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Havens K 1992 Scale And Structure In Natural Food Webs Science Pdf

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Although diversity and limnology of alpine lake systems are well studied, their food web structure and properties have rarely been addressed. Here, the topological food webs of three high mountain lakes in Central Spain were examined.

We first addressed the pelagic networks of the lakes, and then we explored how food web topology changed when benthic biota was included to establish complete trophic networks. We conducted a literature search to compare our alpine lacustrine food webs and their structural metrics with those of 18 published lentic webs using a meta-analytic approach.

The comparison revealed that the food webs in alpine lakes are relatively simple, in terms of structural network properties linkage density and connectance , in comparison with lowland lakes, but no great differences were found among pelagic networks.

The studied high mountain food webs were dominated by a high proportion of omnivores and species at intermediate trophic levels. Omnivores can exploit resources at multiple trophic levels, and this characteristic might reduce competition among interacting species. Accordingly, the trophic overlap, measured as trophic similarity, was very low in all three systems. Thus, these alpine networks are characterized by many omnivorous consumers with numerous prey species and few consumers with a single or few prey and with low competitive interactions among species.

The present study emphasizes the ecological significance of omnivores in high mountain lakes as promoters of network stability and as central players in energy flow pathways via food partitioning and enabling energy mobility among trophic levels.

This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All relevant data are within the paper and its Supporting Information files. Competing interests: The authors have declared that no competing interests exist. Ever since the concepts of food chains and food webs were introduced in the in the late s, many studies on feeding relationships have been carried out to address food web complexity and functioning [ 1 ].

The importance of omnivorous species as promoters of stability [ 2 — 4 ] has been recognised as a result of their ability to use different food resources leading to reduced inter- and intraspecific competition [ 4 ].

In addition, the prevalence of omnivores in food webs may be related to two other important features: firstly, omnivores can have an important impact on energy flows and nutrient cycling [ 5 ] and secondly, omnivores can increase the number of links usually measured as linkage density or the average number of links per species and hence the food web connectance i.

Fish are usually at the top of freshwater food chains [ 6 — 9 ]. In lakes, a major pathway of energy transfer is often through pelagic food chains [ 10 ], but also benthic prey can be important resources for fish [ 11 , 12 ]. Fish, via their foraging behaviour, are able to modify important food web properties such as for example linkage density, connectance and omnivory [ 13 ].

Food web topology in lakes has received attention [ 14 — 19 ], but the majority of the studies have focused on the pelagic zone [ 15 , 17 — 19 ], and relatively few have included the macroinvertebrates from the littoral and profundal zones [ 14 , 16 ]. The inclusion of the benthic biota in food web analysis allows a broader perspective of ecosystem functioning, especially when it is considered that the pelagic, littoral and profundal zones may be coupled through fish [ 12 , 20 ].

High mountain lakes that are present across the world constitute simple systems due to low species diversity [ 21 — 23 ] and low primary production [ 24 , 25 ]. Originally fish-free alpine lakes have frequently been stocked with salmonid species for recreational purposes, and food webs can be affected by fish introductions because fish are able to modify the structure and composition of both the zooplankton and littoral macroinvertebrate communities [ 26 — 28 ].

To understand the ecosystem functioning of such high mountain lakes, their food web topology has to be explored, but there are still several issues relating to food web structure, prevalence of omnivory and trophic level about which little is known. A notable exception is the study by Harper-Smith et al. In the present study, we have constructed trophic webs for three high elevation lake systems of Central Spain lakes Caballeros, Cimera and Grande de Gredos to include all relevant trophic levels littoral vegetation, phytoplankton, zooplankton, macroinvertebrates, amphibians and fish.

The main objective was to provide, analyse and compare high-resolution topological food webs for the three systems; one lake without fish, one with introduced brook charr Salvelinus fontinalis Mitchill, henceforth simply charr and one with native brown trout Salmo trutta Linnaeus, henceforth simply trout.

More specifically, this study aimed to: i quantify important structural network properties of alpine lakes such as food web connectance, number of trophic levels and prevalence of omnivory, ii investigate how the structural network properties change when benthic biota are added to complement the pelagic web and complete the lacustrine food web, and iii compare the food web topology of these alpine lakes with published information from other lentic systems using a meta-analytic approach.

We hypothesised that i connectance would be higher in lakes with fish than those without, ii structural network properties should be more complex when benthic biota are incorporated, and iii food webs in alpine lakes are relatively simple in terms of linkage density and connectance, in comparison with lowland lakes.

All efforts were made to minimize animal stress and suffering during this study. Fish were euthanized by cerebral concussion followed by cervical dislocation to ensure the cessation of life.

None of the sampled species were endangered or protected. The topography has origin in tectonic developments during the Alpine Orogeny Cenozoic , and landscape changes during the Last Glacial Period Late Pleistocene , when glaciers formed the lakes of the Gredos Mountains [ 29 ]. The study involves three high mountain lakes Caballeros, Cimera and Grande de Gredos on the northern slope of the Gredos Mountains at altitudes between and m.

Fig 1. The bottom of these lakes is mainly silty with relatively low organic matter content, but in the shoreline area the amounts of sandy bottom and block material are higher [ 30 ]. Ice phenology is under the influence of climate change via precipitation and air temperature changes [ 32 ]. The three lakes are monomictic with winter inverse stratification during the ice-covered period, whereas after the ice-melt periods, water column mixing predominate [ 30 , 31 ].

The others parts of the figure are owned by JSH. The catchment is dominated by Nardus stricta grasslands and psicroxerophytic meadows, but with alpine shrub vegetation on the less steep slopes [ 30 , 31 ].

Macrophytes are scarce in the lake, but small areas of Antinoria agrostidea , Isoetes boryana , Sparganium angustifolium , Callitriche palustris and Carex spp. There are no fish species in the lake. The lake has a maximum depth of 9. There are no submerged macrophytes, but small areas of water-mosses, mainly Drepanocladus exannulatus and Fontinalis squamosa , are present in the littoral zone [ 31 ].

The levels of polycyclic aromatic hydrocarbons in the superficial sediments of the lake are lower than in lakes in France, Austria, Poland, Slovakia, Ireland and Norway, indicating low contamination by persistent organic pollutants [ 36 ]. The only fish present is the charr, which was introduced between and and currently has a stable population [ 35 ]. The catchment area is mainly rocky with small Nardus stricta grassland and psychroxerophytic meadows [ 37 ].

The lake has a maximum depth of 6. The littoral zone is predominantly shallow and there is abundant aquatic vegetation, mainly Subularia aquatica , Isoetes velatum , Isoetes boryana , Juncus bulbosus , Juncus tanageia , Callitriche palustris , Antinoria agrostidea , Ranunculus peltatus , Carex nigra , Drepanocladus exannulatus , Fontinalis squamosa , Sphagnum denticulatum and Sparganium angustifolium [ 30 , 33 , 34 ].

The main anthropogenic impact is from a mountain refuge built in [ 37 , 38 ]. Native trout are the only fish present in the lake. The two primary sources for the data were surveys of macroinvertebrates, amphibians and fish conducted in all three lakes during the summers of and , and retrieved from publications containing relevant information about the three lakes.

Macroinvertebrates were collected from the littoral zone with a pond net by kicking and sweeping 10 samples in each lake , standardised by kicking for 5 minutes. Species lists were supplemented with information from published studies [ 30 , 31 , 39 , 40 ] to establish the final macroinvertebrate data set. Amphibians were monitored by searching for hidden individuals in cavities, soil cracks and under rocks both during daylight and at night with flashlights.

Two anurans Bufo spinosus Daudin, and Rana iberica Boulenger, and an urodelan, Salmandra salamandra L , were found in the three lakes. Fish were captured by fishing using spinning lures; a total of 49 charr 11— Information about phytoplankton and zooplankton compositions were taken from Toro et al.

The species compositions of each group phytoplankton, zooplankton, macroinvertebrates, amphibians and fish in each lake are given as supporting information S1 File. To study the macroinvertebrate trophic structure, each taxon was assigned to a functional feeding group FFG based on information from relevant literature [ 41 ]. This study is based on presence-absence data for species in each lake i.

The establishment of feeding links between the species present in the lakes was performed on the basis of our stomach contents analyses macroinvertebrates and fish together with information from the literature. Literature searches were conducted using databases e. The diets of charr and trout in high mountain lakes are well documented [ 43 — 46 ].

Diet compositions of the amphibian species present in the lakes are also known [ 47 — 49 ]. For the diets of zooplankton [ 50 — 52 ] and macroinvertebrates [ 41 , 53 , 54 ], studies from a broad geographical range had to be used see full reference list used in this study for establishing the feeding links between the species in S2 File.

Due to a lack of information about whether the phytoplankton species present are unicellular, filamentous, colonial or other forms, most phytoplankton species are considered as being unicellular except for some Chlorophyta Pediastrum tetras , Scenedesmus sp. We assumed that filamentous and colonial forms of phytoplankton species cannot be utilized as food by zooplankton because of their size [ 57 ], whereas zooplankton could graze on unicellular species.

Rotifers have only been recorded in Caballeros lake Keratella quadrata and Conochilus sp. The trophic base in the benthic habitats were aggregated into the following groups: coarse organic material leaves, wood , fine detritus, macrophytes, water-moss and periphyton.

Fungi or bacteria are able to break down coarse organic material and fine detritus [ 58 ], but microorganisms have not been included in this study. The topological food webs of the three lakes were established according to Amundsen et al.

The trophic link matrices used for food web construction are given as supporting information S1 — S3 Datasets. To characterise food web topology, a suite of 23 properties was calculated Table 1. We calculated the number of trophic levels, linkage density and connectance using previously described methods [ 18 , 19 ].

When GenSD is higher than VulSD , it means that there are few consumers with numerous prey and many consumers with a single prey [ 3 ].

In line with other studies, trophic similarity Sim was calculated to address the trophic overlap of food webs [ 3 , 63 ]. The measurement of trophic overlap using a similarity index between every pair of taxa in a food web was proposed by Martinez [ 14 ]; index values vary from zero when two taxa have no common predators or common prey to one when two taxa have the same set of predators and prey [ 14 ].

Williams and Martinez [ 64 ] recommended the combination of traditional food web properties with analyses of mean short-weighted trophic level MeanSWTL and mean shortest chain to a basal species MeanShortChn , because these parameters can provide valuable information about energy flow. MeanSWTL can indicate how many steps energy must take to get from an energy source to a consumer [ 1 ] and MeanSWTL has been used to calculate the trophic level averaged across taxa in food webs [ 62 , 63 ].

To calculate MeanSWTL , the FoodWeb3D software assigns a value for basal taxa as one, obligate herbivores have trophic level two, and higher level consumers have a value based on their feeding relationships to other levels; more detail about how this index is calculated can be found in previous works [ 63 , 64 ].

Topological food webs were established separately for the pelagic zone and the complete system pelagic and benthic biota , which allowed us to compare network complexity between the pelagic and complete networks. In addition, topological food webs for Cimera and Grande de Gredos lakes were also constructed without fish species in order to make their structure compatible and comparable with Caballeros lake fishless lake. This approach allowed us to examine whether fish predation could modify the structure of the food webs in high mountain lakes.

Meta-analysis refers to a set of methods used to analyse or compare results from different studies [ 65 ]. The data from the three lakes were compared to food web statistics gathered from 18 published food webs from lentic systems [ 14 — 19 ]. The meta-analysis was carried out separately for complete food webs [ 14 , 16 ], and pelagic food webs [ 15 , 17 — 19 ], and was implemented by using common food web properties presented in all the 18 published food webs: species richness S , number of links L , linkage density D and connectance C.

The data used are provided as supporting information S1 Table. A principal component analysis PCA was used to explore differences in the food web properties among systems. In addition, data matrices were analysed using between-class analysis in order to explore the affinity of the systems in the PCA.

Between-class analysis is a method used to enhance the understanding of similarities between grouped classes [ 66 , 67 ]. The data analysis involved in three steps: i the dudi. Graphical outputs and permutation analysis were computed with the ADE4 library implemented in R freeware [ 69 ].

The combination of benthic biota with the pelagic network to give the complete food web increased the number of links by 4.

In addition, when fishless topologies were constructed for the three lakes, GenSD and VulSD values were lower in the fishless condition, whereas there were no marked differences in connectance Table 2. The remainder of this section refers to the complete networks, but information about the pelagic and fishless food-web metrics can be obtained from Table 2.

In all three lakes, Chironimidae dominated the taxonomic richness of the macroinvertebrate community with Collectors and predators were proportionally the most abundant functional feeding groups, while filter feeders were scarce and were only represented by Pisidium casertanum Poli, Fig 2.

Functional feeding groups of the macroinvertebrate community in each lake.

The use of DNA barcodes in food web construction—terrestrial and aquatic ecologists unite!

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The use of DNA barcodes in food web construction—terrestrial and aquatic ecologists unite!

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Introduction

Although diversity and limnology of alpine lake systems are well studied, their food web structure and properties have rarely been addressed. Here, the topological food webs of three high mountain lakes in Central Spain were examined. We first addressed the pelagic networks of the lakes, and then we explored how food web topology changed when benthic biota was included to establish complete trophic networks. We conducted a literature search to compare our alpine lacustrine food webs and their structural metrics with those of 18 published lentic webs using a meta-analytic approach. The comparison revealed that the food webs in alpine lakes are relatively simple, in terms of structural network properties linkage density and connectance , in comparison with lowland lakes, but no great differences were found among pelagic networks. The studied high mountain food webs were dominated by a high proportion of omnivores and species at intermediate trophic levels.

Research onfood webs is one of the few subdisciplines within ecology that seeks to quantify and analyze direct and indirect interactions among diverse species,rather than focusing on particular types of taxa. Food webs ideally represent whole communities including plants, bacteria, fungi, invertebrates andvertebrates. At the base of every food web are one or more types of autotrophs, organisms such as plants or chemoautotrophic bacteria,which produce complex organic compounds from an external energy source e. Using the language of graph theory and the framework of network analysis, species are represented by vertices nodes and feeding links are represented by edges links between vertices. As with any other network, the structure and dynamics of food webs can bequantified, analyzed and modeled. Examples of formats for standardized notation of binary food web data. Numbers 1—6 correspond to the different taxa.

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5 Comments

Urania Y. 13.05.2021 at 17:30

In book: Ecological Networks: Linking Structure to Dynamics in Food Webs maintained in natural ecosystems provided a framework on which to hang some Additional scale-invariant patterns found using early food-web data included: ; Havens ), or had less even representation of taxa resulting from.

Lily B. 17.05.2021 at 08:56

PDF | For thirty years I have read publications about this spate of invasions; and many of them preserve seen vast growth in the scientific workforce and in our Havens, K. Scale and structure in natural food webs.

Connor N. 18.05.2021 at 16:04

ally to globally scaled food webs with to species, respectively. effects of scale on food-web structure that take into account recently demonstrated , Havens , see Lawton , Pimm illustrious scientific history is food​-chain length (Elton Havens, K. Scale and structure in natural food webs. -.

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