# Describe the exponential and logistic models of population growth and outline the key assumptions of these models.. Ecology

**Density independent **(population growth rates are limited): exponential growth model.

In exponential models, there are no environmental factors which are affecting the population, including food and predators. The size of the population is dependent on birth and death rate. Rate = births - deaths. Assumptions for the model:

- Population is closed - no immigration or emigration
- Population grows without limit
- Rate (births-deaths) remains constant over time
- Rate is dependent of population size and environment

**Density dependent **(population growth rates are limited by density): logistic model. As population increases beyond a certain point the birth rate decreases and deaths increase. Population growth depends on the size of the population; this means you must know the population parameter and the carrying parameter. Assumptions for the model:

- Mortality is dependent on population density
- Birth and mortality are continuous functions which can be overcome by developing agestructures models
- The environment is constant
- Individuals in a population react in the same way to a change in density

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