Questions related to Food Webs
Stream is undoubtedly essential for the river ecosystem. It is the source of water for the river as well as the groundwater. At the same time, it is essential to study the macroinvertebrates to know their role on the food web. But how it is beneficiary to humans or what is the social impact of this kind of study?
What problems will arise if there is either an increase or decrease in the number of any component in a food chain or a food web?
I have a dataset composed of aphid and parasitoid abundances captured in Moericke traps on a monthly scale for 10 years. As I do not have data on parasitism, but on the occurrence of aphids and parasitoids, I cannot use common trophic networks. In this way, I think I could explore some community-level relationships through correlation-based networks. However, I would like to know if there is any impediment to using this approach or if anyone has already used it.
For example, I want to explore the relationships between soil nematode communities and microbial communities under different treatments, including relationships of functional and taxonomic composition between each other. Nematodes and microbes belongs to different trophic levels, i.e., bacterivore nematodes feed on bacterias; fungivore nematodes feed on fungi; herbivore nematode feed on plant roots; and omnivore nematode prey on bacterivore, fungivore, and herbivore nematodes. In conclusion, which statistical tools are suit for analysis of relationships in complex soil food web?
Hello All! I am working on a project that uses stable isotope analysis (C and N) to look at the diets of California reef fishes. I am going to be collecting Liver and White muscle tissue. It was suggested to me to use 20ml borosilicate glass scintillation vials (urea caps with polyurethane lined caps/not foil lined) for my tissues. I will be freezing the tissue samples in the vials and drying them in a 65C drying oven in them as well. The issue I am running into is that every brand of vials are back ordered for about 4 months no matter where I look.
So I wanted to see if 1. Anyone in the southern California/greater LA Area had vials I could buy off of them to use. Or 2. If anyone knew of a substitute I could use. It has been suggested that I could hand make aluminum foil packets, pre combust them, and store/dry the tissue in those. However, I would prefer the glass vials for both, organization/storage sake as well as I will eventual be grinding the powder into a powder and vials would be less likely to fail with the powder.
Thank you in advance for any advice!
So far, most of methods about inferring the trophic or ecological interactions take account of the circumstance of aquatic ecosystem. Many methods have emerged, such as the method based on body size (Gravel and Poisot et al., 2013) and the method based on published data (Gray and Figueroa et al., 2015). However, these methods have many limitations when applied to terrestrial ecosystems. Are there any generic methods to infer the trophic interactions in terrestrial ecosystems?
Any helpful answers would be appreciated!
Gray, C. and D. H. Figueroa, et al. (2015). "Joining the dots: An automated method for constructing food webs from compendia of published interactions." Food Webs 5: 11-20.
Gravel, D. and T. Poisot, et al. (2013). "Inferring food web structure from predator-prey body size relationships." Methods in Ecology and Evolution 4 (11): 1083-1090.
Groups of macro-invertebrates based on a food web exist, simplistically, species A always predates on species B. So, no species B means no species A. With phyto-social communites these interactions are, to my knowledge, not present. So, species co-occurrence is not connected to food web interactions between species. Lets extent this example to the occurrence of macrophytes. Consider a large lowland river with no hard substrate (stones, rocks etc.) We can find E. nuttalli, M. spicatum, N. lutea and S. emersum. We arbitrarily call this a lowland community. Now we throw some rock and stones to stabalize the banks of this river. After some time F. antipyretica starts to grow. Yet, F. antipyretica is not considered to belong to a lowland community, since it is often observed upstreams in mid mountain regions or smaller rivers (with hard substrate due to higher flow velocities and turbulent waters). Thus, F. anitpyretica only started to grow here because it now has hard substrate, not because the other species are present . There, seems to be no existing community structure, since F. antipyretica just starts to grow there because the environment provides the means to do so and it can compete with the other species. The statement 'Everything is everywhere, but, the environment selects' (Baas Becking, 1934; de Wit and Bouvier, 2006), makes sense focusing only on macrophytes (not the interaction with predators or species needing certain macrophytes). For macrophytes, external factors "favor" the occurrence of certain species over others. Species that have similar "preferences" and traits are "selected" over others. From a deterministic standpoint, if we new everything we could predict species occurrence. Yet, we cannot, so we just group them together with species seemingly occurring often together. Certainly, lowland communities can be observed, but a slight change in the environmental factors will change these communities. These communities of species are only observed because of the simultaneous occurrence of often correlated environmental factors under "natural" conditions. Hence, large lowland rivers often have no hard substrate, while upstream rivers do. We, as humans have said, this is a community, since this is the "natural" state of an environment, while these species do not recognize this particular delineation. Does this suggests that delineation of phyt-social communities of macrophytes is just an outdated concept, since macrophyte species do not form communities, but simply occur there because they can? The fact that we can show that these species are often present in groups with ordination methods or cluster analysis, does not make it a community, just a group of species with similar "preferences" and "traits". The first result I get on google searching for a definition of community (definition community biology) results in "Community, also called biological community, in biology, an interacting group of various species in a common location (https://www.britannica.com/science/community-biology)". But, this definitions cause an itch with me regarding macrophytes. The definition does not really fit with my idea of macrophyte communities. I cannot really concretely and shortly explain why, but I hope the example above gives some idea. Either the definition just does not apply to communities of macrophytes, macrophyte communities doe not exist, or I have a wrong idea of macrophyte communities. Someone has any other point of view on this "issue", or can shortly describe what I am struggling to shortly explain and understand.
Hi food web colleagues, diet experts...etc
Our last project started from the crazy idea to build a comprehensive benthic topology food web for the whole North Sea. It quickly seemed impractical for only a few human-beings as we lack data for most non-commercial species. It took almost two years to focus on 152 species, project that got reduced to 50 or so species for practicality.
We still want to go for it but I think we need to find the right people who might have the diet data we need or know where to find them (in situ, lab feeding experiments, published or unpublished data, or inference from other species).
Do you have diet information on species in the North Sea? Know someone who does? We could start from there.
I'll have 2 days doing practical work with R. What do you think I'll have time to do? I was hoping to spend one day on inverse analysis using LIM-Solve and then one day on ecological network analysis using enaR. But to do so, I need a very simple example: does someone have such a simple case?
I am moving from analyzing food web network to bipartite network and I was wondering if anyone knew where to start? What books/articles I must read?
I am especially interested in the metrics I could use (modularity among others). Have an overview of those metrics...etc
I screened through the 'bipartite' package in R.
Thanks in advance,
I'm currently working on OM sources fueling fish communities in the North Sea. I have a dataset of C and N isotopic ratios for fish and I would like to include benthic, pelagic and riverine OM end-members in an isotopic mixing models. I have values for benthic and pelagic productions, but I can’t find papers presenting isotopic ratios for main rivers flowing into the North Sea. Is someone aware of such dataset?
Thanks in advance
With the widespread using of barcoding or metabacording and genomic sequencing, many cryptic species, which morphological similar butgenetic difference largly, were frequently reported in many groups and ecosystems. Especially for Tropical insect.
It seems cryptic species should be very common, In a recent work, Janzen et al.(2017 PNAS) said maybe 10-20% traditional morphologically single species may turn out to be two or more. If that is ture. It will definitely increase the absolute species diversity. Meanwhile, cryptic species may be a common phase in speciation.
What other means of cryptic species to speciation process, food web, plant-animal network and ecological serves? Whether crypitic species will changge some parts of our understanding fundermentaly on above concepts?
Furthermore, what kind of groups have a relatively higher ratio of cryptic species, whether some different pattern between generalist species or specialist species in ecology network?
I study the coevolution between fig tree and fig wasp, in which many cryptic fig wasps were reported. That is also the pattern in many other systems. So I interest How cryptic species arose and what it means in ecology and evolution.
Thanks in advance for anyone suggestions and comments!
I have data of an antagonistic network (predator-prey) and also have data about prey availability in the environment. I would like to incorporate this data (prey availability) in network analysis. Is it possible?
What are the effects of transgenic DNA in the soil food web? What consequences, if any will these have on soil health?
Ever increasing population, urbanization and modernization are posing problems of sewage disposal and contamination of surface waters like lakes. Species and habitat dynamics in the face of climate change are complex and have many aspects. Increased temperatures and CO2 concentrations will have an effect on different processes such as photosynthesis, respiration and decomposition and generally speed up these processes. Climate-induced changes in ice cover period, thermal stratification and nutrient availability and longer growing seasons affect species composition and food web structures.
Who is interested in discussing the interrelationship between biodiversity and vector-borne diseases. Global Change, Biodiversity Loss and Human Health are obviously linked in many ways, but there is no clear proof about the specific processes. Insect vectors for pathogens such as arboviruses would be a nice field for investigation because they are ectothermal and they are part of the food web and thus influenced by biodiversity.
I'm researching New England cottontail diet selection at the population level and am looking for an efficient way to run Manly's G-test. Any help would be greatly appreciated!
Do you know any published paper focusing on feeding interactions (predation, competition, niche partitioning) between alien/invasive top predators originating from different areas when they co-occurr in a new area?
I want to analyse the diets of infaunal invertebrates from a deep-sea methane hydrates site. The organisms had been preserved in 10 % formalin and then transferred to 70 % ethanol for about 4 years now. I know this preservation method affects the carbon stable isotopic signature and, depending on the organisms, the nitrogen stable isotopic signature too. But I'm having some trouble finding information on the literature about the effects of preservation on sulfur stable isotopes.
My project attempts to explicitly include humans as driver nodes within complex food webs, as opposed to simply being considered external factors. I do not know if such a specific model exists, but I am hoping to find something that links market price, labour, equipment, regulations, ect. with the amount of fish caught.
Micro-nutrients play an important role in determining which species of phytoplankton grow. If micro-nutrients are abundant, Diatom Algae grow and this strengthens the food web. So studying micro-nutrients is very important.
The question as I said in the title, I'm not sure about what problems we will get in troubles, If we use the stable isotope approach.
I hava already read some papers about the fish stocking migration between the different habitats.
I think the most problem is that the different tissues hava the different rate of metabolism, for example, the liver and blood cell have very fast rate, just few days, and the white muscle, fin, or bone of fish can present a long period of feeding habit, and the stable isotope values can present previous habitat information. Moreover, the size of fish we collect may be also can influence the result of the stable isotope values, but I'm not sure about it.
you guys can give me some suggetions or advices about the question as much as you konw, if so, thank you very much.
In aquatic ecology research, the relationships between different trophic level are important. Stable carbon and nitrogen isotopes analysis(SIA) are widely used to ravel the interactions between linkages in food web.
The biomass and quantity of top level organisms in food web are always low, and the collection metod requires dead individuals, and which could collect tissue samples easily.
Currently, a large proportion of top predators are rare or threatened. Few articles use the non-lethal methodologies which collect the blood or fins.
Why the non-lethal method is not widely used?
I am aware of some work on the affects of anthelmintics on the fauna feeding on dung but was keen to find if wider work has been done on their effects on wider range of pasture insects and the consequence effects on species that feed on them in particular birds. Changes in land use are and to some extent predation are cited as causes of decline of some species of farmland bird, however for some the impact of veterinary medicines on food chains is also a possible contributor and I am keen to find out who and where such wok may have been carried out. Any thoughts welcome.
In order for a plant to grow and thrive, it requires Carbon, hydrogen, oxygen, nitrogen, phosphorus and potassium. The former three are easily available from air, water and other sources, while the latter three are hard to come by. These nutrients are often found decay of plants or living organisms, while nitrogen is only available by recycling nitrogen from dead to living plants. That’s where fertilizers come into the picture, these provide the necessary nutrients in order to make the plants strong and thrive better.
In my opinion, the simplest way to distinguish between compost and fertilizer is to remember this: Compost feeds the soil and fertilizer feeds the plants. Fertilizer adds to the soil's nutrient supply, but instead of feeding the soil food web, the ingredients in fertilizers are intended to meet the needs of fast-growing plants.
What do you think about the differences between compost and fertilizers? Which one is better?
I am working on food web stoichiometry and I'm looking for a literature on constrains that may be posed on the bees' development because of N and P scarcity in pollen. Herbivores in general are N and P limited. Is this also true for pollen eaters (pollen is a concentrated sustenance, rich in nutrients)?
Thanks in advance!
Quite often in environmental-economic literature (e.g. The Economics of Ecosystems and Biodiversity) welfare theory is used to calculate the supply of "ecosystem services" in "natural capital accounting" (NCA)?
I am interested in literature which views ecosystems in different ways, especially from a "network" perspective. For example, a food web or food chain seem to me to have network structures. Do you have any suggestions about the most important references in this field?
I just completed the shannon Wiener diversity index and calculated a score of (H)=2.154890613. The values range from 0 to 5, with common ranges usually between 1.5 to 3.5. Can I really say that the population is diverse? What other index should I use when getting a score like this? Thanks
I would like to calculate the isotopic food-web baseline for a group of zooplankton that I collected in the Indian Ocean. In the original survey I collected POM samples, but the isotopic signatures of these are all over the place and in some cases with values more enriched than the zooplankton itself. I would like to be able to determine the isotopic signature of the food-web base supporting the zooplankton at each site – there were clear differences in zooplankton d13C signatures between some of the stations.
I am therefore looking for an equation with which I could calculate the baseline of the food-web supporting the zooplankton that I collected.
In the paper linked below a case study of a mason bee (Osmia bicornis) feeding on pollen is presented. We concluded that the growth and development and thus the fitness of the bee might be co-limited by the scarcity of N, K and Na in pollen. Cocoon production may be limited by a greater number of micronutrients. Since O. bicornis may experience limitations to the growth and development of its body and cocoon production because of the availability of certain elements in its food, the amounts of potentially limiting elements should be maximized during pollen collection by the adult female bee for its progeny.
Food nutritional quality is known to regulate populations of wild bees and may be a factor contributing to bee decline. In addition, specific micronutrients, especially Na and K, may be lacking in bee diets, thereby forcing bees to search for a balanced diet. The quality of the pollen diet has a known influence on the survival, physiology and life history traits of bees (of various taxa). These traits are all connected to fitness; therefore, pollen quality may influence bee foraging choices. Is it possible that the nutritional quality of pollen influences foraging behaviour and life-history traits of pollen-eaters? What do you think?
I'm working on source partitioning for two lake food webs. While working on quantifying the sources using SIAR, I have come across some difficulties.
Here are my problems:
First, zoobenthos are the consumers for my systems, and I'm trying to calculate the source portions as detailed as possible; therefore, the "consumers" is sorted into groups based on genus, and most of the time, there is only one sample for each group. When I tried to calculate them in SIAR, it turned out a warning as"
=============== READ THIS ===============
There may be some problems with this data.
Some of the standard deviations seem especially large.
Please check to see whether the target data lie outside
the convex hull implied by the sources.
SIAR rates the problem with this data set as:
Severe - possibly severely affecting results
" . I don't know which part of my data leads to the problem, the consumers or the sources? How should I do with it ?
Second, the convergence diagnostics shows results like follows:"
Worst parameters are ...
detritus-LG5 SD1G2 detritus-LG2 detritus-DG5 detritus-DG2 SD1G1
0.0007164114 0.0033956284 0.0034963043 0.0092774801 0.0251035281 0.0334041570
SD2G3 SD1G4 detritus-HG4 detritus-DG3
0.0372546252 0.0495544969 0.0624383672 0.1138505731
If lots of the p-values are very small, try a longer run of the MCMC. "
I don't quite get the meaning of those numbers, what do the p-values measures?
Third, when estimating the source portion, should I use mode or mean in the results?
Thank you very much!
It is widely accepted that the major factor affecting the evolutionary optimization of animal life histories is energy balance, therefore studies focus on the energy costs and benefits of adaptations, the efficiency of energy acquisition and investment, and limits to energy budgets. However, at the very least in heterotrophs, equally important seems to be the problem of maintaining stoichiometric balance.
There are two approaches in eco-evo studies that consider the matter balance as complementary to the energy balance: ecological stoichiometry and nutritional geometry. However, in my opinion, such studies are limited and after 30 years after Tilman's and Reiners' works (below), still "energocentric" point of view dominates in ecology and evolution, that carelessly underrates the need to balance the diet also in terms of the matter (including the Law of Conservation of Mass).
This is only my point of view, possibly the wrong one. I would like to ask all of you: what is your opinion?
My question was introduced as briefly as possible, don't hesitate to dig deeper and extend it!
Below I present four important studies related to the topic, just to start with.
Recent studies (below) showed that predators may need to optimize their diets concerning not only energy but also quality of matter eaten. However, according to common assumption, this is not intuitive (see papers below). What are your thoughts? Is it possible that predators are limited because of macro- or micro- nutrients concentrations in matter eaten? What about elements? Is it possible that for predators important are ratios other than traditional C:N:P, studied using the framework of ecological stoichiometry? What about K and Na? What about Zn:Fe ratio (these two elements compete for absorption sites)?
I'm looking for available literature data on concentrations of elements (in dry mass) in fresh and decomposed pine (P. sylvestris) litter, other litters, pine pollen (P. sylvestris), pollen of other anemophilous plants and organisms inhabiting forests floors (fungi, insects, molluscs, isopods, worms, millipedes, detritivores, various litter- and soil- dwellers, protozoans etc.). C concentration is of greatest importance for me, since it was rarely reported as % of C in dry matter (surprisingly, concentrations of other elements are easier to find). Also N and P are of great importance. Data on any other element would also be great. I've already found some literature but it is surprisingly scarce, so I will appreciate any additional data. If you know any paper related to the topic, please put a link below. Thank you in advance for your time and help!
As pointed by Greenfield (1999) and Roulston & Cane (2000), pollen is easily digestible: special adaptations are not needed since pollen grains may be simply destroyed mechanically or through osmotic shock. However there exist a belief that pollen is hardly digestible (mostly because of chemical protection by extracellular wall). Lots of invertebrates belonging to various groups are known to supplement their diets with pollen (even predators). So is pollen easily or hardly digestible? Do you know any papers related to this issue?
Past studies have resorted to the removal of a certain species to identify its effects on the food web. Is there a way to identify which predatory relationships are strong enough to cause the destruction of the food web without the haphazard removal of species?
Litter/soil dwellers (arthropods: detritivores and omnivores) feed on unbalanced food (mainly dead plant matter) that is scarce in some physiologically important nutrients. This food alone is insufficient as a source of needed biomass. It is known that fungi may supplement such a diet with nutrient needed by these animals. However it is very hard to find any specific data on how exactly this mechanisms works.
If an arthropod feeds on dead plant matter, what exact substances are scarce in its food? And how much of these substances may be given by fungi? Is it enough?
Do you know of any papers that give information on exact nutrients that are scarce in litter/soil and are given to the litter/soil dwellers by fungi in considerable amounts?
I sampled plant-pollinator networks along a gradient. Using the R package 'bipartite' I calculated a set of network metrics. The 'niche overlap' of the pollinator level as well as the 'functional diversity' (measure of niche complementarity) of both plant and pollinator level show a decrease with the gradient. At first glance, this seems contradicting to me. Is this possible, and what could be the explanation?
My colleagues are working on feeding preferences of macro symbionts of feather stars. They gathered data on stable isotopes from both sea lilies and its symbionts(shrimps, crabs, ,polychaetes, myzostomida etc). The results are quite surprising and not easy to interpret, so we want to have some reference points. Some people (who work with stable isotopes) advise us, that it might be more useful to collect data on primary consumers (not primary producents) from our area to have such a reference point.
But than we realized, that it is not an easy task to find really specialized primary consumer on the coral reef, as there is little known about food spectrum of most coral reefs inhabitant and many of them are mixotrophic.
I am trying citations related to the idea that "diversity begets diversity." In particular, I am interested in finding examples of experiments where diversity has been manipulated at one trophic level, and then diversity of lower or higher trophic levels was measured as a response variable. I am not interested in experiments that have only manipulated diversity as presence-absence. I am more interested in experiments that have multiple levels of diversity. I'm looking for experiments like these:
Haddad, N.M., Tilman, D., Haarstad, J., Ritchie, M., Knops, J.M., 2001. Contrasting effects of plant richness and composition on insect communities: a field experiment. Am. Nat. 158, 17–35. doi:10.1086/320866
De Deyn, G.B., Raaijmakers, C.E., van Ruijven, J., Berendse, F., van der Putten, W.H., 2004. Plant species identity and diversity effects on different trophic levels of nematodes in the soil food web. Oikos 106, 576–586.
Ogada, D., M.E. Gadd, R.S. Ostfeld, T.P. Young and F. Keesing. 2008. Impacts of large herbivores on bird diversity and abundance in an African savanna. Oecologia 156:387-397.
Thanks for any leads!
I have a sizeable data base with mollusca and other specific fauna remains encountered in cold water coral communities. I have no direct evidence for relationships of carnivore to its food source (e.g. a photograph of a mollusk having dinner or mollusk stomach content analyses) but I have some circumstantial data that may prove it. An example:
I have 100 location samples analysed in detail on occurence of mollusks with a high confidence and of other fauna with less confidence. Molluscan carnivore A has been found in 10 stations, the likely food source sponge B has been identified in 15 stations. In 9 stations A and B are found together. The probability that A has been identified in a station is high say p(A)=90%. The probability that B has been observed is lower say p(B)=30%. Is there a statistical measure to prove or disprove a relationship?
Thanks for your thoughts, Leon Hoffman
I am currently working with both SIAR and MixSIR to analyze food web data using three food sources and dual stable isotopes (C/N). Does anyone know about the restrictions of each of the two mixing models when the isotope data of the food sources are quite close to each other? I would like to hear some opinions about the differences in the models' function. And generally, would the restrictions of the number of food sources and the range of data be the same for both mixing models?
Concentrations of PCDD/F, DL-PCB and NDL-PCB are lower in zooplankton (primary consumers and lower-trophic-level invertebrates) than in phytoplankton (primary producers).
I’m interested in levels of these substances in zooplankton (e.g. copepods), especially from Mediterranean area. I found a few publications, some a bit dated.
In particular which concentrations can be considered of concern at this marine food web level?
Does anyone have experience turning large trophic webs into figures for publication? Smaller webs seem decently easy to do in something like photoshop, but for upwards of 100 interacting species, are there any good R packages (or other software packages) to accomplish this?
In spite of the classical notion that interspecific competition constrains niche width it is possible to envision circumstances under which it could cause niche width to increase.
For example, reducing the availability of a valuable resource forces an animal to compensate in some fashion: through increased exploitation of the other resources it currently consumes (as classical theory would dictate), or potentially, through exploiting new resources which can mitigate the loss. If more than one alternative resource is incorporated, an animal will have widened their niche as a direct result of interspecific competition.
Does anyone know of any studies which have shown such effects? Or any papers in which this or other possible ways interspecific competition could widen niche are discussed?
Niger Delta is highly susceptible to pollution due to oil exploration and the nonchalant attitude of oil companies operating in the area towards Nigerian Environmental laws.
I believe that the autochthonous primary production plays an important role in the transfer of energy through food webs in tropical streams.
I'm working on a study looking at scale-dependent properties and drivers of food web stability in well-resolved food webs and am assembling a large compilation of food webs. I already have many webs, open databases of previous webs, as well as webs I've assembled, however more is better in this case. Does anyone have any webs (in any form) that they wouldn't mind sharing to be a part of the study? If used, your webs will be fully cited.
Energy transfer between trophic levels is generally considered as equal to 10% of the net production at the preceding trophic level (the Ten percent law) => this law is used in numerous models, and I thought its origin was from Lindeman 1942, but is it not the case. Do you know what is the origin of this law ?
It is generally accepted that plant-pollinator webs are nested and that nestedness promotes species richness in those networks. I've just read a study of Kondoh et al. ("Food webs are built up with nested subwebs", 2010, Ecology) stating that trophic interaction networks are nested as well, but with the inverse consequences, that is nestedness prevents species coexistence. I am studying host-parasitoid networks and I am wondering if in those networks nestedness would promote or impair species richness. I would be very interested to have your opinions.
A debated question in food-web research is whether omnivory stabilizes or destabilizes species interaction networks. Parasitoids often "consume" species from different trophic levels and their position in food webs is ill-defined. Therefore I would be interested to know whether you think that parasitoids could be considered omnivorous.
I am studying host-parasitoid interaction networks and I computed different indices that are common in food web studies such as linkage density, connectance, generality, orinteraction diversity. It is however well known that those indices are sensitive to the dimension of the network and that we should control for any effect of food-web size before making interpetation of the indices. My problem is what to consider as a measure of network dimension. I find different approaches in the papers I read. Some consider the addition of predator+prey species; some take a multiplicative measure: predator*prey species and still others enter the number of predator and prey species separately. What is your opinion on the most supported approach?
I would like to improve some old ecopath models that have no bacteria compartments in estuaries where we lack information about bacterial production. I would be interested in your advise about using other data related to microbial activity like enzymatic activity or metabolic rates in order to seek for good data sets.
I have data on quantitative food webs from different sites over three years and three different isolation levels (10 sites for each isolation level). The idea was to look at spatial-temporal changes in the food-web structure; however, the food webs from each site considered individually in each year are very small and do not give reliable results.
I have two alternatives: either pool the data from the three years together for each site and look for the spatial pattern only, or pool the data over the different isolation levels for each year. Both methods are critical as they do not take into account variability either in time or in space. I am be very interested to have your opinion about which approach could be more appropriate. Thank you very much