Ecosystem Ecology ECOS1084 - Learning Diary
Book: Principles of Terrestrial Ecosystem Ecology
09.01.2025 - Introduction
What is ecosystem ecology?
• Study of interactions between organisms and their physical environment as an
integrated system
• provide the link between biotic and abiotic systems
• incorporates humans and their activities
What is an ecosystem?
• Bounded ecological system consisting of all the organisms in an area and their
physical environment
General theories in ecology
• theory of evolution
◦ natural selection
• niche theory
• bottom-up and top-down
• colonization- competition
• island theory
• assembly rules
10.01.2025 – Networks (1)
Network: a collection of connected points (minimum two points connected)
• e.g.: technological networks, social networks, information networks
• biological networks (links don´t need to be physical, can be functional)
◦ metabolic networks
◦ neural networks
◦ ecological networks
Network size: number of nodes/points, e.g. 4 nodes are connected by 3 links
degree: number of links the node has
node degree
1 1
2 2
3 3
4 1
5 2
6 1
,linkage density (complexity) : average degree of each node
e.g.: (1+2+3+1+2+1)/6= 1,66 for network example above
connectance: number of links divided by the number of all possible links
total number of links here: 5
number of all possible links (everything is connected to everything) N*(N-1)/2
N= total number of nodes
6*5/2=15
5/15=0,33
- if we add only one link, the connectance changes
- deleting one link can also change the environment, for example if
a circle is divided then
in completely connected networks, the number of
connections increase disproportionally when the
number of nodes grows →
path length: the number of steps required to connect a sequence of
nodes
Path is route through the nodes with the restriction that each
node is allowed to be passed only once->
network path length: average number of steps along the shortest
paths for all possible pairs of network nodes →
Sum of all node averages/ number of nodes
For each node, the length of the shortest paths to
all other nodes is calculated and added. That
number is divided by (N-1)
different network topologies – topology matters! (same
number of nodes but different topology →
hub nodes: a node with a number of links that greatly exceeds the
average (the one with the most links) →
antagonistic networks: negative interactions between networks
mutualistic networks: species interact in mutually beneficial relationships that
enhance survival and ecosystem stability
,compartmentalism: the division of the network into relatively independent sub-
networks
nestedness: a pattern where less-connected species interact with subsets of the
species that more-connected species interact with, creating a hierarchical, ordered
structure.
• generalist: interacts with a lot nodes
• specialist: interacts with only one node
• nestedness of mutualistic networks allows more stability, BUT if the one well-
connected species is lost, the whole network collapses →
• nestedness increases with the complexity (number of interactions) of the
network
modulality: the degree to which a network is divided into smaller, densely connected
groups of nodes (modules)
13.01.2025 – Network (2)
Characteristics of ecological networks
• compared to random networks:
◦ ecological networks follow
power law distribution in
number of links per species →
◦ they have high clustering:
neighboring nodes connected
with each other more
◦ size usually reflects relative abundance (rarity)
◦ compared to random networks, they have short path lengths (e.g. the
shortest path linking the most connected species)
◦ ecological networks are highly connected (connectance number is high)
• mutualistic pollination networks are more connected than plant-herbivory
networks for the same network size
◦ reason being: plants get eaten and make it less attractive for other eaters
◦ plant-herbivory networks are shaped by antagonistic, often specialized
interactions, resulting in lower connectivity
• arctic areas are actually more connected regarding networks
Food webs
• food chain lengths tend to be short
• do not correlate well with total productivity
• minor links can be critical if they supply limiting resources
• minor links can be critical if they are plastic options → may become
important under certain conditions
A) energy flow web: the flow of energy or nutrients among nodes in a food
web
B) functional (or interaction) webs: per capita effect of one species on another
→ even if we know A, we will not necessarily know B
What limits food chain (path) length?
, each food chain in a food web is usually only a few links long, rarely more
than 5 trophic levels
• resource availability of the food (accumulation), e.g. P, N, O2, CO2...
• energy
• Top-down and bottom-up control: stability of the ecosystem (the longer the
food chain, the more unstable)
• trophic transfer efficiency: conversion of energy between trophic levels
being inefficient, with only about 10% of the energy from one level being
passed on to the next (known as the 10% rule).
◦ most energy lost as heat through basic metabolism, respiration and other
processes.
◦ highest efficiency has: chicken breed (because they don´t fly), insects (30%)
and fish, because they do not heat themselves up
◦ efficiency of energy transfer across trophic levels primarily determines food
chain length → higher productivity allows longer food chain lengths
• history of community organization
◦ length of food chains is influenced by the history of how species have
organized over time, and events like species arriving or going extinct
• ecosystem size
◦ is based on the relationship between ecosystem size and species diversity,
habitat availability and habitat heterogeneity
◦ larger ecosystems tend to have longer food chains because they often add
new top predators, experience changes in the middle levels of the food web,
and have more animals that eat from different levels of the food chain
• dynamic stability
◦ resistance against loss of function despite loss of nodes (species) or links
(relationships) → potential resilience to environmental changes
◦ complex (compartmentalized, nested structure) foodwebs tend to be more
stable, more prone to extinctions
◦ food webs containing omnivores would be less stable
◦ higher diversity and connectance promote the persistence and resilience of
mutualistic networks, but they destabilize trophic networks
Simulated effects of the different network
architectural patterns on the persistence
(A and B) and resilience (C and D) of
mutualistic [(A) and (C)] and trophic
[(B) and (D)] networks.
Book: Principles of Terrestrial Ecosystem Ecology
09.01.2025 - Introduction
What is ecosystem ecology?
• Study of interactions between organisms and their physical environment as an
integrated system
• provide the link between biotic and abiotic systems
• incorporates humans and their activities
What is an ecosystem?
• Bounded ecological system consisting of all the organisms in an area and their
physical environment
General theories in ecology
• theory of evolution
◦ natural selection
• niche theory
• bottom-up and top-down
• colonization- competition
• island theory
• assembly rules
10.01.2025 – Networks (1)
Network: a collection of connected points (minimum two points connected)
• e.g.: technological networks, social networks, information networks
• biological networks (links don´t need to be physical, can be functional)
◦ metabolic networks
◦ neural networks
◦ ecological networks
Network size: number of nodes/points, e.g. 4 nodes are connected by 3 links
degree: number of links the node has
node degree
1 1
2 2
3 3
4 1
5 2
6 1
,linkage density (complexity) : average degree of each node
e.g.: (1+2+3+1+2+1)/6= 1,66 for network example above
connectance: number of links divided by the number of all possible links
total number of links here: 5
number of all possible links (everything is connected to everything) N*(N-1)/2
N= total number of nodes
6*5/2=15
5/15=0,33
- if we add only one link, the connectance changes
- deleting one link can also change the environment, for example if
a circle is divided then
in completely connected networks, the number of
connections increase disproportionally when the
number of nodes grows →
path length: the number of steps required to connect a sequence of
nodes
Path is route through the nodes with the restriction that each
node is allowed to be passed only once->
network path length: average number of steps along the shortest
paths for all possible pairs of network nodes →
Sum of all node averages/ number of nodes
For each node, the length of the shortest paths to
all other nodes is calculated and added. That
number is divided by (N-1)
different network topologies – topology matters! (same
number of nodes but different topology →
hub nodes: a node with a number of links that greatly exceeds the
average (the one with the most links) →
antagonistic networks: negative interactions between networks
mutualistic networks: species interact in mutually beneficial relationships that
enhance survival and ecosystem stability
,compartmentalism: the division of the network into relatively independent sub-
networks
nestedness: a pattern where less-connected species interact with subsets of the
species that more-connected species interact with, creating a hierarchical, ordered
structure.
• generalist: interacts with a lot nodes
• specialist: interacts with only one node
• nestedness of mutualistic networks allows more stability, BUT if the one well-
connected species is lost, the whole network collapses →
• nestedness increases with the complexity (number of interactions) of the
network
modulality: the degree to which a network is divided into smaller, densely connected
groups of nodes (modules)
13.01.2025 – Network (2)
Characteristics of ecological networks
• compared to random networks:
◦ ecological networks follow
power law distribution in
number of links per species →
◦ they have high clustering:
neighboring nodes connected
with each other more
◦ size usually reflects relative abundance (rarity)
◦ compared to random networks, they have short path lengths (e.g. the
shortest path linking the most connected species)
◦ ecological networks are highly connected (connectance number is high)
• mutualistic pollination networks are more connected than plant-herbivory
networks for the same network size
◦ reason being: plants get eaten and make it less attractive for other eaters
◦ plant-herbivory networks are shaped by antagonistic, often specialized
interactions, resulting in lower connectivity
• arctic areas are actually more connected regarding networks
Food webs
• food chain lengths tend to be short
• do not correlate well with total productivity
• minor links can be critical if they supply limiting resources
• minor links can be critical if they are plastic options → may become
important under certain conditions
A) energy flow web: the flow of energy or nutrients among nodes in a food
web
B) functional (or interaction) webs: per capita effect of one species on another
→ even if we know A, we will not necessarily know B
What limits food chain (path) length?
, each food chain in a food web is usually only a few links long, rarely more
than 5 trophic levels
• resource availability of the food (accumulation), e.g. P, N, O2, CO2...
• energy
• Top-down and bottom-up control: stability of the ecosystem (the longer the
food chain, the more unstable)
• trophic transfer efficiency: conversion of energy between trophic levels
being inefficient, with only about 10% of the energy from one level being
passed on to the next (known as the 10% rule).
◦ most energy lost as heat through basic metabolism, respiration and other
processes.
◦ highest efficiency has: chicken breed (because they don´t fly), insects (30%)
and fish, because they do not heat themselves up
◦ efficiency of energy transfer across trophic levels primarily determines food
chain length → higher productivity allows longer food chain lengths
• history of community organization
◦ length of food chains is influenced by the history of how species have
organized over time, and events like species arriving or going extinct
• ecosystem size
◦ is based on the relationship between ecosystem size and species diversity,
habitat availability and habitat heterogeneity
◦ larger ecosystems tend to have longer food chains because they often add
new top predators, experience changes in the middle levels of the food web,
and have more animals that eat from different levels of the food chain
• dynamic stability
◦ resistance against loss of function despite loss of nodes (species) or links
(relationships) → potential resilience to environmental changes
◦ complex (compartmentalized, nested structure) foodwebs tend to be more
stable, more prone to extinctions
◦ food webs containing omnivores would be less stable
◦ higher diversity and connectance promote the persistence and resilience of
mutualistic networks, but they destabilize trophic networks
Simulated effects of the different network
architectural patterns on the persistence
(A and B) and resilience (C and D) of
mutualistic [(A) and (C)] and trophic
[(B) and (D)] networks.
