Lecture 8: growth types Flashcards
(12 cards)
What is a closed population in population growth models?
A population with no immigration or emigration; only births increase and deaths decrease population size.
What is the basic population change formula?
N(later) = N(now) + Births - Deaths
Q: What does the Geometric Growth Model assume?
- Discrete breeding (only during specific seasons)
- Constant growth rate (lambda )
Formula: lambda^t x No
What are the assumptions of the Exponential Model?
Same average birth (b) and death (d) rates
* band d are constant
* Continuous births and deaths
* Closed population
* Unlimited resources
What is the differential equation for exponential growth?
:
dN/t = (b - d) x N or dN/dt = r x N
What is the intrinsic rate of increase (r)?
The instantaneous per capita growth rate
* Calculated as r = b - d
When is exponential growth typically observed in nature?
When population size is low
* Resources are unlimited
* No competition, so growth occurs at maximum rate (r)
Why is exponential growth not often seen in nature?
b&d vary with age and environment
* Populations rarely have stable age distributions
* Populations are not closed
* Resources are limited
What are some historical examples of exponential growth?
Harp seals: from 2 to 9 million after harvest regulation
Humans
Why hasn’t human population growth leveled off?
Medical and technological advances
* Decreased death rates
* Increased birth rates
* Food production innovations
What data is used to determine population growth from one generation to the next?
Life tables (age-specific survival and fecundity data)
What do Exponential and Geometric Models require?
Knowledge of:
* Initial population size (NO)
* Growth rate (ror lambda)
* Time (t)
