Populations - Food Webs Flashcards
Food Chains
Representations of extension of competition beyond own trophic levels.
Carnivore in food webs…
Consume herbivores, influence plant communties.
Understand aspects of food webs…
Removal of a species; a predator increase of prey
Trophic Cascade
A preadtor-prey effect that later abundance biomass or productivity of a population community or trophic level across one or more link in a food web.
Analysing dynamics with trophic cascades….
Isolation of a portion of a habitat and removal of one species
Four trophic level systems cascading…
Top-predator increase leads to second-level predator decrease then herbivore increase, with plant abundance decreasing.
Mesopredator release
A phenomenon where populatiosn of medium-sized predators rapidly increase in ecosystems ater removal of top carnivores.
Example of apex predator removal with mesopredator thriving…
Cats and fox are preyed on by dingoes(prey on same animals) so dingoes regulate mesopredators.
Top-down control
Predation by higher trophic levels affecting the accumulation of biomass at lower trophic levels.
Bottom-Up Control
Domination of the lower trophic levels typically plants or the herbivores.
Distinction between community and species level trophic cascades.
Community predators predate herbivores, controlling aabundance, releasing pressure on plants from control
Species increase in predator decreases herbivore increasing plant abundance
Ecosystem Exploitation Hypothesis
Says that plant biomass reflects the primary productivity of an ecosystem modified by the regulating effect of herbivory
Describing structure of a community…
Interaction strengths, food chain length and number of species.
Ecosystem Stability
Measures susceptiblity to disturbance
Different types of disturbances of stability?
Pulse Events and Press Events
Pulse Events
Abrupt changes in ecological parameters
Press Events
Persistent changes determining community state
Ecosystem Resistance
The extent of which a community is altered by a disturbance.
Ecosystem Resillience
The speed of communities return to the former state after disturbance
Ecosystem Robustness
Tendency of communities to suffer secondary/subsequent extinctions following primary extinctions
Keystone Species
Species that have a disproportional effect on their ecosystem in regards to their abundance.
Foundation Species
Differ in that they are spatially dominant creating physical structures with their own body tissue
Three parameters describing food webs…
S - Number of species
C - Connectance of the web
Beta - Average interaction strenght
Relation of instability to connectance and interaction stregnth…
The two increase instability as species increase.
Portfolio Effect
This is where more diversity fares better with changing conditions.
What enhances stability?
Ecological processes like increase in richness, competitiveness.
Complementary Effect
This is resource partioning or positive interactiosn leading to increased total resource use
What drives the complementary effect?
Niche differentaiton.
Selection Effect
Dominance by species with particular traits affecting ecosystem processes
Transgressive overyielding.
This occurs when mixture performance exceeds that of the best performing sole crop.
Insurance Hypothesis
This may be how more diverse plant ecosystems photosynthesise at a greater rate than ecosystems with fewer species present.
Basis of insurance hypothesis…
Responding differently to external influences based on species richness
Compartmentalization of food webs…
Into subunits where within interactions are strong, but between interactions are weka.
Why does compartmentalization increase stability?
More ribustness against removal and knock on effects are more limited against perturbationss
Food Chain Length
Describes the number of feeding links from a basal species to a top predator.
10% Rule
This descriebs how only 10 percent of energy stored as biomass in a trophic level is passed from one level to the next
Productive Space Hypothesis
Predicts food chain length is determined by productivty per unit area multiplied by the space occupied in the ecosystem
Larger ecosystems influence on food chain length…
Larger niche trophic diversity or reduced disturbance reverberations
Evolutionary constraints on predators…
Who they can consume by capture, subuding and consumption adaptations, and the hunting of herbivores, with competition arising
Parasites effects on food webs
Higher diversity and higher complexity
Regime Shifts
These are large, abrupt, persistent changes in structure/function of complex systems.
Regime shifts and small disturbances…
Small disturbances can drive dramatic shifts when tipping poitns exist.
What is an example of a trophic cascade?
Yellowstone wolf extinction in early 1900s
What is a real example of Mesopredator release?
Serengeti loss of lions and hyenas increased jackal/mongoose abundance leading to less smaller mammals and birds.
What is an example of top-down control in ecosystem?
Herbivorous zooplankton in lakes controlling algal biomass.
Where can bottom-up control be applied?
67 forests data determine climate effects like temperature and precipitation, with increasing nutrient cycling with temperature with alterations by precipitation also.
Ecosystem Exploitation Hypothesis
This describes how more complex ecosystems reocver from exploitation and resists it better than simple ones.
What is complexity of an ecosystem given by?
Amount of species and number of interactions between them.
Why does resilience increase with complexity?
Energy/resource pathways more widely avaiable and greater adaptive capacity.
Jacobian Matrix
This assesses stability of dynamic systems descriing how rates of change of each species abundace are influenced by changes in abundances of all other species in the web.
How does jacobian matrix model food webs?
Takes partial derivatives of species per capita growth rate with repsect to abundace of every other species in the web.
What is food web stability in Jacobian Matrix given by?
Eigenvalues
Partial Derivatives
This is the derivative of a function of several variables with respect to change in just one of its variables.
Eigenvalues
These are vectors that can only be scaled lengthwise without rotation after applying the matrix transformation.
Matrix
A rectangular array of numbers/symbols or expressions arranged in rows and columns.
What if eigenvalues are negative?
System is table and can return to equilibrium when perturbed
How can jacobian matrix be used to identify keystone species??
Largest magnitude eigenvalues mean they removal have significant impacts.
Insurance Hypothesis
This proposes that number of speceis in an ecosystem increases, the ecosystem becomes more resistant and resilient.
