Lecture 20 Flashcards
Exponential growth
- when R = 1, the population size remains constant
- when R > 1, it’s increasing
- when R < 1, it’s decreasing
Abundant resources —> population growth
some bacteria can double in abundance every 20 mins (under ideal conditions)
population doesn’t REALISTICALLY grow according to exponential growth
Limits to population growth
density-independent
- affects the growth of a population regardless of density of population
- often ABIOTIC
density-dependent
- affects growth of a population differently depending on density of population
- often BIOTIC
Negative density-dependence vs positive density-dependence
- population growth rate decreases because the population is too crowded
- NEGATIVE FEEDBACK
- positive density-dependence: pop growth rate decreases bc the pop is too small
Carrying capacity
the maximum population size of a species that an environment can sustain
w negative density-dependent mechanisms
- food
- space (too crowded)
- disease
- predation
- toxic waste can lead to density-dependence
What does R consist of in the exponential model?
- consists of survivors, plus recruits (births)
- ignores movement
r is the per capita rate of increase (exponential model)
r = 0 –> stable population size
r > 0 –> increasing population size
r < 0 –> decreasing population size
What are some assumptions of the logistic model?
- no variability in the environment (constant intrinsic growth rate & carry capacity)
- no effects of chance (particularly relevant for small populations)
- linear change in per capita growth rate with density (other forms possible)
- no consideration of population structure
- no delays (i.e. populations adjust growth instantaneously approaching carrying capacity smoothly)
- if there are delays, a population may overshoot carrying capacity and during an overshoot period, the carrying capacity may be lowered by resource destruction)
