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Trophic networks. Food web. Food chain. Parasites. Large predators. Small predators. Herbivores. Plant producers. Typical terrestrial food with six trophic levels and 15 functional groups. Each functional group (guild) may contain many species. . - PowerPoint PPT Presentation
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Trophic networks
Bacterial producers
Small herbivores
Small carnivores
Larger carnivores
Large carnivores
Medium omnivores
Large omnivores
Large herbivores
Parasitoids
Hyperpara-sitoids
Parasites
Smaller decomposer
Larger decomposer
Plant producers
Bacterio-phages
Typical terrestrial food with six trophic levels and 15 functional groups. Each functional group (guild) may contain many species.
Plant producers
Herbivores
Small predators
Large predators
Parasites
Food chainFood web
Web size The total number of elements S (species) in the web
Connectance The proportion of realized links L in the web
Linkage density The proportion of realized connections per species
Food chain length The average length of single food chains
𝐶=𝐿
𝑆(𝑆−1)/2≅𝐿𝑆2
𝐷=𝐿𝑆 ≅ 𝐶𝑆
Proportions of top, intermediate, and basal species. The proportion of omnivores. Omnivores are species that feed on more than one basic source of food (more than one trophic level)
Plant
Herbivore
Predator
Herbivore
Predator
Web size: 5Links: 4Connectance: 4/(5*4/2) = 0.4Linkage density: 4/5 = 0.8Food chain length: 2Omnivores: 0Basal species: 1Intermdeiate species: 2Top species: 2
Loop, intraspecific feeding
Loops do not count
1
2 3
4 5 6 7 8 9 10 11
12 13 14 15 16
17 18 19
S = 19Lmax = 19x18/2=171L = 35C = 35 / 171 = 0.2Ch = 100Li = 40ChL = 100 / 40 = 2.5L / S = 35 / 19 = 1.8
Photo Nepenthes
Pitcher plant food (Nepenthes albomarginata) web
Loop,Cannibalism
100
80
2
Herbivores
Small predators
Large predators
100
15
2
20Plants 120
10
1
100
0.1
Abundance Biomass Energy
Trophical cascades
Trophical cascades vary from habitat to habitat.They are habitat specific
In terrestrial habitats about 10% of energy is passed from each level to the next higher level (rule of Lawton).
In marine food webs the biomass and abundance pyramids are sometime inverted.
The paradox of the plankton
Why is the world green?
With predators of herbivores
Without predators of herbivores
Terborgh et al. 2006, J. Ecol.
Venezuela
Comparing the defoliation by herbivores on small (without predators), intermediate (some arthopod predators ) and large islands/mainlands (all types of predators) Terborgh et al. (2006) corroborated the hypothesis of Hairston, Smith, and Slobodkin (HSS) that herbivore predators control defoliation
and keep the world green.
Mortality Recruitment
Plant defense did not play a major role
Predaceous birds and snakes Parasitoid spider wasps Songbirds
Lizards
Predaceous insects
Scorpions
Spiders
Herbivorous insects
Land plands, seed detritus
Rodensts
Scavenging insects
Detritovorous insects
Seabird ectoparasites
Algal detritusSeabird guanoFish and bird carcasses
Seabirds
Marince planctonic food web Marine macroalgae
An example how complex food webs might be. Each trophic level may contain several up to several hundreds of species. Islands in the Gulf of California.
Polis 1998, Nature395:
744-745
Terrestrial arthropod dominated food chains are often shorter than marine food chains
Schoenly et al. 1991, Am. Nat 137: 597-638
Terrestrial food chains have rarely more than five levels.
Mikiola fagiTorymus auratus Platygaster spec. galls
Food chain involing insect parasitoids have often more
than five levels.
Do terrestrial and marine food webs differ in structure ?
Haven, 1997, Oikos 78: 75-80
Schoenly et al. 1991, Am. Nat 137: 597-638 Terrestrial webs
Marine webs
Numbers of food chain in a web increase to the power of species richness.
The upper boundary marks the limit of stability.
Predator numbers increase linearly with the number of asvailable prey
species
The total richness of predators is often higher than the number of prey
species
Schoenly et al. 1991, Am. Nat 137: 597-638
Betula pendula
Quercus robur
Thelaxes dryophila
Tuberculoides annulatus
Myzocallis castanicola
Stomaphis quercus
Euceraphis betulae
Betulaphis quadrituberculata
Calaphis betulicola
Betulaphis brevipilosa
Mamamelistes betulinus
Symydobius oblongus
Lysiphlebus thelaxis
Aphelinus chaonia
Trioxys betulae
Protaphidius wissmannii
Trioxys pallidus
Trioxys curvicaudus
Trioxys tenuicaudus
Aphidencyrtus aphidivorus
Praon flavinode
Aphidencyrtus quercicola
Aphidius aquilus
Callaphidius elegans
Trioxys compressicornis
Rajmanek and Stary 1979, Nature 280:
311-313
Parasitoid – aphid relationship on oaks
Rajmanek and Stary 1979, Nature 280: 311-313
𝐷√𝑆𝐶<1
Food web connection and stability
The May equation predicts low linkage density at higher connection rate
D: Linkage densityS: species numberC: connectivity
The May equation predicts an upper limit of connectance for a stable food web.
Schoenly et al. 1991, Am. Nat 137: 597-638
𝐷√𝑆𝐶<1
Food web complexity is limited by species richness
Aquatic food webs
Schoenly et al. 1991, Am. Nat 137: 597-638
Mechanisms that stabilize food webs:
• Weak and variable links• Low connectance• Dietary switches• Omnivory
SC: measure of food web complexity
The May eqaution is based on simplified random food webs with density dependent regulation.
Omnivory stabilizes food webs
Undisturbed Disturbed
High proportion of specialist species
Intermediate proportion of specialist species
High proportion of omnivorous species
Tem
pora
l var
iabi
lity
amon
g sp
ecie
s
Fagan 1997, Am. Nat. 150: 554-567
Mount Saint Helens blowdown zone
Mount St. Helen’s recovery is a natural experiment on succession and community ecology.
The temporal stability of food webs
Food chain length and habitat properties
Post et al. 2000,
Nature 405: 1047-1049
Fresh water food chain length of North American lakes increase with lake size but
not with productivity
Average food chain length asymptotically reaches a plateau independent of species
richness.
Hall and Raffaelli 1991, J. Anim. Ecol. 60: 823-841.
Compilation of well resolved food chains
Schneider 1997, Oecologia 110: 567-575
Food web complexity and ecosystem
variability in ponds
Linkage density of fresh water insect dominated small pond food webs increased with• Species richness• Habitat duration and decreases with• Pond environmental
variability
Connectance was lowest at average species richness, variability, and pond duration.
Empirical interaction matrices
Pollination networks
Plants
BeesKratochwil et al. 2009, Apidologia 40: 634-650
Plant Asclepias AsclepiasAspidonepsisMiraglossumMiraglossumPachycarpusSisyranthusXysmalobiumXysmalobiumPollinators cucullata woodii diploglossa verticillare pilosum natalensistrichostomus gerrardii involucratumHemipepsis 0 0 0 18 9 20 2 41 1Pompilidae sp. 2 0 0 0 0 0 0 0 1 0Tiphia 0 1 0 0 0 0 0 0 0Arge 0 0 0 0 0 0 1 0 0Apis 0 0 1 0 0 0 1 3 0Halictidae sp. 1 0 0 2 0 0 0 0 0 0Halictidae sp. 2 1 0 0 0 0 0 0 0 0Other wasps 0 1 1 0 0 0 0 1 3Other bees 0 0 0 0 0 0 0 1 1Other solitary bees 0 1 2 0 0 9 0 0 0Atrichelaphinis 0 15 0 1 0 0 35 15 6Cyrtothyrea 0 8 0 1 0 0 42 6 0Lycidae sp. 0 0 0 0 0 0 0 2 0Cantharidae sp. 0 0 0 0 0 0 0 2 0Elateridae sp. 0 0 0 0 0 0 0 0 4Chrysomelidae sp. 1 0 0 0 0 0 1 0 0 1Chrysomelidae sp. 2 0 0 0 0 0 0 1 1 1Scarabaeinae sp. 1 0 0 0 0 0 0 0 3 0Scarabaeinae sp. 2 0 0 0 0 0 0 0 3 1Scarabaeinae sp. 3 0 0 0 0 0 0 0 1 0Curculionidae sp. 1 0 0 0 0 0 0 10 4 1Curculionidae sp. 2 0 2 0 0 0 0 0 0 0Coleoptera sp. 3 0 0 0 0 0 0 0 2 0Coleoptera sp. 8 0 0 0 0 0 0 1 0 0Other Coleoptera 0 0 0 0 0 0 0 4 4Aspilocoryphus 1 0 0 1 0 4 1 139 1Lygaeidae sp. 2 0 0 0 1 0 1 0 8 2Coreidae sp. 0 0 0 0 0 0 0 1 0Spilostethus 0 0 0 0 0 1 0 0 0Homoecerus 0 0 0 0 0 1 0 0 0Pentatomoidea sp. 0 0 0 0 0 0 0 1 0Other Heteroptera 0 0 0 0 0 0 0 1 0Calliphoridae genus 1 0 0 0 0 0 0 0 1 0Calliphoridae genus 2 0 0 0 0 0 0 2 6 0Calliphoridae genus 3 0 0 0 0 0 0 0 1 0Sarcophaga sp. 0 1 0 6 0 11 0 53 1Musca 0 0 2 0 0 0 0 3 0Muscidae genus 2 0 0 1 0 0 0 0 0 0Empididae sp. 1 2 0 0 0 0 1 0 0 0Empididae sp. 2 0 0 0 0 0 0 0 1 0Chloropidae 0 0 1 0 0 0 0 1 0Microphthalma 0 0 0 0 0 1 0 0 0Microphthalma 0 0 0 0 0 0 0 1 0Tachinidae subfamily Goniinae 0 0 0 0 0 0 0 1 0Tachinidae genus 2 0 0 0 0 0 0 0 1 0Actea 0 0 0 0 0 0 0 1 0Sepsidae sp. 1 0 0 0 0 0 0 0 3 1Sepsidae sp. 2 0 0 0 0 0 0 0 0 1Sepsidae sp. 3 0 0 0 1 0 0 0 0 0Dacus 0 0 0 0 0 1 0 0 0Bibionidae 0 0 0 0 0 0 0 1 0Diptera sp. 3 0 0 0 0 0 0 1 0 0Diptera sp. 22 0 0 0 0 0 1 0 0 0Other Diptera 0 1 0 1 0 1 0 15 0Unidentified butterfly 0 0 0 0 0 0 1 0 0Unidentified micromoth 2 0 0 0 0 0 0 0 0
From Ollerton et al. 2003, Ann. Botany
92: 807-834
The matrix approach to mutualistic and food webs
What are mutualistic webs:
• Plant – pollinator webs• Plant seed disperser webs• Plant herbivore webs• Predator prey webs• Host parasite webs• Competition webs
Pollinators
Plan
ts
Nestedness is defined as the ordered loss of links in a mutualistic matrix where rows and coloumns are sorted according to species richness.
Unexpected link
Linkages: number of filled cells in the matrixLinkage density: L/S1
Connectance: Matrix fill, L/(S1S2)
Generalists
Specialists
Generalists Specialists
• Generalist pollinator visit most plant species
• Specialist pollinator visit the most popular plant species
• Mutualistic networks contain forbidden links
Foods webs
Pollination networks
Seed disperser
Bascompte 2003, PNAS 100: 9383-9387
Bastolla et al. 2009, Nature 458: 1018-1021
• Mutualistc networks are often nested.• The nested architecture promotes diversity
and stability
The architecture of mutualistic networks
Jordi Bascompte1967-
Weak Anthropic Principle (Carter 1973): We must be prepared to take account of the fact that our location in the universe is necessarily privileged to the extent of being compatible with our existence as observers.
In ecology this means:Ecological systems do not have a random strucure. They have that non-random structure that enabled them to survive during evolution.
Nestedness as an emergent property of ecological systems
Nestedness tends to stabilize mutualistic networks.
1 2 3 4 5 6 7 8 SA 1 1 1 1 0 0 0 0 4B 1 1 1 1 0 0 0 0 4C 1 1 1 1 0 0 0 0 4D 1 1 1 1 0 0 0 0 4E 0 0 0 0 1 1 1 1 4F 0 0 0 0 1 1 1 1 4G 0 0 0 0 1 1 1 1 4
4 4 4 4 3 3 3 3 28
1 2 3 4 5 6 7 8 SA 1 1 1 1 1 1 1 1 8B 1 0 1 1 1 1 0 0 5C 1 1 1 1 1 0 0 0 5D 1 1 1 1 0 0 0 0 4E 1 1 0 0 0 1 0 0 3F 1 0 0 0 0 0 0 0 1G 1 0 0 0 0 0 0 0 1
S 7 4 4 4 3 3 1 1 27
Food webs are often compartmented
Foods webs have a modular structure.
Modularity tends to stabilize food webs.
Modules itself have a nested structure.
Mutualistic webs (comparirson of two trophic levels) are most often nested.
Stability, resilience and tipping points
Instable equilibrium Local stable
state Global stable state
Ecologial systems (particularly networks) can be in various states:• Instable equilibria are at tipping points
and can move towards different directions.
• Local stable equilibria can easily be forced to achieve other stable states.
• Global equilibria need much energy to leave their state.
• Inequilibria can easily move between different states.
• Resilience refers to the speed of a systen to return to a stable state.
• Resistence is the ability of a system to avoid displacement.
• Robustness is the ability of a system to exist witin a wide range of conditions.
• Stability refers to the amplitude of variability
• Sustainability i the capacity to endure
Low stability
Tipping point
Low resistence
Local stabilityGlobal instanility
Instable equilibrium Local stable
state Global stable state
Multiple states
State
Prob
abili
ty
Tipping points define states where a system irreversably changes the probability distribution of states.
Food webs and tipping points
Indicators of critical tipping points:• Resilience slows down• Dominant eigenvectors of the food web
matrices shorten• Increased variance• Variance / mean relationships increased• Multimodality of states• Increasing connectivity and decreasing
diversity
A state reaches its tipping point
Robustness
Dunne 2002, Ecol. Lett 5: 558
In empirical foods webs robustness increases with connectance.
In random foods webs robustness decreases with connectance.
Therefore, empirical food webs have a special non-random structure that promotes stability.
The importance of wild bees for pollination stability
Meta-analysis of empirical food ebs
Wild insects increase fruit production more effectively than honey bees alone.
Species richness increases ecological functioning
Garibaldi et al. 2013. Science 339: 1608
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