An ecological network is a representation of the biotic interactions in an ecosystem, in which species (nodes) are connected by pairwise interactions (links). These interactions can be trophic or symbiotic. Ecological networks are used to describe and compare the structures of real ecosystems, while network models are used to investigate the effects of network structure on properties such as ecosystem stability.
Historically, research into ecological networks developed from descriptions of trophic relationships in aquatic food webs; however, recent work has expanded to look at other food webs as well as webs of mutualists. Results of this work have identified several important properties of ecological networks.
Complexity ([linkage density): the average number of links per species. Explaining the observed high levels of complexity in ecosystems has been one of the main challenges and motivations for ecological network analysis, since early theory predicted that complexity should lead to instability.
Connectance: the proportion of possible links between species that are realized (links/species2). In food webs, the level of connectance is related to the statistical distribution of the links per species. The distribution of links changes from (partial) power-law to exponential to uniform as the level of connectance increases. The observed values of connectance in empirical food webs appear to be accountable for by constraints on an organisms diet breadth driven by optimal foraging behaviour.This links the structure of these ecological networks to the behaviour of individual organisms.
Degree distribution: the degree distribution of an ecological network is the cumulative distribution for the number of links each species has. The degree distributions of food webs have been found to display the same universal functional form. The degree distribution can be split into its two component parts, links to a species' prey (aka. in degree) and links to a species' predators (aka- out degree). Both the in degree and out degree distributions display their own universal functional forms. As there is a faster decay of the out-degree distribution than the in degree distribution we can expect that on average in a food web a species will have more in links than out links.
Clustering: the proportion of species that are directly linked to a focal species. A focal species in the middle of a cluster may be a keystone species, and its loss could have large effects on the network.
Compartmentalization: the division of the network into relatively independent sub-networks. Some ecological networks have been observed to be compartmentalized by body size and by spatial location. Evidence also exists which suggests that compartmentilization in food webs appears to result from patterns of species' diet contiguity  and adaptive foraging 
Nestedness: the degree to which species with few links have a sub-set of the links of other species, rather than a different set of links. In highly nested networks, guilds of species that share an ecological niche contain both generalists (species with many links) and specialists (species with few links, all shared with the generalists). In mutualistic networks, nestedness is often asymmetrical, with specialists of one guild linked to the generalists of the partner guild. The level of nestedness is determined not by species features but overall network depictors (e.g. network size and connectance) and can be predicted by a dynamic adaptive model with species rewiring to maximize individual fitness or the fitness of the whole community.
Network motif: Motifs are unique sub-graphs composed of n-nodes found embedded in a network. For instance there exist thirteen unique motif structures containing three species, some of these correspond to familiar interaction modules studied by population ecologists such as food chains, apparent competition, or intraguild predation. Studies investigating motif structures of ecological networks, by examining patterns of under/over representation of certain motifs compared to a random graph, have found that food webs have particular motif structures 
Trophic coherence: The tendency of species to specialise on particular trophic levels leads to food webs displaying a significant degree of order in their trophic structure, known as trophic coherence, which in turn has important effects on properties such as stability and prevalence of cycles.
The relationship between ecosystem complexity and stability is a major topic of interest in ecology. Use of ecological networks makes it possible to analyze the effects of the network properties described above on the stability of an ecosystem. Ecosystem complexity was once thought to reduce stability by enabling the effects of disturbances, such as species loss or species invasion, to spread and amplify through the network. However, other characteristics of network structure have been identified that reduce the spread of indirect effects and thus enhance ecosystem stability. The relationship between complexity and stability can even be inverted in food webs with sufficient trophic coherence, so that increases in biodiversity would make a community more stable rather than less.
Interaction strength may decrease with the number of links between species, damping the effects of any disturbance and cascading extinctions are less likely in compartmentalized networks, as effects of species losses are limited to the original compartment. Furthermore, as long as the most connected species are unlikely to go extinct, network persistence increases with connectance and nestedness. No consensus on the links between network nestedness and community stability in mutualistic species has however been reached among several investigations in recent years. Recent findings suggest that a trade-off between different types of stability may exist. The nested structure of mutualisitic networks was shown to promote the capacity of species to persist under increasingly harsh circumstances. Most likely, because the nested structure of mutualistic networks helps species to indirectly support each other when circumstances are harsh. This indirect facilitation helps species to survive, but it also means that under harsh circumstances one species cannot survive without the support of the other. As circumstances become increasingly harsh, a tipping point may therefore be passed at which the populations of a large number of species may collapse simultaneously.
Additional applications of ecological networks include exploration of how the community context affects pairwise interactions. The community of species in an ecosystem is expected to affect both the ecological interaction and coevolution of pairs of species. Related, spatial applications are being developed for studying metapopulations, epidemiology, and the evolution of cooperation. In these cases, networks of habitat patches (metapopulations) or individuals (epidemiology, social behavior), make it possible to explore the effects of spatial heterogeneity.
The Alpine Convention is an international territorial treaty for the sustainable development of the Alps. The objective of the treaty is to protect the natural environment of the Alps while promoting its development. This Framework Convention involves the European Union and eight states (Austria, Germany, France, Italy, Liechtenstein, Monaco, Slovenia, and Switzerland). Opened to signature in 1991 and consisting of a Framework Convention, various implementation protocols and declarations, it entered into force in 1995, contributing to reinforce the recognition of special qualities and specific characteristics of the Alps, going beyond national boundaries and seeking international action.Bargerveen Nature Reserve
Bargerveen Nature Reserve is a nature reserve in the Dutch province of Drenthe that has been included in the Natura 2000 ecological network. Since 2006 it is part of the Internationaler Naturpark Bourtanger Moor-Bargerveen (engl. Bourtanger Moor-Bargerveen International Nature Park), a nature reserve located on both sides of the border between the Netherlands and Germany. Most of the transboundary nature reserve, some 134 km2 (52 sq mi), lies in Germany, in the west of the state of Lower Saxony. The sparsely populated landscape consists of large peat areas, heather, and small lakes.
The Dutch part of the nature reserve was founded in 1992 as Natuurreservaat Bargerveen. It was designated as a Ramsar site (a wetland of international importance) the following year. Bargerveen has a size of 21 km2 (8.1 sq mi). It consists mainly of peat bog.Belasitsa Nature Park
Belasitsa Nature Park (Bulgarian: Беласица Природен Парк) covers the northern slopes of Belasitsa Mountain in the Southwest Region of Bulgaria. The total area of the park is 117 km² (45 sq mi). Belasitsa is part of the European ecological network NATURA 2000 and is managed by the Belasitsa Nature Park Directorate which is a legal entity under the authority of the Executive Forest Agency of Ministry of Agriculture and Food. The Directorate office is located in the village of Kolarovo.
The nature park is bordered to the west by the Republic of Macedonia and to the south by Greece, both of which contain regions of Belasitsa Mountain. Belasitsa Nature Park includes the villages of Gabrene, Skrut, Klyuch, Yavornitsa, Kamena, Samuilovo, Kolarovo, Belasitsa, and Petrich, all located in the municipality of Petrich, Blagoevgrad Province.European Centre for Nature Conservation
European Centre for Nature Conservation (ECNC) is an independent European biodiversity expertise centre for sustainable development, based on a foundation structure. ECNC’s stated mission is a beautiful Europe based on a rich biodiversity, healthy ecosystems and sustainable development. The organization promotes an integrated approach for both land and sea and stimulates interaction between science, society and policy.European Green Belt
The European Green Belt initiative is a grassroots movement for nature conservation and sustainable development along the corridor of the former Iron Curtain. The term refers to both an environmental initiative as well as the area it concerns. The initiative is carried out under the patronage of the International Union for Conservation of Nature and Mikhail Gorbachev. It is the aim of the initiative to create the backbone of an ecological network that runs from the Barents to the Black and Adriatic Seas.
The European Green Belt as an area follows the route of the former Iron Curtain and connects National Parks, Nature Parks, Biosphere Reserves and transboundary protected areas as well as non-protected valuable habitats along or across the (former) borders.Krupa (Lahinja)
The Krupa is a 2.5 km (1.6 mi) river in White Carniola, southeastern Slovenia. Its source is a karst spring in the village of Krupa below a rock wall. The bed has canyon characteristics in some places. At Gradac, the river joins the Lahinja from the left side. Its drop from the source to the outflow is only 6 metres (20 ft).The river is protected as a natural monument and has been included in the Natura 2000 ecological network. It is the main feature of the Lebica–Krupa Karst Nature Trail (Slovene: Kraška učna pot od Lebice do Krupe). Its source lake is the only habitat of the cave mollusk Congeria kusceri in Slovenia, found in Cave Mussel Spring (Izvir Jamske školjke). It is also home to some cave snails and the olm.The Krupa River is infamous because of its extremely high pollution with PCBs due to improper handling of PCB waste material which has been used for decades by the capacitor manufacturing company Iskra Kondenzatorji in nearby Semič.List of network theory topics
Network theory is an area of applied mathematics.
This page is a list of network theory topics.Natura 2000
Natura 2000 is a network of nature protection areas in the territory of the European Union. It is made up of Special Areas of Conservation and Special Protection Areas designated respectively under the Habitats Directive and Birds Directive. The network includes both terrestrial and Marine Protected Areas.Pindus National Park
Pindus National Park (Greek: Εθνικός Δρυμός Πίνδου Ethnikós Drymós Píndou), also known as Valia Calda (meaning the Warm Valley in Aromanian), is a national park in mainland Greece, situated in an isolated mountainous area at the periphery of West Macedonia and Epirus, in the northeastern part of the Pindus mountain range. It was established in 1966 and covers an area of 6,927 hectares (17,120 acres). The park's core zone, 3,360 hectares (8,300 acres), covers the greatest part of the Valia Calda valley and the slopes of the surrounding peaks.The national park has an elevation range from 1,076 to 2,177 metres (3,530 to 7,142 ft) and is characterized by dense forests of European black pine and common beech, rocky ridges, several peaks over 2,000 metres (6,600 ft), rapid streams and mountain lakes. The area belong to the wider Pindus Mountains mixed forests ecoregion and is a representative part of
Pindus mountain range. Moreover, it belongs to the Natura 2000 ecological network of protected areas and is one of the three places in Greece that hosts a population of bears.Podilski Tovtry National Nature Park
National Nature Park "Podilski Tovtry" (Ukrainian: Націона́льний приро́дний парк «Поді́льські То́втри») is a national park, located in the Horodok, Kamianets-Podilskyi, and the Chemerivtsi Raions (districts) of Khmelnytskyi Oblast (province) in southern region of the western Ukraine. It is the biggest nature conservation area in Ukraine.
The National Environmental Park "Podilski Tovtry" was created on the decree #476/96 of the President of Ukraine, then Leonid Kuchma, on July 27, 1996, in order to maintain and protect the natural landscape of the Podillia region. The park is a nature-conservational, recreational, culturally enlightening, and scientifically researching institution of national importance. According to the Law of Ukraine of September 21, 2000 #1989-III, the National nature park "Podilski Tovtry" belongs to the National Ecological Network of Ukraine of the Podillya region (Podillya).Productivity (ecology)
In ecology, productivity refers to the rate of generation of biomass in an ecosystem. It is usually expressed in units of mass per unit surface (or volume) per unit time, for instance grams per square metre per day (g m−2 d−1). The mass unit may relate to dry matter or to the mass of carbon generated. Productivity of autotrophs such as plants is called primary productivity, while that of heterotrophs such as animals is called secondary productivity.Protected areas of Croatia
The main protected areas of Croatia are national parks, nature parks and strict reserves. There are 444 protected areas of Croatia, encompassing 9% of the country. Those include 8 national parks in Croatia, 2 strict reserves and 11 nature parks. The most famous protected area and the oldest national park in Croatia is the Plitvice Lakes National Park, a UNESCO World Heritage Site. Velebit Nature Park is a part of the UNESCO Man and the Biosphere Programme. The strict and special reserves, as well as the national and nature parks, are managed and protected by the central government, while other protected areas are managed by counties. In 2005, the National Ecological Network was set up, as the first step in preparation of the EU accession and joining of the Natura 2000 network.The total area of all national parks in the country is 994 km2 (384 sq mi), of which 235 km2 (91 sq mi) is sea surface.
Each of the national parks is maintained by a separate institution, overseen and funded by the government ministry of nature conservation and spatial development. The State Institute for Nature Protection provides centralized oversight and expertise.Roques de Anaga
The Roques de Anaga are two monolithic rocks forming some of the most emblematic natural monuments of Tenerife (Canary Islands, Spain). Roque de Tierra stands 179 meters above sea level and is closer to the main island while Roque de Fuera, at 66 meters above sea level, is farther away. Both rocks are also included in the European Union's Natura 2000 ecological network of protected areas. They are located off the north-east coast of Tenerife.
Roques de Anaga is a part of the Anaga Rural Park and has been classified as a Special Protection Area for birds.Särö Västerskog
Särö Västerskog is a nature reserve located in Kungsbacka Municipality, Sweden, on a peninsula west of the locality of Särö. It was established in 1974 and is currently part of the Natura 2000 ecological network.
The reserve has an area of 55 hectares; it is mostly covered with forest, but there are also pastures and beaches, as well as graves from the Nordic Bronze Age. The most common trees are oak and pine, some of which are 200–300 years old. In 1914, a pine tree with 480 growth rings was found - probably the oldest known pine in Halland. Furthermore, the reserve houses the largest population of the common yew in Sweden.55 species in the IUCN Red List have been found in the reserve, including many lichens and beetles.Vistula River Gorge of Lesser Poland
The Lesser Poland Gorge of the Vistula (Polish: Małopolski Przełom Wisły) is a geographical region located in central-eastern Poland, which administratively belongs to three Polish voivodeships – Lublin, Masovian, and Świętokrzyskie. The Gorge is for the most part made by the valley of the Vistula, with two Polish uplands on both sides of the river – Lesser Poland (or Małopolska) Upland to the west, and Lublin Upland to the east. The gorge is about 70 kilometers long, extending from the town of Zawichost in the south, to Puławy in the north. It is considerably narrow, only up to 3 kilometers wide. In some places, the banks of the Vistula valley are very steep, up to 70 meters above the water level.
The region comprises a densely populated agricultural land, with two main towns; historic Kazimierz Dolny, and Annopol. Other towns are Józefów, Bochotnica, Janowiec and Wilków. The Gorge is one of several protected areas designated in the Natura 2000 territory of the European Union's ecological network around the Vistula and Pilica rivers (out of the total of around 500 Natura 2000 sites in Poland). They are listed as – Natura 2000 PLB 14000, and Natura 2000 PLH 060045.Vrtare Male
Vrtare Male is a pit cave located near Dramalj, a seaside village in Croatia. Its depth is believed to be 39 metres (128 ft), with around 10 metres (33 ft) submerged. It was first explored in 1966 by the Mountaineering Society Velebit. In 1996, Dragan Pelić, a photographer and spelaeologist from nearby Crikvenica, descended into the cave and found a rare Decapoda specimen, which was confirmed by Croatian spelaeologist Branko Jalžić. This prompted further cave expeditions, starting in 2005, and the establishment of a protected area around Vrtare Male.The cave is home to the freshwater cave prawn (Troglocaris anophthalmus), endemic to Dinaric karst. Vrtare Male is part of the National Ecological Network of Croatia. It is registered under the code HR3000257, and potential for inclusion in Natura 2000. In 2009, it was proclaimed a geological-palaeontological natural monument. The area under protection covers around 310 square metres (3,300 sq ft).Wümme Depression
The Wümme Depression (German: Wümmeniederung) is a bog, geest and forest landscape within the Elbe–Weser triangle in the German state of Lower Saxony. It belongs mainly to the district of Rotenburg and is part of the Stade Geest. To the south it borders on the Achim-Verden Geest. It has no sharply defined boundary with the Lüneburg Heath; as a result many places are seen as belonging to both regions. Typical of the gently undulating terrain are the many small rivers, streams and lakes. These include the rivers Wümme, Wieste, Fintau, Rodau, Wiedau and Vissel, as well as the twin lakes known in German as the Bullenseen. In this ancient landscape Low German is commonly spoken.
The Wümme Depression is designated by the European Environment Agency (EEA) as a Special Area of Conservation (SAC), no. DE2723331, within their Natura 2000 ecological network.
The SAC has an area of 8,578.95 hectares (33.1235 sq mi).The villages and towns of the Wümme Depression are:
Rotenburg an der Wümme
VisselhövedeZakynthos Marine Park
The National Marine Park of Zakynthos (Greek: Εθνικό Θαλάσσιο Πάρκο Ζακύνθου) founded in 1999, is a national park located in Laganas bay, in Zakynthos island, Greece. The park, part of the Natura 2000 ecological network, covers an area of 135 square kilometres (52 sq mi) and
is the habitat of the loggerhead sea turtle (Caretta caretta). It is the first national park established for the protection of sea turtles in the Mediterranean.Zlatia (region)
Zlatiya (Bulgarian: Златия, often with a definite article: Златията, Zlatiyata; also Zlatia, Zlatija) is a small geographic region in Northern Bulgaria. Zlatiya is a low asymmetrical plateau in the northwestern part of the country, a subregion of the Danubian Plain. It lies between three rivers: the Tsibritsa to the west, the Ogosta to the east and the Danube to the north. The plateau's elevation is around 100–150 metres above mean sea level, the highest point reaching 176 m near the Danube. The soil is a fertile chernozem; no rivers cross the plateau, but by heavy rainfall the ravines are drained away to the east by the Ogosta river and ultimately into the Danube. Zlatiya has been an Important Bird Area since 2005 (parts of it since 1997) and has been included in the EU's Natura 2000 ecological network. The protected area covers 434.987 square kilometres.
Although most of the region is composed of arable land, there are still some extant small forests. The main local product has traditionally been grain, leading to Zlatiya's labeling as "Bulgaria's northwestern granary", a comparison to Dobruja.
The population mainly consists of Bulgarians, although there is a sizable Roma minority. A local centre is the town of Valchedram, Montana Province. The region's name roughly means "golden land".