
the surrounding fields. 3 ponds were well distinguished from the others and dominated by dimorphic or brachypterous species. Among them, the
pond with the highest connectivity and fragmentation showed species typical of forests, including Abax continuus, an Italian endemic species: it is
possible that the recent landscape fragmentation didn’t show its heaviest consequences yet. Another pond, even if grouped together with the basins
dominated by winged species, proved that a wide strip without the man’s influence together with a low-impact management of the surrounding
fields can shape the community of beetles. The shores of the ponds proved to be relatively stable habitats, which give an important contribution
to the biodiversity of the agricultural ecosystems.

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... more

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.