predator-prey relationship Flashcards
paradox of enrichment
Increased availability of resources (prey) in an ecosystem can lead to destabilisation or collapse of the predator-prey dynamic. Hence seemingly positive change (increase resource availability) can have unexpected neg. results.
Normally prey is the limiting resource
Initially prey increase is beneficial but neg in long term
Why is predator prey interaction study important?
Population dynamics:
Behavioural ecology: adaptations such as hunting strategies, defence and communication methods
e.g. African Tiger Fish species that eats birds
Conservation implication: wolf reintroduction to Yellowstone to manage deer population and allow recovery of plant and tree producer species.
Lotka-Volterra model
Lotka Volterra model – first predator-prey interaction model - see equation
- Developed by Alfred J. Lotka and Vito Volterra
- Proposed the first trophic predator-prey interaction model* Product defined by population response
Assumptions
* Unlimited prey food reserves
* No limitation without interaction
* Continuous predator and prey breeding
Limitations: oversimplified, linear interaction suggested – immediate impact on predator population is not true
reflects:
Predator increase/ prey decrease
Predator decrease/ prey increase
Logistical model adds value to the initial model
Rosenzweig-Macarthur Model
Paradox of enrichment – increase in prey resulting in ecosystem collapse
e.g. overfeeding fish in a pond results in overpopulation, lack of oxygen and die back as a result
More realistic including areas where prey may hide to avoid predation
Still oversimplified and even so it was challenging to apply
Prey consumption varies between species
Rate of predation is affected by prey population density: Prey density affects rate of consumption
Predation rate reaches a plateau at maximum carrying capacity of predatory individuals
Time delay for gestation and growth - Increased prey consumption does not immediately impact predator population that is delayed by gestation rate etc.
Advantages: More realistic, Incorporates logistic growth for resource populations, Accounts for other factors
Issues: still too simple. Shares same issues with the Lotka-Volterra Model. Deterministic. More challenging to apply to limited data
Lippel, B. (unknown) Michael L. Rosenzweig. Available at: http://www.eebweb.arizona.edu/faculty/mlro/serious2b.jpg
Richard (2008) American ecologist Robert MacArthur. Available at: http://www.eebweb.arizona.edu/faculty/mlro/serious2b.jpg
Predator handling time
Predator handling time
includes time for predators to…
* Catch prey
* Eat prey
* Use food energy to mate,gestate and produce offspring
Also includes time for prey to…
* Reproduce
* Mating and gestation
Prey consumption varies between species
- Predator search rate is vastly different between predators
- Different species employ different hunting strategies
Rate of predation is affected by prey population density
- Prey density affects the rate of prey consumption
- Predator search rate remains constant
- Both the rate of predator and prey population growth is a function of prey population density.
Factors that limit population growth include
- Seasonal fluctuations e.g. salmon run for bears
- Habitat availability
- Disease
- Abiotic conditions
&
Time Delay for Gestation and Growth:
- Increased prey consumption does not instantly result in increased predator populations
e.g. newborn mammals feed on milk before becoming predators - MacArthur model incorporates time formating, gestation, and offspring development of predators and prey
Issues of Lotka Volterra and how Rosenzweig-MacArthur Model is more ‘advanced’
Issues about Lotka-Volterra Model:
* Not realistic and too simple
* Linear interactions between predator and prey
* Oversimplified predator-prey dynamic
How Rosenzweig-MacArthur Model is an ‘advanced’ model of Lotka-Volterra Model:
* More realistic
* Incorporates logistic growth for resource populations
* Accounts for other factors
Issues on Rosenzweig-MacArthur Model Issues about Rosenzweig-MacArthur Model:
* Too simple
* Shares same issues with the Lotka-Volterra Model
* Deterministic
* More challenging with limited data
Even though there are some limitations of the models, they are still useful because:
- Ecology is scientific study of the distribution and abundance of organisms and the interactions that determine their distribution and abundance
- To understand organisms and their place in the environment, we need to study their interactions
- These models are useful to help ecologists understand the interaction between prey and predator
Advanced model – Numerical response model
Used to analyse how a dependent variable changes in response to variations in one or more independent variable
Helps us understand the relationship between different factors and a numeric outcome
Advantages: more realistic, predator responses to change in prey abundance, takes account of handling time, prey-switching and capturing population dynamics (non-linear interaction)
Considerations involve data requirements and mathematical complexity
Are parasites predators?
They don’t kill their hosts but they do consume a part of their host. They are predators e.g. a flea on a dog is consuming its hosts blood, they are also often prey as these small parasites are consumed by birds, cleaner fish etc. Despite the fact that they do not kill their host they do reduce fitness.
Models tend to function with one prey and one predator species – this has severe limitations
In a real ecological network very few predators are so specialistic that they consume only one prey species so how can this be modelled?
MacArthur model can be applied to Lemmings including multiple predators with many prey species
Grunert et al. (2021)Evolutionarily stable strategies in stable and periodically fluctuating populations: The Rosenzweig–MacArthur predator–prey model
https://doi.org/10.1073/pnas.2017463118
