Lecture 13 Flashcards
What is resilience in ecosystems?
The ability of an ecosystem to absorb disturbances and return to its original state.
What is hysteresis in ecosystems?
When an ecosystem requires greater effort to return to its original state after a shift.
What are tipping points?
Critical thresholds where small changes in conditions lead to significant and often irreversible changes.
What do NPZ models simulate?
Nutrient-Phytoplankton-Zooplankton interactions within ecosystems.
What are resilience metrics?
Metrics that measure an ecosystem’s ability to recover, such as recovery time and resistance to perturbations.
How do scaling laws relate to ecological processes?
Ecological processes often follow power-law relationships, where variables such as metabolism scale with body size.
Why is a larger system sometimes chosen for models?
To avoid effects from migration and boundary issues in the model.
How can different time frames affect model dynamics?
A longer timespan can capture important oscillations, while shorter timespans may miss key patterns.
What is a forcing function and how is it used in models?
Forcing functions, like fishing mortality or catch rates, are external inputs to models and are not simulated but influence state variables.
How are unknowns in linear systems solved?
By fixing some parameters using literature values and solving for the remaining unknowns.
What is EE in Ecopath, and why is it challenging to measure?
EE (Ecotrophic Efficiency) represents how efficiently energy is transferred through a trophic level and is often estimated through model-solving rather than direct measurement.
What type of model does Ecopath use?
A snapshot, non-dynamic model that represents averaged values over a defined period.
How does vulnerability impact predator-prey interactions?
Vulnerability parameters control whether prey are easily accessible or hidden, influencing energy transfer in Lotka-Volterra equations.
What is an end-to-end model?
A comprehensive ecosystem model that integrates multiple levels of the food web, often requiring significant computational time to run.
What challenge do end-to-end models face?
They can take decades to fully simulate due to their complexity.
How can MATLAB code be used in ecosystem modelling?
MATLAB scripts are used to parameterize, solve equations, and visualize ecosystem model outputs efficiently.
How are trophic flows solved in complex systems?
By applying a combination of literature values, forcing functions, and model-derived estimates, ensuring all flows are balanced.
How many observations per fitted parameter are typically required to avoid overfitting?
3-9 observations per parameter. For example, if there are 23 yearly observations (e.g., 2000-2023), dividing this by 5 indicates that 4 parameters can be fitted (e.g., fishing mortality, temperature, carrying capacity).
What can be done if the number of observations is insufficient?
Additional observations can be sourced, such as size-based data, to improve parameter fitting.
Why is it important to avoid small system boundaries in modelling?
To prevent migration effects from distorting model predictions.
Why might two models be created for different time spans?
To capture dynamics before and after a regime shift, as system characteristics may change.
Why are oscillations significant in ecosystem models?
Oscillations reflect meaningful predator-prey and environmental interactions rather than noise, so excluding them may oversimplify the system.
How can forcing functions such as catch rates influence the model?
Forcing functions provide external inputs, like fishing effort, that affect variables but are not directly simulated.
What is meant by solving a linear system with unknowns?
By setting known values from literature for some variables, the remaining unknowns (e.g., Ecotrophic Efficiency) can be solved.
How is Ecotrophic Efficiency (EE) used in Ecopath?
EE represents the proportion of energy flow used within a trophic level and is often the primary unknown solved by Ecopath.
Why is Ecopath considered a non-dynamic model?
It provides a snapshot for a given period, averaging values instead of simulating changes over time.
What approach does Ecopath use for mass balance?
It calculates an average value for each component (e.g., prey availability) to achieve equilibrium across trophic levels.
What do Lotka-Volterra predator-prey equations describe?
The interactions between predators and prey, with terms for vulnerability controlling the accessibility of prey.
What does the vulnerability parameter signify?
A high vulnerability value indicates that prey are readily available, whereas a low value indicates that prey are hidden or inaccessible.
How does the flow proportionality influence prey dynamics?
Bottom-up control dictates that prey availability drives energy flow and influences predator population sizes.
How is vulnerability incorporated into Lotka-Volterra models?
It can be easily added to simulate different prey availability scenarios.
What are end-to-end models, and why are they significant?
They are comprehensive models that integrate the entire food web, from primary producers to top predators, often requiring long computation times.
What challenge is associated with running end-to-end models?
These models can take decades to run due to their complexity and detailed representation.
What insights do slides about diet composition provide in ecological modelling?
They illustrate the importance of diet data in parameterizing models and highlight potential uncertainties in trophic flow estimates.
Why are average values important for non-dynamic snapshots?
By calculating averages over a defined period, the model represents stable conditions rather than short-term fluctuations.
How does MATLAB support ecosystem modelling?
MATLAB code is used to fit parameters, solve equations, and visualize system outputs, making the process more efficient.
What is the significance of slide 60’s equation Q(ij)?
This equation incorporates Lotka-Volterra principles and includes terms for prey availability and predator-prey interactions
Why might vulnerability be adjusted in a model?
To account for changes in prey accessibility due to environmental conditions or predator behavior.
How can linear systems be solved when equations have unknowns?
By fixing known variables (e.g., three out of four unknowns from literature), the final unknown (e.g., Ecotrophic Efficiency) can be derived.
What challenge did slide 71 highlight about end-to-end models?
The long runtime required for such comprehensive simulations.
What is the difference between dynamic and non-dynamic models?
Dynamic models simulate temporal changes, while non-dynamic models provide a static average representation for a specific period.
Why might trophic flow models rely on estimate-based unknowns?
Certain variables, like EE, are difficult to measure directly and are derived through model-based calculations.
