Food webs Food webs Food webs some basic
![Food webs Food webs](https://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-1.jpg)
Food webs
![Food webs Food webs](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-2.jpg)
Food webs
![Food webs: some basic concepts and descriptive parameters • trophic species: functional groups of Food webs: some basic concepts and descriptive parameters • trophic species: functional groups of](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-3.jpg)
Food webs: some basic concepts and descriptive parameters • trophic species: functional groups of all organisms in a web that share the same set of consumer and resource species • guild: a group of species utilising the same resource in the same manner [e. g. leaf-miners] • taxon-guild: a taxonomically defined part of a guild [e. g. leafmining beetles] • no. of trophic levels • connectance: the proportion of existing trophic links from those theoretically possible, i. e. linking all species • proportion of basal, intermediate and top species • no. of prey species per predator species • no. of host species per consumer species • no. of omnivores (feeding on spp. from different trophic levels) • no. and length of food chains (linked paths starting with a basal species) • no. of spp. involved in loops (chains involving a species twice)
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![Thompson et al. 2012, TREE 7, 689 Thompson et al. 2012, TREE 7, 689](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-7.jpg)
Thompson et al. 2012, TREE 7, 689
![Bipartite network metrics: unweighted links Connectance Generality and vulnerability Nestedness Degree distribution Bluthgen et Bipartite network metrics: unweighted links Connectance Generality and vulnerability Nestedness Degree distribution Bluthgen et](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-8.jpg)
Bipartite network metrics: unweighted links Connectance Generality and vulnerability Nestedness Degree distribution Bluthgen et al. Ecology, 89(12), 2008, pp. 3387– 3399
![Bipartite network metrics: weighted links Interaction strength Interaction diversity Interaction evenness Weighted generality and Bipartite network metrics: weighted links Interaction strength Interaction diversity Interaction evenness Weighted generality and](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-9.jpg)
Bipartite network metrics: weighted links Interaction strength Interaction diversity Interaction evenness Weighted generality and vulnerability Bluthgen et al. Ecology, 89(12), 2008, pp. 3387– 3399
![Problems of food-web science: • taxonomic and sampling difficulties • ignoring quantitative aspects of Problems of food-web science: • taxonomic and sampling difficulties • ignoring quantitative aspects of](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-10.jpg)
Problems of food-web science: • taxonomic and sampling difficulties • ignoring quantitative aspects of inter-specific interactions • great complexity of the food webs including indirect interactions so that some time-honoured truths are now in doubt: relationships between connectance and species richness or constant predator - prey ratios
![Leaf-miner species (dots) connected by shared parasitoids: qualitative and quantitative description of reality Leaf-miner species (dots) connected by shared parasitoids: qualitative and quantitative description of reality](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-11.jpg)
Leaf-miner species (dots) connected by shared parasitoids: qualitative and quantitative description of reality
![A real-world example: trophic links between plants and leaf-miners in a tropical forest A real-world example: trophic links between plants and leaf-miners in a tropical forest](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-12.jpg)
A real-world example: trophic links between plants and leaf-miners in a tropical forest
![Parasitoids of a leaf-mining genus Phyllonorycter in England Pollinators in England Memmott J. &1999. Parasitoids of a leaf-mining genus Phyllonorycter in England Pollinators in England Memmott J. &1999.](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-13.jpg)
Parasitoids of a leaf-mining genus Phyllonorycter in England Pollinators in England Memmott J. &1999. Ecol. 2: 279. Rott Godfray 2000, Letters J. Anim. Ecol. 69: 274
![38 tree species folivorous insects 38 tree species folivorous insects](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-14.jpg)
38 tree species folivorous insects
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![Quantitative plant - herbivore matrices and their uses Diversity of host plants plant-herbivore matrix Quantitative plant - herbivore matrices and their uses Diversity of host plants plant-herbivore matrix](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-16.jpg)
Quantitative plant - herbivore matrices and their uses Diversity of host plants plant-herbivore matrix Diversity of host plants for herbivore H 1: H: - [(5/7)*log 2(5/7)+(2/7)*log 2(2/7)] = 0. 863 2 H = 1. 82 = the number of interactions occurring in equal proportion that would produce the same value of H.
![Quantitative plant - herbivore matrices and their uses dominance of herbivores on each plant Quantitative plant - herbivore matrices and their uses dominance of herbivores on each plant](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-17.jpg)
Quantitative plant - herbivore matrices and their uses dominance of herbivores on each plant dominance of plants in herbivore's diet plant-herbivore matrix two matrices multiplied: x = Host plant isolation: Probability that a randomly selected conspecific herbivore feeds on the same plant species
![Isolation of leaf-chewing communities on plants from a New Guinea rainforest Number of plant Isolation of leaf-chewing communities on plants from a New Guinea rainforest Number of plant](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-18.jpg)
Isolation of leaf-chewing communities on plants from a New Guinea rainforest Number of plant species plants: from locally monotypic families coexisting with confamilial species coexisting with congeneric species Isolation of plant's herbivore community from plants sharing generalist herbivores from others [isolation 0. 1] to plants hosting monophagous herbivore communities [isolation 1. 0]
![Indirect interactions: in a well-connected food web, the potential for interaction between any two Indirect interactions: in a well-connected food web, the potential for interaction between any two](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-19.jpg)
Indirect interactions: in a well-connected food web, the potential for interaction between any two species via intermediate species is almost endless: “the enemy of my enemy is my friend” principle
![Direct and indirect interactions in a simple food web Direct [blue] and indirect [red] Direct and indirect interactions in a simple food web Direct [blue] and indirect [red]](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-20.jpg)
Direct and indirect interactions in a simple food web Direct [blue] and indirect [red] interactions between willows and insects in Japan. Plus and minus signs indicate effect on the target species. Ohgushi, Annu. Rev. Ecol. Evol. Syst. 2005. 36: 81– 105
![Interactions along a rainforest food chain Tarsobaenus added Fewer ants More herbivores Smaller plants Interactions along a rainforest food chain Tarsobaenus added Fewer ants More herbivores Smaller plants](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-21.jpg)
Interactions along a rainforest food chain Tarsobaenus added Fewer ants More herbivores Smaller plants Dyer et al. 1999. Oecologia 119: 265
![Apparent competition Indirect interaction: an effect of one species on another, mediated through the Apparent competition Indirect interaction: an effect of one species on another, mediated through the](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-22.jpg)
Apparent competition Indirect interaction: an effect of one species on another, mediated through the action of shared natural enemies.
![Plant-leaf miner-parasitoid food web in a forest understorey in Belize Removal of a single Plant-leaf miner-parasitoid food web in a forest understorey in Belize Removal of a single](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-23.jpg)
Plant-leaf miner-parasitoid food web in a forest understorey in Belize Removal of a single host plant species eliminated its specialist leafminers (hatched) but also caused an increase in abundance and lower parasitism of other spp. (red, blue) connected via shared parasitoids Morris et al. 2004. Nature 428: 30
![Ficus Lowland rainforest 100 m asl. Montane rainforest 1800 m asl. F. pachyrrhachis F. Ficus Lowland rainforest 100 m asl. Montane rainforest 1800 m asl. F. pachyrrhachis F.](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-24.jpg)
Ficus Lowland rainforest 100 m asl. Montane rainforest 1800 m asl. F. pachyrrhachis F. iodiotricha Asota plana F. pachyrrhachis F. dammaropsis Phyliris moira F. wassa Talanga excelsalis F. wassa Euploea leucosticos Novotny et al. 2005, J. Biogeogr. 32: 1303
![Novotny 2009, Insect Conservation & Diversity 2: 5 -9 Novotny 2009, Insect Conservation & Diversity 2: 5 -9](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-25.jpg)
Novotny 2009, Insect Conservation & Diversity 2: 5 -9
![Caterpillars on Macaranga trees Novotny et al. 2007, Nature 448: 692 Caterpillars on Macaranga trees Novotny et al. 2007, Nature 448: 692](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-26.jpg)
Caterpillars on Macaranga trees Novotny et al. 2007, Nature 448: 692
![Predators can reduce inter-specific competition among their prey species Paine's intertidal zone experiment: Removal Predators can reduce inter-specific competition among their prey species Paine's intertidal zone experiment: Removal](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-27.jpg)
Predators can reduce inter-specific competition among their prey species Paine's intertidal zone experiment: Removal of starfish predator Pisaster resulted in one Mytilus species competitively dominating the system and driving other species to extinction
![direct interactions indirect interactions No. of gulls rat: present absent Barnacles cover Algae cover direct interactions indirect interactions No. of gulls rat: present absent Barnacles cover Algae cover](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-28.jpg)
direct interactions indirect interactions No. of gulls rat: present absent Barnacles cover Algae cover Top-down regulation: introduction of rats on polar islands caused decrease in marine birds, increase in molluscs, decrease in algae and thus increase in anemones and barnacles introduction of rats decrease of birds increase of molluscs decrease of algae increase of anemones and barnacles Kurle et al. 2008, PNAS 105: 3800
![Trophic cascades across ecosystems More pollinators visited Hypericum plants near ponds with fish, which Trophic cascades across ecosystems More pollinators visited Hypericum plants near ponds with fish, which](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-29.jpg)
Trophic cascades across ecosystems More pollinators visited Hypericum plants near ponds with fish, which reduced larval density of dragonflies, predatory in their adult stage on the pollinators
![Why are trophic chains limited to 3 -4 trophic levels? Energy flow hypothesis: 90% Why are trophic chains limited to 3 -4 trophic levels? Energy flow hypothesis: 90%](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-30.jpg)
Why are trophic chains limited to 3 -4 trophic levels? Energy flow hypothesis: 90% of energy lost in every trophic transfer [but more prodictive environments do not have longer chains] Stability hypothesis: trophic chains integrate population variability of all their component species so that long chains can become unstable, with the extinction of the top species Design constraints hypothesis: it is difficult to come with a predator capable of feeding on the existing top predators [have to be big, therefore low population density] or parasitising the existing hyperparasites
![Food webs Food webs](http://slidetodoc.com/presentation_image_h2/b81cfd70d2f5685efa194a09e3810e19/image-31.jpg)
Food webs
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