Population Ecology Flashcards
What are three key features of population growth that models try to capture
- Ability to increase from low density
- Population growth must eventually stop due to environmental limits
- Populations fluctuate in seemingly random ways
When is a continuous time model more appropriate in population ecology
When birth and death occur continuously, such as in bacterial populations
When is a discrete time model more appropriate in population ecology
When reproduction is seasonal or synchronised, such as in wildebeest
What does the parameter r represent in population models
The intrinsic rate of increase - a life history trait influenced by reproduction and mortality patterns
What does K represent in population models
the carrying capacity - the maximum population size an environment can support, based on available resources
What causes environmental stochasticity
Random environmental changes like weather affecting resource availability and thus K
What is the effect on a high r on population response to environmental fluctuations
Populations with high r can track changes in K more closely and recover faster from declines
What is the effect of a low r on a populations ability to recover
Slower recovery from declines, more susceptible to extinction after hazards
What is Occam’s razor and how does it apply to population ecology models
The principle of favouring simpler explanations; useful for isolating effects in complex systems
How does environmental stochasticity interact with hazard events
Random catastrophic events (e.g. harsh winters) can cause crashes, recovery time is inversely related to r
How do K-selected species differ from r-selected species
K-selected: Few, high-quality offspring, slow growth (e.g. whales)
r-selected: Many, fast-growing offspring, quick recovery (e.g. rodent
What is demographic stochasticity
Randomness in individual births and deaths, especially impactful in small populations
What is the Allee effect
A decrease in population growth rate when population size becomes too small, sometimes leading to extinction
What is a strong Allee effect
When a population drops below a critical size, growth rate becomes negative and the population cannot recover
What are three biological causes of strong Allee effects
- Breakdown of group defence (e.g., Musk Ox)
- Reduced hunting success in small packs (e.g., African wild dogs)
- Difficulty finding mates (e.g. Kakapo)
What is the minimum viable population (MVP)
the smallest population size needed to avoid extinction due to stochastic effects, estimated median is ~4000 individuals
Why is the Kakapo so vulnerable to extinction
It’s a K-selected species with low reproductive rate, long lifespan, infrequent breeding, and high sensitivity to environmental change and predators
What does a high r mean in terms of recovery from population crashes
Species with high r can recover rapidly after catastrophic events
What are the typical traits of r-selected species
High reproductive rate
Small body size
Early maturation
Frequent and large litters
Thrive in less competitive environments
What are typical traits of K-selected
Low reproductive rate
Large body size
Late maturation
Few, well-invested offspring
Live in competitive environments
What is the r/K or fast/slow continuum
A general framework comparing species with fast (r-selected) vs. slow (K-selected) life histories - though it’s a simplification
Why is r so difficult to estimate
Because it integrates many life-history traits and can be influenced by varying environmental and demographic factors
What is the Poisson distribution used for in population models
To generate whole number population sizes from random processes, where the mean and variance are the same
What is the impact of demographic stochasticity on small populations
Increased risk of extinction due to random variation in births and deaths
